Prolonged food restriction and mild exercise in Shetland ponies: effects on weight gain, thyroid hormone concentrations and muscle Na(+),K(+)-ATPase.

This research study has investigated the effects of different food consumption rates and low-intensity physical training on Shetland ponies’ weight, thyroid hormone levels and their skeletal muscles’ Na(+),K(+)-ATPase concentration. The research found prolonged food shortages led to significant weight loss and decreased serum total and free T(3), while physical training mildly influenced Na(+),K(+)-ATPase levels in muscles.

Research Purpose and Methodology

• The research aimed to determine the impacts of food intake and low-intensity exercise on aspects of growth, thyroid hormone concentrations and concentrations of Na(+),K(+)-ATPase, which is a key enzyme involved in cellular activity, in the skeletal muscle of Shetland ponies.
• Twenty-two Shetland ponies were divided into two groups (with 11 ponies in each group) under two different feeding regimes for two and a half years. One group followed a food restriction regime (with a body condition score maintained at 2) and the other was fed ad libitum (free to eat at any time, with a body condition score kept at 8).
• Five ponies in each group took part in low-intensity training. The gluteus medius muscle and serum samples were collected in April 1998.
• Following this, all ponies were fed ad libitum, and the training program was stopped. Muscle biopsies and serum samples were then recollected in November 1998.

Key Findings

• The restricted food intake resulted in a 30-50% reduction in body weight gain. Even though total thyroxine (T(4)) level raised, the free T(4) preserved at the control level. Total and free tri-iodothyronine (T(3)) in the blood were reduced by 30% and 49% respectively.
• After six months of refeeding, there was no difference in any of the hormone levels between the ad libitum fed and the food-restricted groups.
• A slight but insignificant reduction was observed in the Na(+), K(+)-pump concentration in the gluteus medius muscle of the Shetland ponies due to food limitation.
• Low-intensity training led to a reduction in weight gain by 25% in the ad libitum fed group, but it did not substantially affect the concentration of the Na(+), K(+)-pumps (Na(+),K(+)-ATPase concentration)

Conclusion

• From the results, the researchers concluded that long-term food deprivation in Shetland ponies contributes to a 30-50% reduction in weight gain and commensurate decreases in serum total and free T(3).
• There is also an indication that muscle tissues of different species could react differently to variations in circulating thyroid hormones as the reduction in serum T(3) only marginally influenced Na(+),K(+)-ATPase concentration in skeletal muscle.