title: Effects of induced hypothyroidism on ovarian response to superovulation in Brahman (Bos indicus) cows.
abstract: To evaluate the effects of hypothyroidism on ovarian function, multiparous, nonlactating Brahman cows (n = 18) were assigned randomly to dietary treatments containing either 0 (C; n = 9) or 4 mg x kg BW(-1) x d(-1) 6-n-propyl-2-thiouracil (PTU; n = 9), to suppress thyroid function, in the feed concentrate. Weekly changes in BW and body condition score (BCS) were recorded. Dietary treatments began on d 10 of the estrous cycle. Ten days after the first treatment estrus, all cows received daily i.m. injections of 25 IU of porcine FSH over a 3-d period. Seven days after AI, embryos were collected nonsurgically, and the ovaries were removed via midflank laparotomy. Based on thyroxine (T4) concentrations after 49 d of treatment, five cows were hypothyroid (H-PTU) and four were partially suppressed (P-PTU). Cows in the PTU group had greater (P<.01) ADG, (P<.05) ovarian weights, and numbers of large (> or =8 mm) (P<.05) follicles. Cows in the PTU group had lower embryo recovery rate (P<.001), fertilization rate (P<.001), and percentage of blastocysts (P<.1) than C cows. The H-PTU cows had greater numbers of luteinized follicles (P<.06), greater concentrations of progesterone (P4) in the follicular fluid at all size categories (P<.1), and greater numbers of corpora lutea (P<.05) than C cows. The ratio of luteal to serum P4 on d 7 was greater (P<.05) in hypothyroid cows. Induced hypothyroidism improved weight gain and BCS, increased ovarian response to FSH, and affected ovulation, fertility, and P4 secretion in superovulated Brahman cows.
authors.affiliation: Texas A&M University Agricultural Research and Extension Center, Overton 75684, USA.
authors.forename: A
authors.initials: A
authors.lastname: Bernal
authors.forename: G V
authors.initials: GV
authors.lastname: DeMoraes
authors.forename: T A
authors.initials: TA
authors.lastname: Thrift
authors.forename: C C
authors.initials: CC
authors.lastname: Willard
authors.forename: R D
authors.initials: RD
authors.lastname: Randel
mesh_terms: D000818:Animals; D001823:Body Composition; D001835:Body Weight; D002417:Cattle / Q000097:blood / Q000502:physiology*; D003338:Corpus Luteum / Q000378:metabolism; D005260:Female; D007037:Hypothyroidism / Q000139:chemically induced / Q000503:physiopathology*; D010053:Ovary / Q000502:physiology*; D011374:Progesterone / Q000097:blood; D011441:Propylthiouracil; D013480:Superovulation / Q000502:physiology*; D013974:Thyroxine / Q000097:blood; D020858:Tissue and Organ Harvesting / Q000662:veterinary; D014284:Triiodothyronine / Q000097:blood
chemical_list: D014284:Triiodothyronine; D011374:Progesterone; D011441:Propylthiouracil; D013974:Thyroxine