Feed intake, digestion, and renal function in Merino sheep selected for higher clean fleece weight

Abstract

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. There were no differences between lines in voluntary feed consumption, feed digestibility, urea synthesis and excretion, or renal function. Voluntary feed consumption, digestibility, urea synthesis and excretion, glomerular filtration rate, and urea and creatinine clearances were higher 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 greater than the glomerular filtration rate, indicating that creatinine was secreted in the kidney tubules. The results support the conclusion that differences between selection lines in physiological parameters not directly associated with wool follicle function are unlikely to be consistent enough to be useful predictors of genetic merit for fleece weight.