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Effects of induced hypothyroidism on ovarian response to superovulation of Brahman (Bos indicus) cows
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Multiparous nonlactacting Brahman cows (n=20) exhibiting normal estrous cycles were randomly assigned within BW and body condition score (BCS) to dietary treatments containing either 0 (C; n=10) or 4 mg/kg BW/d 6-npropyl-2-thiouracil mixed with the concentrate (PTU-n=10). Water, minerals and Coastal bermudagrass hay were available free choice and each animal received 1.8 kg of a 5.-l corn-soybean meal concentrate daily. Dietary treatments began on d 10 of the estrous cycle. Ten d after the second standing estrus, the cows received daily i.m. injections of 25 IU of porcine FSH (Superov') over a 3-d period. Estrus was induced by administration of PGF20C. Artificial insemination was performed at 12 and 24 h after observed estrus. Seven d after insemination, collection of embryos by non-surgical procedures was performed and the ovaries were removed via mid-flank laparotomy. Blood samples were collected on a weekly basis and the d of embryo collection. Serum triiodothyronine and thyroxine (T4) concentrations were lower (P<.05) in PTU than in C by d 28 of treatment and remained low thereafter. Based on T4 concentrations on d 49, five cows were hypothyroid (H-PTU) and four were partially suppressed (P-PTU). Cows in the PTU group had greater (P<.l) average daily gain, greater (P<.05) paired ovarian weights, greater (P<.06) amount of luteal tissue, greater (P<.06) number of large follicles (>4 mm), lower (P<.001) embryo recovery rate, lower (P<.l) percentage of fertilized embryos, and lower (P<.l) percentage of blastocysts collected than those in C. Further, H-PTU cows had a greater (P<.06) number of luteinized follicles and a greater (P<.05) number of corpora lutea than C. Concentration of P4 per g of luteal tissue did not differ (P>.l) between treatments, but the ratio of luteal to serum P4 on d 7 was greater (P<.l) in PTU. Serum concentration of cortisol did not differ (P>.l) between treatment groups. It was concluded that induced hypothyroidism improved weight gain and BCS, did not affect adrenal function and increased ovarian response to FSH in superovulated Brahman cows. Enhanced ovarian response may have affected fertility. Ovulation and P4 release appeared to be impaired in hypothyroid Brahman cows.
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Includes bibliographical references: p. 83-100.
Issued also on microfiche from Lange Micrographics.
Bernal, Alejandro (1996). Effects of induced hypothyroidism on ovarian response to superovulation of Brahman (Bos indicus) cows. Master's thesis, Texas A&M University. Available electronically from
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