Laboratory of Animal Genetics, Breeding and Reproduction, Ministry of Agriculture of China, National Engineering Laboratory of Animal Breeding, College of Animal Science and Technology, China Agricultural University, 100193, Beijing, China.
Department of Clinical Sciences, Swedish University of Agricultural Sciences, SLU 75007, Uppsala, Sweden.
J Dairy Sci. 2021 Nov;104(11):11867-11877. doi: 10.3168/jds.2020-19943. Epub 2021 Sep 3.
Supernumerary teats (SNT) are a common epidermal abnormality of udders in mammals. The SNT negatively affect machine milking ability, udder health, and animal welfare and sometimes act as reservoirs for undesirable bacteria, resulting in economic losses on calves and lactating cows due to the cost of SNT removal surgery, early culling, and low milk yield. This study aimed to analyze the incidence and genetic parameter of SNT and detect SNT-related genes in Chinese Holstein cattle. In this study, the incidence of SNT was recorded in 4,670 Chinese Holstein cattle (born between 2008 and 2017) from 2 farms, including 734 genotyped cows with 114,485 SNPs. The SNT had a total frequency of 9.8% and estimated heritability of 0.22 (SE = 0.07), which were obtained using a threshold model in the studied Chinese Holstein population. Furthermore, we calculated approximate genetic correlations between SNT and the following indicator traits: 12 milk production, 28 body conformation, 5 fertility and reproduction, 5 health, and 9 longevity. Generally, the estimated correlations, such as 305-d milk yield for third parity (-0.55; SE = 0.02) and age at first calving in heifer (0.19; SE = 0.03), were low to moderate. A single-step GWAS was implemented, and 10 genes associated with SNT located in BTA4 were identified. The region (112.70-112.90 Mb) on BTA4 showed the highest genetic variance for SNT. The quantitative trait loci on BTA4 was mapped into the RARRES2 gene, which was previously shown to affect adipogenesis and hormone secretion. The WIF1 gene, which was located in BTA5, was also considered as a candidate gene for SNT. Overall, these findings provide useful information for breeders who are interested in reducing SNT.
副乳头（SNT）是哺乳动物中常见的一种乳房表皮异常。SNT 会降低机器挤奶能力、乳房健康和动物福利，有时还会成为不良细菌的储库，导致因 SNT 切除手术、早期淘汰和低产奶量而给犊牛和泌乳牛带来经济损失。本研究旨在分析中国荷斯坦牛 SNT 的发生率和遗传参数，并检测与 SNT 相关的基因。在本研究中，记录了来自 2 个农场的 4670 头中国荷斯坦牛（出生于 2008 年至 2017 年之间）的 SNT 发生率，其中包括 734 头已基因分型的母牛，其 114485 个 SNP。SNT 的总频率为 9.8%，遗传力估计值为 0.22（SE=0.07），这是在研究的中国荷斯坦人群中使用阈值模型获得的。此外，我们计算了 SNT 与以下指标性状之间的近似遗传相关性：12 个产奶量、28 个体型、5 个繁殖力和生殖力、5 个健康和 9 个寿命。一般来说，估计的相关性，如第三胎产奶量（-0.55；SE=0.02）和初产牛的初配年龄（0.19；SE=0.03），为低至中等。实施了一步 GWAS，鉴定出 10 个与 SNT 相关的基因，这些基因位于 BTA4 上。BTA4 上的 112.70-112.90 Mb 区域对 SNT 的遗传方差最高。BTA4 上的数量性状位点被映射到 RARRES2 基因上，该基因先前被证明会影响脂肪生成和激素分泌。WIF1 基因位于 BTA5 上，也被认为是 SNT 的候选基因。总的来说，这些发现为有兴趣减少 SNT 的饲养员提供了有用的信息。
