|Mc clanahan, Linda|
Submitted to: Agronomy Society of America, Crop Science Society of America, Soil Science Society of America Meeting
Publication Type: Abstract only
Publication Acceptance Date: 7/17/2007
Publication Date: 11/5/2007
Citation: Aiken, G.E., Mc Clanahan, L.K., Dougherty, C.T. 2007. Influence of Rough Hair Coats and Steroidal Implants on Hair Growth, Rectal Temperatures, and Sweating by Steers Grazed on Toxic Tall Fescue During the Summer. Agronomy Society of America, Crop Science Society of America, Soil Science Society of America Meeting. 2007. Session No. 271. Article 270-7. Interpretive Summary:
Technical Abstract: Cattle grazing toxic tall fescue months [Schedonorus arundinaceus (Schreb.)] typically retain their rough hair coats into the summer, which can exacerbate heat stress induced by fescue toxicosis. Further, previous research has indicated that progesterone and estradiol implants may increase body temperature. Steers were assigned to six, 3.0-ha pastures of endophyte-infected ‘Kentucky 31’ tall fescue on 3 May, 2006. Ten clipped (between shoulder and rump; 30 to 40% of total surface area) and 10 unclipped steers were assigned to separate pastures as main plot treatments. 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 the sub-plot treatments. A small area over the shoulder of all steers also was clipped to measure hair growth rate and sweating rate (g/m2/h). Response variables were measured at 28, 56, 84, and 104 days of grazing. Rectal temperatures for clipped steers were similar (P > 0.10) between clipped and unclipped steers, except at 84 days when the highest mean ambient temperature (33°C) was recorded (clipped = 39.5°C, unclipped = 39.3°C; P < 0.05). Sweating rate declined (P < 0.001) as ambient temperatures increased. Sweating rates tended (P < 0.10) to be higher with the estradiol than the progesterone-estradiol implant. Hair growth rates averaged 0.28 mm/d and were unaffected (P > 0.10) by the clipping and implant treatments. Results indicated that retention of rough hair coats, continuous growth of hair, and reduction in sweating rate at higher ambient temperatures contribute to heat stress of fescue cattle during the summer.