Substance depressing digestion or metabolic utilization of proteins

SUBSTANCE DEPRESSING DIGESTION OR METABOLIC UTILIZATION OF PROTEINS

Protease Inhibitors:

  • Substance that inhibit proteolytic enzymes and thereby growth in non-ruminants are abundant in seeds and legumes.
  • Six protein inhibitors have been identified in soybean; out of these, two inhibitors namely Kunitz anti-trypsin inhibitor and Bowman-Birk chymotrypsin inhibitors are practically significant.
  • Trypsin inhibitors especially interferes the protein digestion in monogastric animals.
  • Protein indigestibility affects growth rate, egg production and feed efficiency and also may lead to hypertrophy of pancrease and excess endogenous loss of essential amino acids.
  • The inhibitory substances are mostly heat labile and thus before feeding any leguminous grain to non-ruminants, it is generally corrected by proper heat treatment.
  • Since overheating can damages some nutrients, such as amino acids and vitamins, quality control tests have been developed to assess the adequacy of heat treatment.
  • These include trypsin inhibitor and urease assays, cresol red absorption, protein dispersibility index (PDI) and nitrogen solubility index (NSI).

 
  • Kunitz anti-trypsin inhibitor; Bowman-Birk chymotrypsin inhibitors are important
  • Interferes the protein digestion.
  • Affects growth rate, egg production and feed efficiency.
  • Heat treatment nullifies the toxic effect.
  • Test for overheating

Lectins or ricin (hamagglutinins):

  • Ricin in castor bean cake is a toxic fraction capable of agglutinating human red blood cells.
  • Lectins are proteins capable of binding carbohydrate moieties in the epithelial cell lining of small intestine, disrupting the brush border and reducing the efficiency of absorption.
  • Lectins are destroyed by the same conditions as those used to inactive protease inhibitors.

  • Lectins reduce absorption capacity.
  • Heat treatment destroys lectins

Saponins:

  • Leguminous fodders such as lucerne, white clover, red clover and soyabean contains saponin at 3% and causes saponin poisoning in livestock that can be avoided by mere water soaking and rinsing.
  • Saponins are bitter in taste, lather forming and inhibit the action of proteolytic enzymes.
  • They also causes haemolysis of red blood cells.
  • Adverse Actions upon excessive eating:
    • In ruminant saponins results in formation of bloat by altering the surface tension of the ruminant contents due to entrapment of countless bubbles of fermentation gases throughout the ingesta.
    • The compound has got the ability to lyse red blood cells.
    • In general the effects of ingestion of saponins include excessive salivation, increased respiratory tract secretion, gastroenteritis, vomiting, diarrhoea, haemolysis, haematuria, bloating, reduction of gastric motility, reduction of food intake, reduction of growth rate.
  • Legume fodders are liable to produce “bloat” if given in large quantities and thus it is advisable that they should always be given along with some dry fodder.

  • Saponins are bitter in taste & lather forming.
  • Saponins alter the surface tension of rumen fluid.
  • Gas is trapped in small bubbles in foam in the rumen causing Bloat.
  • Saponin rupture RBC.
  • Increased secretion of saliva.
  • In respiratory tract.
  • In GI tract – Vomition / Diarrhoea

Polyphenolic compounds (tannins):

  • Also known as tannic acid, gallotannin and gallotannic acid.
  • Thy are naturally occurring compounds having high molecular weight (500-3000) and containing a sufficiently large number of phenolic hydroxyl groups to enable them to form effective cross-links between proteins and other macromolecules.
  • Chemically tannins may be grouped into two broad categories:
    • Hydrolysable tannin and
    • Condensed tannins.
  • Tannins bind proteins.
  • The low palatability of some herbage plants and some grains have been attributed to their high tannin content.
  • Many plants employ tannins to deter animals from being grazed.
  • They are also markedly astringent – that is they cause a dry or puckery sensation in the mouth, by reducing the lubricant action of the glycoproteins in the saliva.
  • Tannins reduce the bioavailability of plant sources of iron.
  • High tannin content also depress cellulose activity and thereby affects digestion of crude fibre.
  • Tannins may cause loss of mucus, epithelial edema, irritation and damage of alimentary canal tissue, which in turn facilitate greater tannin absorption, thus causing toxicity.

  • Form effective cross-links between proteins; other macromolecules.
  • Binds protein.
  • Lowers palatability.
  • Dry sensation in mouth.
  • Reduces iron absorption.
  • Depress cellulase activity.
  • Damaged GI tissue facilitate greater tannin absorption; toxicity.

Last modified: Monday, 29 August 2011, 10:20 AM