Influence of Postpartum Cloprostenol Treatment in Sows on Subsequent Reproductive Performance under Field Conditions C Vanderhaeghe 1 , J Dewulf 1 , A Daems 2 , A Van Soom 1 , A de Kruif 1 and D Maes 1 1 Department of Reproduction, Obstetrics and Herd Health, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium; 2 Schering- Plough NV/SA, Brussels, Belgium Summary During the previous decade several studies focused on post- partum treatment with prostaglandin for improvement of reproductive performance in sows. The aim of the study was to investigate the effect of administration of a prostaglandin F 2a (PGF 2a ) analogue in sows within 24–48 h after farrowing on sow and litter performance. In five commercial farms, the sows were randomly assigned to either treatment A (2 ml clopros- tenol, Planate IM ) or treatment B (2 ml physiological saline solution, i.m.). Fifteen per cent of all sows were at random selected for progesterone analysis. Litter performance was assessed by measuring pre-weaning mortality and average daily weight gain (ADG). Sow performance was assessed by measuring weaning-to-oestrus interval (WOI), the percentage of sows returning to oestrus and litter size during subsequent farrowing. Administration of a PGF 2a analogue within 24–48 h postpartum had no effect on the rate of progesterone decline measured over 24 h compared with that of the controls. Litter performance and WOI were not affected by treatment. The subsequent litter size in sows of parity seven and more showed a significant difference of 1.98 piglets (p < 0.01) between both groups, to the benefit of the cloprostenol group. In conclusion, administration of a syn- thetic PGF 2a analogue, cloprostenol, within 24–48 h after farrowing improved litter size at next farrowing in older (‡7 parity) sows. Introduction Prostaglandins have three principal effects which have been used to influence reproductive activity in sows: the induction of luteolysis, the stimulation of smooth muscle contractility and the stimulation of hormonal release of endocrine tissues (Dial 1984). Because of their luteolytic effect, prostaglandins are widely used for the induction of farrowing so that partur- ition can be supervised and cross-fostering facilitated, which may result in an increased number of live born pigs and decreased pre-weaning mortality (Dial 1984). During the previous decade, several studies have reported on the benefits of using natural prostaglandin F 2a (PGF 2a ) postpartum in sows with or without reproductive problems (Lorenzo et al. 1992; Flaus and Gilette 1994; Chenault et al. 1996; Morrow et al. 1996a,b; Izeta-Mayorga et al. 1998; Lauderdale et al. 1998; Kurt et al. 2000; Koketsu and Dial 2002). It has been suggested that PGF 2a facilitates the uterine con- tractions and evacuation of uterine debris postpartum, reducing the incidence of endometritis and allowing sows to more fully express their milk yielding potential and improving post-weaning fertility. Reported improvements include a reduction in weaning-to-oestrus interval (WOI) (Chenault et al. 1996; Izeta-Mayorga et al. 1998), an increased number of pigs born alive in the subsequent cycle (Lorenzo et al. 1992; Flaus and Gilette 1994; Lauderdale et al. 1998; Koketsu and Dial 2002), increased piglet weight at weaning and less neonatal mortality (Morrow et al. 1996a,b; Kurt et al. 2000). However, data to support these effects using a PGF 2a analogue are lacking. Cloprostenol is a synthetic analogue of PGF 2a and it has been shown to promote myometrial contractions in rats (Beretta and Cavalli 2004), and to increase both the frequency and amplitude of uterine contractions around oestrus in sows (Langendijk et al. 2002). Within 24 h after delivery, progesterone concentra- tions in sows show a sharp decline to a level of <1 ng/ ml (Baldwin and Stabenfeldt 1975; Tarrier et al. 1989) or even <0.5 ng/ml (Lein et al. 1995). However, Cana- dian researchers showed that some sows have abnor- mally high (>1 ng/ml) progesterone concentrations after farrowing (De Passille´ et al. 1993). The source of the postpartum progesterone might be the corpora lutea, placenta or body fat (De Passille´ et al. 1993; Miller et al. 2004). De Passille´ et al. (1993) indicated that piglets suckling sows with high progesterone levels grew more slowly in the first days postpartum. Liptrap (1980) suggested that the process of lactogenesis may be compromised by any factor that prevents or delays the final decline in progesterone levels after parturition. As the decline in progesterone, originated from the corpora lutea, appears to result from PGF 2a -induced luteolysis, a lack of adequate amounts of PGF 2a could result in incomplete luteolysis and thus prevent the eventual decrease in progesterone values. Therefore, cloprostenol treatment early post-farrowing may improve litter weight gains in the current litter, and thereby possibly decrease piglet mortality by more rapidly removing the corpora lutea of pregnancy and thus removing the supposed negative effect of progesterone on milk pro- duction. The significant effect of parity on litter size at birth (Hughes 1998; Rodriguez-Zas et al. 2003) and on litter size in the next cycle (Koketsu and Dial 1997) has been reported. Koketsu and Dial (1998) showed a decrease in litter size as lactation length decreased for parity ‡3 sows, but an injection of PGF 2a within 24–48 h postpartum could reduce this negative effect of a short lactation on litter size (Koketsu and Dial 2002). These data led to the speculation that older sows might have a slower rate of uterine involution and that postpartum PGF 2a treatment might somehow improve the involu- tion process. Reprod Dom Anim 43, 484–489 (2008); doi: 10.1111/j.1439-0531.2007.00942.x ISSN 0936-6768 Ó 2008 The Authors. Journal compilation Ó 2008 Blackwell Verlag