The effects of concentrate composition and sequence of allocation on the metabolism and performance of growing sheep

Richardson, Jane Mary (2001). The effects of concentrate composition and sequence of allocation on the metabolism and performance of growing sheep. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0000f983

Abstract

Four experiments were carried out to investigate the effects of concentrate composition and sequence of allocation on the metabolism and performance of growing lambs. In the first experiment five feed ingredients were characterised using the in situ incubation technique. The degradability constants determined were then used in the construction of a spreadsheet which enabled prediction of hourly nitrogen and organic matter release from the diets to be used in subsequent experiments. In the second experiment 48 lambs were fed at a restricted level diets containing either barley or sugar beet pulp as the main energy source. Within each energy source the sequence of allocation of the individual ingredients was altered to give a pattern of nitrogen and organic matter release within the rumen which was synchronous, intermediate or asynchronous. Lambs fed the barley based diets deposited significantly more fat in the whole body than lambs on the sugar beet based diets (p<0.001) and lambs on the asynchronous diets tended to deposit less fat in the whole body than lambs on the synchronous or intermediate diets (p<0.1). There were significant differences between energy sources and degree of synchrony in the pattern of rumen and plasma nitrogen metabolites. In the third experiment the same diets were fed to 24 lambs and the effects on nutrient digestibility and microbial protein supply were assessed. Lambs on the sugar beet based diet showed significantly higher digestibilities of organic matter and neutral detergent fibre than lambs on the barley based diet, however the Iambs on the barley based diet had a significantly higher level of purine derivative excretion (p<0.05) and a significantly higher calculated microbial protein supply (p<0.05). In the fourth experiment the barley based diets used in the previous experiments were fed ad libitum to 24 lambs. No significant effects on growth rate or carcass characteristics were seen and there were few significant differences in rumen or plasma metabolites. Overall, energy source within the diet had a greater effect on growth and metabolism of lambs than degree of synchronisation of nitrogen and organic matter supply to the rumen.