JULY/AUGUST 2024 THE RIDER /13


Study to Examine Selenium blood concentration in Ontario Broodmares and foals


Guelph, ON June 19, 2024 - Selenium deficient soil can lead to several conditions in domes- tic animals including white muscle disease. Of importance to Ontario horse breeders is the fact that most foals are born with low blood selenium con- centrations. Some clinical signs of low selenium levels may in- clude dysphagia or weak suckle reflex due to pharyngeal/masti- catory muscle weakness. Southern Ontario soil is known to be low in selenium. Ontario Veterinary Col-


lege researcher, Dr. Luis Ar- royo, graduate student Isidora Rodriguez, and Dr. Alison Moore from OMAFRA, are currently involved in a study funded by the Ontario Animal Health Network-Equine. They aim to investigate some of the gaps in knowledge of the sele- nium levels of broodmares and foals in Southern Ontario. Preliminary results have


not undergone intensive analy- sis yet and clinical significance has not been established but, of the over 100 submissions so far, it seems most mares have ade- quate levels of selenium while most foals are below the refer- ence values. Selenium is an extremely


important dietary element, and


there are several other places with major soil deficiencies, like Netherlands and New Zealand. Reports describe an array of clinical conditions in cattle, for example, from re- tained fetal membranes, cystic ovaries, anoetrus, early and late embryo death, mastitis and in- creased somatic cell counts which are associated with sele- nium deficiency. Arroyo postu- lates, “We have not fully determined the extent of what these micronutrients can do if they are not at adequate levels.” In the Ontario study, they


will be looking at the current reference values in use and comparing them to the levels being reported in the study. The Ontario Veterinary


College (OVC) has seen clini- cal cases of rhabdomyolysis in foals. Muscle damage or white muscle disease is well known in calves, particularly fast- growing animals. Within a few months of life, they can de- velop muscular damage, in- cluding heart damage, which can be fatal. Arroyo discusses some of


the classical clinical signs of low selenium levels in a foal. They can exhibit trembling at the walk and milk coming out of the nose if they cannot swal-


Study aims to fill in gaps in knowledge of the selenium levels of brood- mares and foals in Southern Ontario. Photo Credit: Jolene Purdue


low well. “There are also less overt clinical signs that we see in foals every year, when they come to the clinic at OVC,” ex- plains Arroyo. “They cannot nurse if they have pharyngeal collapse. We place a feeding tube and give support for a few days and supplement the sele- nium and then usually the foals are back to normal. So, there is a little bit of clinical evidence that perhaps these foals are hav- ing a milder form of selenium deficiency.” This study will include a


survey of the broodmare’s Every Breath Counts


health status and geographical details. The researchers will look at all the mares and see which ones fall within adequate levels or levels below the refer- ence values. They will be as- sessing if reference values and intra and inter assays variabil- ity.


“This will help determine


accuracy of the tests and form the basis to design further stud- ies,” says Arroyo “Studies that could compare factors such as horses diet, “hay versus grass pasture” or the effect of dietary supplementation with selenium


versus not supplemented.” This could potentially lead to find conditions that can result from low levels of selenium and per- haps that help to make better in- formed interventions. “Then there is the ques-


tion of absorption,” says Ar- royo. “Even when sufficient levels are present in the diet, this does not guarantee proper absorption or necessarily trans- late into adequate levels in blood.” Nutrient absorption is


highly impacted by the horse’s overall diet. For example, some nutrients can affect absorption of others (for example Copper and Molibdenum). Dr Arroyo states almost every foal in On- tario will get an injection of se- lenium and vitamin E right at birth to ensure they are receiv- ing it systemically. It is because foals receive


this shot within the first day of foaling, that the samples for their study are to be collected prior to the injection to elimi- nate this external factor from influencing the research results. The researchers will be


measuring the selenium and vi- tamin E levels in both the mares and foals, at time of birth, as well as the colostrum. Milk is known to be an in-


significant source of selenium, but the study will measure how much may be available in milk regardless. Stay tuned for the results


of this important study which will aim to shed some light on the signs of low selenium in foals.


Ontario Animal Health


Network has kindly provided funding for this initial study. Additional funding will be re- quired to further investigate the preliminary findings and to de- termine additional factors such as the effects of different diets on selenium levels in horses.


About Equine Guelph: Equine Guelph is the


horse owners’ and care givers’ Centre at the University of Guelph in Canada. It is a unique partnership dedicated to the health and well-being of horses, supported and overseen by equine industry groups. Equine Guelph is the epicentre for academia, industry and gov- ernment - for the good of the equine industry as a whole. For further


information, visit www.equineguelph.ca.


Story by: Jackie Bellamy- Zions, Equine Guelph


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