Resumen de Evaluation of the performance of a commercial dairy herd using a computerized system of records

M. A. R. de Freitas, M. M. Guilhermino, B Sampaio Maia, S. F. Grossi

• The aim of this study was to assess performance indexes relative to fertility and milk production in a herd of 750 cows of the Girolando breed enrolled in a dairy herd monitoring program (PMRL) developed by the Estação Experimental de Zootecnia de Ribeirão Preto, SP, Brazil from 1990 to 1999. Results showed that the indexes studied improved over the years. In the regression model some variables, such as total number of cows in the herd, interval from calving to first service, pregnancy rate at first service and pregnancy rate at all services, showed high coefficient of determination (R2 >51%), indicating that these traits responded strongly to the action recommended by the PMRL. Other traits, such as age at first calving, interval from calving to conception, number of services per conception, total milk yield per lactation and at 305 days of lactation, depend more on other factors inherent to the animal itself than on the PMRL. For this group of traits, other sources of variation were included in the analysis model, namely age of cow or number of calving, sex of the calf, genetic group, and month/season and year of calving, in an attempt to improve the R2. In both cases, the variable year of calving indirectly measured the efficiency of the system. The period studied (10 years) was not long enough to perceive the effects of certain other sources of variation such as genetic progress, which could also be involved.