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

Environmental and genetic factors influencing the proportions of hock bones in young Polish Warmblood horses were analyzed through x-ray measurements taken during official breeding performance tests before and after training. The study used statistical models to evaluate how training, sex, age, and other variables impacted specific bone proportion indices.

Study Objective and Background

• The research aimed to analyze bone proportions in the hock (tarsal) area of young Polish Warmblood horses to understand environmental and genetic influences on bone structure during performance training.
• The hock joint is critical for horse locomotion and athletic performance, so understanding its bone structure could influence breeding decisions and training methods.
• Using x-rays provides precise measurement of internal bone dimensions, allowing for objective assessment of anatomical changes.

Study Subjects and Measurements

• The sample consisted of 69 young Polish Warmblood horses, including 19 stallions and 50 mares.
• Six specific x-ray-based bone measurements were used to calculate four different width and length proportion indices of the hock bones.
• Among these indices, one important proportion was the ratio of the widest part of the distal tibia to the widest part of the proximal metatarsus (referred to as AM in the study).

Training Regimen and Environmental Effects

• Horses underwent a performance test training program consisting of daily work 6 days per week.
• The training included walking, trotting, and cantering for 40-50 minutes, both with and without a rider.
• Additionally, horses performed light jumping exercises, fewer than 12 jumps, with obstacles less than 100cm in height.
• X-ray measurements were taken twice: before training began and after the training period.
• This allowed for assessment of training (environmental) effects on bone proportions by comparing pre- and post-training measurements.

Statistical Analysis

• The effect of training and other factors on the hock bone proportions was analyzed using an analysis of variance (ANOVA) mixed model (procedure MIXED in SAS software).
• The model accounted for fixed effects such as:
• Training session (1st vs. 2nd x-ray investigation)
• Training center location (1st vs. 2nd)
• Sex of the horse (stallions vs. mares)
• Limb side (left vs. right)
• Age as a continuous variable (regression on age in days)
• A random effect for individual horse was included to account for repeated measures on the same subjects.
• This allowed separation of the variance components attributed to environmental factors (like training), genetic or individual differences (random horse effect), and fixed covariates.

Key Findings and Interpretation

• The main variable highlighted, the AM proportion (widest part of distal tibia to widest part of proximal metatarsus), showed a significant p-value (p=0.7 mentioned but context unclear), likely referring to statistical results related to this measurement.
• The study investigated how training affected bone proportions, indicating whether skeletal conformation changes with training stress or if proportions are more genetically determined.
• By assessing sex and age effects, the research provides insights on whether male and female horses develop hock bone structures differently or how maturation influences these dimensions.
• Training center as a factor helps examine if differences in environment or training protocols at different locations impact bone structure.
• Assessment of left vs. right limb helps detect any asymmetry caused by training or inherent anatomical differences.

Conclusions and Implications

• The study contributes to understanding the balance of environmental (training) and genetic factors on hock bone proportions in young performance horses.
• Results can help breeders select horses with desirable bone conformations, potentially linked to improved soundness and athletic ability.
• Understanding environmental impacts can guide training programs to avoid negative effects on bone development.
• The research methodology combining radiographic measurements and rigorous statistical analysis provides a useful approach for future studies on equine skeletal conformation.