Abstract
An experiment on multiple pregnancy in ewes was carried out from August in 1957. Twenty five ewes were selected from among those which had been kept under the same conditions and were divided at random in to the experimental and the control groups. The experimental group was injected with pregnant-mare serum (PMS) four days before the next prospective estrus. All the ewes were bred in their estrus and conceived without exception. After parturition, they were observed on their behavior of nursing.
1) The optimum period of PMS injection is probably four days before the next prospective estrus, as all the ewes, except one, of the experimental group showed estrus two to five days, 3.3 days, on the average after injection and conceived on breeding.
2) The injection used was lyophilized fresh serum of pregnant mare. It was dissolved in distilled water and injected intramuscularly. Treated ewes showed no sign of allergic reaction.
3) The rate of occurrence of lamb twins was 29.4% in the control and 43.4% in the experimental group. In the statistical analysis, there is the difference of ratio between the two groups at 8.2% of significant level. Further investigation may be necessary to confirm a significant difference in twinlambing ratio.
4) It has already been demonstrated that the number of lambs is directly proportional to the dose administered. The dose of 500 I.U. of PMS, as employed in this experiment, seems to be adequate for the general purpose of obtaining lamb twins.
5) The term of gestation was a little shorter in the experimental group than in the control, but there is no significant difference between the two groups in statistical analysis. No significant differences were present between the groups in the sex, body weight, and survival of newborn lambs. A succeeding experiment is to be carried out in the next year.
