Control of nutritional secondary hyperparathyroidism in grazing horses with calcium plus phosphorus supplementation.

This research article discusses a study on the effectiveness of a calcium and phosphorus supplement in controlling nutritional secondary hyperparathyroidism (NSH) in grazing horses. The study was conducted on four farms in Queensland, Australia over a six-month period.

Study Background and Purpose

• Nutritional secondary hyperparathyroidism (NSH), also known as ‘big head’ or ‘bran disease’, is a metabolic bone disorder commonly affecting horses grazing on certain types of pastures, including buffel grass.
• The disease is usually induced by consumption of a diet with an imbalanced calcium to phosphorus ratio, or high in oxalates which can bind to dietary calcium, making it unavailable for absorption.
• The purpose of this study was to examine if a specific feeding regime, involving a calcium and phosphorus supplement, could prevent or control NSH in grazing horses.

Methods

• 33 local stock horses, including 13 with clinical NSH and 7 recent additions, were grazed on buffel grass for six months from September 1979 to February 1980.
• Every week, the researchers fed each horse 1.0 kg of a mixture of ground limestone and dicalcium phosphate (in a 1:2 ratio) dissolved in 1.5 kg of molasses.

Results

• Despite the buffel grass pasture having a high total oxalate content and a low calcium to oxalate ratio, which are conditions detrimental to equine health, no new cases of NSH were reported during the study period.
• The horses with previously diagnosed NSH presented improvement with the controlled diet, with most of them returning to normal health state.
• After the initial six months, however, three new NSH cases were identified on one of the farms.
• The researchers responded by doubling the supplemental dose and substituting the previous mixture with rock phosphate in molasses, which seemed to rectify the problem.

Conclusion

• The research indicates that the occurrence of NSH in grazing horses can be controlled with a specific diet supplement of calcium and phosphorus.
• The breakdown in the original feeding regime was thought to be due to borderline inadequate supplement dosage and behavioural factors of the horses.
• Thanks to this study, horse breeders and caretakers have a proven method to prevent this widespread disease in horses grazed on oxalate-rich pastures.