Comparative digestion of herbage by two breeds of sheep: effects of grass maturity stage and level of intake

Abstract

AbstractTwo trials were conducted to study the effect of the stage of maturity of fresh herbage on its digestibility by two breeds of sheep (Churra v. Merino). The sward consisted of a mixture of grasses and clover, and was harvested either in late May (early cut, EC) or in late July (late cut, LC). In each trial, 12 mature sheep of each breed were used. Each animal received a different amount of fresh herbage, so that levels of food intake ranged between 8·1 and 24·7 g dry matter (DM) per kg body weight per day. EC herbage showed higher crude protein content (116 v. 67 g/kg DM), lower neutral-detergent fibre concentration (494 v. 664 g/kg DM) and higher DM digestibility (0·687 (s.e. 0·005) v. 0·463 (s.e. 0·007)) than the LC herbage. DM digestibility coefficients observed in Churra (0·694 (s.e. 0·028) for EC and 0·476 (s.e.0·028) for LC herbage) tended to be greater than those observed in Merino sheep (0·680 (s.e. 0·021) for EC and 0·452 (s.e. 0·040) for LC herbage). With the EC herbage DM digestibility tended to decrease as the level of intake increased. Samples of dried herbage were incubated in the rumen of Churra and Merino sheep to determine the DM degradability by the in situ technique. Fractional degradation rates (c values) were significantly faster in the rumen of Churra than in Merino (0·046 (s.e. 0·003) v. 0·031 (s.e. 0·002)), with large differences between breeds in the DM disappearance rates at intermediate incubation times, and no significant differences between Churra and Merino sheep in the mean a + b values. Microbial N supply, calculated from the urinary excretion of purine derivatives, was significantly affected by the herbage maturity stage and by the level of DM intake, but not by the breed of sheep. It is suggested that differences between breeds of sheep in food digestibility may be related to their ability to digest fibrous diets.