Quality Meat Production from Beef Cattle During Winter Finishing.

End of Project ReportA series of experiments were carried out to examine the performance of the UK metabolisable energy (ME)/metabolisable protein (MP) system in an Irish context, and to determine the response in lean tissue growth to changes in the form of nutrients available for absorption from the intestine. In Experiment 1, the response of finishing continental heifers to an increase in MP supply was examined. It was demonstrated that this type of animal responded positively to an increase in MP supply in excess of requirements as presently estimated by the UK ME/MP system. Such an anomaly requires clarification. In Experiment 2, growth, digestibility and nitrogen retention in finishing continental steers offered ad libitum, concentrates based on barley and soyabean or on a mixture of industrial by-products were examined. The observed higher nitrogen retention in animals offered the by-product based ration suggested that there is opportunity to increase carcass protein content by judicious choice of feed ingredients. This suggestion was explored in Experiment 3. In Experiment 3, nitrogen retention and carcass composition were measured in sheep offered rations which resulted in different patterns of volatile fatty acid supply from the rumen. Nitrogen retention and the growth of carcass lean tissue were increased by the inclusion of sodium propionate in a starch-based ration but not in a fibre-based ration. The apparently contradictory effects of an increase in propionate supply by dietary means (starch vs fibrebased rations) or by addition of a salt of propionic acid suggests that the pattern, as well as the total supply of propionate is physiologically important in the growing ruminant. The endocrine mechanism of changes in carcass composition was also explored in this experiment. Differences in plasma concentrations of hormones which play a major role in the partition of absorbed nutrients towards muscle or adipose tissue suggests a role for the endocrine system in the regulation of growth, independent of energy intake. In Experiment 4, the effect of starch form and concentration (a dietary means of increasing propionate supply) in high concentrate rations on growth, efficiency and estimated lean content was examined in Friesian bulls. Supporting mechanistic measurements were made in Friesian steers fed the corresponding experimental rations. For optimum growth, ground starch should not exceed 210 g/kg of the ration. When included at approximately 300 g/kg, ground rather than rolled starch had a negative impact on growth. Coarse rations containing 300g or 480g starch/kg resulted in similar growth and efficiency. An increase in ground but not rolled starch concentration decreased the insulin response to a glucose challenge