Transvaginal Ovum Pick-Up in sows: Impacts on welfare and reproduction

There are few existing publications that describe transvaginal ultrasound-guided Ovum Pick-Up (OPU) in sows, and the impacts of the procedure for the welfare of the animals are unknown. In this study, we evaluated the effects of OPU, performed following restraint in a claw-trimming chute, on the animal welfare and reproductive health of second parity hybrid sows. The study utilized a generalized randomized block design at a commercial sow pool. We assessed salivary cortisol levels before, during, and after the procedure to compare the physiological stress response between OPU and restraint chute procedures (control group). We found a significant increase in salivary cortisol caused by the physical restraint procedure, and that the salivary cortisol level at the end of the procedure did not differ between OPU and control groups (p = 0.51). Furthermore, we conducted a novel approach-aversion test for sows, designed to assess if a feed reward would motivate the animals to willingly participate in the OPU-procedure. The animals were trained daily to enter the chute to access a feed reward. Ten animals in each group failed to complete the training period and did not voluntarily enter the restraint chute on the experimental day. This indicates that even the short daily restraint procedure during the four-day long training period was aversive to some animals. There was no difference in aversion towards the restraint chute between OPU and control groups one day after the procedure. The reproductive performance of the animals was subsequently evaluated through oestrus synchronization and insemination of the sows after the experiment. There was no observed difference in the farrowing rate (p = 0.72) and total number of born piglets (p = 0.84) between OPU and control sows. On average, we retrieved 9.0 ± 5.9 oocytes during the OPU-sessions (N = 26). Our results show that a majority of the sows prioritize the motivation for feed over their aversion to the OPU procedure. However, the physical restraint procedure is unpleasant for the animals and elicits a temporary stress response. We suggest that transvaginal OPU may be used for the recovery of oocytes from live sows, but refinements are needed to avoid stress during the lifting procedure. Such modifications could also potentially reduce the observed inter-individual variations in oocyte recovery outcomes.