Influence of [alpha]-ketoisocaproate on growth, carcass composition and protein metabolism in cattle and sheep
Experiments were conducted to determine if [alpha]-ketoisocaproate (KIC), a proposed regulating factor of metabolism, would influence lamb and cattle growth, feed conversion and nutrient deposition. In Experiment 1, daily intraperitoneal injections of Na-KIC (~3g/d) increased lamb growth 11% (p F =.001). In Experiment 3, steer growth was increased in a quadratic dose-responsive manner, when 0,.02,.07 or.2% Ca (KIC)[subscript]2 protected from ruminal degradation was fed (p <.03;.02% KIC increase gain 14%). In Experiment 4,.05% KIC protected from ruminal degradation increased lamb growth by 8% (nonsignificant; p =.27), whereas.05% leucine (leu) and isovalerate IVA) did not affect growth.;Other observed responses to KIC included: (1) decreased internal and external fat depots of lambs (-15 to 20%), (2) more steers grading choice or prime, (3) increased lamb humerus and tibia weight and density (~10%), (4) increased lamb psoas major, longissimus and gastrocnemius weights (~10%) and (5) unaltered leu used for protein synthesis (avg 4.42 umol/(min*kg)), leu from proteolysis and absorption (avg 4.66 umol/(min*kg)), leu transamination to KIC (avg.83 umol/(min*kg)), KIC transamination to leu (avg.62 umol/(min*kg)), KIC oxidation (avg.22 umol/(min*kg)), phenylalanine (phe) flux (avg 1.29 umol/(min*kg)), tyrosine derived from phe (avg 51.8%) and 3-methylhistidine flux (avg 12.0 nmol/(min*kg)) when lambs in Experiment 4 were infused with (6,6,6-[superscript]2H[subscript]3) leu, (1-[superscript]13C) KIC, (1-[superscript]13C) phe and 3-methyl-[superscript]2H[subscript]3-histidine.;In summary, parenteral administration of KIC improved daily gain and feed conversion and decreased subcutaneous and intramuscular fat depots, whereas oral administration improved daily gain and feed conversion and reduced subcutaneous fat when fed with conventional diets, but depressed daily gain and feed conversion when fed with corn gluten meal, which is high in leucine content. Secondly, KIC protected from ruminal degradation, improves performance at doses 10-to-20 fold lower than when fed unprotected. Finally, although KIC increased muscle weight, protein metabolism of overnight-fasted lambs was not altered.