Morphological, haemato-biochemical and endocrine changes in young Standardbreds with 'maladaptation' to early...

The demands in the Standardbred trotters industry require young, still growing horses, to be trained well above light exercise level. During that period, the risk of occurrence of energy imbalance and maladaptation to training is high. In man, the lack of energy homeostasis is considered as the basic problem in the development of chronic fatigue.

To find objective biomarkers of early maladaptation to training in young racehorses under field conditions.

Sixty-five 2-year-old Standardbreds were followed during their first 3 months of training in 5 different training centres. Monthly measurement of morphological variables (weight, height at withers, body condition score, body composition), basic haemato-biochemical variables and endocrine levels (testosterone, cortisol, thyroid hormones, leptin, IGF1, prolactin) were undertaken. Feeding levels and training programmes were also evaluated. At the end of the 3 month period, on the basis of an abnormal weight loss, 14 young horses were suspected of maladaptation to training (MT group). Morphological, haemato-biochemical, endocrine changes were compared between MT group (n = 14) and control group (C group, n = 40). Analysis of variance was calculated to study the effects of time and maladaptation to training.

Compared to C group, MT group showed a significant higher weight loss in relation to a higher loss of fat mass and body condition score (P < 0.05). MT group presented higher GGT and white cell counts and lower red cell counts (P < 0.05). Finally, MT group showed significant lower levels of T4 (P = 0.03) than C group.

Some young horses presented signs of energy imbalance which were also associated with haematobiochemical and endocrine changes. Those markers might be useful for identification of maladaptation to training.