Milk Production Response to Supplementation with Encapsulated Methionine per Os or Casein per Abomasum,

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Abstract
An encapsulated methionine product containing kaolin, tristearin and DL-methionine, formulated to protect the amino acid from rumen degradation, was fed to provide 45, 15, or 5 g per day of methionine to eight lactating dairy cows averaging 26 kg milk per day. The cows were at least six weeks postpartum and were fed concentrate according to production and urea supplemented corn silage ad libitum. The total ration contained 15 to 16% crude protein on a dry matter basis. The cows were divided into two groups of equal production in a switchback experiment. No statistically significant effects on production due to methionine feeding were noted for any treatment. Though not determined at 45 g per day, plasma methionine (P < 0.10) and methionine/valine ratio (P < 0.01) increased in all cows at 15 g per day of methionine. At 5 g per day, only the methionine/valine ratio in the highest producing cows was elevated (P < 0.01). In a second experiment, either casein or control solutions were administered 24 hours per day by way of abomasal fistulae to three cows averaging 31 kg milk per day. The same basal ration and switchback design were used. With the casein treatment, each cow received an average of 800 g per day sodium caseinate plus 24 g per day methionine. Glucose-urea (isocaloric, isonitrogenous with the casein solution) or saline solutions were infused as controls. Significant effects noted with casein infusion were a 6.2% increase (P < 0.10) in milk protein (N X 6.38), an 11.6% increase (P < 0.05) in protein production and a 10% decrease (P < 0.05) in grain intake. Significant effects on plasma amino acids observed with casein infusion were decreased glyeine (P < 0.10), decreased total nonessential amino acids (P < 0.05), increased isoleucine (P < 0.05), leucine (P < 0.05), valine (P < 0.10), phenylalanine (P < 0.05) and increased total essential amino acids (P < 0.05).