Influence of a New PGF/oxytocin Protocol on the Timing of Farrowing and Serum Progesterone

K.K. Mehedyn and R.N. Kirkwood

Alberta Pork Research Centre; AAFRD, 905 O.S. Longman Building, 6909-116 Street, Edmonton, AB, Canada, T6H 4P2

A recent study has shown that injection of oxytocin 6-h following a luteolytic injection of cloprostenol can improve the predictability of farrowing. The present studies were undertaken to confirm this effect and to determine why some sows fail to farrow following PGF injection.

Eighty-six mixed parity sows were assigned to have their farrowing induced by either a single injection of 175 µg cloprostenol (PGF) IM or the PGF injection followed 6-h later by 30 IU oxytocin (OT) IM. A blood sample from each sow was obtained at the time of PGF injection and again 24-h later for the determination of progesterone (P4) concentration. Sows were monitored for piglet delivery from 0700 to 1700-h and assigned to a farrowing period of; first day (D1;day of induction), first overnight (N1), second day (D2), second overnight (N2) and non-response (NR). Percent sows farrowing in each period were 7.0, 25.6, 53.5, 7.0, 7.0 for PGF alone and 23.3, 14.0, 60.5, 0 and 2.3 for PGF/OT. Fewer (P<0.06) PGF/OT sows farrowed in the N2 and NR periods. Number of sows farrowing in the first 24-h was not affected by treatment, but the distribution changed with more PGF/OT (P<0.03) sows farrowing during D1. This may reflect a close proximity to natural onset of parturition and, rather than a reinforcement of the PGF signal, the uterine contraction effect predominated. To attempt to determine why some sows fail to farrow promptly in response to PGF, changes in serum P4 were compared in sows farrowing either 16 to 24-h (S) or >30-h (L) following PGF. The percentage decrease in P4 24-h after induction was greater (P<0.1) in PGF/OT sows and in sows having a shorter PGF-to-farrowing interval (P<0.08) (59.9, 31.7, 63.4 and 65.1% for PGF/OT-L, PGF-L, PGF/OT-S and PGF-S, respectively.

Implication: These data suggest that a delayed response to PGF induction of farrowing may be due to a failure to induce terminal luteolysis. The addition of oxytocin to the induction protocol enhanced luteolysis and so improved the farrowing response to induction.