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ESTIMATION OF OPTIMUM TIME FOR INSEMINATION OF GILTS AND EWES BY DOUBLE-MATING AT CERTAIN TIMES RELATIVE TO OVULATION

Summary.: Forty litters of pigs were produced following the doublemating of gilts at a 6-hr interval by boars whose offspring could be distinguished from each other. The time of insemination relative to ovulation was designated precisely (± hr) for each gilt. For analysis, gilts were put into four groups with reference to the time the first boar was used; 30 to 24, 20 to 16, 14 to 12 and 10 to 6 hr before ovulation. The first boar sired 33% and 30% of the offspring when he was used at the longest intervals and 78% and 71% of the offspring at the two shortest intervals.

Matings of 147 ewes took place first at 23, 19, 15, 11 or 7 hr before ovulation and again 4 hr later. The conception rates were 39%, 32%, 81%, 43% and 32%, respectively. The proportion of offspring from the first ram was 51% from the matings at the two longest intervals and 67% from the three shortest. The optimum time for insemination appeared to be about 12 hr before ovulation in both species.