Associations between small ruminant lentivirus infection and total milk yield and somatic cell count in a dairy sheep flock

Davies, Peers; Jones, Scott; Dunham, Stephen; Tarlinton, Rachael E.

Abstract

Background
Small ruminant lentiviruses (SRLVs) are lentiviruses of sheep and goats, formerly known as maedi–visna (MV) in sheep and caprine encephalitis and arthritis in goats. In sheep, SRLVs commonly cause progressive pneumonia, wasting and indurative mastitis. SRLVs have a long latent period, and chronic production losses are often not recognised until very late. Few studies quantifying the production losses in ewes have been published, and none have been published under UK flock husbandry conditions.

Methods
Production records of milk yield and somatic cell count (SCC) from a dairy flock of 319 milking East Friesian × Lacaune ewes identified as MV infected via routine serological screening for SRLV antibodies were used in multivariable linear regression modelling to estimate the impact of SRLV status on total milk yield and SCC.

Results
Milk yield was reduced in seropositive ewes by 8.1%–9.2% over an entire lactation. SCC counts were not significantly different in SRLV-infected and unifected animals.

Limitations
Further parameters, such as body condition score or clinical mastitis, that were not available may have clarified the underlying cause of milk yield drop.

Conclusions
The study demonstrates substantial production losses in an SRLV-affected flock and highlights the impact of the virus on a farm's economic viability.

Citation

Davies, P., Jones, S., Dunham, S., & Tarlinton, R. E. (2023). Associations between small ruminant lentivirus infection and total milk yield and somatic cell count in a dairy sheep flock. Veterinary Record, 192(11), Article e2731. https://doi.org/10.1002/vetr.2731

• Journal Article Type: Article
• Acceptance Date: Feb 6, 2023
• Online Publication Date: Feb 21, 2023
• Publication Date: Jun 3, 2023
• Deposit Date: Mar 14, 2023
• Publicly Available Date: Mar 14, 2023
• Journal: Veterinary Record
• Print ISSN: 0042-4900
• Electronic ISSN: 2042-7670
• Publisher: BMJ Publishing Group
• Peer Reviewed: Peer Reviewed
• Volume: 192
• Issue: 11
• Article Number: e2731
• DOI: https://doi.org/10.1002/vetr.2731
• Keywords: Maedi–Visna, milk, sheep, small ruminant lentivirus
• Public URL: https://nottingham-repository.worktribe.com/output/17665478
• Publisher URL: https://bvajournals.onlinelibrary.wiley.com/doi/full/10.1002/vetr.2731