How do organoarsenics improve digestion efficiency in poultry?

How do organoarsenics improve digestion efficiency in poultry?

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It struck me as very surprising that these organoarsenic compound with structure looking not very compatible with living system is widely used as food additive to increase weight gain and improve food efficiency in poultry. I wonder what is the mechanism of action that causes the effects in these animals?

For instance, here is the structure of one particular additive - Roxarsone:

Use of enzymes to improve feed conversion efficiency in Japanese quail fed a lupin-based diet

[Truncated] There is growing interest in quail production worldwide because, compared to broiler chickens, they are fast-growing, healthy, easy to handle, and have a high feed conversion ratio (FCR). Australian quail have a large body mass and therefore the potential to be some of the best meat-producing quail in the world, but Australian quail producers have been experiencing unprecedented increases in feed costs, mostly driven by the price of imported soybean meal. Feed is the biggest cost (70%) of total quail production, so there is great interest in replacing soybean meal.

One possibility is to replace soybean meal with Australian sweet lupin meal because they have similar contents of protein and energy. However, lupin meal rarely comprises more than 5% of commercial poultry diets. This is mainly because 35% of the lupin kernel is composed of complex non-starch polysaccharides (NSPs). The main NSP in lupin is pectin with branched side-chains of xylan.

Non-starch polysaccharides are indigestible in monogastric animals because they do not secrete the required enzymes to break them down. The digestion of lupin meal is thus very limited with several adverse consequences: i) accumulation of undigested NSP or pectin increases the viscosity of the gut, reducing digestibility of dry matter and growth performance ii) undigested pectin in the gut increases the water intake, resulting in wet droppings (wet litter), causing odours, coccidiosis outbreaks, soiled eggs iii) undigested nutrients are excreted into the environment.

Thiamine Deficiency

Like other B-complex vitamins, thiamine is sometimes called an "anti-stress" vitamin because it may strengthen the immune system and improve the body's ability to withstand stressful conditions. Chickens are more susceptible to neuromuscular effects of thiamine deficiency than mammals. Thiamine deficiency affects many systems of the chicken's body, including the muscles, heart, nerves, and digestive system. A principal function of thiamin in all cells is as the coenzyme cocarboxylase or TPP. TPP is essential in reactions that produce energy from glucose or that convert glucose to fat for storage in the tissues. When there is not enough thiamin in the diet, these basic energy functions are disturbed, leading to problems throughout the body.

  • Ataxia
  • Tremors, with the severity of the spasms increased when frightened.
  • As the deficiency progresses, paralysis of the muscles occurs, beginning with the flexors of the toes and progressing upward, affecting the extensor muscles of the legs, wings and neck.
  • Chicks will sit on their flexed legs and draw back their head in a stargazing position, which is often referred to as wry neck. Retraction of the head is due to paralysis of the anterior neck muscles.
  • Inability to stand or sit upright
  • Lethargy
  • Head tremors
  • General weakness
  • Impaired digestion
  • Severe loss of appetite. The bird will not resume eating unless given foods containing thiamine.
  • Chickens will sit on their flexed legs and draw back their head in a stargazing position, which is often referred to as wry neck. Retraction of the head is due to paralysis of the anterior neck muscles.
  • Emaciation
  • Frequent convulsions
  • High mortality of embryos prior to hatching in eggs produced by deficient parents. Any chicks that do hatch will demonstrate clinical signs of severe thiamine deficiency

Thiamin Dietary Requirements

  • High carbohydrate-based diets
  • Fish-meal based feed, supplements, or table scraps
  • Consuming moldy or spoiled feed

Thiamin Food Sources

The largest food sources of thiamin is Brewer’s yeast. Cereal grains and their by-products, soybean meal, cottonseed meal and peanut meal are relatively rich sources of thiamin.


Limits of feed intake

In order to increase broiler growth rate, and therefore increase the energy use efficiency towards the biological limit, the daily metabolizable energy (ME) intake must be increased to facilitate growth (Equation (1)). This can be achieved by increasing the daily feed intake and this has actually been the trend in commercial broiler breeding over recent decades 32,33,34,35 . In practice, this means that the birds must eat increasingly higher amounts at an increasingly younger age, which is biologically challenging. Ultimately, the theoretical maximum of feed intake would be set by the capacity of the digestive system. Experiments where the energy density of the feed was reduced (so the birds are forced to increase their feed intake) provide data on the fast-growing broiler feed intake limit 36,37,38 . The highest potential feed intake shown in literature was presented by Leeson et al. 36 In that study, broilers increased their gross feed intake by a total of 25% upon reaching a live weight (LW) of 2.8 kg on a low energy content feed compared to a high energy feed fed control group. The potential daily feed intake can therefore be determined from these data. As an outcome, the average daily feed intake at a LW of 1.0 kg and 2.8 kg could be increased by 10% and 1.1% respectively compared to current fast-growing birds 21 (Fig. 1). This indicates that younger birds have the greatest potential to increase feed intake which reduces as they approach slaughter weight (2.2 kg 39 ). Although much genetic progress has been achieved since the study of Leeson, et al. 36 , more recently Linares and Huang 37 showed that the feed intake of current fast-growing broilers could be increased by a further 6% between day 10 and day 42 when fed on a low energy content feed, compared to a high energy content feed. The limit to feed intake considered here is consistent with the latter study 37 .

The average daily feed intake of a current fast-growing broiler () and the potential average daily feed intake defined by the apparent biological limit of feed intake (broken line). Based on the data presented by Leeson et al. 36 .

Limits of digestive efficiency

In artificial selection programmes, emphasis has been placed on the growth of certain body parts, such as the breast muscles, in order to increase carcass yield 5,34,40 . Consequently, the morphometries of the internal structures, in particular the organs that comprise the digestive system, have been shown to differ between high digestive efficiency genotypes and birds bred for high commercial performance 41,42 , i.e. increased energy use efficiency. In modern fast-growing birds, digesta throughput each day has increased to facilitate growth. Despite this, there is no evidence that breeding for increased commercial performance has led to any change in overall digestive efficiency per unit mass of digesta 7 thus, selection pressure placed on increasing energy use efficiency and carcass yield at the very least must have conserved digestive efficiency whilst the size of the system has not increased at the same rate as other components of the body. Hence, the digestive efficiency as used in the energy flow model was expected to remain at its current level despite continuing selection for increasing energy efficiency. Since the digestible energy content of the feed per unit mass does not appear to be substantially compromised by augmented throughput 5,7 , nor does it appear to be improved genetically via selection for increased energy use efficiency 42,43,44 , it follows that the ME available to the broiler will be limited only by the capacity of feed intake.

Potential changes in energy partitioning

Broilers currently have a body protein and lipid content of around 20% and 8%, respectively, based on recent data presented by Mussini 5 . The abdominal fat pad constitutes about 2% of the body weight 45,46 . Reducing this feature to zero would result in a bird with a body lipid content of around 6%. This value places the animal firmly at the lower end of the estimated biological limit for fatness 47,48 . Less energy is required to grow a leaner bird than a fatter bird at the same overall growth rate (Equation (1)). Therefore, reducing the body lipid content to its minimum redirects a higher proportion of the ME into the growth of the fat-free body components, thus allowing the bird to reach slaughter weight faster. As a result, reducing the fat content from the current level to the apparent biological limit would reduce the necessary energy intake upon reaching slaughter by 1.7% (Table 1).

In an earlier study, we found that the rate of metabolic heat production (MHR MJ kg −1 d −1 ) of commercial broilers has either remained the same or been weakly positively correlated with the increase in growth rate 7 , over the recent decades, indicating that selection has not reduced the energy used for metabolic processes. Based on performance data for the current fast-growing birds 21 , the MHR was calculated to be 0.36 kg −1 d −1 . This same value was used to determine the energy distribution in the birds with maximum energy efficiency, as a conservative estimate for the further change.

Predicted future broiler performance

The average age modern fast-growing broiler lines reach a LW of 2.2 kg (slaughter weight) is currently between 34 and 35 days of growth 21,49,50 . The outcome of our analysis shows that even if the broiler growth rate is increased to the apparent biological limit, this will result in birds that reach their slaughter weight only 1.2 days sooner (Fig. 2). This results in an 8% reduction in the total feed energy intake of the bird upon reaching slaughter weight (Table 1).

The growth rate of a current fast-growing broiler () and the potential growth rate of future birds as defined by the different scenarios accessed maximum energy efficiency (broken line) and increased welfare scenario ().

The analysis made above can be considered to represent a broiler bird with a maximum energy efficiency (and maximum growth rate). In an alternative scenario (increased welfare scenario), we calculated the energy intake of a slow-growing bird resulting from a higher welfare breeding strategy (i.e. growth rate is reduced so that birds reach a LW of 2.2 kg at 56 days of age, 23 days later than the current fast-growing bird). 5.7 MJ more energy per g of LW gain is required by birds from this slow-growing line to reach slaughter weight than is required by current fast-growing birds. This equates to 27% more total feed energy upon reaching slaughter than current fast-growing birds (Table 1).

Environmental impact assessment of future breeding scenarios

The maximum energy efficency scenario showed slightly reduced environmental burdens compared to current fast-growing birds, whereas the opposite was true for the scenario aiming to produce slow-growing “increased welfare” birds. The GHG emissions (Fig. 3(a)) and ALU (Fig. 3(b)) associated with feed production in the maximum energy efficency scenario were reduced by 8% when compared to current production. For the increased welfare scenario, both of these environmental indicators were increased by 27% when compared to current production on a standard feed. The environmental burdens were also calculated for the slow-growing line based on an alternative feeding programme (see Supplementary Table S1) this alternative feed had a lower protein content (19.6%) than the standard diet (21%), as to cater to the slow-growing line’s lower daily protein intake needed to maintain the required growth rate. When fed the alternative feed, GHG and ALU were increased by 16% and 24% respectively compared to current fast-growers reared on a standard feed (Fig. 3).

The environmental impact implications associated with feed provision for one broiler of each scenario grown to 2.2 kg. (a) shows greenhouse gas emissions (CO2 eqv.) and (b) shows the agricultural land use (m 2 ). The following scenarios are presented: current fast-growing birds, maximum energy efficiency birds and slow-growing increased welfare birds placed on a standard feed, as well as slow-growing increased welfare birds placed on an alternative feed formulated specifically for the slow-growing line.

The excretion of N and P were reduced by 23% and 15% respectively in the maximum energy efficiency scenario compared with current production, whereas these nutrients were excreted in higher quantities in the increased welfare scenario: an increase of 64% and 50% in the total N and P excretion was shown compared to current production on a standard feeding programme (Fig. 4). Applying the alternative feeding programme increased N and P excretion less than when the birds were raised on the standard feed, although this increase was still substantial (43% and 26% respectively).

The nutrients, nitrogen (N) and phosphorus (P), that are expected to be excreted when one broiler is raised to 2.2 kg slaughter weight. The following scenarios are presented: current fast-growing birds, maximum energy efficiency birds and slow-growing increased welfare birds placed on a standard feed, as well as slow-growing increased welfare birds placed on an alternative feed formulated specifically for the slow-growing line.

Compared on a standard feeding programme with the maximum energy efficiency scenario, the slow-growing birds (increased welfare scenario) were associated with 37% more GHG and ALU, along with a 115% and 77% increase in N and P excretion respectively. When the alternative feeding programme was applied, with reduced feed protein content, the difference between the environmental burdens of the two future lines were reduced to 26%, 35%, 87% and 48% for GHG, ALU, N and P respectively.

Growth and body composition

As mentioned above, faster growth rate of modern broilers compared to older breeds has strongly contributed to the energy efficiency of the birds, as they now reach their slaughter weight in a shorter time and therefore need relatively less energy for metabolic heat production, such as for protein turnover, and physical activity. Furthermore, potential changes in body composition may have also affected the energy dynamics of the birds. The relationship between the amount of protein and lipid in the body can be influenced by diet composition, degree of maturity, sex and genotype (Leclercq and Whitehead 1988). As broiler growth rate has improved, birds reach slaughter weight at decreasing degrees of maturity (Emmans and Kyriazakis 2000). This in turn could lead to reduced carcass fatness, as relative lipid content of the gain increases with the degree of maturity of the animal (Leenstra 1986 Katanbaf et al. 1988). Protein and lipid accretion differ in both energy values and the transfer efficiency of energy from feed to tissue. Fat contains much more combustible energy than protein does (Pym and Solvyns 1979) therefore, any change in the proportion of the retention of these two components will influence the metabolisable energy content of the body and the efficiency of the weight gain.

A modern breed has been shown to be significantly heavier at every age with a significantly increased proportion of breast meat upon reaching slaughter than an old-type breed (Mussini 2012) Schmidt et al. (2009) showed that the growth rate of breast meat has increased twice as fast as the overall body growth rate. Further, in an old-type breed, the breast muscle plateaued at 9 % of the body mass at day 14. In contrast, by day 14, breast muscle constituted 14 % of the body mass of the modern breed this ratio continued to increase to 18 % by day 35. Apparently, a major difference occurred at day 14 after which, the old-type birds maintained a constant allocation of resources to breast muscle production, whereas the modern birds continued to incorporate additional resources into this tissue. Similarly, Fleming et al. (2007) reported that the proportion of breast meat by weight at slaughter has increased by 54 % since the 1970s. The relative weight of wing and heart muscle has been shown to have reduced significantly in modern breeds, when compared to breeds grown commercially 50 years ago (Katanbaf et al. 1988 O’Sullivan et al. 1992a Havenstein et al. 2003a). When compared with the same diet for example, wings were shown to have reduced by 2.2 and 2.0 % relative to bodyweight at the ages of 43 and 57 days, respectively, due to genetics between the 1950s and 2001 (Havenstein et al. 2003a). Meanwhile, the same experiment showed that in the old-type breed, the heart grew to 0.57 and 0.50 % of the body weight at 43 and 57 days of age, respectively at the same ages, a 2001 breed was shown having a heart that constituted only 0.50 and 0.44 % of its total body weight, respectively (Havenstein et al. 2003a). A lower relative heart weight through the starter period could be in part due to diversion in protein allocation from the heart to the breast tissues (Schmidt et al. 2009). In contrast, heart weight relative to body weight was shown to be similar in old-type and modern breeds in younger broilers by Mussini (2012), but by the age of 28 days, the less selected old-type birds showed significantly larger hearts relative to their overall body mass. Similar disparity exists in scientific reports in the observed change in the relative mass and maturation rates of the liver due to selection (Nir et al. 1978 Katanbaf et al. 1988 O’Sullivan et al. 1992a Schmidt et al. 2009 Mussini 2012). Contrasting findings in organ growth may be due to differences in the response to selection for high body weight only and the multi-trait breeding programs that have led to modern commercial breeds (Neeteson-van Nieuwenhoven et al. 2013).

Wang et al. (2004) suggested that the modern broiler is actually phenotypically fatter than broilers grown commercially in the 1970s due to their very inactive lifestyles and energy-rich diets. This idea has been perpetuated since (e.g. Roeder 2012) despite there being more evidence to suggest the birds have become leaner over this time (Pym and Solvyns 1979 Remignon and Le Bihan-Duval 2003). This is expected because high carcass fat is considered unfavourable by the customer and has been selected against in breeding programs in order to improve the quality of the product (Muir and Aggrey 2003 Laughlin 2007). There has been more convincing evidence presented in literature to show that, although body fat increased up until the late 1970s in response to selection for greater live weight at a specific age and rapid growth, modern breeds now have significantly reduced fat deposition due to commercial selection pressures (Leclercq and Whitehead 1988 Zuidhof et al. 2014). Fleming et al. (2007) showed body fat content to have reduced from 26.9 % in the 1970s to 15.3 % in commercial breeds used in the last decade, when birds were compared after being reared on a modern diet. In that study, it was obvious that this fat reduction was due to an increased amount of energy being allocated to the growth of breast meat as discussed above.

In a 2 × 2 factorial design experiment it was found that, when fed on both a modern diet and a 1950s style diet, a modern broiler breed achieved a different body composition compared to an old-type breed, when raised to the same slaughter weight (Havenstein et al. 1994b, 2003a). When placed on the 1950s diet, modern broilers were much smaller but slightly leaner than those placed on the modern diet, nevertheless fatter than the old-type birds. When placed on the more balanced modern diet, which had a higher energy and protein content (Havenstein et al. 1994a, 2003b), the old-type birds became fatter at every age than they did when fed on the 1950s diet. It is likely that the less-balanced 1950s diet did not contain enough nutrients required by the modern breed each day to reach its full genetic potential and so this led to a reduced growth rate. Furthermore, the modern breed had a higher body fat percentage compared to the old-type breed when both breeds were fed on the old diet, probably because energy was overconsumed in order to increase intake of important nutrients (Leeson et al. 1996 Wiseman and Lewis 1998 Swennen et al. 2004 Leeson and Summers 2005 Gous 2007).

Conversely, in other studies, the percentage body fat was similar between the modern and old-type broilers, at least until slaughter weight, when placed on a modern high-protein diet (Mussini 2012 Fancher 2014). Contrary to the findings reported above, these data suggest that there has been little or no overall change in the body composition in commercial breeds due to artifical selection (Aletor et al. 2000). Elsewhere, there has been no difference in body composition found between breeds, when compared at an equivalent body protein weight, even where there has been heavy selection for the yield of specific parts and huge differences in growth rate and mature mass are displayed (Danisman and Gous 2011, 2013). As was highlighted above, modern diets are of higher quality because they contain more energy, more protein and are more balanced compared to diets used in the past. If the reduction in carcass fatness in commercial breeds is the result of considerable improvements made in the nutrition as opposed to genetics, this could, in part, explain the possible peak in carcass fat in the 1970s. This is because 1970s diets contained relatively more energy to protein in an attempt to maximise growth and storing energy as fat is energetically more efficient.

Broilers can be specifically selected for fatness or leanness based on cholesterol levels in the blood plasma (Whitehead and Griffin 1984), resulting in “genetically lean” and “genetically fat” divergent lines. These lean and fat lines were able to achieve the same body composition when the latter was fed on a higher-protein diet (Whitehead and Parks 1988 Whitehead 1990). When fed in such a way that they reach the same body composition, Whitehead (1990) showed the “genetically lean” birds to have a better energy use efficiency and to retain a higher proportion of the protein that was taken in than the “genetically fat” line. This may be simply explained by the lower growth rate (and therefore longer time and higher metabolic heat production required to reach a certain body weight) achieved by the “genetically fat” birds when grown to a body composition comparable to the “genetically lean” birds. When fed on old diet formulations, growth rate is reduced and the energy use efficiency suffers in “genetically lean” lines, as it does in modern commercial breeds. Therefore, the conclusion drawn by Whitehead (1990) is consistent with the trend presented by both Mussini (2012) and Havenstein et al. (2003a). Since selecting for leanness leads to birds which display greater performance traits (e.g. higher growth rate), selecting for greater performance traits will result in leaner broilers.

Modern commercial broiler body composition is the product of decades of bird and diet coevolution, as breeders and nutritionists have attempted to produce the most efficient birds with the most desirable characteristics, with concomitant advancements made in nutrition. From the data of the experiments discussed here, it would seem that this has led to commercially reared birds that are leaner now than they were half a century ago. However, body composition displays strong genotypic and environmental interactions the absolute influence on body composition in commercial breeds that can be attributed to each of these factors remains uncertain due to conflicting literature. An interesting example of such interaction is the potential for genetic adaptation to high- and low-protein diets which has been demonstrated in poultry (Sorensen 1985 Marks 1993) when selection takes place on high-protein diets, this results in birds which require such environments for maximum growth, whereas populations selected on low-protein diets do not require high-protein diets for full expression of their genetic potential for growth. Therefore, the body composition of modern broiler breeds can be seen as a culmination of (1) adaptation to a better diet via artificial selection for improved feed use efficiency and this has resulted in a bird which is genetically lean (Whitehead 1990 Mussini 2012 Havenstein et al. 2003a), and (2) genetic change in the body composition irrespective of the dietary changes due to selection pressures placed on reduced fatness (Fleming et al. 2007 Zuidhof et al. 2014).

New global study reveals how diet and digestion in cows, chickens and pigs drives climate change 'hoofprint'

The resources required to raise livestock and the impacts of farm animals on environments vary dramatically depending on the animal, the type of food it provides, the kind of feed it consumes and where it lives, according to a new study that offers the most detailed portrait to date of "livestock ecosystems" in different parts of the world.

The study, published today in the Proceedings of the National Academy of Sciences (PNAS), is the newest comprehensive assessment assembled of what cows, sheep, pigs, poultry and other farm animals are eating in different parts of the world how efficiently they convert that feed into milk, eggs and meat and the amount of greenhouse gases they produce.

The study, produced by scientists at the International Livestock Research Institute (ILRI), the Commonwealth Scientific and Industrial Research Organisation (CSIRO) and the International Institute for Applied Systems Analysis (IIASA), shows that animals in many parts of the developing world require far more food to produce a kilo of protein than animals in wealthy countries. It also shows that pork and poultry are being produced far more efficiently than milk and beef, and greenhouse gas emissions vary widely depending on the animal involved and the quality of its diet.

"There's been a lot of research focused on the challenges livestock present at the global level, but if the problems are global, the solutions are almost all local and very situation-specific," said Mario Herrero, lead author of the study who earlier this year left ILRI to take up the position of chief research scientist at CSIRO in Australia.

"Our goal is to provide the data needed so that the debate over the role of livestock in our diets and our environments and the search for solutions to the challenges they present can be informed by the vastly different ways people around the world raise animals," said Herrero.

"This very important research should provide a new foundation for addressing the sustainable development of livestock in a very resource-challenged and hungry world, where, in many areas, livestock can be crucial to food security," said Harvard University's William C. Clark, editorial board member of the Sustainability Science section at PNAS.

For the last four years, Herrero has been working with scientists at ILRI and the lIASA in Austria to deconstruct livestock impacts beyond what they view as broad and incomplete representations of the livestock sector. Their findings -- supplemented with 50 illustrative maps and more than 100 pages of additional data -- anchor a special edition of PNAS devoted to exploring livestock-related issues and global change. Scientists say the new data fill a critical gap in research on the interactions between livestock and natural resources region by region.

The initial work was funded by ILRI and the CGIAR Research Program on Climate Change, Agriculture and Food Security (CCAFS).

By the Numbers

Livestock production and diets

The study breaks down livestock production into nine global regions -- the more developed regions of Europe and Russia (1), North America (2) and Oceania (3), along with the developing regions of Southeast Asia (4), Eastern Asia (5, including China), South Asia (6), Latin America and the Caribbean (7), sub-Saharan Africa (8) and the Middle East and North Africa (9).

The data reveal sharp contrasts in overall livestock production and diets. For example:

  • Of the 59 million tons of beef produced in the world in 2000, the vast majority came from cattle in Latin America, Europe and North America. All of sub-Saharan Africa produced only about 3 million tons of beef.
  • Highly intensive industrial-scale production accounts for almost all of the poultry and pork produced in Europe, North America and China. In stark contrast, between 40 to 70 percent of all poultry and pork production in South and Southeast Asia, the Middle East and Africa is produced by small-scale farmers.
  • Almost all of the 1.3 billion tons of grain consumed by livestock each year are fed to farm animals in Europe, North America, Eastern China and Latin America, with pork and poultry hogging the feed trough. All of the livestock in sub-Saharan Africa combined eat only about 50 million tons of grain each year, relying more on grasses and "stovers," the leaf and stalk residues of crops left in the field after harvest.

Greenhouse gas emissions

Scientists also sought to calculate the amount of greenhouse gases livestock are releasing into the atmosphere and to examine emissions by region, animal type and animal product. They modelled only the emissions linked directly to animals -- the gases released through their digestion and manure production.

Some important findings include:

  • South Asia, Latin America, Europe and sub-Saharan Africa have the highest total regional emissions from livestock. Between the developed and developing worlds, the developing world accounts for the most emissions from livestock, including 75 percent of emissions from cattle and other ruminants and 56 percent from poultry and pigs.
  • The study found that cattle (for beef or dairy) are the biggest source of greenhouse emissions from livestock globally, accounting for 77 percent of the total. Pork and poultry account for only 10 percent of emissions.

Analyzing Efficiency and Intensity

Scientists note that the most important insights and questions emerging from the new data relate to the amount of feed livestock consume to produce a kilo of protein, something known as "feed efficiency," and the amount of greenhouse gases released for every kilo of protein produced, something known as "emission intensity."

Meat v. dairy, grazing animals v. poultry and pork

The study shows that ruminant animals (cows, sheep, and goats) require up to five times more feed to produce a kilo of protein in the form of meat than a kilo of protein in the form of milk.

"The large differences in efficiencies in the production of different livestock foods warrant considerable attention," the authors note. "Knowing these differences can help us define sustainable and culturally appropriate levels of consumption of milk, meat and eggs."

The researchers also caution that livestock production in many parts of the developing world must be evaluated in the context of its "vital importance for nutritional security and incomes."

The study confirmed that pigs and poultry (monogastrics) are more efficient at converting feed into protein than are cattle, sheep and goats (ruminants), and it further found that this is the case regardless of the product involved or where the animals are raised. Globally, pork produced 24 kilos of carbon per kilo of edible protein, and poultry produced only 3.7 kilos of carbon per kilo of protein -- compared with anywhere from 58 to 1,000 kilos of carbon per kilo of protein from ruminant meat.

The authors caution that the lower emission intensities in the pig and poultry sectors are driven largely by industrial systems, "which provide high-quality, balanced concentrate diets for animals of high genetic potential." But these systems also pose significant public health risks (with the transmission of zoonotic diseases from these animals to people) and environmental risks, notably greenhouse gases produced by the energy and transport services needed for industrial livestock production and the felling of forests to grow crops for animal feed.

Feed quality in the developing world

The study shows that the quality of an animal's diet makes a major difference in both feed efficiency and emission intensity. In arid regions of sub-Saharan Africa, for example, where the fodder available to grazing animals is of much lower quality than that in many other regions, a cow can consume up to ten times more feed -- mainly in the form of rangeland grasses -- to produce a kilo of protein than a cow kept in more favourable conditions.

Similarly, cattle scrounging for food in the arid lands of Ethiopia, Somalia and Sudan can, in the worst cases, release the equivalent of 1,000 kilos of carbon for every kilo of protein they produce. By comparison, in many parts of the US and Europe, the emission intensity is around 10 kilos of carbon per kilo of protein. Other areas with moderately high emission intensities include parts of the Amazon, Mongolia, the Andean region and South Asia.

"Our data allow us to see more clearly where we can work with livestock keepers to improve animal diets so they can produce more protein with better feed while simultaneously reducing emissions," said Petr Havlik, a research scholar at IIASA and a co-author of the study.

Not absolute indicators of sustainability

While the new data will greatly help to assess the sustainability of different livestock production systems, the authors cautioned against using any single measurement as an absolute indicator of sustainability. For example, the low livestock feed efficiencies and high greenhouse gas emission intensities in sub-Saharan Africa are determined largely by the fact that most animals in this region continue to subsist largely on vegetation inedible by humans, especially by grazing on marginal lands unfit for crop production and the stovers and other residues of plants left on croplands after harvesting.

"While our measurements may make a certain type of livestock production appear inefficient, that production system may be the most environmentally sustainable, as well as the most equitable way of using that particular land," said Philip Thornton, another co-author and an ILRI researcher at CCAFS.

"That's why this research is so important. We're providing a set of detailed, highly location-specific analyses so we can get a fuller picture of how livestock in all these different regions interact with their ecosystems and what the real trade-offs are in changing these livestock production systems in future."


4.1 Effect of organic acids on nutrient digestibility and mineral utilization

Organic acids are accepted to be an appealing alternative for improving the nutrient digestibility in swine and poultry industry. The multifunctional role of organic acids including the reduction of gastric pH, increased gastric retention time, stimulation of pancreatic secretions, influence on mucosal morphology and serving as substrate in intermediary metabolism all lead to improved digestion and absorption (Partanen & Morz, 1999 ). Blank, Mosenthin, Sauer, and Huang ( 1999 ) exhibited increased digestibility of apparent ileal protein by 7% and amino acids from 4.9% to 12.8% in early weaned piglets with 2% fumaric acid. In case of grower pigs, Mosenthin et al. ( 1992 ) found improved ileal digestibility of certain essential amino acids but reported no effect on the apparent ileal digestibility of dry matter, organic matter, crude protein or ash when 2% propionic acid was added to a barley–soybean-meal-based diet. However, with dietary inclusion of formic acid (1.4%), fumaric acid (1.8%) or n-butyric acid (2.7%) in grower pigs (Mroz et al., 2000 ) illustrated a significant increase of 6% in the apparent ileal digestibility of protein and several essential and non-essential amino acids.

In case of broilers, Ghazala, Atta, Elkloub, Mustafa, and Shata, ( 2011 ) showed improved metabolizable energy (ME) and nutrient digestibility of crude protein (CP), ether extract (EE), crude fibre (CF) and nitrogen-free extract (NFE) through dietary fumaric (0.5%) or formic acid (0.5%) and acetic (0.75%) or citric acid (2%). The improved CP and ME digestibility through organic acid supplementation is also related to the control of microbial competition for host nutrients, endogenous nitrogen losses and ammonia production (Omogbenigun, Nyachti, & Solminski, 2003 ). As low ME of soybean meal is related to its poor digestibility of carbohydrate portion in chicken, inclusion of 2% citric acid in soybean meal found to improve α-galactosidase activity and decreased the crop pH (Ao, 2005 ). Smulikowska (Smulikowska, Czerwiński, Mieczkowska, & Jankowiak, 2008 ) illustrated increased nitrogen retention in the host supplemented with fat coated organic acids, because of their enhanced bioavailability in the distal digestive tract and the greater epithelial cell proliferation. In broiler chickens, Ndelekwute and Enyenihi ( 2017 ) reported that citric and ascorbic acids of lime juice improved digestibility of nutrient at 7 weeks of age of broiler chickens. Also, Ndelekwute et al. ( 2018 ) found that digestion coefficients of protein, fibre and ether extract were significantly improved by addition of organic acids in drinking water (p < .05). But, nitrogen-free extract and dry matter digestibility were significantly reduced by organic acid supplementation (p < .05). On the same context, Ndelekwute et al. ( 2019 ) found that the per cent of faecal moisture and nitrogen-free extract digestibility were reduced by organic acid supplementation. But, digestibility of protein, crude fibre and ether extract were improved due to organic acid in comparison with control (Ndelekwute et al., 2019 ). Yang et al. ( 2019 ) evaluated the impact of protected organic acids on pig performance, faecal microbial counts and nutrient digestibility, and they found that 0.2% of protected organic acids increased the apparent digestibility of dry matter compared with control (p < .05). Supplementation of protected organic acid blends to pig diets revealed beneficially affects ileal noxious gas and the nutrient digestibility, (Devi, Lee, & Kim, 2016 ).

The dietary organic acids complex with minerals have been found to improve digestibility and reduced excretion of supplemental minerals and nitrogen, thereby controlling their discharge into environment. The acidic anions have been found to promote the cation absorption of minerals such as calcium, phosphorus, magnesium and zinc (Edwards & Baker, 1999 ). In contrast, addition of 15 g of citric acid has shown to alleviate the symptoms of parakeratosis in pigs fed with suboptimal level of zinc but no appreciable effects were found on the apparent absorption and digestion of any of the minerals (Hohler & Pallauf, 1994 ). Boling, Webel, Mavromichalis, Parsons, and Baker ( 2000 ) stated that citric acid could effectively improve the utilization of phytate phosphorus but the response was found much smaller in pigs than chicken. Nourmohammadi, Hosseini, Farhangfar, and Bashtani ( 2012 ) demonstrated supplementation of 3% citric acid along with microbial phytase enzyme in broiler chicken caused better ileal nutrient [CP, apparent metabolizable energy (AME), Ca and total P] digestibility and increased mineral retention. It was reported that lower pH facilitates the P solubility and the microbial phytase was more active through acidification resulting in improved P absorption. The organic acid supplementation together with the developing desirable gut microflora was found to contribute for mineral retention and bone mineralization through increased digestibility and availability of nutrients as stated by Ziaie et al. ( 2011 ).

4.2 Impact on performance and production

A meta-analysis of Partanen and Morz ( 1999 ) stated that the growth performance in the weaned piglets did not show much difference among the formates, fumarates and citrates, whereas the formates showed better performance in fattening pigs followed by fumarates. In comparison, Suryanarayana, Ravi, and Suresh ( 2010 ) showed greater average daily gain (g) and feed: gain ratio in grower pigs augmented with 0.9% sodium formate. When 0.8% or 1.2% potassium diformate were added in the diets of primiparous and multiparous sows, the author found positive effect on the back fat thickness of sows in gestation with no change in average daily feed intake or body weight gain. Irrespective of the dose, the piglets born to the supplemented sows exhibited increased birthweight, weaning weight and average daily gain (Overland et al., 2009 ). Similarly, sows fed with 0.8% potassium diformate (Lückstädt, 2011 ) demonstrated higher feed intake from third day post-farrowing, reduced weight loss during weaning time and significantly lower back fat reduction. As per Xia et al. ( 2016 ) potassium diformate boost the secretion of hydrochloric and lactic acid through increased mRNA expression of H + -K + -ATPase and gastrin receptors in the oxyntic mucosa of stomach. Dietary incorporation of sodium butyrate in pregnant sow and post-weaning piglets increased their growth performance with beneficial impact on muscle and adipose tissue oxidative genes.

Mroz, Grela, Krasucki, Kies, and Schoener ( 1998 ) demonstrated that formic acid has anti-agalactia properties in lactating sows. A few studies on other organic acids like acetic acid, lactic and sorbic acid have also shown an equivalent growth promoting effects in swine (Roth & Kirchgessner, 1988 ). Eckel, Kirchgessner, and Roth, ( 1992 ) recommended that the strong odour and flavour of acids like tartaric and formic acid may lead to lower daily gain in piglets corresponding to reduced feed intake when their threshold dose in their diet exceeds. This suggests that the palatability of the diet can influence the growth performance and hence minimum effective concentration of each acid should be established (Partanen & Morz, 1999 ). Inclusion of salts of organic acids can also be a solution, as they are tasteless and do not influence the feed intake.

In chicken, Brzóska, Śliwiński, and Michalik-Rutkowska ( 2013 ) showed growth-enhancing and mortality-reducing effect in broiler chicken using dietary organic acid (0.3%–0.9%) but found no significant influence on carcass yield or individual carcass parts. On the contrary, Fascina et al. ( 2012 ) reported better performance and carcass characteristics by incorporation of organic acid mixture (30.0% lactic acid, 25.5% benzoic acid, 7% formic acid, 8% citric acid and 6.5% acetic acid) in broiler diets. The superior growth performance can be attributed to low pH in diet and digestive tract acting as microbial barrier, reduced buffering capacity and improved nutrient digestibility. Broiler birds fed with 0.5% citric acid has shown progress in weight gain, feed intake, tibial ash deposition, carcass weight and non-specific immunity through increased density of lymphocytes in lymphoid tissues (Haque et al., 2010 ).

A study on acidifying drinking water of broilers with citric acid (pH 4.5) demonstrated improved gut modulation, liver health and thyroid hormones (T3 and T4) with respect to lipid profile showing equilibrium in internal homeostasis (Abdelrazek, Abuzead, Ali, El-Genaidy, & Abdel-Hafez, 2016 ). But the same study with acetic acid worsened the performance and gut health of broilers. Evaluation of encapsulated acidifier or herb-acidifier blend in the broiler diet revealed better performance in terms of intestinal histology, intestinal pH, serum total protein, serum albumin and gut eubiosis than without encapsulation (Natsir, Hartutik, Widodo, & Widyastuti, 2017 ). A latest investigation on resistance to heat stress by drinking water acidification with sodium butyrate in broilers suggested alleviation of detrimental effects of heat stress on growth, carcass quality, haematological, biochemical traits, inflammatory markers, oxidative stability and histology of liver and immune organs. Sodium butyrate and acidifier blends were also proved to be antioxidants to check free radical injury due to heat stress (Awaad et al., 2018 ). With regard to layer chicken, employment of acidifiers markedly increased the egg production (Yesilbag & Colpan, 2006 ). Dietary inclusion of 0.2% protected organic acid to pigs has the potential to enhance the growth rate. Feeding protected organic acid rations to piglets improved the average body gain during 0–2 weeks and overall period (0–6 weeks) (Yang et al., 2019 ). In broilers, the dietary supplementation with organic acid improved body weight gain and feed efficiency when compared with control. But, dietary organic acids had no significant impacts on feed intake or relative organ weights (Basmacioğlu-Malayoğlu, Ozdemir, & Bağriyanik, 2016 ).

4.3 Carcass and meat quality

The relative weights of carcass depot fat, leg and breast muscles, liver and gizzard were not affected by dietary acidifier at 3, 6 and 9 g/kg of the diet. Breast and leg muscles represented 27.9% and 20.7% (acidifier groups) and 27.7% and 21.5% (control group) of the carcass weight respectively. On the other hand, dietary acidifier treatments did not affect chemical composition of leg and breast muscles, including content of dry matter, fat and protein (Brzóska et al., 2013 ).

On the same trend, in broiler chicks, carcass traits (breast, thigh, liver, heart and gizzard) were not significantly affected by the acidifier (1 ml/L of NufocidL as an organic acid supplement in the drinking water) supplementation (Heidari, Sadeghi, & Rezaeipour, 2018 ). Also, supplementation of acidifiers, Bacillus subtilis and their combination did not affect (p > .05) carcass yield, dressing % and the relative weight of internal organs. The Bacillus subtilis group showed the highest value of breast weight when compared with the acidifier groups (Malik et al., 2016 ).

Youssef et al. ( 2017 ) found that the percentage of carcass yield did not show any significant effect due to dietary treatments, but exhibited a numerical improve in probiotic group (72.84%), followed by lactic acid and antibiotic groups (71.45%) in comparison with the normal group (70.35%). On the same context, the relative weights of gizzard, breast, liver, proventriculus and heart were not affected by the dietary supplements (lactic acid, antibiotic and probiotics) when compared with the control (p > .05). Acidifier's impacts are supported by the findings of other studies which reported that the acidifiers did not affect carcass characteristics and dressing yield of broiler chickens (Ghasemi, Akhavan-Salamat, Hajkhodadadi, & Khaltabadi-Farahani, 2014 Kopecký, Hrnčár, & Weis, 2012 ).

4.4 Impact of acidifier on immunity

The immune system plays a key role in regulating the bird's health (Gadde, Kim, Oh, & Lillehoj, 2017 Yan et al., 2018 ). In this trend, the use of acidifiers in the poultry diets plays a critical role in enhancing the immunity system ((Dibner & Buttin, 2002a , 2002b ). An improvement in the immunological status was observed when broiler chickens fed 0.5% citric acid (Chowdhury et al., 2009 ). Similarly, Abdel-Fattah, Ei-Sanhoury, Ei-Mednay, and Abdul-Azeem ( 2008 ) showed an improvement in the immune response of broilers. Furthermore, the weight of lymphoid organs was increased by the action of acidifiers in this sense, Yan et al. ( 2018 ) observed an increase of the spleen weight in birds that consumed 0.30 g/ kg of sorbic acid, fumaric acid and thymol throughout the grower and finisher period. In addition, on day 42, in the ileal and duodenal mucosa, higher levels of immunoglobulin A were recorded. With regard to layer chicken, employment of acidifiers markedly increased serum protein and serum albumin concentration (Yesilbag & Colpan, 2006 ). Devi et al. ( 2016 ) studied the effects of blends of dietary protected organic acid supplementation on growth parameters, digestibility of nutrient, gas emission, faecal microflora and blood constituents of pigs. The authors found that white blood corpuscles (WBC), immunoglobulin G level and lymphocyte % were improved with protected organic acid groups (0.1% and 0.2%) in sucking piglets and lactating sow. Emami, Daneshmand, Naeini, Graystone, and Broom ( 2017 ) studied influence of three commercial organic acids on growth parameters, caecal microbiology, immunity and intestinal morphology of Escherichia coli K88-challenged (ETEC) broiler chickens. The authors found that dietary supplementation of these organic acids can enhance the ileal morphology and immunity of ETEC- challenged broilers.

Also, Lee et al. ( 2017 ) evaluated the beneficial effects of organic acids on immune responses against viral antigens (H9N2) in broiler chickens and they found that the CD4 + CD25 + T-cell percentage was higher in the OV group (diet supplemented with organic acids and administered a H9N2 vaccine [OV]) than in the control, demonstrating the potential induction of regulatory T cells by feed additive. Liu et al. ( 2017 ) used 450 1-day-old Cobb 500 chicks to evaluate the beneficial role of protected organic acids and essential oils mixture product at 0.30 g/kg. Authors pointed out that supplementation of the product improved crypt depth and villus height of the jejunum, and spleen index at 42 days as compared to control (p < .05). Furthermore, trypsin and chymotrypsin activities of intestinal tract and secretory immunoglobulin A concentration of ileal mucosa were higher in the organic acids and essential oils treatment.

4.5 Impact on intermediary metabolism

Most organic acids contribute a substantial amount of energy during metabolism and should not be overlooked in energy estimation of feedstuffs. Being the intermediates of citric acid cycle, they act as energy source after getting absorbed through the gut epithelium by passive diffusion. As 1 m of fumaric acid generates 18 m ATP or 1,340 kJ, it necessitates approximately 74.3 kJ per m ATP which is comparable with glucose. The same works with citric acid, while the acetic and propionic acid require 18% and 15% more energy per m ATP respectively. Sofos and Busta ( 1993 ) elucidated that sorbic acid and long chain fatty acids are metabolized through ß-oxidation of fatty acids. Giesting and Easter ( 1985 ) assured that weaned piglets under stress may get the advantage of glucogenic, tricarboxylic acid cycle intermediates such as citric or fumaric acid that restrain some tissue breakdown resulting from gluconeogenesis and lipolysis. The growth enhancing effects of acidifiers were also ascribed to their energy contribution. Blank et al. ( 1999 ) illustrated that fumaric acid as a readily available energy source may also have affinity to the small intestinal mucosa and enhance their absorptive surface and capacity due to the rapid recovery of the gut epithelial cells of pigs after weaning.

4.6 Preservation of feedstuffs

For successful livestock farming, continuous supply of good quality feedstuff should be ensured all year round. Even under hygienic conditions, factors like high moisture and warm environment can incur growth of certain fungi, yeast or bacteria, minimizing the feed nutritive value by metabolizing its starch and protein. Depending on the type of organism and the level of infection, conservative agents inhibit the microbial growth and lessen the pathogen uptake by the animal which otherwise cause acute health risks. Formaldehyde, which acts as a potent mould inhibitor (Spratt, 1985 ), enhances the keeping quality of feed for approximately 20 days and is commonly sprayed over the finished feed before package. The buffered propionic acid combined with sodium benzoate in preservation of wet corn showed appreciable difference between the treated and untreated corn (Luckstadt, Zhang, & Wu, 2006 ). The range of fungal counts was only 0 to 30 CFU/g in treated corn while that of untreated group resulted higher levels of 2.6 and 2.7 × 10 6 CFU/g in the low and high moisture content respectively. The authors have also found reduced yeast counts in treated corn and elevated mycotoxins (aflatoxin B1 and zearalenone) in the untreated group.

Use of silage additives has also been intensified over the recent years with acidification being made to enhance fermentation, aerobic stability and nutritive value. Moreover, addition of organic acids and their salts exhibit their antimicrobial activity through undissociated acids as discussed earlier and reduce protein losses by rendering the plant protease enzymes inactive. Formic acid has been used conventionally for ruminant silage while propionic acid is known for its antifungal activity and aerobic stability of silages. The expense of propionic acid has restricted its use to the last few loads at the top of conventional or bunker silos thereby reducing the surface spoilage (Aragon, 2007 ).

4.7 Factors influencing efficacy of acidifier

With the increasing knowledge about the different actions of acidifiers in animal nutrition, a handful of aspects are yet to be inferred. Despite the improved performance recorded in many publications, there exist some conflicting results due to some attributes which could be associated with acid, animal or the dietary factors. This includes the following: the chemical nature (acid, salt, coated or uncoated), pK value of acids, molecular weight, inclusion level and minimum inhibitory concentration of acid, type of microorganism, species and their concentration, animal species, site of action, dietary composition and buffering capacity of feed.

Digesting a chicken sandwich how the digestive, cardiovascular and endocrine systems cooperate in order to provide the cells of the body with energy - Life Sciences bibliographies - in Harvard style

These are the sources and citations used to research Digesting a chicken sandwich how the digestive, cardiovascular and endocrine systems cooperate in order to provide the cells of the body with energy. This bibliography was generated on Cite This For Me on Thursday, May 28, 2015

Alberts, B.

Molecular biology of the cell

2002 - Garland Science - New York

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Food Energy and ATP

2014 - Boundless

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Hepatic Portal Circulation

2014 - Boundless

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Bowen, R.

Enteric Endocrine System

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Cann, K.

Understanding Glycolysis: What It Is and How to Feed It

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Digestive system

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Blood Supply to the Stomach and Pancreas

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Food and Our Digestive Tract

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How does the pancreas work?

2013 - Institute for Quality and Efficiency in Health Care (IQWiG)

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Hormones of the Gut

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The Human GI Tract

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Digestive System - Digestion And Absorption In The Small Intestine

In-text: (Digestive System - Digestion And Absorption In The Small Intestine, 2015)

Protein digestion kinetics in pigs and poultry

Increasing the protein efficiency is considered a main strategy for sustainable feeding of pigs and poultry. In practice, protein in pig and poultry diets originates from different ingredients, selected in diet formulation based on their nutritional value and cost. Currently, the nutritional value of protein sources in pig and poultry diets is based on the concentration of essential amino acids (AAs), and their digestibility up to the end of the ileum or the gastrointestinal tract (GIT) (NRC, 2012 CVB, 2016). The ileal and faecal digestibility of protein and AAs, however, only provide information on the quantity of protein and AAs apparently absorbed up to the end of the ileum or over the entire GIT, respectively. They, however, do not provide information on the kinetics of protein digestion, which might affect the post-absorption metabolism of dietary AAs. The aim of this thesis, therefore, was to provide further insights into digestion kinetics of dietary protein sources in the GIT of pigs and poultry, and the consequences of differences in digestion kinetics of dietary protein for the growth performance of broilers.

Protein digestion kinetics in pigs and poultry

In Chapter 2, in vitro protein digestion kinetics of various protein sources (soybean meal (SBM), wheat gluten (WG), rapeseed meal (RSM), whey powder (WP), dried porcine plasma protein (DPP), yellow meal worm larvae (MW), and black soldier fly larvae (BSF)) were determined using a two-step method. Protein sources were incubated with pepsin at pH 3.5 for 0-90 min and subsequently with pancreatin at pH 6.8 for 0-210 min at 39 °C. Protein sources showed substantial differences in in vitro protein digestion kinetics as measured by the kinetics of N solubilisation and the release of low molecular weight peptides (< 500 Da). The N solubilisation rate ranged from 0.025 min-1 for BSF to 0.685 min-1 for WP during the incubation with pepsin, and from 0.027 min-1 for RSM to 0.343 min-1 for WP during the incubation with pancreatin. The rate of release of low molecular weight peptides ranged from 0.027 min-1 for WG to 0.093 min-1 for WP during the incubation with pepsin, and from 0.029 min-1 for SBM to 0.385 min-1 for WP. Over all protein sources evaluated, no correlation was found between the rate of N solubilisation and the rate of release of low molecular weight peptides.

Based on the in vitro results, SBM, RSM, WG, DPP and BSF were selected for further investigations into in vivo protein digestion kinetics in both pigs (Chapter 3) and broiler chickens (Chapter 4). Forty pigs were randomly allocated to one of the five experimental diets containing the respective protein sources as the only source of protein. Four pigs per experimental diet were fitted with an ear-vein catheter and blood samples were collected before and after a morning meal. At dissection, digesta samples from the stomach and the small intestine, divided into four segments of equal length, were quantitatively collected. Apparent digestibility of crude protein (CP), and retention time (RT) of the solid fraction of digesta along the stomach and the SI were determined to calculate protein digestion kinetics. The initial protein digestion rate ranged from 0.68 % · min-1 for the RSM based diet to 3.04 % · min-1 for the DPP diet. A higher digestion kinetics of dietary protein resulted in a more rapid and pronounced postprandial appearance of AAs and peptides in systemic blood of pigs.

In the broiler trial, a total of 378 26-day-old male broilers with average body weight of 1430 ± 48 g were randomly allocated to 42 pens. Pens were randomly allocated to one of the seven diets (i.e. a basal diet and six experimental diets with SBM, soy protein isolate (SPI), WG, RSM, DPP or BSF as the main protein source). At dissection, digesta samples from the crop, gizzard, duodenum, proximal jejunum, distal jejunum, and ileum were quantitatively collected. The CP digestion kinetics of the experimental diets were calculated by relating the apparent CP digestibility coefficient at each segment of the small intestine to the sum of digesta retention up to that segment. The initial protein digestion rate ranged from 1.76 % · min-1 for the RSM based diet to 30.7 % · min-1 for the WG based diet.

Mechanism of protein hydrolysis in the GIT of pigs and poultry

It was hypothesised that proteins present in highly digestible protein sources (i.e. WG and DPP) are more susceptible to hydrolysis by digestive enzymes than slow digestible protein sources (i.e. SBM, RSM and BSF) and that enzymatic hydrolysis of protein progress stepwise in the small intestinal intestine, resulting in hydrolysis products (peptides) becoming smaller in size towards the end of the small intestine. As a consequence, relatively more low and intermediate molecular weight peptides were expected to be present in ileal digesta of pigs and broilers fed highly digestible protein sources, compared to sources with a lower digestibility. The molecular weight distribution of soluble proteins and peptides in digesta from the different segments of the GIT of pigs and broilers was analysed using size exclusion chromatography (Chapter 3 and 4). The molecular weight distribution of proteins and peptides in ileal digesta of pigs and broilers fed highly digestible protein sources was comparable to those of pigs and broilers fed low digestible protein sources. In addition, the molecular weight distributions were rather similar throughout segments of the GIT. These results indicate that proteins from both highly and low digestible sources follow a “one-by-one” type of hydrolysis mechanism, meaning intact proteins are hydrolysed to low molecular weight peptides and free AAs and absorbed by the intestinal mucosa in one sequence. As a result, proteins and peptides with a wide range of molecular weights were not observed in digesta of different segments of the GIT. Approximately 30 % of peptides present in ileal digesta of pigs are < 10 kDa in dependent of protein source, whereas almost no peptides < 10 kDa were found in the ileal digesta of broilers.

Synchronisation the supply of dietary starch and protein

The effects of synchronising the supply of dietary protein and starch using information on their kinetics of digestion on the growth performance and carcass characteristics in broilers was investigated (Chapter 5). Two starch and two protein sources were used: pea starch (PS) and SBM as slowly digestible sources while rice starch (RS) and SPI as fast digestible sources. Broilers fed diets synchronised for digestion rate of starch and protein (i.e. PS-SBM (slow-slow) and RS-SPI (fast-fast)) did not show a higher growth performance and breast meat yield compared to broilers fed the asynchronised diets (i.e. RS-SBM (fast-slow) and PS-SPI (slow-fast)). The evaluation of the effect of synchronising the supply of dietary starch and protein, however, was hindered by feed intake being affected by dietary protein and starch source. Feed intake of birds was higher when fed diets with SBM compared to SPI and when PS was fed instead of RS.


The results of the present thesis indicate that the kinetics of protein digestion in the GIT of pigs and poultry differs substantially among protein sources. Wheat gluten and DPP can be regarded as fast digestible protein sources while SBM, RSM and BSF are more slowly digestible protein sources in both pigs and broilers. Broilers showed on average a 2.7-fold higher small intestinal protein digestion rate than pigs, excluding and with the exception of WG, for which the protein digestion rate was very high in broilers compared to pigs. However, despite differences in intrinsic characteristics (e.g. AA composition, protein conformation, physicochemical properties) of protein sources and in digestive physiology of pigs and poultry, the mechanism of hydrolysis of dietary proteins in the gut seems rather similar. Synchronising the digestion kinetics of dietary starch and protein using both fast digestible sources or both slowly digestible sources did not improve the performance nor the breast muscle yield of ad libitum fed broilers kept under an intermittent light regime.

  • Wageningen University
  • Hendriks, Wouter , Promotor
  • Jansman, Alfons , Co-promotor
  • Wierenga, Peter , Co-promotor

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