RELATIONSHIP OF WEANING-TO-ESTRUS INTERVAL TO TIMING OF OVULATION ANDFERTILIZATION IN SOWS

Data from two experiments were used to study the relationship between weaning-to-estrus interval (WEI, varying from 3 to 6 d) and the durati on of estrus, the interval from onset of estrus to ovulation and ferti lization results at 120 h after ovulation, in 201 multiparous sows. An increase in WEI resulted in a decrease in the duration of estrus (Dur ation of estrus (h) = [81 (exp1) or 88 (exp2)] - .33 x WEI, R(2) = .25 , P <.001) and a decrease in the interval from onset of estrus to ovul ation (onset estrus to ovulation (h) = [54 (exp1) or 59 (exp2)] - .20 x WEI, R(2) = .23, P <.001). Sows that were inseminated between 0 and 24 h before ovulation showed consistent high fertilization results (91 % normal embryos), irrespective of WEI. Sows that were inseminated out side this range showed an increased proportion of unfertilized eggs (P <.001). This increase occurred similarly in all weaning to estrus int ervals. These results suggest that negative effects of a longer WEI on subsequent litter sizes and farrowing rates as described in literatur e might be a result of suboptimal timing of insemination relative to o vulation and not of poor fertility in these sows.