Response of Holstein steers fed a soybeanhull-based diet to amino acid supplementationwhen the methionine requirement was met

摘要

A study was conducted to determine theresponse to amino acid supplementationwhen the first limiting amino acid(methionine) was provided in excess. Threeruminally cannulated Holstein steer calves(281 lb) were fed 4.8 lb of a soybean hullbaseddiet (87% soyhulls and 8% wheatstraw) daily. Methionine is the first limitingamino acid on diets of this type, and allsteers were abomasally infused with 10g/day of methionine to ensure that this requirementwas met. Treatments consisted ofincreasing amounts (100, 250, or 400 g/day)of an amino acid mixture suppliedabomasally. Calves received decreasingamounts of supplemental energy in the formof volatile fatty acids and dextrose as aminoacid infusion increased in order for treatmentsto remain isoenergetic. Nitrogenbalance increased as amino acid supplyincreased, indicating that amino acids otherthan methionine limited protein deposition.The nitrogen balance change between the100 and 250 g/day amino acid treatmentswas greater than that from 250 to 400 g/d,suggesting that 250 g/day supplied amountsof amino acids near the requirement.