Forma en que se hereda el peso al nacer y la longitud de gestación en el ganado Charoles

Abstract

A genetic investigation was conducted on the mode of inheritance of birth weight and length of gestation in Charolais cattle kept for 26 years São Paulo, Brazil. The average birth weight of male calves was 40.7 kgs and 37.8 kgs. for female calves. The average length of gestation was 287.1 days. Males were carried for 286.56 days and females for 287.5 days. Corrections were made for non hereditary influences on these two variables, if they were found to affect them significantly. All corrections were made leaving intact the class with the largest numbers. The corrections for birth weight: sex, season, of birth, gestation of mother of the dam. For length of gestation the only significant influence found was that of birth weight. Regression values of 0.243 days were found for males and 0.447 for females, in days for each additional Kg. of birth weight Correction for birth weight rendered nil the difference between sexes in length of gestation. With the corrected values, the heritabilities were calculated by the method of intra sire correlations. The values found were 0.11±0.021 for birth weight and 0.37±0.021 for length of gestation. These values are comparatively lower than those found for other breeds in other environments. The existing evidence indicates that there is no reason for fear genetic causes (additive) for expecting problems of difficult parturition due to excessive weight of prolonged length of gestation when Charolais bulls are used. This does not exclude the possibility of non additive factors causing trouble in the purebreds (double muscling), or possible interactions between the Charolais bull and the uterine environment, or even purely genetic interactions with the breed of the dam. Evidence obtained from the same station when Charolais bulls were used on Zebu cows indicates no evidence of these dangerous interactions. What may happen with other breeds will only be found experimentally