Effect of environmental and genetic factors on weights at 180 days of age Holstein calves

Abstract

The objective of this study was to evaluate the factors affecting the performance of black and white Holstein calves, at 180 days of weight, raised under artificial milking conditions, at the Experimental Farm in the State of São Paulo (Brazil). A total of 814 calves (389 males and 425 females) with a mean weight of 136.8kg, born from 1945 to 1963, were used. The animals were represented by 54 groups of paternal half-sibs. The environmental effects were submitted to a multiple regression analysis. Year of birth was the most significant source of variation of weight followed by sex of the calf and gestation period. Interactions between these factors were not significant. The equation obtained for weight at 180 days of age (Ŷ) in function of year of birth (a and a²), sex of the calf (s) and gestation period (g and g²), with a determination coefficient of 32.43%, was given as follows: Ŷ = -1,070.7500 - 2.178a + 0.0014 a² + 8.5933 pg - 0.00148 pg² - 9.3541s. Mean weights of the calves decreased curvilinearly from 1945 to 1963, showing a difference of 38.7kg among the estimated weights of these years. Male calves were 9.4kg heavier than female calves. Ninety-two percent of the data on gestation period were obtained during the interval from 271 to 280 days. Weight of the calves showed a positive curvilinear response to the increase of the gestation period. Heritability values estimated by the intra-class correlation among 54 groups of paternal half-sibs amounted to 0.612 with data adjusted for year of birth, sex of calf and gestation period. The confidence interval of the heritability estimate was 0.332 to 0.892, at a probability level of 95%.