Sulfur amino acid utilization by growing steers (1995)

Abstract

SummaryTwo studies were conducted to evaluate sulfur amino acid requirements of growing steers. In trial 1, six ruminally cannulated steers (352 lb) were used to determine methionine requirements . Treatments were abomasal infusi ons of 0, 2, 4, 6, 8, or 10 g/day of Lmethion ine. Steers were fed 5.8 lb of a soyhull and wheat straw based diet. Continuous infusion s of acetate, propionate, and butyrate into the rumen and of dextrose into the abomasum were made to increase energy. Amino acids other than methionine were infused into the abomasum to ensure that they did not limit steer performance. Nitrogen retention increased dramatically as methionine supplementation increased and, in the presence of excess cystei ne, predicted a requirement of 4 g/day of supplemental L-methionine. Plasma methionin e rose with methionine supplementatio n and predicted a supplemental methionine requirement of 2 g/day. In trial 2, five ruminally cannulated steers (429 lb) were used to det ermine how efficiently methionine is converte d to cysteine in growing cattle. The experimenta l procedures were similar to those of trial 1, except steers received a basal supplemen t of amino acids containing 4 g/day L-methionin e (requirement in the presence of excess cysteine established in trial 1) and no cysteine. Treatments consisted of abomasal infusions of 0, 1.62, or 3.25 g/day of L-cysteine or 2 or 4 g/day of additional L-methionine. Nitrogen retention was increa s ed by methionine, but not by cysteine, suggesting that cysteine could supply less than one-half of the total sulfur amino acid requirement (methionine + cysteine) of growing steers.

Determination of the methionine requirement of growing double-muscled Belgian blue bulls with a three-step method.

“…Considering that Met represents roughly 2% of the body protein (Gabel et al, 1988), the efficacy of deposition of the infused Met reached 12.5% in this study, whereas values obtained by Campbell et al (1997) and Titgemeyer et Merchen (1990a) were, respectively, 24 and 33%. These values confirm that Met is probably used to ends other than protein accretion.…”

“…Campbell et al (1997) reported, however, that Met requirement was near 8.4 g/d when the Cys supply reached 2.1 g/d and that supplementation of Cys did not spare Met. The proportion of Met and Cys provided in this study is, therefore, very close to that of Campbell et al (1997).…”

“…If the apparent intestinal digestibility of Cys is supposed to be equivalent to that of TAA, the digestible supply of Cys would reach 5.6 g/d. If the digestibility of Cys is assessed to 59% (Campbell et al, 1997), the supply of this AA would reach 4.7 g/d and could be too low to minimize Met transulfuration. Campbell et al (1997) reported, however, that Met requirement was near 8.4 g/d when the Cys supply reached 2.1 g/d and that supplementation of Cys did not spare Met.…”

“…If the digestibility of Cys is assessed to 59% (Campbell et al, 1997), the supply of this AA would reach 4.7 g/d and could be too low to minimize Met transulfuration. Campbell et al (1997) reported, however, that Met requirement was near 8.4 g/d when the Cys supply reached 2.1 g/d and that supplementation of Cys did not spare Met. The proportion of Met and Cys provided in this study is, therefore, very close to that of Campbell et al (1997).…”

“…For Campbell et al (1997), Met may be used for several functions other than protein accretion, in particular as donor of methyl groups or as precursor of Cys. Even if it is an NEAA, Cys may influence the Met requirement.…”