(E31) Case Series of Nutritional Secondary Hyperparathyroidism in Horses in Hawaii

Abstract:

Background: Equine nutritional secondary hyperparathyroidism (NSHP, Bighead Disease) is a consequence of diets with abnormal calcium: phosphorus ratios. With the advent of fortified feeds and availability of legume forage, the disease has largely disappeared. The Hawaiian Islands are unique in that legume forage is unavailable and pastures have high oxalate concentrations.

Objective: This case series reported on the use of calcium supplementation in horses diagnosed with NSPH. Animals: Seventeen adult horses imported from the continental US to the Waiki’i region, Hawai'i that grazed on pastures with known oxalate-rich kikuyu grass.

Methods: This was a cohort study. Plasma ionized calcium and parathyroid hormone concentrations at baseline and after eight months were evaluated. Purina® Outlast® was fed to Group 1 (eight horses) and Leg Up® Stomach pellets was fed to Group 2 (five horses) as calcium supplements.

Results: At screening 8/17 horses were normal and 9/17 horses were diagnosed with NSHP. In Group 1, 1 NSHP horse resolved, 4 NSHP horses remained affected, 2 non-NSHP horses remained unaffected, and 1 non-NSHP horse developed NSHP. In Group 2, 2 NSHP horses resolved, 1 NSHP horse remained affected, and 2 non-NSHP horses remained unaffected. A statistically significant difference between treatment cohorts was found in post-treatment ionized calcium (p-value =0.0063) and parathyroid hormone (p-value =0.0236) concentrations. Conclusions and Clinical Importance: The results of this study demonstrate that NSHP remains a common disease in regions without consistent access to fortified feeds and with high oxalate grasses. Calcium supplementation may be effective in some horses, but continued monitoring is required.