Action of exogenous oxytocin on stress modulation in crossbred Red Angus cows

Abstract

Cattle (Bos taurus and Bos indicus) are organised on the basis of leadership and dominance in such a manner that a disturbance by an external stressor causes negative effects on their health, productivity, well-being, and behaviour. One of these effects is the excessive release of glucocorticoids, which results in increased alertness. We evaluated the action of exogenous oxytocin (OT) on serum cortisol levels in crossbred Red Angus heifers. Twelve Red Angus crossbred heifers were moved daily from the pasture to the corral in weeks 1 and 2 for adaptation to human contact and handling in the cattle crush. In weeks 3 and 4, they were divided into two groups of six (T1 and T2). The T1 group was administered 20 IU (2 mL) of OT via intramuscular injection and the T2 group was administered 2 mL of saline solution 0.85% (SS). In weeks 5 and 6, they were only contained in the cattle crush for evaluation. On days 01, 07, 14, 21, 28, 35, and 42, blood samples were collected by jugular venepuncture in vacuum tubes without anticoagulants. Then, serum cortisol levels were measured using a radioimmunoassay. In the period of adaptation, during weeks 1 and 2, serum cortisol levels decreased in both the groups, with higher levels in the SS group; the same result was obtained in weeks 5 and 6. During treatment, however, there was a significant difference between the two groups in week 4, with a reduction in cortisol levels in the OT group. This result suggests a modulator effect of OT on neuroendocrine response to stress.