Environmental and genetic effects on measured hock bone proportions in young Polish Warmblood horses undergoing performance test training for breeding horses.

The hock bone proportions in young Polish Warmblood horses (69) were studied based on x-ray image measurements done during official breeding horse performance testing. Six measurements were used to identify 4 width and length proportion indices. The radiological examinations were done before and after horse training, which consists of work with or without the rider at walk, trot and canter (40-50 min) with some light class (< 100 cm) jumping (<12 jumps) 6 days a week. The training effect was investigated using analysis of variance (procedure MIXED, Statistical Analysis System). The statistical model included a random horse effect and fixed effects: training (1st, 2nd investigation), training centre (1st, 2nd), sex (19 stallions, 50 mares), limb (left, right), and regression on age in days. Proportion of the widest part of distal tibia to the widest part of proximal metatarsus (shortcut AM in the text; p < 0.0001) and proportion of the length of the tarsus (proximal intertarsal to distal tarsometatarsal joint) to tibiotarsal and calcaneus length (shortcut DN; p = 0.0288) were greater after training. Distal epiphysis of the tibia (A) seems greater after training than the proximal epiphysis of the 3rd metatarsal epiphysis (M). The width proportions revealed most strongly affected by training compared to the length proportions, the other proportions varied randomly. The correlations between the measured values changed over the course of the training in parallel with the overall values - ranging from -0.2 to 0.2. Repeatabilities of measured indices were mostly high (>0.7).