The impact of repeated skin testing and slaughter on bovine tuberculosis control in Holeta Dairy Farm: An update on subsequent prevalence and herd demographic changes

Bovine tuberculosis (bTB) is a serious animal health problem in Ethiopia, ranking among the top three livestock diseases. If the factors contributing to the spread and persistence of bTB are not managed, the situation may get worse. Therefore, prioritizing bTB control is essential. A retrospective study was conducted to evaluate the effect of repeated skin testing and slaughter on subsequent bTB prevalence and herd demographic changes in Holeta dairy farm. A total of 810 Friesian (F) * Boran (B) crosses, and pure Boran animals were involved in the study; all animals on the farm, except calves <6 months of age, were tested using single intradermal comparative cervical tuberculin test (SICCTT). On the basis of 21.3% prevalence in the first-round test in December 2014, three successive rounds of test and slaughter were conducted. During this period, the prevalence of bTB infection exhibited an oscillating pattern. It initially declined to 8.4% (n = 496) during the second-round test but then experienced resurgence, reaching 24.8% (n = 503) in the third-round. Finally, the prevalence decreased to 5.4% in the fourth-round test. The time interval between successive SICCTT tests varied from 0.95 years to 1.84 years. The test and slaughter intervention resulted in the culling of a substantial number of cows (n=342). With an increased culling rate, the average age of the herd and the average number of lactations per cow decreased. Similarly, animal entries and exits also influenced the breed composition of the herd. During the first round test, over 63% of the herd was composed of 50% HF*B crosses, followed by pure Boran, and 75% HF*B crosses, respectively. However, between the first and fourth test rounds, the proportion of Borans declined to 5%, while high-grade (75% HF*B) animals increased almost fivefold. In conclusion, the findings of this study showed the effect of prolonged time interval between consecutive tests which might result in failure of test and slaughter intervention, hence, due attention should be given on maintaining the recommended regular time interval (2-6 months) during consecutive test and slaughter procedures. Finally, the study recommends further study on assessing other alternative control strategies such as test and segregation methods to reduce the economic impact of culling of bTB reactor animals at a farm level.