Experiment on the Effect of Pregnant Mare Serum upon Multiple Pregnancy in Ewes (Second Report)

Abstract

A study was conducted with 23 Japanese Colliedale ewes. Each of them was administered with a dose of pregnant-mare serum gonadotropin (PMS) in her normal breeding season to determine the effect of the hormone on multiple pregnancy and to compare the rate of multiple pregnancy with untreated control ewes.
Each experimental ewe was injected intramuscularly with a dose of 500 IU of PMS four days before the next expected estrus. On estrus they were inseminated and observed throughout the duration of pregnancy and at parturition.
Eighteen of the 23 ewes treated lambed twins. The rate of twin-birth caused by the treatment was 78.3 per cent. So this figure coincides well with that given in the previous report; that is 76.9 per cent (G. Oita: this journal, 12, 146, 1959).
The difference in the rate of twin-birth between the PMS treated and the untreated control was highly significant (significant level, 0.008).
Then, ewes treated with PMS in two consecutive years were counted and the sum was compared with that given by the untreated control. The rate of twin-birth between the treated (sum in two consecutive years) and the untreated (sum in the late four consecutive years) was significant, the significant level being 0.001<P<0.05. It was demonstrated that PMS treatment was capable of increasing the rate of twin-birth in ewes when the treated were compared with the untreated control.