GENETIC AND PHYNOTYPIC CORRELATIONS OF AGE AT FIRST CALVING WITH SOME CALF-HOOD FITNESS AND HEALTH TRAITS IN HOLSTEIN HEIFERS
Egyptian Journal of Animal Production
Objectives of this study were to estimate the effects of calf-hood fitness and health traits on age at first calving (AFC). Data of 2230 US Holstein heifers were collected from three farms located in Minnesota from 2003 to 2011 were used. AFC, calculated as a difference between birth date and date of first calving ranged from 571 to 1059 days ( = 716.66 ± 47.4). Multiple trait animal models were applied using REMLf90 software. Fixed effects considered as revealed in; a previous nutritional
... us nutritional experiment applied on almost half of these animals (n = 1226), (P < 0.01), and interaction between month and year of birth, while covariate effects were serum protein upon arriving to facility (SP), (P < 0. 01). Fitness traits effects included arrival to facility body weight (ABW), weaning weight (W56), weaning hip height (HH56), adjusted weight to 200d (W200), and adjusted hip height to 200d (HH200). Health traits recorded were scours (Sc) and respiratory disease (RD). Health traits were recorded as categorical traits according to incidence of occurrence (0: non occurrence; 1: occurrence once; and 2: occurrence twice or more). Heritability estimate of AFC was (0.07). Genetic correlations between calf-hood fitness traits and AFC were highly significant (0.45, 0.38, 0.34, 0.75, and 0.33) with ABW, W56, HH56, W200, and HH200, respectively. Meanwhile, genetic correlations between AFC and both health traits (Sc and RD) were (-0.19 and -0.01), respectively. Therefore, it is possible to build a selection index comprising calf-hood's fitness and health performance and AFC.