Strucken Eva M, Laurenson Yan C S M, Brockmann Gudrun A
Animal Science, School of Environmental and Rural Science, University of New England Armidale, NSW, Australia.
Breeding Biology and Molecular Genetics, Faculty of Life Sciences, Humboldt-Universität zu Berlin Berlin, Germany.
Front Genet. 2015 Mar 26;6:118. doi: 10.3389/fgene.2015.00118. eCollection 2015.
Lactation is a dynamic process, which evolved to meet dietary demands of growing offspring. At the same time, the mother's metabolism changes to meet the high requirements of nutrient supply to the offspring. Through strong artificial selection, the strain of milk production on dairy cows is often associated with impaired health and fertility. This led to the incorporation of functional traits into breeding aims to counteract this negative association. Potentially, distributing the total quantity of milk per lactation cycle more equally over time could reduce the peak of physiological strain and improve health and fertility. During lactation many factors affect the production of milk: food intake; digestion, absorption, and transportation of nutrients; blood glucose levels; activity of cells in the mammary gland, liver, and adipose tissue; synthesis of proteins and fat in the secretory cells; and the metabolic and regulatory pathways that provide fatty acids, amino acids, and carbohydrates. Whilst the endocrine regulation and physiology of the dynamic process of milk production seems to be understood, the genetics that underlie these dynamics are still to be uncovered. Modeling of longitudinal traits and estimating the change in additive genetic variation over time has shown that the genetic contribution to the expression of a trait depends on the considered time-point. Such time-dependent studies could contribute to the discovery of missing heritability. Only very few studies have estimated exact gene and marker effects at different time-points during lactation. The most prominent gene affecting milk yield and milk fat, DGAT1, exhibits its main effects after peak production, whilst the casein genes have larger effects in early lactation. Understanding the physiological dynamics and elucidating the time-dependent genetic effects behind dynamically expressed traits will contribute to selection decisions to further improve productive and healthy breeding populations.
泌乳是一个动态过程，其进化是为了满足成长中后代的饮食需求。与此同时，母亲的新陈代谢也会发生变化，以满足对后代营养供应的高要求。通过强烈的人工选择，奶牛的产奶品系往往与健康和繁殖力受损有关。这导致将功能性状纳入育种目标，以抵消这种负面关联。潜在地，在整个泌乳周期更均匀地分配总产奶量可以降低生理应激峰值，并改善健康和繁殖力。在泌乳期间，许多因素会影响乳汁的分泌：食物摄入量；营养物质的消化、吸收和运输；血糖水平；乳腺、肝脏和脂肪组织中细胞的活性；分泌细胞中蛋白质和脂肪的合成；以及提供脂肪酸、氨基酸和碳水化合物的代谢和调节途径。虽然乳汁分泌动态过程的内分泌调节和生理学似乎已为人所知，但这些动态背后的遗传学仍有待揭示。对纵向性状进行建模并估计加性遗传变异随时间的变化表明，性状表达的遗传贡献取决于所考虑的时间点。这种随时间变化的研究可能有助于发现缺失的遗传力。只有极少数研究估计了泌乳期间不同时间点的确切基因和标记效应。影响产奶量和乳脂的最显著基因DGAT1在产奶高峰期后发挥主要作用，而酪蛋白基因在泌乳早期有更大的影响。了解生理动态并阐明动态表达性状背后随时间变化的遗传效应，将有助于做出选择决策，以进一步改善高产且健康的育种种群。
