Adverse effects of excess DL-methionine in calves with different body weights

Adverse effects of excess methionine were examined using 12 Holstein bull c alves trained to maintain reflex closure of the reticular groove even after weaning at 5 wk of age. Two nitrogen balance experiments were conducted fo r 2 wk each from 6 wk (Stage 1; BW = 62 kg) and 12 wk of age (Stage 2; BW = 103 kg) by dividing the calves into three groups at each stage. Calves wer e fed a corn-soybean meal diet at 62 g/kg of metabolic BW at both stages. A t Stage 1, feed efficiency (gain:feed intake) and nitrogen retention did no t differ between the group supplemented with .333 g of DL-methionine and .1 11 g of L-lysine monohydrochloride/kg BW per day and the group supplemented with isonitrogenous diammonium citrate, although the level of DL-methionin e was considered to be enough to induce toxicity. Conversely, administratio n of isonitrogenous casein increased nitrogen retention. At Stage 2, admini stration of the same levels of methionine and lysine resulted in reduced fe ed intake, depressed nitrogen retention, and BW loss. Conversely, administr ation of the isonitrogenous casein did not increase nitrogen retention comp ared with the supplement of isonitrogenous diammonium citrate. Administrati on of excess methionine and lysine increased plasma methionine concentratio ns up to 230 (Stage 1) or 190 mu mol/dL (Stage 2). Plasma lysine concentrat ions were less than 24 mu mol/dL at every stage. Administration of the amin o acid mixture decreased plasma concentrations of branched-chain amino acid s and phenylalanine more obviously at Stage 2 than at Stage I. These result s indicated that abomasal administration of .333 g of DL-methionine/kg BW p er day induced methionine toxicity at Stage 2 but methionine imbalance at S tage 1.