Shearing Lambs Improves Growth Performance During Periods with Elevated Thermal Load

The purpose of this study was to determine if average daily gain (ADG) is improved in shorn lambs versus non-shorn lambs in the summer months in the upper Midwestern United States. Forty-nine purebred Hampshire and Columbia ram (n = 10 Hampshire and 4 Columbia) and ewe (n = 22 Hampshire and 13 Columbia) lambs were grouped by breed, sex, age (104 ± 1.7 days of age), and initial weight (109 ± 3.5 lbs) into shorn (n=26) and non-shorn (n=23) groups. After shearing (3 June 2004), shorn sheep had approximately 0.1 inches of wool-cover. Lambs were weighed 1, 29, and 57 days following shearing. During the first 28 day period following shearing (period 1), there was no difference in average daily gain between shorn and non-shorn lambs (0.8 ± 0.04 vs 0.82 ± 0.04 lbs/day, respectively). In the second 28 day period (period 2), shorn lambs had a greater average daily gain than non-shorn lambs (1.02 ± 0.06 vs 0.92 ± 0.06 lbs/day, respectively). Period 2 had greater mean (68.9 vs. 63.4 oF, respectively), minimum (59.7 vs 54.1oF, respectively), and maximum (78.2 vs. 73.8oF, respectively) daily ambient air temperature and greater mean humidity (73.97 vs. 68.2 %, respectively) than period 1. The calculated temperature humidity index (THI) was also greater in period 2 than period 1 (66.9 vs. 62.24, respectively). These data indicate that shorn lambs grow more rapidly than non-shorn lambs during periods of elevated temperature, humidity, and THI