Determining ovulation frequency in individually penned lactating sows using a faecal 'Progestin' assay

Trials were performed to evaluate the validity of a modified faecal 'proges tin' assay for monitoring ovarian activity (Trial 1) and to determine the o ccurrence of ovulation among individually housed lactating sows by repealed measurements of faecal 'progestins' (Trial 2). In trial 1 faecal and plasm a samples were collected from six multiparous sows, from the day after wean ing until oestrus occurred in the third oestrous cycle. A progesterone radi oimmunoassay was applied to skimmed milk extracts of the faecal samples, an d plasma progesterone concentrations were determined with a chemiluminescen t assay. In addition, high performance liquid chromatography (HPLC) analysi s was performed on faecal extracts and the immunoreactivity in the differen t fractions was determined. In Trial 2, faecal samples were collected from 88 multiparous sows at weekly intervals from the day of farrowing until 2 w eeks after breeding. Samples were subjected to 'progestin' analysis. Trial showed that the excretion patterns of faecal 'progestins' and plasma proges terone were significantly correlated (r = 0.79, p < 0.05) during the oestro us cycles. Parallelism was obtained in the assay, but recovery was low(11.4 %). The HPLC analysis revealed one major peak of immunoreactivity in a frac tion; which corresponded with progesterone. This finding suggests that inta ct progesterone was a source for immunoreactivity in the assay. In Trial 2, a 10-fold decrease in mean 'progestin' concentrations was noted from the d ay of farrowing to day 7 of lactation. The mean 'progestin' values remained low throughout lactation and started to increase 2 weeks after breeding. L arge individual variations in luteal phase values were noted. Only 1.1% (on e) of the sows ovulated during lactation.