All components of food are not digested in mono-gastric animals like poultry and pigs. It is now common to supplement enzymes to their diet for improved performance. Plant cell walls are fibrous in nature and cannot be digested by endogenous enzymes of chicken and pigs. With advances in biotechnology, enzymes are now produced in large quantities and at low cost.
Cellulase can improve the availability of starch, oils, and proteins by digesting the plant cell walls. Addition of cellulase in pigs and poultry resulted in 5 to 10% improvement in growth rate and 10% improvement in feed conversion ratio. Beta glucans and arabinoxylans present in the cell walls are resistant to break down and they hinder the digestion and absorption of other nutrients by forming a viscous gum. Increase in viscosity of digesta disturbs peristalsis and pancreatic secretion and results in poor performance with sticky droppings in poultry.
Supplements of beta glucanase to barley and sorghum-based diets improved the performance of broilers and reduced litter problems. Viscous digesta prevents proper mixing of endogenous enzymes with digest and thereby prevents the release of nutrients. Enzyme phytase addition to diets of poultry and pigs results in greater availability of phosphorous from cereal grains and oilseeds. This will reduce the amount of inorganic phosphorous added in the diet.
In young animals the rate of endogenous enzyme production is low and supplementation of amylase, protease, and lipase increased the availability of nutrients and improved performance. Enzyme supplementation increased the digestion and absorption of nutrients in the small intestine rather than allowing fermentation of nutrients in the hindgut which results in the production of lower value like volatile fatty acids and also prevents diarrhea.
In order to be effective, supplemented enzymes must survive storage at ambient temperature, fluctuation in pH of the gut and should be resistant to intestinal proteases. Commercial enzymes are derived to survive these conditions. Commercial enzymes are derived from fungi such as Aspergillus niger, Humicola insolens.
Oligosaccharides (2 -20 monosaccharide units) act as beneficial nutritional modifiers for monogastric animals. Generally, they are known as pre-biotics which are defined as compounds other than dietary nutrients that modify the balance of microbial population by promoting the growth of beneficial bacteria. The addition of a limited amount of oligosaccharides to animal feeds (below 1%) can result in significant improvement of growth rate, feed conversion ratio, and health status of the animal.
Commonly used pre-biotics are galacto-oligosaccharides (GOS), fructo-oligosaccharides (FOS), and manno-oligosaccharides (MOS). Species such as Salmonella and E.coli have a mannose-specific lectin which binds to mannose residues on the gut mucosal surface. By adding MOS, pre-biotics are not digested by host digestive enzymes and pass into the hindgut and fermented by favorable bacteria which shift microbial population away from harmful species. Pre-biotics interfere with attachment of harmful bacteria to the gut wall. Species such as Salmonella and E.coli have a mannose-specific lectin which binds to mannose residues on the gut mucosal surface. By adding MOS in the diet, the binding by pathogenic bacteria is disrupted and instead they bind to the oligosaccharides and are excreted. Yeast has mannose in the cell wall structure and thus yeast products are useful.
A probiotic is defined as a live microbial food supplement that beneficially affects the host animal by improving the intestinal microbial balance. The inclusion of probiotics in foods is designed to encourage certain beneficial bacteria in the gut at the expense of harmful bacteria. In poultry at the time of hatching the intestinal tract is sterile but becomes rapidly colonized by microorganisms from the environment. Within a few hours, Lactobacilli appear and persists there throughout the life. It takes several weeks for the complete establishment of adult type micro-flora.
The beneficial micro-organisms produce enzymes which complement the digestive ability of the host and their presence provides a barrier against invading pathogens. Digestive upsets are common at times of stress such as weaning but feeding with desirable bacteria such as Lactobacilli in these situations is preferable to using antibiotic which destroy the desirable bacteria along with harmful species.
Pro-biotics exert competitive exclusion process of harmful bacteria such as E.coli by attaching themselves with specific oligosaccharide receptor sites of the gut wall. They neutralize the endotoxin produced by pathogenic bacteria. Lactobacilli ferment lactose to lactic acid reducing the pH which cannot be tolerated by harmful bacteria. Hydrogen peroxide is also produced which inhibits the growth of gram-negative bacteria. Some probiotics also produce antibiotics which kill the harmful bacteria. Pro-biotics also prevent synthesis of amines by Coliform bacteria which are toxic and produce diarrhea. They also enhance immunity. To be effective the beneficial microbes should not be harmful to the host, should be resistant to bile, should colonize the gut efficiently, should inhibit pathogenic activity and should be viable under manufacturing and storage conditions.
In ruminants, the Saccharomyces cerevisiae proved effective in beneficially modifying rumen fermentation. Live yeast cultures scavenge oxygen and maintain anaerobic conditions in the rumen. It also improves live weight gain, milk yield, and milk fat contents.
(4) Role of vitamins in animal nutrition
The vitamins are divided into fat-soluble (vitamins A, D, E, and K) and water-soluble vitamins (B complex vitamins and vitamin C).
- Vitamin A: is concerned with vision in dim light and its deficiency may cause night blindness. It is involved in the formation and protection of epithelial tissues and mucous membranes. Ruminants do not suffer from Vit-A deficiency as they consume pasture grass which has high Beta- carotene the precursor of Vit-A. Poultry requires supplementation of Vit-A as most of the concentrate foods are lacking it.
- Vitamin D:Ruminants which are on pastures do not suffer from Vit-D deficiency as the provitamins are converted into Vit-D on exposure to sunlight. Poultry requires Vitamin D3 supplementation as they are not exposed to sunlight. Deficiency of Vit- D causes rickets in young animals and osteomalacia in adult animals.
- Vitamin E: works as an antioxidant along with Selenium. Vit- E deficiency causes muscular dystrophy in cattle and pigs. Vit- E deficiency causes muscular dystrophy, encephalomalacia, and exudative diathesis in poultry.
- Vitamin K: is very important for the blood clotting process. This vitamin is present in adequate amount in many foods and deficiency is rare.
- Vitamins B: complex function in the body as a coenzyme or prosthetic groups
- Thiamine: is widely distributed in foods and therefore deficiency is limited.
- Riboflavin: occurs in all biological materials. Chicks reared on a riboflavin-deficient diet grow slowly and develop curled toe paralysis.
- Nicotinamide: Nicotinic acid is synthesized from the amino acid tryptophan in body tissues. Deficiency symptoms in pigs cause poor growth. While in poultry causes feathering abnormalities and bone disorders.
- Vitamin B6: acts as a coenzyme for many enzymes and plays important role in protein metabolism. In practice, Vit- B6 deficiency is unlikely to occur because of its wide distribution.
- Pantothenic acid: is widely distributed in foods. It is a constituent of coenzyme A which is required in the metabolism of nutrients.
- Folic Acid: is widely distributed in foods and a deficiency condition rarely occurs.
- Biotin: is also widely distributed in foods and is essential as a prosthetic group of several enzymes.
- Choline: It is a component of Lecithin. It plays important role in lipid metabolism. Fatty infiltration of the liver occurs in of chicks and pigs. Green leafy materials, yeast, egg yolk, and cereals are rich sources.
- Vitamin B12: is synthesized by microorganisms. The main natural source of the vitamin is foods of animal origin. Adult animals are less affected by Vit-B12 deficiency than young growing animals. The growth is retarded and mortality is high in such cases. A dietary source of cobalt is required for synthesis of Vit-B12 by rumen microbes.
Rumen microbes generally synthesize all B-Complex vitamins required by ruminants and therefore ruminants are unlikely to suffer from their deficiency.
- Vitamin C: is well known to available in citrus fruits and green leafy vegetables. As an antioxidant, ascorbic acid works in conjunction with Vit-E in protecting cells against oxidative damage caused by free radicals. Farm animals can synthesize this vitamin from glucose.
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