This is the first study describing the effect of PGE2 in farrowing sows and the impact on piglets’ health during the birth process. The time point of application was chosen based on a data set of a study describing the influence of time at which oxytocin was administrated during labour in sows (Mota-Rojas et al., 2007). Administration of the drug after expulsion of the fourth piglet had the highest impact on the birth duration and only mild side effects on the piglets’ health (Mota-Rojas et al., 2007).
In order to evaluate the effect of PGE2, a proof-of-concept as an adaptive dose response pilot trail was conducted to efficiently gain more information about the dose response in farrowing sows. These data can be utilized for an informed decision, which dosage should be used for further investigations. The small sample size with only three animals per group is a major limitation of this pilot study. However, this study design has been chosen, because it is sufficient to obtain first and novel information about the dose response to PGE2 in sows (Cook et al., 2015; Miller et al., 2014; Smith et al., 2006).
Considering the limitations, this study still showed a trend in dose-dependent effects of PGE2 administered after the fourth piglet on the overall birth process. The shortest farrowing duration and shortest total duration of birth could be detected in the group III with a mean of 140 min and 285 min, respectively. Comparing the results with the group I (farrowing duration: 296 min; total birth duration: 554 min) and the farrowing duration of sows in free farrowing from literature (Oliviero et al., 2008; Hales et al., 2015), this is notably a very short birth duration, which has not been described so far. Taking the effect of PGE2 on duration of birth into account, this might be a good alternative drug to oxytocin, because it is assumed to also decrease the risk for postpartal diseases in sows. Notwithstanding, the most optimal piglet interval (9.9 min) has been observed in the group treated with the highest dose of PGE2, followed by group III (10.8 min), whereas the group with the lowest dose of PGE2 showed no beneficial effect. Based on these findings, we can conclude that PGE2 in the concentrations of 1 mg and 2 mg has an uterotonic effect in sows, as known from human medicine (Chuck and Huffaker, 1995). The intravaginal application route of PGE2, like in women, was chosen to improve animal welfare and to establish a safe and effective route of application that can be used by farmers, when accommodating free farrowing sows. Due to significant similarities between swine and human vaginal mucosa, the swine vaginal mucosa has been proven to be the gold standard as in vitro model for the transmucosal absorption of drugs (Squier et al., 2008). Therefore, it can be assumed, that intravaginal applied PGE2-gel, which was designed for human medicine, can also be absorbed by swine mucosa. However, there is still a species difference and the absorption of certain agents might remain slightly unequal. An example has been described for oxytocin, where the transvaginal absorption is 53% more efficient in the sow compared to the absorption in human vaginal tissue (Eyk and Bijl, 2005). In this pilot study a higher effect in sows when using the human dosage (2 mg PGE2) was observed, which might be related to the effect of absorption as mentioned.
The significant percentage of weak- and stillborn piglets are a major problem of intensive pig production systems and cause ethical discussions in the society (Vanderhaeghe et al., 2010). Therefore, one outcome variable in this dose finding study was piglets’ distress. A proven indicator of intrauterine foetal distress is the meconium-stained skin of the piglets after birth (Mota-Rojas et al., 2002). In this pilot study, severe meconium staining was found in the placebo group and in all PGE2 groups. Some degree of distress caused by foetal hypoxia during birth seems to be physiological due to compression of the umbilical cord when the foetus enters the pelvis. Severe meconium staining in piglets from sows with a placebo treatment were described in a study from Mexico in 1.1% of the born piglets (Mota-Rojas et al., 2002). An explanation for this low percentage compared to group P might be that the average number of total born piglets was just 9.6 compared to 16.7 in this study. Late born piglets are likely to suffer asphyxiation to a greater degree because of the cumulative effects of successive uterine contractions. These piglets have a greater predisposition to get in a hypoxia state which can provoke sever distress and thereby sever meconium-stained skin in piglets (Mota-Rojas et al., 2002). Furthermore, piglets that take longer to be born are more likely to have umbilical cord lesions at birth. The importance of an intact umbilical cord to improve piglets’ survival up to three days after birth has been shown in one study (Rootwelt et al., 2013). In the present study, the highest percentage of umbilical cord lesion was recorded in group II. Interestingly, there was no association found between umbilical cord lesions and the meconium scoring or the birth order. In comparison with other studies testing uterotonic substances (Mota-Rojas et al., 2002, 2005, 2006, 2007), we rarely found umbilical cord rupture, which can occur in up to 33% of normal deliveries. The main findings in the PGE2-groups were oedematous and haemorrhagic umbilical cords. Several factors can lead to such changes of the umbilical cord, occurring either prenatal or during the birth process and therefore is still under investigation in human medicine.
Further important clinical parameters for piglets’ vitality were ‘reanimation of piglets’ and ‘intra-partum deaths’. Both parameter were only detected in group II and IV. In group II strong uterine contraction in the sows were observed, which might have caused the high number of weak born piglets and intra-partum death. Strong uterine contraction was not observed in group IV. The reason for this high number of intra-partum death of group IV remains unclear and might be just by chance due to the small sample size. Sever hypoxia during delivery originates from the uterus, umbilical cord or placenta. In humans, placental dysfunction is considered the major cause of late foetal death (Mantakas et al., 2018). Because the pig placenta is epitheliochorial, the need for an adequately intimate connection between sow and the piglets is met by the large total surface area of the diffuse placenta. However, there is few data available about the interaction between placenta expulsion and piglets vitality during birth. An interaction may arise, when considering the relationship between the placental parts and the intrapartum death and reanimation in these groups, due to a placental dysfunction during birth.