Limits...
Go with the flow-biology and genetics of the lactation cycle.

Strucken EM, Laurenson YC, Brockmann GA - Front Genet (2015)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Animal Science, School of Environmental and Rural Science, University of New England Armidale, NSW, Australia.

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.

No MeSH data available.


Related in: MedlinePlus

(A) Milk production and (B) energy supply and requirements during the lactation cycle of 340 days. (A) The curve represents the milk yield per day of lactation and reaches a peak production around lactation days 40–50. Shortly before lactation and until peak production the udder and the alveolar system are highly developed. In later lactation the alveolar system regresses continuously until the end of lactation and into involution. (B) The blue curve represents the energy that is needed for milk production and maintenance of vital body functions. The energy needed for milk production is highest when milk production reaches a peak. At the same time the energy taken in through food (purple curve) cannot cover the energy requirements for milk production which leads to a loss in body energy stores (black curve). This imbalance in energy homeostasis changes with the decline of milk production in late lactation.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4374477&req=5

Figure 1: (A) Milk production and (B) energy supply and requirements during the lactation cycle of 340 days. (A) The curve represents the milk yield per day of lactation and reaches a peak production around lactation days 40–50. Shortly before lactation and until peak production the udder and the alveolar system are highly developed. In later lactation the alveolar system regresses continuously until the end of lactation and into involution. (B) The blue curve represents the energy that is needed for milk production and maintenance of vital body functions. The energy needed for milk production is highest when milk production reaches a peak. At the same time the energy taken in through food (purple curve) cannot cover the energy requirements for milk production which leads to a loss in body energy stores (black curve). This imbalance in energy homeostasis changes with the decline of milk production in late lactation.

Mentions: The milk production of a cow follows a dynamic curve (Figure 1A; Stanton et al., 1992). After an initial rapid increase in milk yield during early lactation, milk yield (as well as protein and fat content) peak around 6 weeks into lactation, after which production slowly decreases until the end of lactation. Dairy cows experience an energy deficiency during early and peak lactation (Figure 1B; Collard et al., 2000) due to the high energy requirements for milk production not being met because of physiological limitations which constrain food intake (i.e., bulk capacity; Allen, 1996) and mobilization of bodily energy resources. This energy deficit has been proposed to have detrimental effects on health and fertility which have been reviewed and discussed by Oltenacu and Broom (2010), and negative genetic correlations have been reported between milk production and a variety of functional traits (Zimmermann and Sommer, 1973; Dekkers et al., 1998; Ingvartsen et al., 2003; Muir et al., 2004). However, it has to be noted that total milk yield and the energy balance during early lactation seem to be independent, as correlations have been reported to be very low (Spurlock et al., 2012). Further, the negative impact of lactation on fertility may serve a functional purpose to provide optimal birth spacing for the survival of offspring. Therefore, there may be other endogenous factors yet to be discovered that negatively affect health and fertility traits.


Go with the flow-biology and genetics of the lactation cycle.

Strucken EM, Laurenson YC, Brockmann GA - Front Genet (2015)

(A) Milk production and (B) energy supply and requirements during the lactation cycle of 340 days. (A) The curve represents the milk yield per day of lactation and reaches a peak production around lactation days 40–50. Shortly before lactation and until peak production the udder and the alveolar system are highly developed. In later lactation the alveolar system regresses continuously until the end of lactation and into involution. (B) The blue curve represents the energy that is needed for milk production and maintenance of vital body functions. The energy needed for milk production is highest when milk production reaches a peak. At the same time the energy taken in through food (purple curve) cannot cover the energy requirements for milk production which leads to a loss in body energy stores (black curve). This imbalance in energy homeostasis changes with the decline of milk production in late lactation.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4374477&req=5

Figure 1: (A) Milk production and (B) energy supply and requirements during the lactation cycle of 340 days. (A) The curve represents the milk yield per day of lactation and reaches a peak production around lactation days 40–50. Shortly before lactation and until peak production the udder and the alveolar system are highly developed. In later lactation the alveolar system regresses continuously until the end of lactation and into involution. (B) The blue curve represents the energy that is needed for milk production and maintenance of vital body functions. The energy needed for milk production is highest when milk production reaches a peak. At the same time the energy taken in through food (purple curve) cannot cover the energy requirements for milk production which leads to a loss in body energy stores (black curve). This imbalance in energy homeostasis changes with the decline of milk production in late lactation.
Mentions: The milk production of a cow follows a dynamic curve (Figure 1A; Stanton et al., 1992). After an initial rapid increase in milk yield during early lactation, milk yield (as well as protein and fat content) peak around 6 weeks into lactation, after which production slowly decreases until the end of lactation. Dairy cows experience an energy deficiency during early and peak lactation (Figure 1B; Collard et al., 2000) due to the high energy requirements for milk production not being met because of physiological limitations which constrain food intake (i.e., bulk capacity; Allen, 1996) and mobilization of bodily energy resources. This energy deficit has been proposed to have detrimental effects on health and fertility which have been reviewed and discussed by Oltenacu and Broom (2010), and negative genetic correlations have been reported between milk production and a variety of functional traits (Zimmermann and Sommer, 1973; Dekkers et al., 1998; Ingvartsen et al., 2003; Muir et al., 2004). However, it has to be noted that total milk yield and the energy balance during early lactation seem to be independent, as correlations have been reported to be very low (Spurlock et al., 2012). Further, the negative impact of lactation on fertility may serve a functional purpose to provide optimal birth spacing for the survival of offspring. Therefore, there may be other endogenous factors yet to be discovered that negatively affect health and fertility traits.

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Animal Science, School of Environmental and Rural Science, University of New England Armidale, NSW, Australia.

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.

No MeSH data available.


Related in: MedlinePlus