A live-attenuated strangles vaccine already in use in Europe has proven safe and effective in pregnant mares, according to a recent study.

The researchers studied the strangles vaccine EQUILIS StrepE (manufactured by Intervet/Schering-Plough Animal Health), a live attenuated strangles vaccine available in Europe for submucosal administration in the upper lip, on pregnant Warmblood mares on a large stud farm in Germany. The main outcome of the the study was that the vaccine did not have any deleterious effect on the pregnancy outcome of vaccinated mares.

A group of 224 pregnant mares were vaccinated every three months until parturition with EQUILIS StrepE. A group of 206 mares were used as controls and only received water as a placebo vaccine. None of the 430 mares developed strangles or suffered adverse vaccine reactions at the site of injection or systemically.

Ten mares aborted during the study (six in the vaccine group and four in the control group). In addition, two foals were stillborn in the vaccinated mare group and two foals in the control group died within two days after birth. However, none of the abortions or foal deaths was due to infection with Streptococcus equi, the organism that causes strangles