Here's a message from our Veterinary Services Team:
Thank you for contacting Doctors Foster and Smith with your question.
As a general guideline, we do not recommend giving multiple supplements simultaneously without first consulting your veterinarian. It is very easy to cause mineral or vitamin imbalances that could be harmful to your horse if the supplements contain the same ingredients. Another factor to consider is the nutrient content of the horse’s diet, in particular the pasture and hay. If the pasture and hay are nutrient dense, meaning they are not deficient in any vitamins or minerals, it would be much easier to overload with specific nutrients. Different horses have different nutritional needs as well. A supplement or feed that is appropriate for one horse may not be appropriate for another horse.
The best recommendation would be to consult with your veterinarian whether this combination would be appropriate for any or all of the horses before adding the additional supplement. Your veterinarian may also want your feed analyzed prior to making a recommendation regarding supplements containing vitamins and minerals to prevent over-supplementation and vitamin or mineral imbalances.
Thanks again for contacting us. We hope this information is helpful.
Doctors Foster and Smith