Performance and age distribution of 1,075 cows were recorded during five years (May 1994 to May 1999) in a herd with an extensive cow-calf system in the Pantanal region. During this period new management technologies were introduced with the objective of modify the traditional system and improve herd production. Cows were identified and after pregnancy checking they were maintained or culled from the herd depending on the overall evaluation of the reproductive performance. Data were modeled using generalized estimating equation (GEE) with logistic function and binomial distribution, which is an extension of generalized linear models (GLIM). The GEE approach takes into account the structure of covariance categorical repeated measurements in the subject for parameter estimates. Cows culling rate was significantly affected by pasture, management, and linear and quadratic cow age. Use of new technologies did not clearly increase the probability of pregnancy. Breeding season increased cows culling rate leading to a greater replacement of cows in the herd.
extensive beef production systems; herd evaluation; generalized estimation equation
