Factors associated with likelihood of horses having a high serum Streptococcus equi SeM-specific antibody titer

Abstract

To identify factors associated with an increased likelihood that horses would have a serum Streptococcus equi SeM-specific antibody titer > or = 1:1,600. Cross-sectional study. 188 healthy client-owned horses. A single serum sample from each horse was tested for SeM-specific antibody titer with an ELISA. Multivariate logistic regression was used to identify factors associated with having a titer > or = 1:1,600. Age, breed, and vaccination status were significantly associated with the likelihood of having a titer > or = 1:1,600. The odds of having a titer > or = 1:1,600 increased by a factor of 1.07 with each 1-year increase in age. Quarter Horses and horses of other breeds were 4.08 times as likely as were Thoroughbreds and warmbloods to have a titer this high. Horses that had previously received an intranasal S equi vaccine were 4.7 times as likely as were horses without any history of vaccination to have a titer this high. Results indicated that older horses, horses other than Thoroughbreds and warmbloods, and horses that had been vaccinated with an attenuated-live intranasal S equi vaccine between 1 and 3 years previously had an increased likelihood of having a serum SeM-specific antibody titer > or = 1:1,600.