Kenneth Bruerton PhD 11 August 2011 Breaks down ◦ Protein Digested to amino acids by rumen micro-organisms and resynthesized into microbial protein. This is digested in the small intestine to amino acids which are absorbed and used for growth (enzymes, immune proteins, muscle protein). Some amino acids can be used to make glucose for energy production in specialized tissues such as brain and formation of rapid energy stores (liver and muscle glycogen). ◦ Fibre (cellulose, hemicellulose, lignin). Only digested in the rumen by certain micro-organisms. What is undigested is excreted in the faeces. Producing volatile fatty acids (VFAs) such as propionate and butyrate which are absorbed in the small intestine and used for energy production and fat synthesis. ◦ Starch, sugars Digested rapidly in the rumen to form lactate or acetate. Excess fermentation of starch can cause acidosis, particularly in lotfed cattle receiving grain. Urea Supplies Nitrogen (N). Contrary to common belief Urea is not protein. Urea is a simple N compound. Urea is ~45% N = 281% crude protein equivalent. Rumen microorganisms can convert N to ammonia which is converted to amino acids and microbial protein. Urea can supply up to 1/3 of the total protein requirement of cattle. However at these levels sufficient fermentable energy must be supplied to allow utilization of available N Urea CO2 Carbohydrates Keto Acids Microbial Urease Microbial Enzymes Keto Acids + NH3 Amino Acids Amino Acids Microbial Protein Microbial Protein Free Amino Acids NH3 + FA + Microbial Enzymes Microbial Enzymes Small Intestine Enzyme Free Amino Acids Absorbed Toxic dose generally regarded as 0.5grams/kg LWT in a single feeding episode. Sulphate of Ammonia (NH4)2SO4 Supply N as with urea. Contains approx ½ the level of N as urea Important source of Sulphur (S) Sulphur required as a precursor to the production amino acids N:S ratio should be in the range of 12-15:1 SO4 often used to control intake (more bitter than urea ) More expensive source of N than urea Elemental Sulphur Source of S. Less available source of S than SO4. Protein Meal Source of Rumen Escape Protein Source of Energy to aid utilization of Urea. Used to manipulate intake. Commonly used meals include Cotton Seed Meal 43% Copra Meal 20% Canola Meal 35% Soybean meal 48% PKE 15% Very important to calculate the input cost of the protein.