Is the Thoroughbred race-horse under chronic stress?

Abstract

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.

Low plasma cortisol and fecal cortisol metabolite measures as indicators of compromised welfare in domestic horses (Equus caballus)

“…Our results expand earlier findings evidencing low or no change in cortisol levels after chronic training and racing of thoroughbred fillies [ 84 ] or chronic sub-optimal living conditions of horses [ 23 , 24 ]. Our findings go further and show that cortisol could be lowered in cases of chronic compromised welfare as evidenced by behavior, anatomy, and haematology (present study).…”

Cortisol concentration in the saliva of horses subjected to different kinds of exercise

“…According to Jimenez et al (1998), the concentration of this hormone in horse plasma is related to the intensity and duration of the effort. Nogueira and Barnabe (1997) determined the cortisol concentration in the plasma of racing mares aged from 1 to 4 years and found significant differences between age groups, for example 148.8 nmol/dm 3 (1-2 years), 125.7 nmol/dm 3 (2-3 years) and 101.1 nmol/dm 3 (3-4 years). The lowest concentration was observed in the oldest horses.…”

The influence of selected factors and sport results of endurance horses on their saliva cortisol concentration

“…Cortisol secretion depends on the animal experience in competitions (Nogueira et al 2002), ride duration, transport conditions (Schmidt et al 2009), animal age (Nogueira and Barnabe 1997), character (Fazio et al 2011) and staying in new environment before the start (Alexander and Irvine 1998a).…”

“…Some authors claim that the age factor and lack of experience significantly boost the stress hormone secretion. Cortisol level falls as the animal gets older (Lassourd et al 1996, Nogueira andBarnabe 1997). This is probably related to gaining more experience or to the phenomenon of chronic stress.…”

“…The stress phenomenon is mainly related to the sport use of horses in equestrian competitions, during which they are subject to different types of physical and mental factors that can negatively influence their final scores, as well as their well-being or the riders' safety (Peeters et al 2010). According to the research, the stress level increase during the competitions is related to the horses' young age and resulting lack of experience (Nogueira and Barnabe 1997), transport conditions (Schmidt et al 2010d) or even staying in an unfamiliar stable. The last factor was identified in a study on American trotting horses awaiting the start (Irvine and Alexander 1996).…”