An experiment was carried out to investigate the hypothesis that the diet selection of ruminant animals from two foods of different rapidly rumen degradable protein contents could be affected by the differences in the rate of synchrony between carbohydrate fermentation and degradation of protein in the rumen. The diet selection of the animals was measured both in the 'long-term' (daily) and 'short-term' (2h intervals within the day).

Twelve rumen fistulated mature female sheep (liveweight 59.1 kg) were used. Four foods (A,B,C and D) with the same ME (9.6 MJ/kg fresh food) and similar, high metab/sable protein contents were made into pellets. Two of the foods were based on a rapidly fermentable carbohydrate source (barley, A and B foods) and the other two on a slowly fermentable carbohydrate source (plain sugar beet pulp, C and D foods). Within each source one food (A or C) had a low (70) and the other a high (140 g/kg) concentration of effective rumen degradable content (RDP).