Submitted to: American Society of Animal Science Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 3/1/2001
Publication Date: 7/1/2000
Citation: BURKE, J.M., SPIERS, D.E., KOJIMA, F.N., SALFEN, B.E., WOOD, S.L., PATTERSON, D.J., SMITH, M.F., LUCY, M.C., JACKSON, W.G., PIPER, E.L. INTERACTION OF ENDOPHYTE-INFECTED FESCUE AND HEAT STRESS ON OVARIAN FUNCTION IN THE BEEF HEIFER. AMERICAN SOCIETY OF ANIMAL SCIENCE PROCEEDINGS. 2000. V. 79(Suppl. 1). P. 199. Interpretive Summary:
Technical Abstract: Objective was to examine interaction of fescue and heat stress (HS) on ovary development. Heifers were fed endophyte-free (E-) or endophyte- infected seed (E+; 18.4%) at thermoneutral (S-) or HS (S+; E-S-, E-S+, E+S-, E+S+; n = 6/treatment) 4 wk before and 3 wk after synchronized ovulation (7-11 Synch; D 0 was d of expected ovulation). Serum was collected and ovaries were monitored every other d after PGF until D 20 or ovulation. Size of follicles >4 mm and CL were recorded. Heifers were subjected to 19 degrees C, 50% RH from D-8 to -2 and S+ heifers to 31 degrees C/25 degrees C from D-1 until D 20. Feed intake was not different between E- and E+ heifers, but was reduced in S+ vs S- heifers (HS x d, P<.01). Water intake was not different among treatments. There was an interaction between diet, HS, and d for AM (P<.001) and PM (P<.001) rectal temperature and a diet x d (P<.001, AM; P<.01, PM) and HS x d (P<.001, AM; P<.001, PM) interaction for respiration rate. Serum P4 was reduced in S+ heifers and to a greater extent in E+S+ heifers (HS x d, P<.06; yE-S- = -3.6 - 2.3x - .21x2 - .0049x3, yE-S+ = -1.7 - 1.3x2 - .0023x3, yE+S- = -1.7 -1.8x -.17x2 - .0043x3, yE+S+ = -.66 - .72x - .061x2 - .0013x3, where y=P4 and x=d; P<.003). Diameter of the CL was reduced in S+ heifers (yS- = 13.5 - 1.5x - .067x2, yS+ = 14.8 - .77x - .034x2, where y = CL diameter and x=d; P<.07). Serum E2 was reduced in E+ heifers (yE-S- = 6.6 + .67x + .026x2, yE-S+ = 2.6 - .0035x - .0024x2, yE+S- = 5.9 + .72x + .029x2, yE+S+ = 4.6 + .49x + .019x2, where y=E2 and x=d; P<.001). Similarly, diameter of ovulatory dominant follicle was reduced in E+ heifers (diet x d; P<.07). Intake of E+ reduced P4 only during HS, but reduced E2 under S- and S+ conditions.