Effects of pharmacological doses of Vitamin D3 on mineral balance and profiles of plasma Vitamin D3 metabolites in horses.

The research explores the effects of excessive Vitamin D3 consumption on mineral balance and patterns of Vitamin D3 metabolites in horses. The study also looks into countermeasures that can be undertaken during Vitamin D3 intoxication to reduce severe consequences, such as soft tissue calcification, that could be fatal due to nephrocalcinosis.

Properties and Roles of Vitamin D3 in Horses

• The metabolism and functions of Vitamin D in horses differ from those in other animals like humans, pigs, and rats. Specifically, horses exhibit significantly lower blood plasma levels of calcidiol and calcitriol – both Vitamin D metabolites.
• The paper highlights that horses respond differently to toxic doses of Vitamin D3 compared to other domestic animals. In horses, overdoses of Vitamin D3 lead to less significant alterations in calcium and calcitriol concentrations but result in a noteworthy increase in inorganic phosphate response. This leads to an overall increase in the product of calcium and inorganic phosphate levels (Ca x Pi product).
• Previous observations have shown that horses tend to develop soft tissue calcifications, a condition often lethal due to nephrocalcinosis, during Vitamin D3 intoxication. The researchers posit that the elevation of the Ca x Pi product could be playing a causative role in this calcification.

Experimental Findings on Vitamin D3 Intoxication

• To test their assumption, the researchers administered excessive amounts of Vitamin D3 (40,000 IU kg-1) to two horses. During the experiment, they simultaneously restricted the dietary intake of calcium and inorganic phosphates in an attempt to control the increase of the Ca x Pi product.
• The findings showed that in these tested horses, the number, distribution, and severity of calcification centres were considerably lower compared to control horses (from a previous experiment) that received the same dosage of Vitamin D3 but without dietary restrictions on calcium and inorganic phosphates.
• These findings suggest that the increase in the Ca x Pi product in horses during Vitamin D3 intoxication contributes significantly towards soft tissue calcification.

Recommendations and Conclusions

• Based on the results, the study concludes that in case of Vitamin D3 intoxication in horses, it would be beneficial to immediately restrict dietary calcium and inorganic phosphate intake. This action could help prevent, or at the very least lessen, the occurrence of fatal soft tissue calcifications caused by nephrocalcinosis.