title: Effect of heat stress on follicular development during the estrous cycle in lactating dairy cattle.
abstract: In this study we examined, in two experiments, patterns of follicular development and dominance under conditions of heat stress. Estrous cycles were programmed to include two follicular waves (wave 1 and 2). On Day 1 of the estrous cycle (Day 0 = estrus), cows were assigned randomly to cooled (C; n = 6) or heat-stressed (H; n = 6) groups. In experiment 1, on Day 12 prostaglandin (PG) F2 alpha was injected and a controlled intravaginal drug release device (1.9 g progesterone) was inserted (this was removed on Day 17). In experiment 2, PGF 2 alpha was injected on Day 14. Ovarian structures were examined daily by ultrasonography, and blood samples were collected at each scanning. Cycle lengths were 20 and 17 days in experiments 1 and 2, respectively. Mean maximal body temperatures were higher (p < 0.01) in H (40.3 degrees C) than in C (38.8 degrees C) cows. In experiment 1, the rate of increase in number of large follicles (> or = 10 mm) was greater in H than in C cows (p < 0.01), resulting in 53% more large follicles in H cows during wave 1; this was associated with a lower (p < 0.05) number of medium-sized (6-9 mm) follicles between Days 7 and 10 of the cycle. Heat stress hastened (p < 0.02) the decrease in size of the first-wave dominant follicle and hastened (p < 0.01) the emergence of the second dominant (preovulatory) follicle by 2 days.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Animal Science, Faculty of Agriculture, Hebrew University, Rehovot, Israel.
authors.forename: D
authors.initials: D
authors.lastname: Wolfenson
authors.forename: W W
authors.initials: WW
authors.lastname: Thatcher
authors.forename: L
authors.initials: L
authors.lastname: Badinga
authors.forename: J D
authors.initials: JD
authors.lastname: Savio
authors.forename: R
authors.initials: R
authors.lastname: Meidan
authors.forename: B J
authors.initials: BJ
authors.lastname: Lew
authors.forename: R
authors.initials: R
authors.lastname: Braw-Tal
authors.forename: A
authors.initials: A
authors.lastname: Berman
mesh_terms: D000818:Animals; D001831:Body Temperature; D002417:Cattle / Q000502:physiology*; D004958:Estradiol / Q000097:blood; D004971:Estrus / Q000502:physiology*; D005260:Female; D006358:Hot Temperature; D007774:Lactation / Q000502:physiology*; D006080:Ovarian Follicle / Q000254:growth & development*; D011374:Progesterone / Q000097:blood; D013312:Stress, Physiological / Q000503:physiopathology*
chemical_list: D011374:Progesterone; D004958:Estradiol