Is the thoroughbred race-horse under chronic stress?
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 leads 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.
Nogueira
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Departamento de Reprodução Animal, Faculdade de Medicina Veterinária e Zootecnia, Universidade de São Paulo, Brasil. guilherme@infocenter.com.br
Barnabe
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D000818:Animals; D002908:Chronic Disease; D006734:Horse Diseases / Q000097:blood*; D006736:Horses; D006854:Hydrocortisone / Q000097:blood*; D010805:Physical Conditioning, Animal; D013312:Stress, Physiological / Q000097:blood / Q000662:veterinary*
D006854:Hydrocortisone