The effect of injectable barium selenate on the selenium status of horses on pasture.

This research explores the effect of barium selenate injections on the blood selenium concentration in pastured horses, finding it to be an efficient method for correcting selenium status in these animals, albeit with minor injection site reactions.

Research Purpose and Methodology

• This study aims to investigate the impact of intramuscular barium selenate injections on the blood selenium concentration in horses with marginal selenium status. Selenium, a vital nutrient for horses, plays an important role in their well-being, and its appropriate concentration in the horse’s blood is essential.
• Eighteen mares were divided into six groups, with each group receiving varying treatments. While Groups 1-4 received barium selenate injections at different dosage rates (ranging from 0.5 to 1.5 mg Se/kg) into the right pectoral muscle, Group 5 received sodium selenate orally at 0.05 mg Se/kg every eight weeks. Group 6 was left untreated to act as a control.
• Blood samples were collected at various intervals over a year to analyse the whole blood and plasma selenium levels. Any reaction at the injection site was noted on every sampling date.

Results and Findings

• The treatment with barium selenate significantly increased selenium concentrations in the blood, plasma, and blood cells. This was true regardless of the dosage rate, outperforming the effects of no treatment or oral administration of sodium selenate.
• The mean whole blood selenium concentration remained in the adequate range (>1600 nmol/l) until the experiment’s conclusion after one year.
• Although the severity of reactions at the injection site increased with the dose rate, it was deemed acceptable at lower dose rates. These reactions included swelling and fibrosis (tissue overgrowth).

Conclusion and Implications

• The study concluded that carefully administered barium selenate injections at a deep intramuscular site were effective in rectifying the selenium status of pasture-grazing horses. Selenium content in the relevant pastures ranged from 0.01 to 0.07 mg/kg DM.
• The study recognized that while all dose rates used resulted in some level of swelling and fibrosis at the injection site, the reaction was manageable at the lower dose rates.
• This research holds promise for the long-term selenium supplementation of horses, especially given that New Zealand currently lacks a licensed long-acting selenium supplementation product for horses.
• In conclusion, the findings suggest that barium selenate could be a useful method for selenium supplementation in horses, maintaining an effective duration of at least one year following a single injection.