Beef Species Symposium: An assessment of the 1996 Beef NRC: Metabolizable protein supply and demand and effectiveness of model performance prediction of beef females within extensive grazing systems

Interannual variation of forage quantity and quality driven by precipitation events influence beef livestock production systems within the Southern and Northern Plains and Pacific West, which combined represent 60% (approximately 17.5 million) of the total beef cows in the United States. The beef cattle requirements published by the NRC are an important tool and excellent resource for both professionals and producers to use when implementing feeding practices and nutritional programs within the various production systems. The objectives of this paper include evaluation of the 1996 Beef NRC model in terms of effectiveness in predicting extensive range beef cow performance within arid and semiarid environments using available data sets, identifying model inefficiencies that could be refined to improve the precision of predicting protein supply and demand for range beef cows, and last, providing recommendations for future areas of research. An important addition to the current Beef NRC model would be to allow users to provide region-specific forage characteristics and the ability to describe supplement composition, amount, and delivery frequency. Beef NRC models would then need to be modified to account for the N recycling that occurs throughout a supplementation interval and the impact that this would have on microbial efficiency and microbial protein supply. The Beef NRC should also consider the role of ruminal and postruminal supply and demand of specific limiting AA. Additional considerations should include the partitioning effects of nitrogenous compounds under different physiological production stages (e.g., lactation, pregnancy, and periods of BW loss). The intent of information provided is to aid revision of the Beef NRC by providing supporting material for changes and identifying gaps in existing scientific literature where future research is needed to enhance the predictive precision and application of the Beef NRC models

Amino acid requirements of South African Mutton Merino lambs 3. Duodenal and whole empty body essential amino acid profile

CITATION: Ferreira, A. V., Van Der Merwe, H. J. & Loest, C. A. 1999. Amino acid requirements of South African Mutton Merino lambs 3. Duodenal and whole empty body essential amino acid profile. South African Journal of Animal Sciences, 29(1):40-47.The original publication is available at https://www.sasas.co.za/The duodenal and whole empty body essential amino acid (EAA) profile of South African Mutton Merino lambs fed a standard growth diet was investigated. The data of 20 lambs were used. With the exception of phenylalanine, significant (p < 0.05) differences between the EAA concentrations of the duodenal digesta and whole empty body occurred. From the chemical score, it was concluded that the duodenal digesta was first-limiting in histidine and second-limiting in methionine, followed by threonine and arginine for the whole empty body growth of South African Mutton Merino ram lambs fed a standard diet high in rumen degradable protein. A calculated essential amino acid composition for the correction of imbalances in duodenal digesta was as follows (%): 11.21 arginine; 14.53 histidine; 8.17 isoleucine; 9.97 leucine; 8.64 lysine; 13.87 methionine; 9.97 phenylalanine; 12.54 threonine and 11.11 valine.https://www.sasas.co.za/journals/amino-acid-requirements-of-south-african-muttton-merino-lambs-3-duodenal-and-whole-empty-body-essential-amino-acid-profile/Publisher's versio