Submitted to: Professional Animal Scientist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 25, 2011
Publication Date: August 1, 2011
Citation: Aiken, G.E., Klotz, J.L., Looper, M.L., Tabler, S.F., Schrick, F.N. 2011. Disrupted hair follicle activity in cattle grazing endophyte-infected tall fescue in the summer insulates core body temperatures. Professional Animal Scientist. 27:336-343. Interpretive Summary: Tall fescue is a cool-season perennial grass that covers approximately 15 million ha in the eastern USA between the temperate northeast and the subtropical southeast. An endophytic fungus is associated with the presence of alkaloids that impart plant tolerances to drought, heat, and grazing stresses, but also produces ergot alkaloids that induce toxicosis in cattle. Symptoms of toxicosis include rough haircoats in the summer, elevated body temperature, labored respiration, and poor animal performance. It has long been believed that rough haircoats on cattle grazing endophyte-infected tall fescue during the summer are caused by retention of winter hair coats. An experiment was conducted to determine if the rough hair coat of fescue cattle is composed of winter, summer, or a combination of both. It was shown that a small portion of the rough hair coat is composed of winter hair coat but the majority of hair follows sheding of winter hair coat and these hairs that are representative of summer hair coat grow to excessive lengths. A second experiment combined results of 5 experiments with beef steers grazing endophyte-infected tall fescue to determine the insulation effect of rough hair coats on core body temperature. Rectal temperatures in cattle with rough hair coats were elevated compared those with sleek hair coats and exhibiting other symptoms of toxicosis when air temperatures from the previous day were > 74°F. Rough hair coats showed to insulate body temperatures over a wide range of air temperatures. Results or these experiments indicated that rough hair coats on cattle grazing tall fescue in the summer is composed of retained winter hair coat and excessive growth of summer hair coat and that this rough hair coat can insulate body heat.
Technical Abstract: Ergot alkaloids produced by an endophyte (Neotyphodium coenophialum) that infects most plants of tall fescue (Lolium arundinaceum) causes cattle to have rough hair coats during the summer and persistent vascular constriction that impedes heat dissipation via blood flow to peripheral tissues. Experiment 1 determined hair length distributions for winter and summer hairs in the overall coats on steers grazing endophyte-infected (E+) and endophyte-free tall fescue pastures. Experiment 2 combined data from 5 grazing trials with calves grazing E+ fescue to evaluate linear relationships of rectal temperature with ambient temperature and temperature-humidity indices (THI) for rough, transitional, and sleek hair coat rating (HCR). For experiment 1, hair was bleached over 2 areas clipped at different times to discern winter and summer hairs and hair length distributions. Winter and summer hair coats were present for steers with rough hair coats and their distributions did not change between clipping times. Steers with transitional (25 to 75% shedding) HCR had summer hair with a greater percentage of hair lengths > 15 mm than those on E- pastures with sleek HCR. Summer hair in the total coat was > 80% for rough and transitional HCR. Calves with rough and transitional HCR in experiment 2 showed linear increases in rectal temperatures as mean ambient temperature and THI increased, but the relationship was weak for sleek HCR. Results indicated that rough hair on cattle grazing E+ fescue in the summer is composed of retained winter hair and excessively grown summer hair that insulate body temperature.