Bovine viral diarrhea virus is inactivated when whole milk from persistently infected cows is heated to prepare semen extender

Abstract

Bovine viral diarrhea virus (BVDV) can be present in cryopreserved bovine semen and be transmitted through artificial insemination. Because BVDV can be shed in milk, the virus might also be introduced as a contaminant of milk-based semen extenders. Thus, the purpose of this study was to evaluate the epidemiologic risk of using heated, BVDV-contaminated milk to prepare semen extender. Milk was obtained from cows free of and persistently infected (PI) with BVDV. Six replicates of milk samples were processed by heating (85–92.2 °C, 10 min). Samples of milk collected before and after heating were assayed for BVDV. Additionally, milk was injected intravenously into eight BVDV seronegative calves to monitor for seroconversion and viral infection. Virus was not detected in any milk samples from negative animals. Virus was consistently isolated from unheated milk samples from PI cows by passage of somatic cells, ultracentrifugation, and animal inoculation. Virus was usually detected in these samples by RT-nPCR (reverse transcription nested polymerase chain reaction). In heated milk samples from PI cows, no infectious BVDV was detected using any technique, but viral RNA was detected using RT-nPCR in four of six replicates. Bovine viral diarrhea virus in milk from PI cows was inactivated by heating. Therefore, properly heated milk used in semen extenders will not result in transmission of infectious BVDV. Although RT-nPCR detected the presence of viral RNA in milk samples after heating, the virus was not infectious as demonstrated by lack of replication despite using multiple sensitive techniques.