Induction of parturition in sheep

Abstract

ALTHOUGH induction of birth has been quite widely used in cattle and is extensively used in pigs, it remains a relatively uncommon procedure in sheep. A major limitation to the technique in sheep is the poor survival of premature lambs and the frequent lack of precise information concerning the stage of gestation of ewes. Induction of parturition to facilitate batch lambing in groups of synchronised ewes can be very successful. However, the adverse economics of the sheep industry in recent years may have precluded its more widespread use. In instances where the welfare and possibly the survival of a ewe is at risk, as in the case of pregnancy toxaemia, a reliable protocol to induce parturition safely and maximise lamb viability is essential.

Two treatment protocols for induction of preterm parturition in ewes—Evaluation of the effects on lung maturation and lamb survival

“…Hence two treatment protocols for induction of preterm parturition in ewes were developed and evaluated in healthy pregnant ewes. The glucocorticoid dexamethasone (DEXA) was used in both protocols based on previous studies and recommendations (Kastelic et al, 1996;Ingoldby and Jackson, 2001). In addition to induction of parturition its positive effect on foetal and particularly lung maturation was utilized to increase survival rates of the premature lambs (Liggins, 1969(Liggins, , 1994Ballard et al, 1997;Zaremba et al, 1997).…”

“…During midand late-stage pregnancy abortion, premature birth and parturition can be induced using corticosteroids such as dexamethasone, flumethasone, betamethasone or cortisol acetate (Ingoldby and Jackson, 2001;Edmondson et al, 2012;Purohit et al, 2012). A dose of 16 mg dexamethasone per sheep is recommended for induction of parturition (Ingoldby and Jackson, 2001). The exogenous glucocorticoids mimic the natural pathway with cortisol produced by the foetal adrenal cortex acting as the trigger in the hormonal cascade leading to parturition.…”

Analyses of parental and seasonal influences on the synchrony of dexamethasone-induced lambing and lamb characteristics

“…Fetal cortisol enters maternal circulation and governs the shift in placental steroidogenesis to stimulate oxytocin receptor production in the myometrium, cervical softening, and the release of prostaglandin F 2α (PGF 2α ). These events ultimately cause an increase in uterine activity and further cervical dilation mediated by relaxin release, which lead to the onset of labour (Kastelic et al, 1996;Ingoldby and Jackson, 2001).…”

“…Dexamethasone is an exogenous corticosteroid used to induce parturition by mimicking the natural fetal cortisol influx into maternal circulation (Ingoldby and Jackson, 2001). A single dose of 10-20 mg of dexamethasone given intramuscularly (Edey et al, 1985;Ingoldby and Jackson, 2001;Rawlings and Bartlewski, 2007;Menzies, 2007) is the common procedure to induce labour and can be given as early as day 137 of a 144-149-day gestation period (Kastelic et al, 1996;Ingoldby and Jackson, 2001). However, administration of dexamethasone before day 142 is generally avoided to promote increased fetal viability (Rawlings and Bartlewski, 2007;Menzies, 2007).…”

“…The most significant advantage of synchronized lambing is to optimize supervision and assistance available at the facility to ensure a high health status of periparturient ewes (Kastelic et al, 1996;Batista et al, 2008). Immediate care of lambs is also facilitated in synchronized parturition (Ingoldby and Jackson, 2001). In biomedical investigations, studies on the hormonal control of parturition using a sheep model can yield Livestock Science 131 (2010) …”