Interaction of nutrition and air temperature with water metabolism of Merino wethers shorn in winter

Abstract

p>Field observations were made on Peppin Merino wethers maintained at 6 and 9 per acre throughout the year on improved pasture in Canberra. Estimations of water distribution with the use of tritium, thiocyanate, and T1824 indicated that stocking rate in autumn had little effect on body composition or water intake. Before shearing in July, however, the 9-per-acre sheep had lost 16% more weight than those at 6 per acre, although body water distribution was similar in the two groups. After shearing, both groups shivered continuously for 3 weeks. The 9-per-acre animals had lower rectal and higher skin temperatures than the 6-per-acre sheep. Skin and rectal temperatures were reciprocal to wind velocity. Both groups lost over 3 kg weight (5.9 and 8.4% of body weight) in 2 weeks, but in the 9-per-acre sheep, body water increased by 8.7% while in the 6-per-acre group 4.4% of body water was lost. The 9-per-acre sheep lost 30.7% of tissue solids, compared with 7.5% in the better-fed animals. It is likely that cellular water content increased in the 9-per-acre animals. An increase in density of stocking from 6 to 9 per acre cost three times as much tissue and fat during the cold period, while this loss of solids was partly obscured by replacement of tissues with water.