Comparison of serum cortisol concentrations as indicators of the perioperative stress response in cows undergoing correction of left displaced abomasum by right flank laparotomy with omentopexy versus left flank laparoscopy with abomasopexy.

Serum cortisol is widely used as an indicator of hypothalamic-pituitary-adrenal (HPA) axis activation in cattle, although it is not specific to pain and may also reflect handling, restraint, fear, and environmental change. This study compared perioperative serum cortisol responses in dairy cows with left displaced abomasum (LDA) undergoing right flank laparotomy with omentopexy or left flank laparoscopy with abomasopexy. Forty lactating Holstein-Friesian cows were alternately allocated to laparotomy (n = 20) or laparoscopy (n = 20). Blood samples were collected immediately before surgery (T0), immediately after surgery (T1), and three hours postoperatively (T2). The linear mixed-effects model showed a significant effect of time (P < 0.001) and a significant surgical technique × time interaction (P = 0.006), whereas the main effect of surgical technique was not significant (P = 0.851). Estimated marginal means increased from 0.0505 µmol/L at T0 to 0.1649 µmol/L at T1 in the laparotomy group and from 0.0974 to 0.1312 µmol/L in the laparoscopy group, with similar values at T2 (0.1258 and 0.1247 µmol/L, respectively). Exploratory Mann-Whitney analyses showed greater T0-T1 and T0-T2 changes in the laparotomy group (P = 0.002 and P = 0.034), but no difference in T1-T2 change (P = 0.394). The temporal cortisol response therefore differed between groups, particularly immediately postoperatively. However, non-random allocation, baseline cortisol imbalance, and non-standardised preoperative handling limit causal attribution to surgical technique. Serum cortisol should therefore be interpreted as an objective marker of perioperative neuroendocrine stress rather than a specific measure of surgical pain.