Milk production and energy metabolism in ruminants fed 2-ketoisocaproate
Three trials were conducted to examine the effect of dietary 2-ketoisocaproate (KIC) supplementation on milk production and energy metabolism in ruminants. In the first two trials, 10 goats were fed either 0 or 1.1% calcium-KIC for 2 wk and 12 cows were fed either 0 or.75% sodium-KIC for 3 wk. Supplementation with KIC significantly increased milk fat content, milk fat yield, and 4% fat-corrected milk yield in cows by an average of 5, 10, and 8%, respectively, for the treatment period. In cows, response of milk fat yield to KIC was 14% during wk 1 of treatment but diminished to 7% by wk 3. Milk yield and milk protein yield tended to be greater in cows fed KIC, but milk production efficiency and body weight were unaltered in either species. In goats, supplementation with KIC had no significant effects on milk production or composition, but trends toward increased milk fat and protein content were observed;In the third trial, 30 mixed-breed growing lambs were fed a control diet or ruminally-protected leucine, KIC, or isovalerate at a molar equivalent of.05% leucine in the diet. Lambs were fed their respective diets for about 13 wk and slaughtered upon reaching 50 kg body weight. During wk 8, plasma glucose and acetate turnover rates were measured. Perirenal lipid deposition was decreased in lambs fed KIC by 45% (P <.01) and tended to be decreased in lambs fed leucine by 29%. KIC also tended to decrease backfat thickness (25%, P <.09). Leucine tended to decrease growth rate and efficiency of feed conversion when compared with KIC. Plasma glucagon concentration was less for lambs fed leucine, KIC, and isovalerate than for controls during wk 4 but not wk 8. Acetate flux tended to be greater in lambs fed KIC and leucine than in those fed isovalerate. Dietary treatment did not alter glucose concentration or flux or acetate concentration or oxidation rate;In summary, feeding KIC acutely stimulated milk fat production in lactating cows and decreased lipid deposition and plasma glucagon concentration in growing lambs. In growing lambs, the effect of KIC on lipid deposition was greater than that of either leucine or isovalerate. These results indicate that KIC may alter lipid metabolism in ruminants so that nutrients are partitioned away from body lipid stores and toward milk production.