Università degli Studi di Milano, Dipartimento di Scienze Veterinarie e Sanità Pubblica, via Celoria 10, 20133 Milan, Italy.
J Dairy Sci. 2013 Mar;96(3):1856-64. doi: 10.3168/jds.2012-5978. Epub 2013 Jan 9.
Milk yield and composition are of great economic importance for the dairy goat industry. The identification of genes associated with phenotypic differences for these traits could allow for the implementation of gene-assisted selection programs in goats. Associations between polymorphisms at 3 candidate genes and milk production traits in Alpine goats farmed in Italy were investigated in the present research. Considered genes were acetyl-coenzyme A carboxylase α (ACACA), the major regulatory enzyme of fatty acid biosynthesis; stearoyl-coenzyme A desaturase (SCD), involved in the biosynthesis of monounsaturated fatty acids in the mammary gland; and lipoprotein lipase (LPL), which plays a central role in plasma triglyceride metabolism. An approach somewhat similar to the granddaughter design for detecting quantitative trait loci in dairy cattle was followed. Effects of genotypes of a sample of 59 Alpine bucks on phenotypes of their 946 daughters raised in 75 flocks were investigated. Data comprised 13,331 daily records for milk yields (L/d), fat and protein yields (kg/d), and fat and protein contents (%) of 2,200 lactations. Population genetics parameters were calculated and associations between milk production traits and 10 single nucleotide polymorphisms (SNP) at the 3 genes were tested. Two markers at the ACACA, 1 for the SCD and 1 at the LPL locus, deviated significantly from the Hardy-Weinberg equilibrium, with an observed heterozygosity lower than expected. Flock, age of the goat, kidding season, and stage of lactation affected all traits considered, except fat percentage. Three SNP were found to be significantly associated with milk production traits. The SNP located on the ACACA gene showed an effect on milk yield, with daughters of TT bucks having an average test-day milk yield of about 0.3 to 0.25 L/d lower than the other 2 genotypes. The marker on the LPL locus was highly associated with milk yield, with the largest values for CC daughters (about 0.50L more than GG). The TGT deletion located on the untranslated region of the SCD gene showed significant effects on average milk and protein yields. The homozygote-deleted genotype had values about 0.5 L/d and 16 g/d lower for milk and protein daily yield, respectively, compared with the TGT/TGT genotype. Differences between genotypes were quite constant across most of the lactation. Associations found in the present study, which should be tested in a larger sample, especially for those markers that show rare genotypes, may offer useful indications for the genetic improvement of dairy traits in goats.
产奶量和组成对奶山羊业具有重要的经济意义。鉴定与这些性状表型差异相关的基因可以允许在山羊中实施基因辅助选择计划。本研究调查了意大利阿尔卑斯山羊中 3 个候选基因的多态性与产奶性状的关联。考虑的基因是乙酰辅酶 A 羧化酶α（ACACA），脂肪酸生物合成的主要调节酶；硬脂酰辅酶 A 去饱和酶（SCD），参与乳腺中单不饱和脂肪酸的生物合成；脂蛋白脂肪酶（LPL），在血浆甘油三酯代谢中起核心作用。采用与检测奶牛数量性状的孙女设计相似的方法。研究了 59 只阿尔卑斯公山羊的基因型对其在 75 个羊群中饲养的 946 只母羊的表型的影响。数据包括 2200 个泌乳期的 13331 个每日产奶量（L/d）、脂肪和蛋白质产量（kg/d）和脂肪和蛋白质含量（%）的记录。计算了群体遗传学参数，并检验了 3 个基因中的 10 个单核苷酸多态性（SNP）与产奶性状之间的关系。ACACA 上的 2 个标记、SCD 上的 1 个标记和 LPL 上的 1 个标记均显著偏离哈迪-温伯格平衡，观察到的杂合度低于预期。羊群、山羊年龄、产羔季节和泌乳阶段均影响除脂肪百分率以外的所有性状。发现 3 个 SNP 与产奶性状显著相关。位于 ACACA 基因上的 SNP 对产奶量有影响，TT 公山羊的女儿的平均测试日产奶量比其他 2 种基因型低约 0.3 至 0.25 L/d。位于 LPL 基因座上的标记与产奶量高度相关，CC 女儿的产奶量最大（比 GG 高约 0.50 L）。SCD 基因非翻译区的 TGT 缺失对平均产奶量和蛋白产量有显著影响。与 TGT/TGT 基因型相比，纯合缺失基因型的产奶和蛋白日产量分别低约 0.5 L/d 和 16 g/d。在大多数泌乳期，基因型之间的差异相当稳定。本研究发现的关联，特别是对于那些显示罕见基因型的标记，应在更大的样本中进行测试，这可能为山羊奶性状的遗传改良提供有用的信息。
