Ruminal degradation and dose response of dairy cows to dietary L-carnitine

In Experiment 1, in vitro degradation of L-carnitine was measured in ruminal fluid obtained either from a cow that was fed a 75% concentrate diet or from a cow fed a control (50% forage and 3% fat) diet. Carnitine degradation was greater in ruminal fluid from the cow fed the control diet than in ruminal fluid from the cow fed the 75% concentrate diet and was more rapid in ruminal fluid obtained after 2 wk of adaptation to dietary carnitine supplementation (7 g/d). In Experiment 2, 20 multiparous Holstein cows were used in a replicated 5 x 5 Latin square design to determine the effects of increasing the amount of dietary L-carnitine (0, 0.875, 1.75, 3.5, or 7.0 g/d) that was fed to lactating dairy cows. All cows received the same diet, which contained 3% added fat. Carnitine concentration in milk and plasma increased linearly with carnitine supplementation. The DMI, milk yield, and milk composition were unaffected by carnitine. Apparent total tract digestibilities of NDF and fatty acids decreased quadratically as the amount of supplemented carnitine increased; generally, means were lowest when cows were fed 1.75 g/d of carnitine. The concentration of total VFA and molar percentages of individual VFA in ruminal fluid were unaffected by the amount of carnitine fed. Concentrations of glucose, NEFA, and urea N in plasma were unaffected by the amount of dietary carnitine; however, plasma cholesterol concentration decreased linearly as carnitine increased. Supplementation of < or = 7.0 g/d of dietary carnitine did not benefit DMI, milk yield, milk composition, or digestive measurements in this experiment.