Effect of chemically altered and modified-live infectious bovine rhinotracheitis vaccines on fetal retention in beef replacement heifers during the first four months of gestation

Abstract

The objective of this study was to determine whether vaccination of pregnant heifers with either chemically altered or modified live infectious bovine rhinotracheitis (IBR) vaccine would cause abortion when previously vaccinated with a chemically altered IBR vaccine. During pre-weaning processing and at weaning, 202 crossbred Brangus heifers were administered chemically altered infectious bovine rhinotracheitis virus (IBR) vaccines. At 60 to 120 days of gestation after first fall breeding, heifers were administered either a modified live virus (MLV) or a chemically altered IBR vaccine. Heifers at 60 to 90 days gestation, and those greater than 90 and up to 120 days gestation, were assigned by gestation category to one of three treatments: (1) a single IM injection of chemically altered IBR vaccine; (2) a single IM injection of modified live IBR vaccine; or (3) controls - no injections. Heifers were palpated 56 days after treatment to determine potential fetal loss. Subsequent calving information was used to confirm post-treatment palpation data. One heifer in each group aborted after treatment; these numbers did not differ among treatments (p=1.0) nor between gestation categories (p=1.0). Calving numbers verified that no fetuses were lost after post-treatment palpation. We concluded that a single dose of these vaccines in pregnant replacement heifers did not cause increased abortion rates compared to unvaccinated control heifers.