The present study was undertaken to assess the production and the action mechanism of sex hormones in male dogs. The following results were obtained. 1) Plasma concentrations of LH, androstenedione, testosterone, 5 α-dihydrotestosterone (DHT) and estradio1-17 β were measured by the radioimmunoassay method. The level of LH increased with days of age and stayed constant from 8 years through 13 years of age in male dogs. The level of testosterone increased with days of age and stayed constant from 1 year through 10 years of age. Thereafter, the level of testosterone declined gradually. In contrast, there was no age-related increase in the level of estradiol-17β in mature dogs. 2) By measuring androstenedione, testosterone and DHT simultaneously in peripheral and spermatic vein plasma, and determining the temporal relationship between the two vein plasma levels of these hormones, it was suggested that plasma testosterone and DHT were derived mainly from the testis, while plasma androstenedione was derived from the testis and other organs like the adrenal. 3) Plasma concentrations of LH, androstenedione, testosterone and DHT in mature dogs fluctuated episodically, but neither diurnal rhythm nor annual variation of LH and testosterone concentrations was observed. 4) It was suggested that the pathway for activation of steroidogenesis in canine testes by LH was through cAMP formation. 5) In canine testes, major C₁₉-metabolites of pregnenolone were dehydroepiandrosterone, androstenedione and testosterone. Following the addition of a 17α-hydroxylase inhibitor to the testis caused a significant increase in pregnenolone production, indicating that the formation of testosterone from pregnenolone by the Δ ⁵-pathwaywas dominant in androgen biosynthesis of the testis. 6) Hexestrol dicaprylate (H₈), a long-acting estrogen, was used in an attempt to induce temporary sterilization of male dogs. H₈ treatment caused significant decreases in the gonadotrophic activities of the pituitary gland and testosterone formation by the testis with the inhibition of spermatogenesis in the dog. It was suggested that H₈ interfered with testosterone production by blocking the pituitary function, and also directly inhibited the testicular steroidogenesis. 7) In canine prostates, major metabolites of testosterone were DHT and 5α-androstanediols. DHT had a high binding affinity for androgen receptor in the prostate, while 5α-androstanediols had a low affinity for the receptor. The prostate was shown to contain estrogen receptor. Following injection of estrogen to dogs, it bounded to the estrogen receptor in the prostate gland and caused the enlargement of the gland.

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The purpose of this study was to investigate the fundamental characteristics of ovarian function and uterine involution in postpartum period, and to clarify the relationship between reproductive performance, milk yield and suckling stimulation in grazing Japanese Black cows. The average interval to first postpartum estrus was 48.0 days. Most of the cows were not exhibiting estrus behavior at the first ovulation. Most of the corpora lutea formed after first ovulation were small in size and had a significantly shorter life-span (13.0 days) than that of the second to the third ovulation (21.7 days). Involutional changes of uteri were clearly observed by ultrasonography. The average period required for uterine involution was 37.8 days and it tended to prolong with the increase in calving number.
The milk yield had an inhibitory effect on both the postpartum ovarian activity and the uterine involution. The suckling stimulation, however, had a suppressive effect on the postpartum ovarian activity and a hastening effect on the uterine involution. Classification of factors in order of decreasing importance on postpartum first ovulation were: parity, milk yield, body weight changes, and as the nutrient condition, suckling stimulation. The factors affecting uterine involution could also be classified in decreasing order: parity, milk yield, and suckling stimulation. These results were obtained from the experiments on suckling cows, having restricted suckling twice a day or being weaned early. The data were analyzed using multiple regression equations.

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Bovine embryos were transferred to 1340 recipients for a period of 7 years. The pregnancy rate obtained was 54.7% (716/1310). Some factors which led to an improved conception rate were investigated. These include checking of the corpus luteum (CL), the time of transfer to the recipients and the skill of the operator.
Export of frozen embryos to Korea was also attempted on an experimental basis from 1987 to 1988. The transfer of frozen-thawed embryos resulted in a conception rate of 61.4% which was better than the rate of 40% obtained in our farm.
Twinning of Japanese Black Cattle was also tried by the transfer of 2 embryos to Holstein-Friesian heifer recipients since 1987. The twinning rate obtained was 50%. The abortion rate for single uterine horn transfer was 20% and only 8% for bicornual transfer.

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