ReproGen-Animal Bioscience Group, Faculty of Veterinary Science, University of Sydney, 425 Werombi Road, Camden, NSW 2570, Australia.
Genet Sel Evol. 2011 Jun 21;43(1):22. doi: 10.1186/1297-9686-43-22.
In sheep dairy production, total lactation performance, and length of lactation of lactation are of economic significance. A more persistent lactation has been associated with improved udder health. An extended lactation is defined by a longer period of milkability. This study is the first investigation to examine the presence of quantitative trait loci (QTL) for extended lactation and lactation persistency in sheep.
An (Awassi × Merino) × Merino single-sire backcross family with 172 ewes was used to map QTL for lactation persistency and extended lactation traits on a framework map of 189 loci across all autosomes. The Wood model was fitted to data from multiple lactations to estimate parameters of ovine lactation curves, and these estimates were used to derive measures of lactation persistency and extended lactation traits of milk, protein, fat, lactose, useful yield, and somatic cell score. These derived traits were subjected to QTL analyses using maximum likelihood estimation and regression analysis.
Overall, one highly significant (LOD > 3.0), four significant (2.0 < LOD < 3.0) and five suggestive (1.7 < LOD < 2.0) QTL were detected across all traits in common by both mapping methods. One additional suggestive QTL was identified using maximum likelihood estimation, and four suggestive (0.01 < P < 0.05) and two significant (P < 0.01) QTL using the regression approach only. All detected QTL had effect sizes in the range of 0.48 to 0.64 SD, corresponding to QTL heritabilities of 3.1 to 8.9%. The comparison of the detected QTL with results in cattle showed conserved linkage regions. Most of the QTL identified for lactation persistency and extended lactation did not coincide. This suggests that persistency and extended lactation for the same as well as different milk yield and component traits are not controlled by the same genes.
This study identified ten novel QTL for lactation persistency and extended lactation in sheep, but results suggest that lactation persistency and extended lactation do not have a major gene in common. These results provide a basis for further validation in extended families and other breeds as well as targeting regions for genome-wide association mapping using high-density SNP arrays.
在绵羊奶业生产中，总泌乳性能和泌乳期长度具有经济意义。更持久的泌乳与改善乳房健康有关。延长的泌乳期定义为更长的泌乳期。本研究首次探讨了绵羊延长泌乳期和泌乳持久性的数量性状位点（QTL）的存在。
利用（阿瓦什×美利奴）×美利奴单父系回交家系，共 172 只母羊，在所有常染色体上的 189 个位点框架图谱上，对泌乳持久性和延长泌乳性状进行 QTL 作图。采用 Wood 模型拟合多次泌乳的数据，估计绵羊泌乳曲线的参数，并利用这些估计值推导出乳、蛋白质、脂肪、乳糖、有用产量和体细胞评分的泌乳持久性和延长泌乳性状的测量值。利用最大似然估计和回归分析对这些衍生性状进行 QTL 分析。
总的来说，两种作图方法在所有性状上共检测到一个高度显著（LOD > 3.0）、四个显著（2.0 < LOD < 3.0）和五个提示性（1.7 < LOD < 2.0）的 QTL。利用最大似然估计还检测到一个额外的提示性 QTL，利用回归分析仅检测到四个提示性（0.01 < P < 0.05）和两个显著（P < 0.01）的 QTL。所有检测到的 QTL 的效应大小在 0.48 到 0.64 SD 之间，相应的 QTL 遗传力为 3.1 到 8.9%。与牛的检测结果比较表明，连锁区域保守。为泌乳持久性和延长泌乳所鉴定的大多数 QTL 并不重合。这表明，同一和不同产奶量和成分性状的持久性和延长泌乳期不受相同基因控制。
本研究在绵羊中鉴定出 10 个新的泌乳持久性和延长泌乳的 QTL，但结果表明，泌乳持久性和延长泌乳期没有共同的主效基因。这些结果为进一步在扩展家系和其他品种中进行验证以及利用高密度 SNP 芯片进行全基因组关联作图提供了基础。
