Fate of Carbon-14 Labeled Methionine Hydroxy Analog and Methionine in the Lactating Dairy Cow

Abstract

Carbon-14 labeled methionine hydroxy analog, fed to two similar cows, was more resistant to rumen microbial degradation than labeled methionine, fed to one lactating Holstein cow. The analog gave less respiratory labeled carbon dioxide, less radioactivity in rumen solids and volatile fatty acids, and greater persistence in rumen fluid. Supplementation of diets with hydroxy analog resulted in two to three times more radioactivity in milk, tissues, blood, and excreta and apparently more labeled methionine in blood, milk, urine. liver, and kidney. Radiolabeled methionine in tissues, milk, blood, excreta, and in rumen fluid was evidence for biotransformation of methionine hydroxy analog to methionine in ruminants. Carbon-14 from hydroxy analog and methionine was incorporated in to rumen volatile fatty acids, milk fat and lactose, urinary urea, and fecal protein amino acids other than methionine.