Performance of Lactating Dairy Cows Fed Methionine or Methionine Analog at Two Concentrations of Dietary Crude Protein

Abstract

Holstein cows (24) were in a balanced incomplete block switchback design to determine the effect on milk production and composition of DL-methionine or methionine analog when 2 concentrations of dietary protein were fed to supply either adequate or marginal crude protein in the diet. Dietary treatments consisted of 80% or 100% of the cows'' requirement for crude protein supplemented with no additive, DL-methionine, or methionine analog. Cows fed 100% of crude protein requirements consumed more soybean meal and less corn than cows fed 80% of crude protein requirements, but total dry matter intake was not affected. Milk yield and composition were not affected by concentration of crude protein in the diet. Feeding 100% of crude protein requirements increased rumen NH3-N concentration but did not affect pH or volatile fatty acid concentrations or proportions. Compared to control, supplemental methionine or methionine analog did not affect significantly any of the above measurements at either concentration of crude protein in the diet.