Introduction

Simply speaking, by allowing farrowing to occur at predetermined times, the amount of perinatal mortality can be reduced. The control of farrowing can provide opportunities for labor efficiency, more cross fostering, reduce preweaning mortality, and lead to heavier weaning weights.

Can farrowing be controlled?

Yes. Farrowing control has been in use for over 15 years and methods such as inducing farrowing to occur early and delaying parturition until a more appropriate time have been employed.

Is supervised farrowing necessary when inducing?

It would appear that there is benefit of attended farrowing, especially when inducing. Indications are that 0.5 pigs/litter or up to 1 pig/sow/year can be saved. For example when 250 mg cloprostenol is given in the vulva- mucosa, the presence of an attendant reduced stillborns 0.42 pigs/litter compared to unsupervised farrowing. Further, close observation at farrowing and for an additional 3 days after farrowing improved survival by 0.74 pigs/litter. This serves to reduce crushed and low viability piglets, which account for 45% and 39% respectively, of all pigs lost.

Is induced farrowing always desirable?

No, not on simple investment return, but this may not always be clear, since hidden benefits of induced farrowing can provide opportunities to optimize observation, and save pigs, control personnel:sow ratios, and increase opportunities for cross fostering more piglets. However, it has been suggested that before intervening, there should be a reason for doing so. If stillborns are below 5%, and preweaning mortality is less than 8%, induction may not be cost effective, but still could help in other ways. Before making a decision to induce farrowing, a careful examination of the records, such as a high rate of stillborns, may indicate that induction could result in more pigs saved. It is important to know the average length of gestation for the herd. Most drugs for inducing parturition can also cause abortion so careful use is warranted. New recommendations suggest that sows should not be induced earlier than 2 days before expected farrowing to limit the percentage of immature pigs being born. The date of farrowing is determined from the first breeding day recorded as day 1.

Can delay of farrowing be beneficial?

By administering progestegens, or by using prostaglandin inhibitors such as indomethicin, the process of farrowing can be delayed. The process has been delayed up to ~5 days, with generally acceptable results. Feeding progestegens such as altrenogest (Regumate) during days 110 to 113 delays parturition 2 to 4 days and allows parturition to begin ~30 h after the last feeding. Delays past these times increase stillbirth rates.

How is farrowing induced?

Prostaglandin and its analogues when administered, reduce production of progesterone by corpora lutea. Within 8-24 h of injection, progesterone decreases and corticosteroids increase, but there is no increase in estrogens. Relaxin increases within 45 minutes (although different from the natural biphasic release), and prolactin is also observed to increase.

Are there any risks when using the drugs?

Yes. Inappropriate injections of prostaglandin or the analogues can induce farrowing earlier than d 111, which will significantly increase stillborns and reduce survival of those that are born alive.

Records and identification of the proper sows to treat is critical. Recommendations involve not giving induction drugs until 2 days before the herd average for farrowing!

Is there a standard procedure?

Yes. Many producers induce sows that have not farrowed by d 111with 10 mg prostaglandin or 175 mg of cloprostenol and many follow this with an injection of 20 I.U. of oxytocin for those still not farrowing 25 h later.

Why do induction protocols sometimes fail?

Much of the failure is thought to be due to poor luteolysis, and these are the sows that will fail to farrow within a 24 h period. And also because not all sows are at the same stage of gestation, up to 20% of sows deliver in less than 24 h, and therefore many sows farrow when supervision is not available.

When should farrowing be induced?

For any drug or method chosen, this is probably the most critical aspect for successful induction. It has been clearly shown that abortion and early farrowing result from destroying the corpus luteum with prostaglandin or its analogues at most stages during pregnancy. Farrowing induction has been performed as early as d 110 of gestation but it has been observed with years of field data that stillbirths and low piglet viability increase dramatically when farrowing is induced before day 111 of gestation. For this reason, and due to the fact that there are errors in gestation day estimates, day 112 should be the first target date for induction.

Should humans use caution when handling prostaglandins?

YES. These hormones are readily absorbed through the skin and can cause problems for females and asthmatics. In females, the drug once absorbed can enter the blood and destroy the corpus luteum on the human ovary and cause abortion if females are pregnant. Therefore pregnant women should never handle the drug, and all other women should only handle the drug when wearing disposable plastic gloves.

What behaviors result in sows after administration of prostaglandin or its analogues?

Following administration of prostaglandin, even in crates, sows initiate nest building behaviors by attempted rooting, pawing and biting which continues for ~90 minutes. The lower doses of prostaglandin administered to females, produce less restless behavior. A short transient increase in temperature after injection is also observed, but this does not increase temperature during farrowing. In general, these effects are not observed with the analogues.

However, it should be mentioned that although it is known that low doses are effective at destroying the corpus luteum, high levels of prostaglandin are needed at parturition for normal and rapid delivery of live pigs.

What drugs are used for inducing farrowing?

Prostaglandin (PGF2 a), the natural hormone is manufactured as dinoprost tromethamine and sold under the Lutalyse® (Upjohn) name, while synthetic analogues (cloprostenol) marketed as Estrumate® have been used to induce approximately 55% of sows to farrow during the subsequent 8-10 hour working day. The natural form of prostaglandin (Lutalyse®) is effective at reducing blood flow to the ovary and corpora lutea which ends the production of progesterone. In general the drugs have not increased the duration of farrowing or the percentage of stillborns compared to non-induced sows and the effectiveness of the induction drugs improves as the actual due date gets closer. The cost of a typical injection of Lutalyse® is approximately $2.00/sow

Are there differences between the induction drugs?

Yes, but the differences in effectiveness between the natural prostaglandin (Lutalyse®) and its analogues (Estrumate®) may only be related to the dose administered. The drugs do differ in their effect on sow behavior following injection, respiration rate, and influence on uterine contractility. Lutalyse has a t½ (half-life in circulation) of 10 minutes, Estrumate® a t½ of 4 hours, and Bovilene® (fenprostalene) a t½ of 20 h. Over many studies, there appears to be little difference between prostaglandin and its analogues in farrowing induction. Generally the prostaglandins and analogues alone induce 60% to farrow 23-33 h after the induction. After day 110, prostaglandin induces 87% to farrow within a 48 h period (average: 28.0 ± 5.5 h) and analogues like cloprostenol induce 93-100% to farrow in 48 h (average: 26.0 ± 5.7 h).

Cloprostenol

Cloprostenol tested at 50, 100, and 175 mg doses has resulted in a 250 minute average farrowing duration. The 175 mg dose of cloprostenol induced 25% of sows to farrow in 24 h, 80% to farrow by 36 h, and 90% to farrow by 48 h. Over 76% of these sows have approximately 4 h farrowing durations, similar to non-treated sows of which 82% have 4 h farrowings. A standard protocol involves Cloprostenol administered at 175 mg, to induce ~69% to farrow between 20-30 h after injection. Route of cloprostenol administration did not affect the response when administered i.m. or perianal, and so either one was just as effective. However, Table 2 indicates that intra vulvular injections at half the dose can be just as effective. There are no adverse effects of the drug as greater than 94% of treated sows return to estrus within 10 d of weaning with no observed detrimental effects of drug administration.

Cloprostenol Induced Abortion

500 mg of Cloprostenol has been given 30 to 100 d after mating. This aborts sows within 30 to 42 h, with a duration of abortion lasting 4-14 h. Estrus occurs within 9.3 days and conception rates at this estrus are >90%.

Prostaglandin (PGF2a, Lutalyse)

The interval from prostaglandin administration to farrowing changes with the dose administered. For example a 2.5 mg dose induces farrowing in 55 h while a 20 mg dose induces farrowing in 28 h. Effectiveness also improves as due date gets closer. Injections on day 109 induce farrowing at 62 ± 16 h, and injections on day 113 induce farrowing at 17 ± 7 h. Further, prostaglandin given on d 111, induces 44% of sows to farrow within 40 h, compared with 93% farrowing within 40 h when given on day 112. Split injections of PGF2a 12 h apart have shown no benefit, but data indicates that greater synchrony of farrowing was obtained by a 6 h split injection. Method of prostaglandin administration has been compared. Intravulvular injections of the drugs are thought to increase local concentrations and therefore a lower dose may be just as effective. Data from Table 4 indicates that good results can be obtained at half the dose when give in the vulva instead of in the muscle at full dose. For i.m. injections, the administration of 5 mg appears to be the minimal dose, whereas doses between 10-15 mg (12.5 mg) produces intermediate results and 20 mg the best results.

Oxytocin

Oxytocin lowers the threshold for action potentials in muscle tissue, causes the release of uterine prostaglandins and thereby facilitates smooth muscle contraction. Single oxytocin injections (i.m. or i.v.) do not produce frequent or well propagated contractions in pig myometrium, but does increase muscle activity and uterine pressure slightly for several minutes. This hormone can be administered to the female in labor and is most effective when progesterone levels are low and milk can be ejected. The administration of oxytocin when milk is first visible or can be stripped from the teat has been shown to reduce both the time to the 1st pig and the duration of parturition. There are also certain concerns regarding oxytocin use and oxytocin is thought to be the hormone most frequently misused in the farrowing barn. Misuse of the drug may cause farrowing complications and actually increase stillbirths. The dose of oxytocin to be administered and the timing of the dose is highly controversial. This variation probably reflects the stage of gestation, state of luteolysis, and whether milk can be stripped (closeness to 1st pig delivery). In general, 20 units of oxytocin have been reported to be more effective than 5 or 10 units for reducing interval from parturition to farrowing. But doses greater than 10 I.U. have been reported to cause cessation of delivery after the second pig and even 10 I.U. of oxytocin given 24 h after PGF was reported to increase stillbirths due to hypoxia. Over the years, the doses of oxytocin evaluated include the range of 10 to 50 I.U. When 50 I.U. was administered, delivery was reported to occur within in 0.6 ± 0.6 h from injection, but it has been reported, that at levels of 30 I.U. or above, over stimulation of the uterus and fatigue may result. Despite the controversy, oxytocin given at a doses between 20 to 40 I.U., 24 h after prostaglandin injection, induced between 64-100% of sows to begin farrowing within 2 to 4 h of the injection, and with no observed increase in stillbirths. It has also been reported that 10 I.U. of oxytocin can restore muscle contractions in sows with uterine inertia. The timing of oxytocin administration following induction is also controversial. Experiments evaluated oxytocin (30 I.U.) given at 20 h or 24 h following induction. At 20 h, oxytocin induced 89-100% of sows to begin farrowing during the working hours (21-23 h ± 0.9 h), with farrowing beginning ~1.8 h after injection. In this experiment, stillborns ranged from 0.4-3% and when compared to oxytocin given at 24 h, the 20 h injection appeared to be more desirable because at 24 h, natural farrowing was already beginning and therefore did not improve the percent farrowing. However, giving oxytocin at 16 h after prostaglandin injection, induced a high percentage to farrow but stillborns increased when it was administered before milk letdown. Sows given oxytocin have been observed to have a higher rate of manual intervention. Oxytocin given 16 h after prostaglandin, increased rate of intervention compared to oxytocin given at 24 h.

One cc of long-acting oxytocin (Depotocin) has been used to reduce farrowing duration. This drug when administered 24 h after induction with cloprostenol reduced the duration of farrowing to 130 minutes compared to 194 minutes for sows receiving cloprostenol alone and 164 minutes in untreated sows.