Effect of Plane of Nutrition and Source of Nitrogen on Methionine Synthesis in Cows

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Abstract
A study was made to evaluate the effects of level of feed intake, ration composition and source of nitrogen on the synthesis of methionine in the rumen. The most significant effects on ruminal synthesis of essential amino acids were level of dry matter intake and level of nitrogen intake. Mean daily ruminal synthesis of methionine ranged between 32.8 and 46.2 mg/kg of body weight. The step-by-step insertion of the variables, kilograms of dry matter, grams of alfalfa nitrogen, percentage nitrogen absorbed and treatment of alfalfa, into a multiple regression analysis accounted for 94% of the total variation. It was concluded that methionine synthesis increased at a rate of 1.5 g/kg of feed consumed and 6.7 g/100 g of alfalfa nitrogen eaten. A marked decrease in methionine synthesis was found to be related to reduced nitrogen absorption in the digestive tract. Synthesis of methionine increased as the integrity of plant proteins was preserved and soluble nonprotein nitrogen decreased correspondingly. Methionine synthesis increased 0.4 g/kg of intact protein fed.