Characterization of estrus profile in female swine and its accuracy in estimating ovulation time in comparison to ultrasound diagnosis

The objective of this study was to characterize the estrous profile in female swine in order to estimate the moment of ovulation, by determining the weaningto-estrus interval (WEI) and estrus duration based on conventional estrus detection procedures. In addition, the accuracy of the estimation was evaluated by comparison to ovulation diagnosis using ultrasound. Starting at weaning, 147 females were submitted to back pressure in the presence of a boar three times daily (6:30, 14:30, and 22:30 h) and to an ultrasound examination twice daily (6:30 and 14:30 h). The onset of the estrus was characterized by the first positive response to back pressure, and the end of the estrus was characterized by the first negative response to back pressure. Ovulation was diagnosed using real-time ultrasound. A linear regression model was used to predict the interval from estrus to ovulation considering the variation in the WEI, and a prediction of ovulation time was generated based on the estrus profile (PREDOV). Estrus duration was divided by 3 to allow estimation of the frequency of females ovulating during or outside the final third of estrus. The accuracy of the PREDOV was compared to a standard (ovulation diagnosed through ultrasound). The mean WEI, estrus duration, and interval from onset of estrus to ovulation were 82.6 ± 30.7, 58.3 ± 17.3, and 45.4 ± 14.4 h, respectively. The intervals from the onset of estrus to ovulation and the end of estrus to ovulation did not differ (P > 0.05) considering the WEI, but the weaningto-ovulation interval was increased with a longer WEI (P < 0.0001). In comparison to ovulation diagnosed using ultrasound, the sensitivity and specificity of the PREDOV were 74.2% and 40%, respectively, whereas the positive and negative predictive values were 72.1% and 39.5%, respectively. Thus, reproductive performance may be negatively affected if breeding systems are based only on estrus profile because this method lacks accuracy to estimate ovulation time.