Heritability coefficients for linear type traits and first and cumulative lactation production in Holstein cows from Paraná state
The aim of this study was to estimate the heritabilities for production traits (in the 1st (FL) and accumulated lactation (AL) during the productive life) and the 23 linear type traits (LTT) for two distinct populations of Holstein cows from Paran? state: general (that represents most of dairy cattle production) and high production (lifetime cows: the population which is economically relevant for farmers and was used to identify similarities and differences on the general population). Data belonging to Paran? Association of Holstein Cattle Breeders from 25,885 animals born between 2000 to 2013 were used for genetic analysis. The relationship matrix was composed by 73,411 animals for the general population and 22,282 for the lifetime population. The traits were analyzed with single-trait animal models to estimate the heritability coefficients represented by: Y=X?+Za+e where Y = vector of observations; ? = fixed effects vector of contemporary group (year and season of calving, herd and evaluation method) and status (lifetime or not); a = vector of direct additive genetic effects; X and Z = incidence matrix for fixed and random effects respectively. The heritability for milk, fat and protein yield in the FL were, respectively, 0.34 ? 0.011, 0.39 ? 0.011 and 0.24 ? 0.010 for the general population and 0.54 ? 0.027, 0.43 ? 0.028 and 0.39 ? 0.025, respectively, for the lifetime cows. For the AL, the heritabilities for milk, fat and protein were respectively 0.04 ? 0.005, 0.05 ? 0.005 and 0.05 ? 0.005 for the general population and 0.10 ? 0.017, 0.06 ? 0.015 and 0.11 ? 0.018, respectively, for the lifetime cows. For LTT, the heritability for the general population ranged from 0.06 to 0.39, with the lowest value for foot angle and highest value for pin width. For lifetime cows, heritability ranged from 0.08 to 0.36, with the lowest value for body condition score and foot angle and the highest value for teat length. The mammary system and rump are the compounds that will be responded to direct selection in the population of lifetime cows. For the general population, the mammary system and dairy strength could get a genetic gain by selection. The results indicated the existence of some environmental effects that influence more specifically the lifetime cows' population.