Growth plate cartilage metabolism, morphology and biochemical composition in over- and underfed horses.

This study examines how the diet of weanling Thoroughbred horses, in terms of amount of daily energy and protein, affects their growth plate cartilage. The results show that both over- and underfed horses had adverse effects on cartilage health and growth, with a suggestion of a linkage between dietary excess and developmental bone issues.

Methodology

• The study involved weanling Thoroughbred horses fed diets providing either 70% (underfed), 100% (normal diet), or 130% (overfed) of their daily energy and protein requirements.
• These feeding patterns were sustained for a period of eight months, after which biopsy specimens of growth plate cartilage were taken from the distal right radius.

Results and Interpretations

• It was observed that tissues from both overfed and underfed horses had significantly decreased content of protein, hydroxyproline and hexosamine (all key elements in cartilage development and function).
• The DNA content was found to be increased and Lactate Dehydrogenase (LDH) activity was decreased, implying an imbalance in cellular metabolism and changes in cellular content.
• The thickness of the growth plate was proportional to the diet level. Overfed horses had enlarged reserve and hypertrophic zones, indicating excessive growth cartilage formation in response to over nutrition.
• The columnar organisation of lacunae in the hypertrophic cartilage, a standard characteristic, was lost in overfed horses.
• The cartilage also remained unpenetrated by metaphyseal capillaries, hinting at an interference with normal vascularisation process.
• Under-nutrition was seen to reduce longitudinal growth rates of the upper forelegs, demonstrating a direct impact on bone growth while overfeeding did not enhance growth rates.

Implications

• The findings invoke a similarity between the abnormalities seen in chronic overfeeding and those of equine hypothyroidism, indicating a possible endocrine disorder linked excessive feeding that perhaps accelerates the developmental osteochondrosis, a joint condition in horses.
• These findings emphasise the importance of precise feeding according to the needs of the animal to maintain skeletal health and normal growth in horses.