FEED-INTAKE, DIGESTION, AND RENAL-FUNCTION IN MERINO SHEEP SELECTED FOR HIGHER CLEAN FLEECE WEIGHT

Two-year-old ewes from 2 Merino lines selected for higher clean fleece weight were compared with their control line when given a lucerne hay diet and a lower quality diet of mixed wheaten and lucerne hays. Ther e were no differences between lines in voluntary feed consumption, fee d digestibility, urea synthesis and excretion, or renal function. Volu ntary feed consumption, digestibility, urea synthesis and excretion, g lomerular filtration rate, and urea and creatinine clearances were hig her on the higher quality lucerne hay diet; renal tubular function was not affected by diet. Water intake was higher in the selection lines; consequently, these sheep produced more of a less concentrated urine. The renal clearance of endogenous true creatinine was significantly g reater than the glomerular filtration rate, indicating that creatinine was secreted in the kidney tubules. The results support the conclusio n that differences between selection lines in physiological parameters not directly associated with wool follicle function are unlikely to b e consistent enough to be useful predictors of genetic merit for fleec e weight.