Valros, A., Norring, M., Ahlqvist, K. et al. 2024. Effects of repeated intramuscular injections on sow behaviour reactions and stress-related saliva biomarkers – A pilot study. Applied Animal Behaviour Science 271, 106173.

Medicating large production animals, such as sows, individually can be challenging, especially when repeated treatments are needed. Intramuscular (i.m.) injections have been shown to be aversive, and an increased reaction could be expected over consecutive days of injections. The aim of this pilot study was to assess if daily repeated i.m. injections cause sows to react differently with time and if injection stress is reflected in increased stress- and pain-related saliva biomarkers. Additionally, the aim was to assess if oxytocin was related to the behaviour reaction of sows during injections. In total 37 sows were allocated randomly into four treatment groups: 1. Sham-injected (SHAM: 9 sows), 2. Control (CON: 11 sows), 3. Penicillin (PEN: 9 sows) and 4. Tetracyclin (TET: 8 sows). The reaction of the sows to injections over three days was subjectively assessed by two observers. Further, SHAM and TET sows were saliva sampled for stress-related biomarkers before and after injections. Treatment (p < 0.001) influenced the medication reaction. Pairwise comparisons showed that the reaction to SHAM treatment was less compared to CON (p = 0.002) and PEN treatments (p < 0.001), while reactions to SHAM did not differ from TET (p > 0.1). Reaction to PEN was higher than that to TET (p = 0.01), while PEN and CON did not differ from each other (p > 0.1). Day tended to affect medication reaction (p = 0.08). The reaction to all other treatments decreased numerically from day 1 to day 3, while this was not the case for the TET treatment. Changes in biomarkers were subtle. Oxytocin tended to increase after TET injection on day 3 (p = 0.05). For the SHAM treatment, some of the biomarkers (chromogranin A, alpha-amylase activity and total esterase activity) showed significant or numerically decreasing trends in POST vs PRE-treatment samples on both days. The oxytocin level before injections was higher in sows that did not react to the medication at all than in sows that showed any kind of reaction (p = 0.008). In conclusion, sows appeared to habituate to the handling and injection, depending on the level of discomfort caused by the injectable substance. Further, the results suggest a potential role of oxytocin in decreasing aversive reactions in sows to human handling.