Resumen de GM 18. Changes in performance levels over six years in dual purpose herds participating in a genetics research project
R. Khalil, Lucia Vaccaro, A. Perez, H. Mejias, Rodolfo Vaccaro, Omar Verde
Using data from 8509 calvings in 14 Venezuelan dual purpose herds which participated in a genetic improvement research project, performance trends were measured between 1990 and 1995, a period when national milk yields/cow declined slightly. Data on milk yield/lactation, interval calving-conception (ICC), 4-month calf weight and mortality to 4 months were analysed using linear models which included the factors calving year and year x farm interaction, as well as farm, breed group, number and season of calving. Overall, the project farms improved 6 % in milk yield, -10 % in ICC, 9 % in calf weight and -22 % in calf mortality over six years, equivalent to 10 % (milk+calf)/cow/year. However, the four best herds increased milk yield/lactation by 22-83 % and their total output of (milk+calf)/cow/year by 38-79 %. The effective use of records for selection and culling, as well as an increase in the proportion of intermediate B. taurus x B. indicus crossbreds in the herds were common elements of progress, accompanied by management improvements. It was concluded that major progress could be made in many other dual purpose herds in the region using technology actually in commercial use, and that factors beyond the farmers’ control are often responsible when progress is not made.
