Clipping Heifer Hair Coats Can Briefly Reduce Fescue Toxicosis Symptoms
Beard, Christopher T.
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A substantial challenge for many beef cattle producers is developing beef heifers into mature, productive cows in a timely and profitable manner. At the Shenandoah Valley Agricultural Research and Extension Center (SVAREC), fall-born replacement heifer candidates are artificially inseminated (AI) in December at 14-15 months of age with a target weight of 350-380 kg. Achieving this level of weight gain through the summer months has been difficult due to heat stress and the utilization of toxic endophyte-infected tall fescue. Tall fescue is the predominant species of forage found at SVAREC. The purpose of this project was to determine if clipping the hair coats of beef heifers would reduce the heat stress that the heifers experience during the summer months. Heifer hair coats were scored in the spring when they were approximately 9 months old and had an average weight of 200 kg in year one and 256 kg in year two. Heifers were scored on a five-point ranked scale, with a score of 1 indicating complete shedding of hair and a score of 5 indicating that no shedding has occurred. Heifers with a hair coat score of 4 or 5 were utilized for this project. The selected group of heifers scoring a hair coat score of 4 or 5 (32 in year one and 23 in year two) were randomly assigned to a control cohort and a clipped cohort. The heifers in the clipped treatment group were sheared with variable speed clippers along the body of the heifer, but not from under the belly or along the legs. Heifer hair coats were scored again at the end of the study on day 113. Vaginal temperature loggers were used to record core body temperatures every ten minutes during several sampling periods. At the conclusion of these 16-week trials, most of the control heifers retained their hair coats while the heifers that had been clipped regrew their hair coats. There was significant period by treatment interaction for the response of heifer average daily gains to clipping (P=0.0002). Average daily gains of the clipped heifers (0.4 kg/day) exceeded the average daily gains of the control heifers (0.1 kg/day) only in the first four-week period of each year (P<0.0001), but there were no differences in total seasonal average daily gain (0.3 kg/day; P=0.1631). There was significant treatment by hour interaction in the analysis of heifer vaginal temperatures (P<0.0001), with clipped heifers cooler than control heifers through most of the night and morning hours, but not in the afternoon. In conclusion, clipping heifers resulted in only short-term benefits to weight gains for heifers stocked on toxic endophyte-infected tall fescue pastures, but clipping did result in reduced core body temperatures throughout the summer months. Additional work could explore the effects of clipping heifers at regular intervals during periods of high temperatures and humidity, such as at monthly intervals.