Vaccinating a pregnant mare
It is a common practice for veterinarians to recommend that pregnant mares be given a Pneumobort K vaccine at 5, 7, and 9 months of gestation. They will often also recommend that owners give their horse a five-way vaccine one month prior to giving birth. The five-way consists of Tenatus, Rhinopneumonitis, Influenza, Eastern & Western Encephalomyelitis (Sleeping Sickness). Any mare that is not immune comprised will include these antibodies in the colostrum without us giving her a “booster” a month prior to giving birth.
What they won’t tell you is that a horse can abort from a rhinopneumonitis infection only ONCE in their entire life. A mare can only abort the very first time that she is infected with the virus and only if she is pregnant at the time. Once she has been infected, whether she is pregnant at the time or not, she will build antibodies to the infection and can NEVER abort from this disease again.
Also, all five-way vaccinations are preserved with Thimerosal (mercury), the interesting fact about mercury is that it is one of the heavy metals that can and will cross the placental barrier. So, the mercury that you are giving to your mare, she is sharing with her foal. If a mare has a good healthy immune system she will have a life-long immunity to all of the diseases that are present in a five way vaccine. She will pass these antibodies onto her foal, that’s what mothers do, that’s what colostrum is for.