Circulating Concentrations of Cortisol Encompassing Controlled Cessation of Suckling During Weaning Under Managed Care in Cow and Calf Bottlenose Dolphins (Tursiops truncatus)

Abstract

The evaluation of circulating concentrations of cortisol associated with controlled cessation of suckling encompassing the weaning process in bottlenose dolphins (Tursiops truncatus) under managed care has fundamental and practical implications to enhance and improve management and welfare practices. This study involved five cow–calf pairs of which calves were 12 to 19 months at weaning and accustomed to a fish diet. Blood samples were collected from cows and calves between 0800 and 1100 h episodically for two weeks before weaning day (Day 0) and on Days 1, 3, 5, 8 12, 16, 20, and 31 post-weaning. Pre-weaning involved conditioning through positive reinforcement with respective trainers where cows moved freely from maternity to holding pens while calves remained in maternity pens. After 2 to 6 months, when cows and calves remained separated for at least several minutes without reuniting, weaning day was initiated, and gates between maternity and holding pens were closed. Physical separation resulted in cows and calves exhibiting different types and degrees of behavior dominated by increased vocalization and locomotor activities (rapid and erratic swimming, side jumping, breaching). While pre-weaning cortisol concentrations were at baseline and not different (p > 0.1) between cows and calves, post-weaning concentrations on Day 1 increased in cows (p = 0.0045) and calves (p = 0.0001), reaching higher (p < 0.07) concentrations in calves than in cows. Thereafter, cortisol decreased to pre-weaning concentrations on Day 5 (p = 0.0031) in cows and Day 12 (p = 0.0417) in calves. While stress-like behavior post-weaning returned to pre-weaning conditions by Day 5 in cows and calves, cortisol remained slightly higher (p < 0.1) in calves than in cows until the study ended on Day 31. Thus, although preliminary, the acute, temporal physiological and behavioral responses to the cessation of suckling encompassing weaning in dolphin cow–calf pairs are novel and provide a basis for future studies to comprehensively evaluate short- and long-term physiological and behavioral relationships associated with weaning in dolphins under managed care.