Twelve-year cohort study on the influence of caprine arthritis-encephalitis virus infection on milk yield and composition.

This long-term observational cohort study was carried out to evaluate the effect of caprine arthritis-encephalitis virus (CAEV) infection on the quantitative and qualitative characteristics of milk production in dairy goats. For this purpose, a dairy herd comprising both CAEV-infected and uninfected female goats was observed for 12 consecutive years. Records on daily milk yield, somatic cell count (SCC), and contents of the major milk components (fat, protein and lactose) were collected every month. In total, 3,042 records (1,114 from CAEV-positive and 1,928 from CAEV-negative animals) from 177 female goats were used for statistical analysis. The multi-trait repeatability test-day animal model using the derivative-free multivariate analysis package with the average information-REML method was applied to eliminate the influence of factors other than CAEV infection on milk production in goats. The statistical significance of the differences between estimates for seropositive and seronegative goats was evaluated using Student's t-test. The effect of age of goats (parity) on their serological status was also estimated with the one-trait repeatability test-day model. The serological status of goats was linked to parity: the higher the parity, the greater the probability of CAEV infection. No significant differences between infected and uninfected goats with respect to daily milk yield and SCC were found. On the other hand, the milk of uninfected goats contained more total protein (3.40% vs. 3.35%), fat (3.69% vs. 3.54%), and lactose (4.30% vs. 4.25%) than the milk of infected goats. Even though these differences were highly significant, they were small when expressed numerically.