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 α _s1-casein (α_s1-CN), β-casein (β-CN), α _s2-casein (α_s2-CN), and κ-casein (κ-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 α _s1-β-α _s2-κ-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 BBǀA2A2ǀAAǀAB (order of genes on bovine chromosome 6: α _s1-ǀβ-ǀα _s2-ǀκ-CN) was associated with greater average daily weight gains (ADG) and heavier age-adjusted 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 κ-CN BB and α _s1-CN BB, respectively (P < 0.05; model 1). Age-adjusted WW was largest for calves from dams carrying the κ-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.

中文翻译：

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母牛乳蛋白基因型与肉牛断奶前犊牛生长性状之间的关联。

本研究的目的是调查母牛乳酪蛋白多态性，并确定母体酪蛋白基因型对其吮吸犊牛生长性状的影响。来自德国安格斯 ( GA ) 和德国西门塔尔 ( GS )品种的 433 只母猪的牛奶样品在牛奶蛋白位点 α  _{s1 -}酪蛋白 ( α _s1 -CN )、β-酪蛋白 ( β-CN )、α  _{s2 -}酪蛋白进行分型( α _s2 -CN ) 和 κ-酪蛋白 ( κ-CN) 通过等电聚焦。使用线性混合模型分析母乳中酪蛋白基因型与其 1,872 头犊牛生长性状之间的关联，直至断奶年龄，考虑单个酪蛋白基因座（模型 1）或复合 α  _s1 -β-α  _s2 -κ-CN 的基因型酪蛋白簇内的基因型（模型 2）。除了性别、母猪年龄和产犊季节等环境影响外，统计模型还考虑了遗传影响（品种组和母本和父本的影响）。复合酪蛋白基因型 BBǀA2A2ǀAAǀAB（牛染色体 6 上的基因顺序：α  _s1 -ǀβ-ǀα  _s2 -ǀκ-CN）与更大的平均每日体重增加（ADG）相关) 和较重的犊牛年龄调整断奶体重 ( WW ) ( P < 0.05)。复合基因型对犊牛出生体重的影响相似（P > 0.05；模型2）。对于单个酪蛋白基因座，分别观察到基因型为κ-CN BB 和α _s1 -CN BB 的母牛犊的ADG 和WW 更大 （P< 0.05; 模型 1)。与代表母体 AB 和 AA 基因型的小牛（均为 204 千克）相比，携带 κ-CN 基因型 BB（215 千克）的母牛的小牛的年龄调整后 WW 最大。本研究的结果表明，由于牛奶的营养价值（就后代性能而言的价值），酪蛋白基因型具有选择性，为肉牛育种策略提供了新的视角，以提高断奶前犊牛的性能。