The impact of small ruminant lentiviruses infections on milk yield and milk quality traits in intensively reared dairy sheep

Despite small ruminant lentiviruses (SRLV) are widespread causing severe clinical manifestations, their effects on milk production in dairy sheep remain controversial. This study aimed to assess the impact of SRLV infections on milk yield and quality in intensively reared dairy sheep. A total of 527 purebred Chios and Lacaune ewes from four infected intensive dairy sheep farms in Greece were randomly selected and their infection status was determined at pre-lambing using both ELISA (serological testing) and real-time PCR (molecular testing). Their milk production was recorded bimonthly for 4 months for one milking period, initiating at the post-weaning, and physicochemical analyses (fat, protein, lactose, solids-not-fat) and estimation of SCC were performed in individual milk samples. Mixed linear regression models were generated for the assessment of the effects of serological, molecular, and infection status (consideration of both serological and molecular status) on milk production. Prevalence rates of SRLV infections exceeded 60 % in all farms. While serological status had no significant association, molecular status revealed a 10 % reduction in milk yield among infected ewes. Infected seronegative ewes had approximately 20 % less milk, protein, lactose and solids-not-fat yields, and 12 % less fat yield compared to the uninfected ones and approximately 15 % decreased milk, protein, lactose, and solids-not-fat yields, and 7 % decreased fat yield compared to the infected seropositive ones. Our findings underpin the significance of prospective study design and molecular diagnosis to efficiently elucidate the impact of SRLV infections on sheep productivity.