Selenium-deficient soil can cause several health issues in domestic animals, including white muscle disease. This is particularly significant for horse breeders in Ontario, as most foals are born with low blood selenium levels. Clinical signs of selenium deficiency may include dysphagia or a weak suckle reflex due to pharyngeal and masticatory muscle weakness. Southern Ontario is known for its low selenium soil content.
Current Research on Selenium Levels in Broodmares and Foals
Dr. Luis Arroyo from the Ontario Veterinary College, graduate student Isidora Rodriguez, and Dr. Alison Moore from OMAFRA are conducting a study funded by the Ontario Animal Health Network-Equine to investigate selenium levels in broodmares and foals in Southern Ontario. Preliminary findings indicate that while most mares have adequate selenium levels, most foals fall below the reference values. However, these results have not yet undergone thorough analysis, and their clinical significance remains unconfirmed.
Importance of Selenium and Global Comparisons
Selenium is a crucial dietary element, and other regions such as the Netherlands and New Zealand also experience major soil deficiencies. In cattle, selenium deficiency can lead to various clinical conditions, including retained fetal membranes, cystic ovaries, anestrus, embryo death, mastitis, and increased somatic cell counts. A study published in the “Journal of Dairy Science” reported that selenium supplementation improved reproductive performance and reduced the incidence of retained placentas in dairy cows. Arroyo noted that the full extent of the impact of inadequate micronutrient levels is still not entirely understood. The Ontario study aims to compare current reference values with those reported in their research.
Observations at Ontario Veterinary College
The Ontario Veterinary College has observed clinical cases of rhabdomyolysis in foals, with muscle damage or white muscle disease being well-documented in calves, especially those that grow quickly. Foals can develop muscular damage, including heart damage, which can be fatal within a few months of life.
Clinical Signs and Treatment of Selenium Deficiency
Arroyo described some classic clinical signs of low selenium in foals, such as trembling while walking and milk coming out of the nose due to swallowing difficulties. Less obvious signs are also noted annually when foals are brought to the clinic at OVC. Foals unable to nurse due to pharyngeal collapse are given a feeding tube and selenium supplementation, usually recovering within a few days. This suggests that some foals may experience a milder form of selenium deficiency.
Methodology and Goals of the Current Study
The study includes a survey of broodmare health and geographical details. Researchers will assess which mares have adequate selenium levels and which fall below the reference values. They will also evaluate reference values and assay variability. Arroyo stated that this information would help determine the accuracy of tests and guide future studies comparing factors like diet and selenium supplementation.
Nutrient Absorption Challenges
Arroyo also raised the issue of nutrient absorption, noting that sufficient dietary levels do not always guarantee proper absorption or adequate blood levels. Nutrient absorption is influenced by the horse's overall diet, as certain nutrients can affect the absorption of others. For example, a study in the “Journal of Animal Science” highlighted how high levels of copper and molybdenum can interfere with selenium absorption in livestock.
Selenium Supplementation Practices
Dr. Arroyo mentioned that nearly every foal in Ontario receives a selenium and vitamin E injection at birth to ensure systemic availability. To avoid external influences on the study results, samples for their research are collected before this injection.
Future Directions and Potential Impact
Researchers will measure selenium and vitamin E levels in both mares and foals at birth, as well as in colostrum. While milk is not a significant source of selenium, the study will measure its selenium content. This research aims to provide insights into the signs of low selenium in foals and guide better management practices for breeders.
The Need for Further Research
The results of this study aim to provide insights into the signs of low selenium in foals. The Ontario Animal Health Network has funded this initial research, but further funding will be necessary to investigate the preliminary findings and examine additional factors, such as the impact of different diets on selenium levels in horses. Prior studies, like those conducted by the University of Kentucky, have shown that selenium supplementation can significantly improve the health and performance of foals, emphasising the importance of this research.