Control of time of parturition in pigs

Injection of prostaglandin (PG) F-2 alpha or its analogues has provided a technique to induce parturition after Day 110 of gestation in the sow. The mean interval from PG injection to parturition ranges from 24 to 28 h, but only 50-60% of the sows farrow during an 8-10 h working day, and as many as 20% of sows may begin parturition before the injection of PG or less than 22 h after the injection. The duration of parturition is positively associated with the incidence of stillbirths and perinatal death so that techniques to reduce the duration of parturition may save piglets. Early parturition has been prevented by feeding sows progestagens, PG synthesis inhibitors and hypothalamic function inhibitors. These compounds were detrimental to piglet survival if they delayed parturition too long after the expected time of parturition. Parturition was delayed in sows up to 1.5 days by altrenogest, 1.6 days by meclofenamic acid, 2.7 days by indomethacin, and 3 days by methallibure without increased incidence of stillborn piglets compared with control sows. Injection of PG after administration of altrenogest or meclofenamic acid was successful in experiments with sows; parturition could be confined to a 5-day working week with no increase in stillborn piglets compared with control sows. Relaxin injected at 48 and 24 h before or only 24 h before injection of PG increased the proportion of sows farrowing 22-32 h after PG to 86.2% compared with sows injected only with PG (53.3%, P less than 0.01). Oxytocin injected 20 h after injection of PG increased the proportion of sows farrowing 20-28 h after PG to 90.4% compared with sows injected only with PG (49.2%, P less than 0.005). Injection of 25-60 i.u. ACTH on Day 110 of gestation did not shorten the length of gestation, but did decrease the incidence of still born piglets by 0.2 piglets/litter (P less than 0.05). An injection of the beta-adrenergic antagonist, carazolol, during labour before the birth of the first piglet decreased the duration of parturition and the incidence of stillborn piglets particularly in primiparous sows (P less than 0.05). Carazolol injected with oxytocin 20 h after injection of PG decreased the interval from PG to parturition by 2 h compared with sows injected with only PG and oxytocin.(ABSTRACT TRUNCATED AT 400 WORDS)