Evaluation of response to anti-leptospira bacterin vaccination in pregnant ewes and the passive transfer of antibodies to their offspring

Abstract

Leptospirosis in sheep is often underestimated, and leads to great economic losses for the sheep farming industry. The aim of this study was to evaluate the humoral immune response in pregnant ewes, after the injection of a commercial polyvalent vaccine for leptospirosis, and to observe the transmission of anti-Leptospira antibodies through the colostrum to the offspring. For this, 24 pregnant ewes were vaccinated for leptospirosis.  Blood samples were collected prior to vaccination and then 7, 14, 21, 28, 35, 42 and 49 days after vaccination. In order to evaluate passive immunity transfer, blood samples of 32 lambs were collected during the first 48 hours after birth, and another collection was performed 10 to 21 days after birth. The lambs were placed into 2 groups: Group A (n=16): singleton lambs; and group B (n=16): twins. The sera samples were submitted to the Microscopic Agglutination Test (MAT), in which 21 Leptospira serovars were tested. The results were analyzed in a descriptive form. The number of sheep reactive to MAT gradually increased until 21 days after vaccination, and decreased right after. Of all the serovars contained in the vaccine, the largest proportion of animals were seroconverted to Hardjoprajtino serovar, Serjoe serogroup. Anti-Leptospira antibodies transferred through colostrum to lambs were detected by MAT in the serum collected 24-48 hours after birth.  It was observed that 65.6% (21 out of 32) of the lambs were reactive. In the subsequent collections that occurred from 10 to 21 days after birth, a decrease in the number of animals reactive to the MAT was detected. There was no significant statistical difference for the passive transfer of antibodies between single or twin lambs.