Lactation curve in Guzera breed

[摘要] - The objectives of this work were to identify the mathematical functions that better fitted the milk production of Guzera breed cows, to evaluate the effects of the environmental factors on the lactation curve format and to estimate the genetic parameters for the milk production and for the dependable components of the lactation curve format. A total of 1130 lactations from 583 Guzera breed cows, daughters of 165 bulls, with production over the period from 1983 to 1997 were used. The models y = a n e -cn, y = a - cn + ln (n), y=a -cn e y =a e-c n were the ones that best fitted the milk production of the cows. By the analysis of variance, it was observed that the effects of cow herd, calving year and cow age at calving influenced the total milk production, initial milk production and milk decline production rate characteristics. The coefficients of heritability and repeatability estimates were obtained by means of one and two characteristic analyses. The animal selection, based only on the of the lactation curve format, would be of low efficiency.

[学科分类] 兽医学

[关键词] lactation curve;mathematical function;environmental factors;genetic parameters;Guzera breed     IntroduçãoEm conseqüência da grande extensão territorial do país e da adversidade climática encontrada nas diversas regiões;as raças zebuínas têm-se destacado progressivamente na exploração da atividade leiteira;seja como raça pura;ou em utilização nos diversos sistemas de cruzamento