|Spiers, D - UNIV OF MISSOURI|
|Kojima, F - UNIV OF MISSOURI|
|Salfen, B - UNIV OF MISSOURI|
|Wood, S - UNIV OF MISSOURI|
|Patterson, D - UNIV OF MISSOURI|
|Smith, M - UNIV OF MISSOURI|
|Lucy, M - UNIV OF MISSOURI|
|Piper, E - UNIV OF ARKANSAS|
Submitted to: Biology of Reproduction
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 1, 2001
Publication Date: July 1, 2001
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. 2001. INTERACTION OF ENDOPHYTE-INFECTED FESCUE AND HEAT STRESS ON OVARIAN FUNCTION IN THE BEEF HEIFER. JOURNAL OF ANIMAL SCIENCE. 65:260-268. Interpretive Summary: Tall fescue toxicosis, a collection of disorders occurring when cattle graze tall fescue, reduces the productivity of the American cattle industry by at least 500 million dollars annually. Part of this economic loss is believed to be due reduced reproductive performance. The current study examines the interaction between fescue and heat stress for some important reproductive responses. With heifers, consumption of fescue impaired ovarian function when heat stress was imposed. This information is valuable to producers and extension agents implying that optimal conditions to breed heifers grazing fescue pastures would be in the absence of heat stress.
Technical Abstract: The objective of the experiment was to examine effects of endophyte- infected tall fescue on ovarian function in Angus or Angus Hereford heifers exposed to heat stress (S+) or thermoneutral (S-) temperatures. Heifers were fed endophyte-free (E-) or endophyte-infected seed (E+) at S- or S+ (E-S-, E-S+, E+S-, E+S+; n = 6/treatment) 4 wk before and 3 wk after synchronized ovulation. All heifers were subjected to S- conditions (19 degrees C, 50% RH) from Days -6 to 0 (Day 1 = first day of air temperature increase). Ambient temperature then increased incrementally over 2 d for S+ heifers. Between Days 3 and 21 air temperatures cycled between 25 degrees C and 31 degrees C (50% RH; Day 3 = first day of maximal heat stress). Serum was collected and ovaries monitored every other d after PGF 2alpha for 21 d or until ovulation. Size and location of follicles > 4 mm and corpora lutea were recorded. Serum concentrations of prolactin (diet S+, P<.003) and total cholesterol (diet, P<.04; S+, P<.003) were reduced in E+S+ treated heifers and E+ and S+ treated heifers, respectively. The greatest increase in rectal temperature and respiration rate occurred in the afternoon in E+S+ treated heifers (diet S+ d time, P<.001). Diameter of the corpus luteum (S+ d, P<.07) and serum progesterone (diet S+ d, P<.003) were reduced in S+ heifers and to a greater extent in E+S+ heifers for progesterone. The diameter of the ovulatory dominant follicle was reduced in E+ heifers (diet S+; P<.008). Serum estradiol was reduced in E+ heifers (diet S+ d, P<.001). Numbers of medium and large follicles were reduced in heifers consuming E+ diets (diet, P <.07). Intake of E+ reduced serum concentrations of progesterone only during S+, but reduced estradiol under S- and S+ conditions.