Associations between maternal milk protein genotypes with preweaning calf growth traits in beef cattle

The objectives of this study were to investigate milk casein polymorphisms in dams and to determine the impacts of maternal casein genotypes on growth traits of their sucking calves. Milk samples from 433 dams of the breeds German Angus (GA) and German Simmental (GS) were typed at the milk protein loci alpha(s1)-casein (alpha(s1)-CN), beta-casein (beta-CN), alpha(s2)-casein (alpha(s2)-CN), and kappa-casein (kappa-CN) via isoelectric focusing. Associations between casein genotypes in maternal milk with growth traits of their 1,872 calves were analyzed until the age of weaning using linear mixed models, considering either genotypes of individual casein loci (model 1) or composite alpha(s1)-beta-alpha(s2)-kappa-CN genotypes within the casein cluster (model 2). Besides environmental effects such as sex, age of the dam, and calving year-season, genetic effects (breed group and maternal and paternal effects) were considered in statistical models. The composite casein genotype BB vertical bar A2A2 vertical bar AA vertical bar AB (order of genes on bovine chromosome alpha(s1)-vertical bar beta-vertical bar alpha(s2)-vertical bar kappa-CN) was associated with greater average daily weight gains (ADG) and heavier ageadjusted weaning weights (WW) of calves (P < 0.05). The effects of composite genotypes on birth weight of calves were similar (P > 0.05; model 2). With regard to individual casein loci, greater ADG and WW were observed for calves from dams with the genotypes kappa-CN BB and alpha(s1)-CN BB, respectively (P < 0.05; model 1). Age-adjusted WW was largest for calves from dams carrying the kappa-CN genotype BB (215 kg) compared with calves representing the maternal AB and AA genotypes (both 204 kg). Results from the present study suggested selectable casein genotypes due to their nutritional value of milk (value in terms of offspring performances), offering new perspectives for breeding strategies in beef cattle to improve preweaning calf performance.