Possible risk factors for serological prevalence of Brucella ovis in Zacatecas, Mexico

Epididymitis due to Brucella ovis infection lead to a disease with great importance in Mexican sheep industry. In the affected rams produces a low productivity due to a decreased fertility. The objective of the study was to determine the relevance of different possible risk factors (production system, density of sires, population of ewes, ewes: ram ratio, mating system and sires breed) upon B. ovis prevalence in Zacatecas, Mexico. A sample of 544 rams was obtained in 153 flocks from four production systems. The serological test was determined by double immunodiffusion. The positive sampled rams were 18.6 % (101/544) and 10.5 % (16/153) of the sampled flocks had at least one positive ram. The semi-intensive production system showed a major prevalence (P<0.05) with 86.1 % (87/101) of the positive rams, the extensive system with 11.9 % (12/101), the backyard with 2.0 % (2/101) and the intensive did not register positives. The prevalence of B. ovis was higher in larger flocks, with the largest number of ewes and rams. Katahdin rams showed a major prevalence (30.8 %) (24/78) than Rambouillet (14.0 %) (18/129), Dorper (13.8 %) (31/224) and Suffolk rams (13.8 %) (8/58); (P<0.05). The prevalence was associated more with the production system used, than the ratio ewes: ram or mating system. The results suggest that the amount of sires within each flock is the most important factor in the serological prevalence of B. ovis (OR= 17.38, 95% IC 7.76-38.94), although this potential factor could be subject to the production system.