Contribuition to the genetic study o f age at first calving in Pitangueims cows (518 Red Poll x 318 Zebu). I. Effect o f non genetic factors

Abstract

The present work reference to the genetic study o f age at first calving o f 500 Pitangueiras cows (518 Red Poll x 314 Zebu) mantained under pasture regime in Três Barras Ranch in São Paulo State, Brazil. The variance analyses was carried out according to the least square method as described by HARVEY₁₁ and KEMPHORNE₁₄. The mean age at first calving of 483 animals was 42,87 0,28 months (C.V. = 14.31%). The earliest calving occurred at age of 23.3 months and the latest at about 76,6 months, showing a great amplitude of variation (53.3 months). The constant estimates were: —0.88 and +0.88 for the cows of the first and second generations; —0.24 for dry season (April-September) and +0.24 for rainy season (October-March). The effects of generation and year of calving were significant on age at first calving.