2010: Induction of parturition in swine* Induction of parturition in swine* Craig A. Smith American Veterinary Medical Association, Shaumburg, IL, USA Introduction Reduction of preweaning losses, decreasing the number of stillborn piglets and improving piglet survivability and productivity are all realistic goals that can be achieved by the swine industry. Improved knowledge of parturition, the ability to control its onset and the ability to influence the duration of farrowing are important steps in improving performance in the farrowing house. Keywords: induced parturition, swine, preweaning survival, piglet mortality The onset of parturition The gestation length in swine is typically 114-116 days. Variations may be due to the breed of sow and boar involved. Sows with large litters may have slightly decreased gestation length.1 The initiation of parturition in the pig is apparently controlled by the fetuses,2 with the presence of at least two live fetuses necessary to initiate the hormonal cascade that results in farrowing. The proposed mechanism functions as follows: at the appropriate time at the end of gestation, the fetuses release adrenocorticotrophic hormone (ACTH) from the fetal pituitary, which stimulates fetal adrenal hypertrophy and production of glucocorticoids (primarily cortisol) by the fetal adrenals. The increased levels of cortisol stimulate prostaglandin F2alpha (PF2a) release from the uterus. The increased concentrations of PGF2a cause luteolysis and a decrease in progesterone concentrations and promote release of relaxin from the corpora lutea and oxytocin from the posterior pituitary. Relaxin acts to soften and relax the cervix, while the absence of progesterone allows the oxytocin and PGF2a to increase myometrial activity and uterine contractions that initiate parturition and result in birth of the piglets. Induction of parturition Pharmacological control of the onset of parturition is paramount to maximizing sow productivity and profitability of the swine producer by allowing scheduling of farrowings. Prostaglandin F2alpha and its analogs will induce the onset of parturition. The use of PGF2a or one of its analogs allows more effective utilization of farrowing facilities and farrowing house personnel by minimizing weekend and night farrowings and, when necessary, scheduling additional personnel to supervise farrowings. Improved supervision of farrowing sows should improve piglet survivability. Improved synchrony of farrowing allows for better cross-fostering of piglets. Improved uniformity of piglet age ultimately results in better piglet performance in the farrowing house that ideally is carried over to the nursery. Lastly, induction of parturition with prostaglandin reduces the occurrence of the mastitis-metritis-agalactia (MMA) syndrome in herds with high incidence.3 Parturition-inducing compounds Prostaglandin Prostaglandin F2alpha is the only prostaglandin approved for use in swine in the United States. Prostaglandin analogs are as efficacious as PGF2a but tend to have fewer and less severe * Originally published by the Society for Theriogenology and the American College of Theriogenologists as Publication P-2 (2/91) in the Theriogenology Handbook (revised 2010). 61 side effects. These side effects are usually quite mild and short-lived, and may include restlessness, erythema, increased respiratory rates, salivation, defecation and urination. Vomiting is a rare occurrence. If side effects appear they will occur within ten minutes of administration and dissipate by 60 minutes postinjection.4 The dose of PGF2a is 10 mg, i.m. The dose of cloprostenol is 175 ug, i.m., but doses from 125 to 250 ug have been used.5 A dose of 5 mg PGF2a or 87.5 ug cloprostenol administered in the vulvar mucosa can reliably induce parturition and the side effects are less severe than for i.m. administration of the higher dose.6 Administration of a prostaglandin product will result in females farrowing the first piglet 24 to 32 hours after treatment. Hence, most treatments are administered in the morning so the bulk of farrowings will be accomplished during normal hours of the following workday. A shorter treatment to farrowing interval is observed in animals that are close to spontaneous farrowing.7 Prostaglandin and progesterone Prostaglandins have been used in conjunction with progesterone and progesterone-like compounds to improve the synchrony of the onset of farrowing.8 The use of progestational compounds administered daily on days 109 to 112 during late pregnancy prevented spontaneous farrowings. The subsequent use of prostaglandin at the time of withdrawal of the progesterone compound provided well-synchronized farrowings with no apparent adverse effects on the piglets. Prostaglandin and oxytocin Improved synchronization and a decreased interval from treatment to parturition can be obtained by using oxytocin. Five to 30 units of oxytocin administered 20 to 24 hours after prostaglandin treatment will result in the onset of farrowing within three to six hours in approximately 50% of the females.9 Twenty to 30 units of oxytocin will usually result in shorter intervals to birth of the first piglet but may also result in a higher incidence of dystocia due to stimulation of strong, asynchronous uterine contractions. The intravenous injection of two to three units of oxytocin intensifies normal myometrial activity within 20 seconds in sows, while dosages of ten units result in uterine spasms lasting ten to 15 minutes.7 Dosages of oxytocin greater than ten units may also interfere with the sow’s ability to release milk early in the postpartum period. Therefore, the dose of oxytocin to assist parturition in swine should be five to ten units administered i.m. to the sow no sooner than 20 hours after induction with PGF2a.5 Dexamethasone Administration of dexamethasone (75 mg/sow/day s.c. for three days) on days 101 to 103 of gestation resulted in a shortened gestation, 112 days versus 114 days.10 The need for repeated treatment, inability to accurately and efficiently control the onset of farrowing and decreased piglet birthweights and viability make this an unacceptable method of induction. Furthermore, the addition of dexamethasone to PGF2a-induced farrowing does not suggest a beneficial role for the use of corticosteroids in farrowing induction.11 Development of new compounds and regimens The increased use of drugs for parturition induction and synchronous farrowing will depend in large part on governmental approval of compounds. The prostaglandin analogs are prime examples of efficacious compounds that will be increasingly utilized in the future as they become legally available. Among the other induction agents is epostane, a competitive inhibitor of the 3-beta hydroxysteroid dehydrogenase enzyme system. This system is responsible for the conversion of metabolic precursors to progesterone. Administration of epostane at oral dosages 62 of 5 to 10 mg/kg bodyweight or s.c. injections of 5 mg/kg bodyweight results in a decrease in progesterone concentrations and the initiation of parturition within approximately 32 hours.12 Epostane is currently not approved for use in the United States. Agents that improve the synchrony of the onset of parturition may also be commercially utilized. Relaxin is effective at improving the synchrony of farrowing following prostaglandin induction with more sows farrowing within a 12-hour time span.13 The administration of xylazine (2 mg/kg bodyweight i.m.) 20 hours after prostaglandin treatment resulted in the birth of the first piglet 1.5 hours after xylazine.14 Some of the treated sows showed signs of sedation following xylazine administration. Neither relaxin nor xylazine are approved for such use in swine. Tocolytic compounds The use of tocolytic compounds may enhance our abilities to improve the survivability of neonatal pigs. Clenbuterol is a beta 2-sympathomimetic compound shown to have long-lasting uterine relaxant effects.15 Clenbuterol stimulates adenyl cyclase in cell membranes and outflow of intracellular calcium from the myometrial cells, making them unresponsive to oxytocin. This results in an interruption of the parturition process, which can occur within five minutes after administration. Although the greatest benefits may be the use of cloprostenol during Stage I parturition to prevent the onset of Stage II and farrowing during night-time hours, it can interrupt Stage II labor even after the birth of several piglets. Resumption of normal parturition occurs in a few hours when the drug’s effects wear off, with no apparent adverse effects on the health or vitality of the piglets. In contrast, injection of PGF2a followed by injection of propanolol, which blocks beta1- and beta 2-adrenergic receptors, did not influence time of onset of parturition.16 Disadvantages The results achievable with induced parturition are directly attributable to the level of care provided during the peripartum period. The use of prostaglandin to induce farrowing may actually increase the number of piglets which expire at or shortly after birth by causing the premature birth of some piglets or the birth of smaller piglets that are more susceptible to the extra-uterine environment.17 Likewise, stillbirth rates will not be improved unless trained personnel are present to assist with the delivery and care of neonates. Conclusions The routine use of parturition induction is a valuable tool in modern swine production. Correct implementation can improve efficiency of labor and facility utilization, and decrease neonatal death loss, thus increasing profitability. The routine use of parturition induction by itself will not improve piglet survivability without a commitment by the swine producer to: 1) provide personnel to supervise and assist at the time of farrowing; 2) provide a warm, dry environment for the newborn piglet; 3) ensure colostral intake by the newborn piglet; and 4) utilize management strategies (cross-fostering of piglets, all in-all out batch farrowings) made possible by the use of parturition induction. 63 References 1. BeVier GW, Dziuk PJ: The effect of number of fetuses and their location in the uterus on the incidence of stillbirth. Proc 4th Int Pig Vet Soc Congr, 1976. p. D21. 2. First NL, Bosc MJ: Proposed mechanisms controlling parturition and the induction of parturition in swine. J An Sci 1979;48:1407-1421. 3. Cerne F, Jochle W: Clinical evaluations of a new prostaglandin analog in pigs. I. Control of parturition and of the MMA syndrome. Theriogenology 1981;16:459-467. 4. Dial GD: Clinical applications of prostaglandins in swine. J Am Vet Med Assoc 1984;185:1523-1528. 5. Pressing AL: Pharmacologic control of swine reproduction. Vet Clin North Am Food Anim Pract 1992;8:707-724. 6. Friendship RM, Templeton CL, Deckert AE: An evaluation of vulvomucosal injections of prostaglandins for induction of parturition in swine. Can Vet J 1990;31:433-436. 7. Dial GD, Almond GW, Hilley HD, et al: Oxytocin precipitation of prostaglandin- induced farrowing in swine: determination of the optimal dose of oxytocin and optimal interval between prostaglandin F2a and oxytocin. Am J Vet Res 1987;48:966-970. 8. Gooneratne A, Hartmann PE, McCauley I, et al: Control of parturition in the sow using progesterone and prostaglandin. Aust J Biol Sci 1979;32:587-595. 9. Welp C, Jochle W, Holtz W: Induction of parturition in swine with a prostaglandin analog and oxytocin: a trial involving dose of oxytocin and parity. Theriogenology 1984;22:509-520. 10. North SA, Hauer ER, Fist NL: Induction of parturition on swine and rabbits with the corticosteroid dexamethasone. J Anim Sci 1973;36:1170-1174. 11. Cessar G, Kirkwood RN, Friendship R, et al: Sow and litter performance following farrowing induction with prostaglandin: effect of adjunct treatments with dexamethasone or oxytocin. J Swine Health Prod 2005;13:81-85. 12. Martin PA, Hammitt DG, Strohbehn RS, et al: Induction of parturition in swine and epostane, a competitive inhibitor of 3beta-hydroxysteroid dehydrogenase. J Anim Sci 1987;64:497-506. 13. Butler WR, Boyd RD: Relaxin enhances synchronization of parturition induced with prostaglandin F2alpha in swine. Biol Reprod 1983;28:1061-1065. 14. Ko JCH, Evans LE, Hsu WH, et al: Farrowing induction with cloprostenol-xylazine combination. Theriogenology 1989;31:795-800. 15. Zeroin K, Kondig H: The control of myometrial function during parturition with a beta-mimetic compound, Planipart. Theriogenology 1980;14:21-35. 16. Kirkwood RN, Thacker PA: Effect of propanolol on the onset and duration of parturition in sows. Can Vet J 1995;36:238-239. 17. Young IM, Harvey MJA: Routine induction of farrowing with dinoprost in a commercial breeding unit over a year. Vet Rec 1984;115:539-541. Additional reading 1. Cowart RP: Parturition and dystocia in swine. In: Youngquist RS, Threlfall WR, editors. Current therapy in large animal Theriogenology. 2nd ed. St. Louis: Saunders Elsevier; 2007. p. 778-784. 2. Roberts SJ: Veterinary obstetrics and genital diseases-theriogenology. 3rd ed. Woodstock, VT: Published by the author; 1986. p. 245-259. 3. Almond GW, Flowers WL, Batista L, et al: Diseases of the reproductive system. In Straw BE, Zimmerman JJ, D’Allaire S, et al, editors. Diseases of swine. 9th ed. Ames: Blackwell Publishing; 2006. p. 113-147. 64