Resumen de Genetic and environmental factors influencing birth and 205 day weights of Pantaneiro calves

M. A. C. Lara, J. R. B. Sereno, C. McManus, U. G. P. Abreu

• The present work analyses the growth of calves of the conservation nucleus for Pantaneiro cattle of EMBRAPA Pantanal. Birth and weaning data was available on 171 Pantaneiro calves born between 1996 and 1999. Calves were born from August to December, and raised in the extensive system using native pastures at the Nhumirim farm, situated in the Nhecolândia subregion. The data was analyzed using GLM and CORR procedures of SAS and MTDFREML for analysis of variance components. Year of calving and calf sex was significant for all traits examined. Birth weight for males was 27.08 kg compared with 25.37 kg for females while weaning weights were 116.12 and 112.24 kg respectively. The year effect varied but the trend observed is that of an increase in both birth and weaning weight with time. Month of birth did not affect birth nor uncorrected weaning weight, although a trend was observed whereby calves born later in the season were heavier. With 205 day weight the effect of month was marked, with calves born in August being almost 25 kg heavier than those born in December (124.98 kg vs 99.23 kg) even after correction. Heritability for birth weight is very low while repeatability is a little higher. This study shows that there is little genetic variation available for use in selection for birth or weaning traits in Pantaneiro cattle in Brazil. Controlled breeding policies whereby related individuals are not mated to each other are important to increase the variation for these characteristics.