Comparative fertility of normal and repeat-breeding cows as embryo recipients.
Morphologically normal embryos were transferred surgically into uteri of normal and repeat-breeder cows at seven days post-estrus to compare embryo survival rates in the two kinds of cows. All cows were less than ten years of age and had no abnormal genital discharges, cystic ovarian follicles, or anatomical abnormalities of the reproductive tract. Normal cows had not been inseminated after last calving. Repeat-breeders had at least four infertile services within the past six months (average of 6.2 services after calving). To test fertility of repeat-breeders at synchronized estrus, 22 anatomically-normal repeat-breeders were treated by intramuscular (i.m.) injection with prostaglandin F(2)alpha (PGF(2)alpha) on day 11 of an estrous cycle (estrus = day 0) and inseminated at induced estrus; 11 cows (50%) had a normal fetus at necropsy on day 60. Twenty-three repeat-breeders and 23 normal cows were assigned as embryo recipients and treated i.m. with PGF(2)alpha to synchronize estrus. All embryo donors were normal cows. Donors were treated with FSH and PGF(2)alpha and inseminated at estrus. On day 7 after estrus, embryos were recovered nonsurgically from donors and one embryo was transferred through a flank incision to the anterior end of the uterine horn adjacent to the corpus luteum of each recipient. Recipients that did not return to estrus were necropsied at day 60. Of 28 normal and 23 repeat-breeder recipients, 23 normal cows (82%) and 16 repeat breeders (70%) were pregnant at day 60 (P=0.235). Thus, at seven days post-estrus, the maternal environment of most of these repeat-breeders was satisfactory for maintaining pregnancy.
Tanabe
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Pennsylvania State University, University Park, PA 16802 USA.
Hawk
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Hasler
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