The effects of nutrient supply on the pattern of food intake in sheep

Voluntary food intake (VFI) in ruminants has been extensively researched. Many factors are involved and inter-related, making theories complex. The rumen affects feedback signals controlling food intake, both short-term and long-term. Control of grass silage intake is associated with specific factors, including ensiling end-products, and asynchrony of ruminal nutrient release. Synchronising energy and nitrogen (N) supply to rumen micro-organisms can improve rumen degradability efficiency, which may alter VFI. However, few studies have investigated effects of ruminai nutrient release on intake patterns of grass silage-based diets on an hourly basis. Study 1 characterised a grass silage in terms of organic matter (OM), carbohydrate and N degradability. Results were placed on a database with degradability characteristics of other feed ingredients. In study 2, diet A was formulated from concentrate ingredients, with degradability characteristics similar to the grass silage, and supplement (S) which, when fed with grass silage (G) or A, resulted in a more synchronous ruminai hourly nutrient release. Four diets were offered: G, G+S, A or A+S, to eight growing wether lambs. G had the lowest daily intake (0.937kgDM/day) and supplementation significantly increased daily intake of G (p≤0.01) and A (p≤0.01), slightly altering intake pattern. A had a significantly different (p≤0.01) daily intake and whole tract digestibility (p≤0.01), compared to G. It was concluded that physical factors had a greater effect than chemical factors in controlling intake. In study 3, four complete diets were formulated to further examine nutrient synchronisation, by supplementing the grass silage with concentrate: slow energy, fast N (ASYN), slow energy, slow N (INT(SE)), fast energy, fast N (INT(FE)) or fast energy, slow N (SYN). Diets were fed ad libitum to four wether sheep. There was little variation between diets for daily intake or hourly intake pattern. Plasma urea levels indicated that rumen N capture was dependent on energy release supplied by the supplement, as was rumen fluid pH and osmolality, although differences were not significant (p>0.05). Degree of ruminal nutrient synchronisation appeared not to affect intake pattern and it was concluded that animals were unable to manipulate their intake pattern to improve synchrony