ANN 111: Principles of Animal Nutrition and Feed Technology (2+1)

ADDITIVES THAT PROMOTES GROWTH AND PRODUCTION

Antibiotics

• These are substances which are produced by living organisms (mould, bacteria or green plants) and which in small concentration have bacteriostatic or bactericidal properties.
• They were originally developed for medical and veterinary purposes to control specific pathogenic organisms.
• Later it was discovered that certain antibiotics could increase the rate of growth of young pigs and chicks when included in their diet in small amounts.
• Soon after this report a wide range of antibiotics have been tested and the following have been shown to have growth promoting properties: penicillin, oxytetracycline (Terramycin), chlortetracycline, bacitracin, streptomycin, tyrothricin, gramicidin, neomycin, erythromycin and flavomycin.
• Increased weight gain is most evident during the period of rapid growth and then decreases.
• Differences between control and treated animals are greater when the diet is slightly deficient or marginal in protein, B-vitamins or certain mineral elements.

Mode of action of antibiotics

• Antibiotics “spare” protein, amino acids and vitamin on diets containing 1 to 3 per cent less protein, but balance experiments have often failed to show increased nitrogen retention. Growth stimulation has been greatest when the antibiotic penicillin supplement has been added to a ration containing no protein supplements of animal origin or to a ration low in vitamin B₁₂. Under hygienic conditions growth increases are small.
• Intestinal wall of animals fed antibiotics is thinner than that of untreated animals which might explain the enhanced absorption of calcium shown for chicks.
• Reduce or eliminate the activity of pathogens causing “subclinical infection.”
• Reduce the growth of micro-organisms that compete with the host for supplies of nutrients.
• Antibiotics alter intestinal bacteria so that less urease is produced and thus less ammonia is formed. Ammonia is highly toxic and suppresses growth in non-ruminants.
• Stimulate the growth of micro-organisms that synthesise known or unidentified nutrients.

Following points should be kept in mind while using antibiotics for animal feeding:

• Antibiotics should be used only for
  • growing and fattening pigs for slaughter as pork or bacon;
  • growing chicks and turkey poults for killing as table poultry.
• Antibiotics should not be used in the feed of ruminant animals (cattle, sheep and goats), breeding pigs and breeding and laying poultry stock.
• While adding antibiotics at the recommended level, care should be taken that they are thoroughly and evenly mixed with the feed.
• For best results, antibiotics should be used with properly balanced feeds. Also, the feeds containing antibiotics should be fed only to the type of stock for which they are intended.
• Antibiotics are not a substitute for good management and healthy living conditions, or for properly balanced rations.

Probiotics

• It is defined as a live microbial feed supplement, which beneficially affects the host animals by improving its intestional microbial balance. The probiotic preparation are generally composed of organisms of lactobacilli and/or streptococci species, few many contain yeast caltones.
• They benefit the host by:
  • Having a direct antagonistic effect against specific group of undesirable or harmful organism through production of antibacterial compounds, elementary or minimising their competition of nutrients.
  • Altering the pattern of microbial metabolism in the gastro intentional tract.
  • Stimulation of immunity.
  • Neutralisation of enterotoxins formed by pathegenic organism.
• Thus resulting in increased growth rate, improved feed efficiency