Voluntary intake, gain, digestibility, rate of passage and gastrointestinal tract fill in tropical and temperate breeds of sheep.

In trial 1, Coastal bermudagrass pellets were fed for 63 d to 21 growing rams of Barbados Blackbelly (B), Dorset (D) and Blackbelly X Dorset (B X 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 less than .10) for B X D than for B or D rams. Rate of passage was faster (P less than .05) for B X D rams than for the other breed groups, while D rams were intermediate. Total mean retention time (MRT) was shorter (P less than .05) for B X D rams compared with the other breed groups. Ruminal retention time (RRT) was shorter (P less than .05) and GIT fill was less (P less than .10) for D and B X 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 X D, 7, 35.0.(ABSTRACT TRUNCATED AT 250 WORDS)