Study of Brucellosis Incidence in a Bovine Dairy Farm Infected with Brucella abortus, Where Cattle Was Revaccinated with RB51

Milk production increase in a dairy farm under a six-year Brucellosis control program

The present work aims to quantify milk production in a bovine dairy herd during a 6-year brucellosis control program in Hidalgo, Mexico, where bovine brucellosis is endemic. This 6-year longitudinal pilot study comprised 74 monthly samplings to determine the incidence of brucellosis and to quantify daily milk production. To determine the monthly incidence of brucellosis, an average of 346 Holstein cows was examined each month with the card and Rivanol tests. These animals had been vaccinated as calves with the normal dose of Brucella abortus RB51 and were revaccinated annually with a reduced dose. Brucellosis is endemic in Mexico, where the control programs include vaccination and diagnosis; nevertheless, it is uncommon to carry out other essential control practices, such as separation and elimination of positive cows. In this herd, the cows positive to the card and rivanol tests were separated in specific units, especially at the moment of delivery. These cows were placed at the end of the line for milking and were eliminated from the herd at the end of their productive cycle. In this dairy herd, cows were milked three times a day and there was a monthly average of 300 cows in production. At the beginning of this study the prevalence of brucellosis was 8.43%; from days 180-330 the incidence was from 0.51% to 0.90%. Between days 360-570, the incidence diminished to 0%; between days 600 to 1140, it increased to 4.46%; and from days 1440 to 2220 the incidence was kept beneath 1%. The average of dairy milk production for each cow per day started with 24 L, increasing in direct proportion to the decrease in the presence of new cases of brucellosis: in the subsequent years, the production increased successively to 25, 27, 28, 29, and 30 L. The daily average per year of milk production in the herd was also quantified: at the beginning of the study it was 7220 L and in subsequent years was 7470, 7710, 8340, 8790, 8970, and 9150 L, respectively. We conclude that a direct relation existed between the application of a program of brucellosis control and the increase in milk production.