Swine Species Symposium. Improving Sow Productivity: Recent Developments in Gilt and Lactation Management

portion of UIP and the amino acid spectrum of the UIP. Therefore, it is absolutely essential to measure or predict the relative amounts of MP (metabolizable protein) from microbes and UIP in any given feeding scenario. Both the production potential of the beef animal and microbial protein synthesis are driven by energy. It is impossible to predict MP supplied to the lower gut and MP needs of the animal without having accurate estimates of energy needs, energy supplies and ruminal energy availability. While there are many variations on beef production systems, most are based on high grain (finishing) diets or high forage diets. Forage contains little UIP and that UIP appears to be poorly digested (<50%). Without supplements, essentially all of the MP in forage feeding situations is supplied by microbes. Site of carbohydrate digestion (NDF) is relatively predictable and methodology for measuring forage protein degradation is relatively precise (NDF-N). Degradable intake protein (DIP) may be deficient in some situations. Microbial protein synthesis efficiency decreases as diet TDN decreases from 60% down to 45 to 50%. Low microbial production and low forage UIP create MP deficiencies in many forage feeding situations. On high grain diets, energy supply is high but microbial efficiency is limited by low ruminal pH. Site of carbohydrate digestion (starch) varies with grain type and processing. Estimation of ruminal degradation of grain (starch and protein) is not precise. DIP is usually required. Byproducts reduce starch, raise pH and add protein (maybe DIP or UIP depending on byproduct). Corn is high in UIP and the UIP is highly digested (>90%). Therefore feedlot cattle generally have adequate supplies of MP. It is difficult to produce an amino acid deficiency in feedlot cattle. Growing cattle can be deficient in specific amino acids depending upon the amino acid balance in the UIP.