EFFECT OF REGUMATE ON OVULATION RATE, EMBRYO SURVIVAL AND CONCEPTUS GROWTH IN MEISHAN AND LANDRACE-X LARGE WHITE GILTS

Nineteen Landrace x Large White gilts and 21 Chinese Meishan gilts were randomly assigned, within breeds, to receive either no estrus synchronization or 20 mg/day of the orally active progestagen, allyltrenbolone (Regumate(R)) for 18 days. Following natural mating, gilts remaining pregnant were slaughtered on Days 27 to 31 of pregnancy in order to determine the number of corpora lutea and fetuses and to measure allantoic fluid volume and fetal length and weight. Meishan gilts had higher ovulation rates than Landrace x Large White gilts (20.16 +/- 0.91 versus 15.43 +/- 0.55, respectively). Treatment with the progestagen caused a slight but non-significant increase in the ovulation rate of both breeds. There were no significant differences in the proportion of embryos which survived among the four groups, although the mean embryo survival percentage in Regumate-treated Meishan gilts was 14% lower than that of the control Meishan gilts. Values for each of the three measures of conceptus growth were higher in Landrace x Large White gilts than in Meishan gilts. There was no evidence of greater uniformity among littermate Meishan fetuses than among littermate Landrace x Large White fetuses.