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Impact of prebreeding vaccination with modified-live or inactivated viral vaccines on subsequent reproductive performance in crossbred beef females
Five hundred and fifty-nine Angus crossbred females (410 cows and 149 heifers) were used to compare pregnancy attainment and calving distributions of females administered either a killed or modified-live pre-breeding vaccine per label recommendations. Cows were stratified by days postpartum while heifers were stratified by birth date, then all females were randomly assigned to receive one of 3 treatments; 1) Sterile saline administered i.m. on d -60 and -30 relative to breeding (Control, n = 185), 2) Sterile saline administered i.m. on d -60 relative to breeding and a modified-live vaccine (Bovi-Sheild Gold FP5 L5 HB, Zoetis, Inc., Florham, NJ, USA) administered i.m. on d -30 relative to breeding (MLV, n = 188), or 3) Killed vaccine (Vira-Sheild 6+L5 HB, Novartis Animal Health US, Inc., Larchwood, IA, USA) administered s.q. on d -60 and -30 relative to breeding (Killed, n = 186). All vaccines were administered according to manufacturer’s label recommendations and consisted of 3 different lots and serials. All females were exposed to the 7-d CO-Synch + CIDR synchronization protocol with a single fixed-time artificial insemination (TAI) at 54 h after CIDR removal for heifers and 60-66 h after CIDR removal for cows. Clean-up bulls were placed in breeding pastures 10 d after AI and remained with females until 56 d after TAI. Presence of a viable fetus was determined at d 28, 56, and 90 relative to TAI. At parturition, date, birth weight, calf vigor, and calving ease (1 – 5 with 1 = no problem, 5 = extreme difficulty) were recorded. No differences were observed among treatments in the proportion of females pregnant (d 28: P = 0.94, d 56: P = 0.36, and d 90: P = 0.19). There were also no differences in calving date in the calving season (P = 0.76) as well as no differences in distribution of calves born in 21 day calving intervals (P = 0.49). More calving difficulty (P = 0.05) was observed in females exposed to the saline control treatment compared with females in the MLV or Killed treatments (1.09, 1.02, 1.02, control, modified-live, and killed, respectively). However, no differences were observed among treatments in calf birth weight (P = 0.27) or calf vigor (P = 0.51). When modified-live or killed pre-breeding vaccines were administered per label recommendations no impacts on pregnancy attainment or calving distribution were observed.
Keywords:
modified-live, vaccines, reproductive performance