Year of Publication

2007

Document Type

Thesis

College

Agriculture

Department

Crop Science

First Advisor

Glen E. Aiken

Abstract

Sixty steers were grazed on toxic tall fescue for 104 days to determine the effects of hair coats and steroidal ear implants on physiological measurements. Steers were stratified by body weight and hair coat color for assignment to six, 3.0-ha pastures of 'Kentucky 31' tall fescue. Main plot treatments of either ten clipped or ten unclipped steers were randomly assigned to pastures. Five steers in each pasture were implanted with Synovex-S (200 mg progesterone-20 mg estradiol) and five were implanted with Compudose (25 mg estradiol) as sub-plot treatments. Hair growth rate averaged 0.29 mm/day. Sweating rate declined (P andlt; 0.001) over the grazing period and was higher (Pandlt; 0.10) with the estradiol implant. Rectal temperatures were lower (P andlt; 0.05) in clipped cattle (39.3 vs. 39.5??C) when the highest ambient temperature (33??C) of the study was recorded. At high environmental temperatures, percentage of steers actively grazing was negatively correlated (P andlt; 0.10) with ambient temperature. Winter hair coat retention, continuous hair growth, and reduced sweating caused impaired thermoregulation and thus decreased grazing frequency resulting in poor animal performance.

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