Go with the flow—biology and genetics of the lactation cycle

Abstract

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.

Meta-analysis of sequence-based association studies across three cattle breeds reveals 25 QTL for fat and protein percentages in milk at nucleotide resolution

“…While Daetwyler et al considered phenotypes for FP in early lactation as response variables, we used FP across the entire lactation. Milk fat content is under different genetic control across the lactation cycle [42] and the findings of Daetwyler et al [5] and our study indicate that sequence variation nearby AGPAT6 primarily controls fat content in early lactation which also agrees with the expression of AGPAT6 at different stages of lactation [43].…”

Special Foods and Local Herbs Used to Enhance Breast milk Production in Ghana: Rate of Use and Beliefs of Efficacy

“…Lactogogues taken hot (hot-related) were also widely used in the enhancement of breastmilk production mostly in the Northern region of Ghana especially hot black tea. This nding is in line with a study which identi ed black tea (Camellia sinensis) as a lactogogue even though caution was indicated due to the presence of caffeine in most commonly used brands in our setting which could cause irritability in the child if taken in excess [37]. The women particularly emphasized that the tea needed to be hot to be effective.…”

Efecto de agregar agua sobre el punto crioscópico y componentes de la leche cruda de vacas Jersey y Holstein

“…Además de estos factores, la composición de la leche y por consiguiente el punto crioscópico es afectada por la ocurrencia de mastitis subclinica, consumo de agua, estrés calórico, presencia de CO 2 en la leche (Janštová, Dračková, Navrátilová, Hadra, & Vorlová, 2007) el periodo del año, condiciones ambientales, edad y tipo de alimentación del animal, periodo de lactancia, nivel de producción (Dabija, Mironeasa, Orojan, & Sion, 2018) y el ciclo estral de la vaca (Toledo-Alvarado et al 2018). En este trabajo, ambos sitios presentan condiciones climáticas diferentes, lo que propicia condiciones de estrés calórico en los animales Jersey (Conejo, 2017), que afectan el consumo de materia seca por consiguiente el aporte de nutrimentos para la producción de leche, lo cual, se asocia a los nutrimentos presentes en el torrente sanguíneo y los alveolos de la ubre, durante la síntesis de la leche (Strucken, Laurenson, & Brockmann 2015). Argumento que se fortalece, al analizar el contenido de urea en leche presente en las muestras analizadas, donde se determina una diferencia de 2,82mg/dL que favorece a los animales Holstein, valor asociado a una mayor cantidad de proteína degradable en la ración que reciben los animales durante el día y que indica que los animales Jersey, no alcanzan el rango óptimo de 12 a 16mg/dL de urea en leche (Gonzáles & WingChing-Jones, 2016).…”