Comparison of milk production of dairy cows vaccinated with a live double deleted BVDV vaccine and non-vaccinated dairy cows cohabitating in commercial herds endemically infected with BVD virus.

Ellen Schmitt–van de Leemput,Paul H. Walz,George Caldow,Lucy V. A. Metcalfe,Christian Guidarini,Juan J. Loor

doi:10.1371/journal.pone.0240113

Abstract

Daily milk production and reproductive performance of cows vaccinated with a live double-deleted Bovine Viral Diarrhoea Virus (BVDV) vaccine were compared to those of non-vaccinated cows, cohabitating in endemic BVDV herds. All animals in the treatment group were vaccinated on study day 0 irrespective of lactation or gestation status, while control animals did not receive any treatment. 1463 animals were enrolled in the study from four different farms in three different countries (UK, Italy, France). Endemic presence of BVDV in study herds was demonstrated by the detection of BVDV in the bulk tank milk, and seroconversion was evaluated at the beginning of the study. For individual animals, the day of calving was taken to be the start of lactation for the calculation of days in milk (DIM). The standard lactation period of 305 days was divided into three periods: early lactation (EL, from DIM 8 to DIM 102), mid lactation (ML, from DIM 103 to DIM 204 and late lactation (LL, from DIM 205 to DIM 305). For each farm and each lactation period, a mixed model statistical analysis was performed with daily milk production as response, and group, day as well as the interaction between those two factors as fixed factors. Chi-square test was used to compare abortion rate and prolonged inter-oestrous interval rate between treatment and control groups. A significant increase in milk production in the vaccinated group was observed in farms 1 (1.023 L/day) and 3 (0.611 L/day) during EL (p<0.001) and in farm 2 (1.799 L/day) during ML (P<0.001). In addition, at farm 2, vaccinated cows produced more milk than non-vaccinated cows starting from 80 DIM. No differences were found between groups in abortion rates or prolonged inter-oestrous interval rates. Data demonstrate that cows in herds endemically infected with BVDV and vaccinated with live double-deleted BVDV vaccine produce more milk; the difference in milk production occurs during early lactation.

Highlights

Bovine Viral Diarrhoea Virus (BVDV) is a member of the genus Pestivirus within the family Flaviviridae [1]
BVDV was detected in the bulk tank milk by polymerase chain reaction (PCR) from all farms on at least one occasion during the six months prior to vaccination
BVDV was not detected by PCR in any of the serum samples that were without detectable antibody

Summary

Introduction

Bovine Viral Diarrhoea Virus (BVDV) is a member of the genus Pestivirus within the family Flaviviridae [1]. The virus was first described in New York in 1946 and has been identified in most cattle-producing countries worldwide since [2, 3]. The most important source of BVDV infection is persistently infected (PI) cattle [5]. PI animals are immunotolerant to the persisting virus and shed infectious virions throughout their life. In non-pregnant non-immune cattle, acute infections with BVDV result in transient viremia [6]. Infections of pregnant cattle provide the opportunity for the virus to cross the placenta causing foetal infection. The occurrence of foetal infection depends on the age of the foetus at the time of BVDV infection. Teratogenic effects in the foetus or the birth of a PI calf can be the result [7, 8]. PI calves can be small, weak and ill-thrifty but more often appear healthy and could go undetected within the herd [9]

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