This study investigated the effect of increasing the proportion of forage rape or Persian clover in the diet on dry matter intake (DMI), whole tract digestibility and rumen function. Two experiments were conducted simultaneously; each in a 3 by 3 Latin square design with rumen-fistulated sheep fed either increasing amounts (10, 25 or 40% DM of the diet) of forage rape (experiment 1) or Persian clover (experiment 2). The remaining diet comprised short-rotation ryegrass, cereal-based pellets and maize silage, formulated to give similar metabolisable energy (MJ/kg DM), neutral detergent fibre and protein values between treatments. Purine derivatives excreted in the urine were used to estimate microbial protein synthesis.

The study found similar DMI within forage rape and Persian clover treatments, although total DMI was 16% higher for the latter (29 v. 25 g/kg liveweight.day, respectively). The in vivo DM (mean = 0.75) and neutral detergent fibre (mean = 0.65) digestibility coefficients were similar (P > 0.05) within and between experiments. The mean (±s.e.) rumen pH in sheep fed forage rape-based diets (6.17 ± 0.10) was higher than for Persian clover-based diets (5.70 ± 0.09). The efficiency of microbial N supply expressed as microbial N (g/day) per kg of digestible organic matter fermented in the rumen was also similar (P > 0.05) within and between forage rape and Persian clover treatments (mean = 23.4 g microbial N/kg digestible organic matter fermented). The results indicate that increasing the proportion of high nutritive value forage rape or Persian clover within the diet of sheep did not affect the efficiency of feed utilisation.