Is the Thoroughbred race-horse under chronic stress?

• Main Authors: G.P. Nogueira, R.C. Barnabe
• Format: Article
• Language: English
• Published: Associação Brasileira de Divulgação Científica 1997-10-01
• Series: Brazilian Journal of Medical and Biological Research
• Subjects: horses; cortisol; exercise; chronic stress
• Online Access: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-879X1997001000016
• ISSN: 0100-879X; 1414-431X

Thoroughbred fillies were divided into three groups according to age: group 1, 7 fillies aged 1 to 2 years (G1) starting the training program; group 2, 9 fillies aged 2 to 3 years (G2) in a full training program; group 3, 8 older fillies 3 to 4 years of age (G3) training and racing. Blood samples were collected weekly from July to December. Cortisol was quantified using a solid phase DPC kit. The intra- and interassay coefficients of variation were 12.5% and 15.65% and sensitivity was 1.9 ± 0.2 nmol/l. The semester average of cortisol levels varied between groups: G1 = 148.8 ± 6.7, G2 = 125.7 ± 5.8, G3 = 101.1 ± 5.4 nmol/l, with G3 differing statistically from the other groups. The lower cortisol levels observed in the older fillies lead us to propose that the stress stimulus, when maintained over a long period of time, may become chronic and result in a reduction of hypophyseal corticotropin-releasing hormone receptors. The secretion of endogenous opioids may also lead to low serum cortisol levels.