Vaccination for leptospirosis improved the weaning percentage of 2-year-old farmed red deer hinds in New Zealand.

AIM: To investigate the effect of leptospiral vaccination against serovars Hardjo-bovis and Pomona on fetal loss and weaning percentage in rising 2-year-old farmed red deer hinds.

METHODS

In mid-February 2007, 252 rising 2-year-old hinds on four farms received a single dose of streptomycin (25 mg/kg), to minimise leptospiral infection. They were randomly allocated to vaccinated and control groups. Vaccinated hinds (n=125) received a 2-ml S/C injection of a bivalent whole-cell killed leptospiral vaccine (Leptavoid-2) followed by a booster 4-6 weeks later, and were grazed with control hinds (n=127). These animals were isolated from other hinds on each property, until after mating (June 2007), when all vaccinated and control hinds were combined with hinds not treated with streptomycin, for maximum exposure to natural leptospiral challenge. Evidence of natural challenge by Leptospira spp. was assessed in blood samples from control hinds by serology against L. borgpetersenii serovar Hardjo-bovis and L. interrogans serovar Pomona, using the microscopic agglutination test (MAT), and in hinds not treated with streptomycin by detection of shedding of organisms in urine, using bacterial culture and real-time PCR. Pregnancy diagnosis was carried out in May/June 2007, using transrectal ultrasonography, to determine conception. In late October, prior to calving, the pregnant vaccinated and control hinds were examined by palpation of the abdomen and udder, to determine the percentage of hinds pregnant at term and assess fetal loss. In March 2008, at weaning, vaccinated and control hinds were examined for lactation status, using observation and palpation of the udder. The differences between the groups were evaluated using matched logistic regression analysis.

RESULTS

After mating, pregnancy was diagnosed in 97/125 (77.6%) vaccinated and 106/127 (83.5%) control hinds. All four farms had serological evidence of Hardjo-bovis infection, and a single hind was serologically positive for Pomona between October and March. Real-time PCR confirmed urinary shedding on two farms. The mean percentage of hinds pregnant at term, for those animals confirmed pregnant after mating, in the vaccinated and control groups was 95/97 (98%) (range 95-100%) and 103/106 (97%) (range 94-100%), respectively (p>0.05). The mean weaning percentage for vaccinated and control groups was 86/97 (89%) (range 78-95%) and 88/106 (83%) (range 76-88%), respectively (p=0.015).

CONCLUSION

Vaccination for leptospirosis resulted in no difference in the percentage of hinds pregnant at term, but a higher weaning percentage compared with unvaccinated controls suggesting that vaccination reduced perinatal and/or pre-weaning mortality.