Voluntary Intake, Gain, Digestibility, Rate of Passage and Gastrointestinal Tract Fill in Tropical and Temperate Breeds of Sheep

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Abstract
In trial 1, Coastal bermudagrass pellets were fed for 63 d to 21 growing rams of Barbados Blackbelly (B), Dorset (D) and Blackbelly × Dorset (B × D) breeding to determine the effect of breed on voluntary intake (VI) and total gain. Initially, each breed group consisted of seven rams with mean weights of 18.6, 31.0 and 26.4 kg, respectively. At the end of the intake and growth phase, digestibility, rate of passage and gastrointestinal tract (GIT) fill were determined. Chromium-mordanted fiber was used as a particle phase marker. Intakes during the digestibility-marker phase averaged 75% of the VI determined in the intake and growth phase. Breeds did not differ in VI, total gain or digestibilities of dry matter (DM) and neutral detergent fiber (NDF). Apparent crude protein (CP) digestibility was approximately 3 percentage units higher (P<.10) for B×D than for B or D rams. Rate of passage was faster (P<.05) for B×D rams than for the other breed groups, while D rams were intermediate. Total mean retention time (MRT) was shorter (P<.05) for BxD rams compared with the other breed groups. Ruminal retention time (MRT) was shorter (P<.05) and GIT fill was less (P<.10) for D and B×D than for B rams. In trial 2, chopped orchardgrass-alfalfa hay was fed for 26 d to 19 of the same rams used in trial 1. Breed, number of rams and initial weights (kg) were: B, 5, 25.6; D, 7, 39.4; B×D, 7, 35.0. The B rams had higher (P<.05) VI than D rams. Apparent CP digestibility was highest for BxD rams (P<.05). Breeds did not differ in apparent DM or NDF digestibility. Rate of passage tended to be faster and RRT shorter for B×D rams. The B×D rams had shorter (P<.05) MRT than D rams. Under the conditions of this study, B and B×D rams were competitive with D rams with respect to VI, gain and forage digestibility. Differences in digestive tract kinetics suggest that the B and B×D breed groups could be a valuable genetic resource for sheep production in areas where environment and feed quality limit the use of British and European breeds. Copyright © 1987. American Society of Animal Science . Copyright 1987 by American Society of Animal Science.