Department of Animal Science, Faculty of Agriculture, University of Kurdistan, P.O. Box 416, Sanandaj, Kurdistan, Iran.
Department of Animal Science, Faculty of Agriculture, University of Kurdistan, P.O. Box 416, Sanandaj, Kurdistan, Iran.
J Dairy Sci. 2023 Apr;106(4):2573-2587. doi: 10.3168/jds.2022-22315. Epub 2023 Mar 2.
The relationship between K232A polymorphism of the DGAT1 gene and milk yield and composition was evaluated by meta-analysis of pooled data of more than 10,000 genotyped cattle. Four genetic models, including dominant (AA+KA vs. KK), recessive (AA vs. KA+KK), additive (AA vs. KK), and co-dominant (AA+KK vs. KA) were used to analyze the data. The standardized mean difference (SMD) was used to measure the size of the effects of the A and K alleles of K232A polymorphism on milk-related traits. The results showed that additive model was the best model for describing the effects of K232A polymorphism on studied traits. Under additive model, milk fat content was strongly decreased in cows having the AA genotype (SMD = -1.320). Furthermore, the AA genotype reduced the protein content of milk (SMD = -0.400). A significant difference in daily milk yield (SMD = 0.225) and lactation yield (SMD = 0.697) was found between cows carrying AA and KK genotypes, suggesting the positive effects of the K allele on these traits. Cook's distance measurement suggested some studies as outliers and sensitivity analyses by removing influential studies revealed that the results of meta-analyses for daily milk yield, fat content and protein content were not sensitive to outliers. However, the outcome of the meta-analysis for lactation yield was strongly influenced by outlier studies. Egger's test and Begg's funnel plots showed no evidence of publication bias in included studies. In conclusion, the K allele of K232A polymorphism showed a tremendous effect on increasing fat and protein contents in the milk of cattle, especially when 2 copies of this allele are inherited together, whereas the A allele of K232A polymorphism had negative effects on these traits.
通过对超过 10000 头已基因分型牛的数据进行合并分析，评估 DGAT1 基因 K232A 多态性与乳产量和组成的关系。采用 4 种遗传模型（显性（AA+KA 对 KK）、隐性（AA 对 KA+KK）、加性（AA 对 KK）和共显性（AA+KK 对 KA））分析数据。采用标准化均数差（SMD）衡量 K232A 多态性的 A 和 K 等位基因对与乳相关性状的影响大小。结果表明，加性模型是描述 K232A 多态性对研究性状影响的最佳模型。在加性模型下，AA 基因型牛的乳脂含量显著降低（SMD=-1.320）。此外，AA 基因型降低了牛奶的蛋白质含量（SMD=-0.400）。携带 AA 和 KK 基因型的奶牛在日产奶量（SMD=0.225）和泌乳量（SMD=0.697）上存在显著差异，提示 K 等位基因对这些性状有积极影响。Cook 距离测量表明，一些研究为异常值，通过剔除有影响的研究进行敏感性分析表明，乳产量、脂肪含量和蛋白质含量的 meta 分析结果对异常值不敏感。然而，泌乳量的 meta 分析结果受异常值研究的影响较大。Egger 检验和 Begg 漏斗图显示，纳入研究无发表偏倚的证据。综上所述，K232A 多态性的 K 等位基因对增加牛乳中的脂肪和蛋白质含量有巨大影响，尤其是当 2 个等位基因同时遗传时，而 K232A 多态性的 A 等位基因对这些性状有负面影响。
