THE EFFECT OF ESTRADIOL BENZOATE AND BOAR EXPOSURE ON THE OCCURRENCE OF ESTRUS AND OVULATION IN THE GILT

Abstract

The efficacy of estradiolbenzoate (EB) and exposure to mature boars as means of stimulating estrus and ovulation in gilts was determined on a total of 333 Lacombe gilts. The gilts were placed on the experiment at an average age of 160 d either in the winter (January and February) or summer (July and August) of 2 yr. They were slaughtered either 8 – 12 d after being observed in estrus or after 200 d of age if they were not observed in estrus. A higher percentage of EB-treated than control gilts were in estrus by 200 d of age (87.4 vs. 58.6%, P < 0.01). For the EB vs. control gilts detected at their first estrus, the number of days to estrus after 160 d of age was shorter (4.5 ± 0.1 vs. 16.9 ± 1.1 d, P < 0.01). In the control gilts, exposure to mature boars and season had no significant effect on the number of gilts in estrus or days to first estrus. In comparison with control gilts, EB produced the following additional effects: more gilts in estrus without ovulation (32.7 vs. 15.1%, P < 0.05); a reduction in ovulation rate (6.2 ± 0.4 vs. 12.8 ± 0.5, P < 0.01); and more gilts with cystic follicles (11.9 vs. 0.8%, P < 0.01). Thus, while EB stimulated estrus at an earlier age than exposure to mature boars, the effects on the ovary suggest that breeding at the EB stimulated estrus would not be desirable. Key words: Estradiolbenzoate, boar exposure, estrus, ovulation