Absence of limiting amino acids in calves fed a corn and soybean meal dietpast 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 (Tri al 3; n = 9) in a 4 x 4 (Trial 1) or 3 x 3 Latin square design (Trials 2 an d 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 aft er 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 resul ted in reduced urinary excretion of purine derivatives, suggesting reduced synthesis of ruminal microbial protein (Trial 1). In Trials 1 and 2, admini stration of DL-methionine plus L-lysine monohydrochloride through the retic ular groove did not increase N retention compared with the supplement of is onitrogenous L-glutamine at either level of intake. In Trial 3, administrat ion of either casein or isonitrogenous monosodium glutamate increased N ret ention to a similar extent above that observed with a N-free supplement. Re sults suggested that no specific amino acids were limiting for the corn-soy bean meal diet. Administration of methionine plus lysine resulted in a rema rkable increase in plasma methionine (Trials 1 and 2), especially at the lo wer intake level (Trial 1), and a decrease in plasma branched-chain amino a cids at either intake level. Glutamine supplementation did not increase pla sma branched-chain amino acids compared with the supplementation of diammon ium citrate (Trial 2).