PREDICTION OF THE DAY OF OVULATION IN MARES THROUGH PHYSIOLOGICAL PARAMETERS MEASURED DURING ESTROUS Predicción del día de ovulación en yeguas utilizando parámetros fisiológicos medidos durante el estro

Behavioural, echographic and exploratory characteristics of the estrous period were studied daily for 120 preovulatory periods in 80 mares. The ovulation across preovulatory days of estrous behaviour, follicular size, follicular texture, echographic follicular appearance, uterine tone and echographic uterine appearance were analyzed. Follicular size increased between fourth and second day before ovulation. Follicular texture showed a progressive softening before ovulation. Echographic follicular appearance evidenced a triangularization of follicle near ovulation. The variability of the rest of studied parameters showed tendencies but did not reach statistical significance. In the other hand, the stepwise procedure selected ovarian texture and follicular size, in this order, as the variables that influence significantly the probability of ovulation in the next days. A logit link function with three intercept estimates, -4.35, -3.06 and -1.59 (1,2 and 3 days to ovulation), and the slopes, 0.495 for follicular size and 1.05 for follicular texture, calculate the cumulative probabilities of ovulation in the following days. With a combination of a very soft follicle and a follicle larger than 45 mm in diameter we have 79% of probabilities that the mare ovule in 24h. But several combinations of follicular size and follicular texture offer probabilities higher than 80% that mare ovule in 48h.