Graduate Thesis Or Dissertation
 

Cycling and reproductive phenomena in gilts

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  • Purebred Yorkshire gilts from a confinement managed herd were reared to test weights away from the sow and boar herd. Thirty-eight gilts weighing between 73 and 80 kilograms constituted group A gilts; 38 gilts weighing between 91 and 100 kilograms constituted group B gilts; and 47 gilts weighing 114 kilograms or more, constituted group C gilts. In each experimental group, approximately ten animals were mixed to provide new pen mates for all, and were moved to the broodstock barn where each group was assigned a pen; at all times throughout the study, one contiguous boar was located between those pens of gilts. Each day, gilts were removed from their pens and checked for estrus by direct boar contact for approximately 15 minutes; also, estrual status was estimated by vulvular ratings. Groups A and B were allowed to mate at their third occurrence of estrus; group C gilts were allowed to mate at their first exhibition of estrus. Twenty-five days postmating, the gilts were slaughtered and their reproductive tracts were removed for inspection of their ovaries and uterine contents. No significant differences (P <.01) occurred among the groups for ovulation rates, embryonic survival rates, total embryos, average daily gain measured three weeks prior to breeding, average days between estrual cycles, age at breeding, nor weight at breeding (P<.01). At mating, group A was lightest and group C was youngest; group B, which represents the traditional breeding weight, was oldest and heaviest, but did not differ in performance. With weight, chronological age and sexual age of the groups held constant, the only significant association between chronological age, breeding weight or average daily gain with either ovulation rate or embryo survival was between breeding weight and average daily gain and the two measures of reproductive performance. These results indicate that sexual age is more important than chronological age as a determiner of ovulation rate and embryo survival.
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