Effects of induced hypothyroidism on ovarian response to superovulation inBrahman (Bos indicus) cows

To evaluate the effects of hypothyroidism on ovarian function, multiparous, nonlactating Brahman cows (n = 18) were assigned randomly to dietary treat ments containing either 0 (C; n = 9) or 4 mg kg BW-1.d(-1) 6-n-propyl-2-thi ouracil (PTU; n = 9), to suppress thyroid function, in the feed concentrate . Weekly changes in BW and body condition score (BCS) were recorded. Dietar y treatments began on d 10 of the estrous cycle. Ten days after the first t reatment estrus, all cows received daily i.m. injections of 25 IU of porcin e FSH over a 3-d period. Seven days after Al, embryos were collected nonsur gically, and the ovaries were removed via midflank laparotomy. Based on thy roxine (T-4) concentrations after 49 d of treatment, five cows were hypothy roid (H-PTU) and four were partially suppressed (P-PTU). Cows in the PTU gr oup had greater (P < .01) ADG, (P < .05) ovarian weights, and numbers of la rge (greater than or equal to 8 mm) (P < .05) follicles. Cows in the PTU gr oup 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 g reater numbers of luteinized follicles (P < .06), greater concentrations of progesterone (P-4) 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 P-4 on d 7 was greater (P < .05) in hypothyroid cows. Induc ed hypothyroidism improved weight gain and BCS, increased ovarian response to FSH, and affected ovulation, fertility, and P-4 secretion in superovulat ed Brahman cows.