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

Blackburn, Wendy Elizabeth (2000). The effects of nutrient supply on the pattern of food intake in sheep. MPhil thesis The Open University.



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.

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