Absence of limiting amino acids in calves fed a corn and soybean meal diet past three months of age

We conducted three nitrogen balance trials using Holstein bull calves older than 16 wk (Trial 1; n = 8), 13 wk (Trial 2; n = 6), and 15 wk of age (Trial 3; n = 9) in a 4 x 4 (Trial 1) or 3 x 3 Latin square design (Trials 2 and 3) to identify limiting amino acids for a corn and soybean meal diet. All calves were trained to maintain reflex closure of the reticular groove after weaning at 5 wk of age. The basal diet was fed daily at 20 or 27 g/kg BW (Trial 1) and at 20 g/kg BW (Trials 2 and 3). The lower feeding level resulted in reduced urinary excretion of purine derivatives, suggesting reduced synthesis of ruminal microbial protein (Trial 1). In Trials 1 and 2, administration of DL-methionine plus L-lysine monohydrochloride through the reticular groove did not increase N retention compared with the supplement of isonitrogenous L-glutamine at either level of intake. In Trial 3, administration of either casein or isonitrogenous monosodium glutamate increased N retention to a similar extent above that observed with a N-free supplement. Results suggested that no specific amino acids were limiting for the corn-soybean meal diet. Administration of methionine plus lysine resulted in a remarkable increase in plasma methionine (Trials 1 and 2), especially at the lower intake level (Trial 1), and a decrease in plasma branched-chain amino acids at either intake level. Glutamine supplementation did not increase plasma branched-chain amino acids compared with the supplementation of diammonium citrate (Trial 2).