|Mc Clanahan, Linda - UNIVERSITY OF KENTUCKY|
Submitted to: American Forage and Grassland Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: April 30, 2007
Publication Date: June 24, 2007
Citation: Mc Clanahan, L.K., Aiken, G.E. 2007. Hair Coat and Ear Implant Effects on Physiological Measurements of Steers Grazing Toxic Tall Fescue During the Summer. American Forage and Grassland Conference Proceedings, June 23-26, 2007, in University Park, PA., 31:AFGC Emerging Scientist Comp. pg 60-65. Technical Abstract: Research has shown cattle grazing toxic tall fescue have reduced weight gain, rough hair coats, and exhibit symptoms of heat stress during the summer. Sixty steers were grazed on toxic tall fescue 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, 7.5 ac pastures of ‘Kentucky 31’ endophyte infected (E+) 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 subplot treatments. A small area over the shoulder of all steers was clipped to measure hair growth rate (in/day) and sweating rate (g/m2/h). All responses were measured at 28, 56, 84, and 104 days of grazing. Grazing frequencies were periodically measured during the experiment. Hair growth rate averaged 0.011 in/day and was unaffected (P > 0.10) by treatments. Sweating rate declined (P < 0.001) over the grazing period and was (P< 0.10) higher with the estradiol than the progesterone-estradiol implant. Rectal temperatures were lower (P < 0.05) in clipped cattle (103.1 vs. 102.74°F) only on day 84 when the highest ambient temperature (91.4°F) of the study was recorded. At high environmental temperatures, percentage of steers actively grazing was negatively correlated (P < 0.10) with ambient temperature. Average daily gain declined as ambient temperature increased (P < 0.05). Results indicated that rough hair coat retention and continuous hair growth into the summer caused impaired thermoregulatory ability at greater ambient temperatures and was exacerbated by reduced sweating.