Following decreasing daylight treatment for 7 days, twenty four anoestrous ewes of Japanese Corriedale were injected with P.M.S. 750 i. u. after 3-5 injections of progesterone 25mg daily. The ewes in pretreatment of light were hooded with black thick-cloth, and were under control hours of daylight.
This combined treatment was studied over three years 1959-1961, and the incidence of oestrus, presence of corpora lutea, and the state of follicular development was studied.
Total 13 lambs were produced by nine of twenty-one ewes treated with the method, and average percentage of lamb-production per ewe was 1.44.
The presence of corpora lutea and Graafian follicle was observed cytologically in 8 of I 0 ewes when their ovaries were examined at slaughter time. Seventeen of twenty-one ewes were induced oestrus and the percentage is about 81%.
In the sixth trial, three ewes were under progesterone-P.M.S. treatment alone, and only one cytologically was observed in fertile. The percentage is 33%. Therefore, the hypothesis may be probably explained that the light treatment prior to hormone administration will reduce the threshold in pituitary activity to induce the ovarian activity to much lower level.
There is no difference between the method of three days injection daily and the method of five days injection. Thus the method combined the pretreatment of decreasing daylight by a black hood with progesterone 25mg x 3 and P.M.S. 750 i. u. may be considered of practical application.
The highest response was observed two days after the time of P.M.S. injection, followed by next day, and this is agreed with GoRDON's result.