Abstract
A smaller dose of equine or human chorionic gonadotropin, eCG (500 IU) or hCG (3, 000 IU), was injected on Day 7 of the estrous cycle in Japanese Black or Holstein cows; 13 cows for eCG, 13 cows for hCG and 14 cows for control and they were inseminated at estrus and examined for blood progesterone levels and morphology of the ovaries by rectal palpation on Days 0, 5, 7, 14 and 21 of the estrous cycle. Two cows of each group were examined for the diameter of corpus luteum by ultrasonography. The conception rates of the eCG, hCG and control groups were 61.5%, 46.2%, and 35.7% respectively, while difference was not significant. Blood progesterone levels were significantly higher in the pregnant cases treated with either eCG or hCG on Days 14 and 21 as compared with non-pregnant controls (P<0.05), and small sized follicles and accessory corpora lutea appeared on Day 14 in the eCG and hCG treated cows with significantly increased diameter of corpora lutea. The results suggested that a smaller dose of eCG or hCG administered on Day 7 of the estrous cycle enhances the luteal function and consequently improves the pregnancy rate in cows.
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