Understanding biological mechanisms influencing feed efficiency in beef cattle: insulin resistance

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In beef production, feed represents a major production cost. Although considerable research has been invested in improving feed efficiency in beef cattle, many of the underlying biological mechanisms influencing animal variability are not well understood in beef cattle. Insulin resistance has been observed in cattle and sheep, however the relationship to feed efficiency in beef cattle is uncharacterized. My overall hypothesis is that animal variability in feed efficiency is partially related to animal differences in insulin responsiveness. The specific objectives which will be addressed in this Discovery grant are to 1) To characterize relationships between insulin resistance [indicated by glucose tolerance test (GTT) in cattle and hyperinsulinaemic-euglycemic clamp (HEC) in sheep] and measures of growth performance and feed efficiency in finishing steers and lambs, and identify metabolic markers associated with insulin resistance and feed efficiency (adipokines/inflammatory response, lypolisis/lipogenesis, energy signaling) in muscle and hepatic tissue and pancreas cell morphology, 2) Evaluate indices of insulin resistance in reference to GTT and identify an index that best predicts insulin resistance for use when intensive sampling is not possible, and to develop mathematical models to predict efficiency classification early in the feeding period, and 3) To determine if improvement in insulin resistance will improve feed efficiency. To address this hypothesis a series of animal experiments will be conducted. The proposed research will utilize in vivo (performance trials, GTT, HEC) and western blotting, to evaluate relationships between whole body measures of insulin sensitivity and associated metabolic markers of energy metabolism, lipolysis/lipogenesis and leptin, inflammatory response in hepatic and muscle tissues, and measures of feed efficiency (feed intake, residual feed intake and feed conversion ratio). Accompanying work will evaluate various available models to indicate insulin resistance in beef cattle and suggest a method that may be useful for identification of insulin resistance in steers where intensive sampling is not possible. Additionally, this work will provide training for one MSc, one PhD, and two undergraduate students. This research will provide a novel understanding of the role of insulin resistance and feed efficiency in ruminants, and will deepen the understanding of biological mechanisms influencing feed efficiency as a whole.