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 Pantanalregion. During this period new management technologies were introduced withthe objective of modify the traditional system and improve herd production.Cows were identified and after pregnancy checking they were maintained or culledfrom the herd depending on the overall evaluation of the reproductive performance.Data were modeled using generalized estimating equation (GEE) with logisticfunction and binomial distribution, which is an extension of generalized linearmodels (GLIM). The GEE approach takes into account the structure of covariancecategorical repeated measurements in the subject for parameter estimates. Cowsculling rate was significantly affected by pasture, management, and linear andquadratic cow age. Use of new technologies did not clearly increase the probabilityof pregnancy. Breeding season increased cows culling rate leading to a greaterreplacement of cows in the herd.
