PERIOVULATORY PROFILES OF ESTRADIOL, LH AND PROGESTERONE IN RELATION TO ESTRUS AND EMBRYO MORTALITY IN MULTIPAROUS SOWS USING TRANSRECTAL ULTRASONOGRAPHY TO DETECT OVULATION

The timing of oestrus, the concentrations of oestradiol, LH and proges terone, and embryo survival on day 35 of pregnancy in 16 weaned multip arous sows were studied in relation to the moment of ovulation. Ovulat ion was detected using transrectal ultrasonography. The interval betwe en weaning and ovulation varied between 126 and 214 h (156 +/- 29). Th e peak oestradiol concentration was 27 +/- 17 pg ml(-1); sows with a s horter interval between weaning and ovulation had higher peaks of oest radiol (r = -0.54, P = 0.02). The interval between the peak oestradiol concentration and peak LH concentration was 11 +/- 4 h. The shape, wi dth and height of the LH surge were variable, but did not influence th e interval between the peak LH concentration and ovulation, which vari ed between 26 and 34 h (30 +/- 3). The interval between ovulation and the time when the progesterone concentration rose to more than 1.0 ng ml(-1) above basal progesterone concentrations varied from 6 to 19 h ( 13 +/- 4). Ovulation took place at a more or less constant relative ti me of the oestrous period (after 72 +/- 8% of the duration of oestrus) , irrespective of the duration of oestrus. The timing of the peak conc entrations of oestradiol and LH and the rise in progesterone concentra tions were closely related to the occurrence of ovulation but not to t he onset of oestrus. Embryo survival on day 35 of pregnancy was relate d to the interval between the peak concentrations of oestradiol and LH (p = -0.68, P = 0.02); shorter intervals resulted in higher embryo su rvival. A similar relationship was found between embryo survival and t he interval between the peak oestradiol concentration and the rise in progesterone concentration (r = -0.59; P = 0.05), and between embryo s urvival and the interval between the peak LH concentration and ovulati on (r = 0.60; P = 0.03). In conclusion, the interval between the peak LH concentration and ovulation was on average 30 +/- 3 h and was relat ively constant between sows (from 26 to 34 h). The concentrations and temporal changes in oestradiol, LH and progesterone profiles differed among sows. The temporal relationships between hormonal changes and ov ulation seem to be of importance for embryo survival and require furth er investigation.