Amino acid requirements and biological value of proteins for sheep.

An intragastric infusion model was used to determine the biological value of three protein sources for sheep. Biological value was calculated from the regression of urinary nitrogen on nitrogen intake. A casein-amino acid mixture corresponding to previously determined metabolic amino acid requirements as well as casein alone and gelatin was studied. The biological values determined were 1.00 for enriched casein, 0.87 for casein and 0.07 for gelatin. The intercept values, which correspond to the endogenous losses, were approximately 245 mg N/kg 0.75 body weight and did not differ significantly between protein sources or experiments. The data support the proposed metabolic amino acid requirements for sheep for maintenance and wool growth.