Efficacy of measures to control caprine arthritis-encephalitis in dairy herd with high clinical and serological prevalence

This study examined the effectiveness of control measures for caprine arthritis-encephalitis in a herd with 431 dairy goats in an intensive rearing system. All animals older than six months were initially tested by agar gel immunodiffusion (AGID) and separated into seropositive and seronegative. Control measures were implemented for two years and ten months. Five serological examinations were subsequently performed two by AGID and three by the Western Blot (WB) technique. In these tests, animals that tested negative in the previous serological examination were evaluated along with those older than six months which had not yet been examined. The effectiveness of control was evaluated based on the incidence of the disease. Seroconverted animals were stratified according to age, physiological status and dam serology. For the effect of time, logistic regression was performed at the 5% significance level, with values converted into likelihood. General incidence and incidence as a function of age and physiological status were evaluated by analysis of variance, with means compared by Tukey’s test at 5% significance. The ratio test was used for incidence and physiological status, and the agreement between the AGID and WB tests was determined by the Kappa coefficient. Animals that seroconverted and were born to positive dams were compared with those born to dams negative at birth by the Chi-square test, and the same was applied for the number of discarded animals. Initially, 54.24% (179/330) positive and 257 seroconverted animals were identified after the start of control. Higher incidence occurred in the animals aged between 13 and 36 months and in lactating does. Seroconversions among offspring of seropositive dams were higher than in the offspring of seronegative dams (p < 0.001). High infection rates were identified in the sires. The obtained results were not satisfactory, as the measures did not help to prevent new cases, indicating that there are moments of infection yet to be elucidated. On farms that aim to control the disease, the following measures are required in addition to those already recommended: use of diagnostic tests with less frequency; application of high-sensitivity tests in the offspring; immediate separation of kids from dams at birth; separation of kids according to the serological status of the dams; inclusion of kids from unsupervised births in the group of kids from positive dams; and keeping positive and negative animals on different farms or greatly distanced. In herds for which there is an intention to establish control, it is important to determine whether the productive losses associated with the disease are greater than the costs of implementing more efficient measures.