Modeling the Interaction of Milking Frequency and Nutrition on Mammary Gland Growth and Lactation

Abstract

A mathematical model of biological mechanisms regulating lactation is constructed. In particular, the model allows prediction of the effect of milking frequency on milk yield and mammary regression, and the interaction of nutrition and milking frequency in determining yield. Possible interactions of nutrition with milking frequency on alveolar dynamics are highlighted. The model is based upon the association of prolonged engorgement (as a consequence of milk accumulation) of active secretory alveoli with changes in gene expression that result in impairment and, ultimately, cessation of milk secretion. The emptying of alveoli at milking, following alveolar contraction induced by oxytocin, prevents this process and also allows quiescent alveoli to reactivate. Prolonged engorgement results in apoptosis of the secretory cells and, hence, regression of the mammary gland. Milk yield is linked to alveolar populations, with secretion rates being modulated by nutrition and udder fill effects. The model was used to investigate different management scenarios, and is in agreement with experimental results. The model shows that while milking frequency drives alveolar population, and therefore potential milk production, actual production varies considerably with nutrition. A significant portion of the loss associated with once-daily milking was due to udder fill rather than loss of secretory tissue. The model showed qualitative agreement with experimental data, on the acute and chronic effects of temporary once-daily milking.

Genetic parameters of a biological lactation model: early lactation and secretion rate traits of dairy heifers

“…In this analysis, the value of N 5 2.8 3 10 10 was used to calculate all the secretion rate variables for all lactations, after Vetharaniam et al (2003). Clearly this is a simplification since N is expected to vary between lactations but the use of this estimate does make the secretion rate traits have more 'realistic' values.…”

“…All correlations were calculated using ASREML and their standard errors estimated as described by Gilmour et al (2002). A further model was used to analyse the secretion rates of the milk component traits derived from (FP 3 S M )/ (2.8 3 10 10 ), the secretion rate per cell, using the standard value for N derived from Vetharaniam et al (2003). This model was:…”

“…This model comprised three different parts corresponding to the growth of differentiated mammary cells, their reduction through apoptosis and the secretion rate per cell. Vetharaniam et al (2003) showed how the differentiation may be viewed in two parts, active and quiescent secretory cells. Pollott and Gootwine (2000) demonstrated how the original seven-parameter -E-mail: gpollott@rvc.ac.uk model may be simplified for use in practice.…”

A teleonomic model describing performance (body, milk and intake) during growth and over repeated reproductive cycles throughout the lifespan of dairy cattle. 1. Trajectories of life function priorities and genetic scaling

“…The first attempt was performed by Neal and Thornley (1983) by way of a theoretical hormone controlling the division rate of basic udder cells to provide active secretory cells in the mammary gland. Further developments were carried out by Dijkstra et al (1997), Vetharaniam et al (2003a and2003b) and Pollott (2004). This principle of modelling was also used to direct adipose tissue anabolism and catabolism (Sauvant and Phocas, 1992;Baldwin, 1995;Martin and Sauvant, 2007) or to provide kinetics of plasma growth hormone and insulin driving exchanges between the tissues and udder (Danfaer, 1990).…”

The effect of level of feeding, genetic merit, body condition score and age on biological parameters of a mammary gland model

“…A t ¼ de 2k 2 t þ l 6 e w 6 t þ l 7 e w 7 t ð14Þ Figure 1 Schematic diagram of the mammary gland model (adapted with permission based on Vetharaniam et al (2003a)). Abbreviations: A t ¼ active secretory alveoli at time t, Q ¼ quiescent alveoli, S ¼ secretion rate per active alveoli, r pa ¼ rate of differentiation from progenitor to active secretory alveoli, r aq ¼ rate at which active secretory alveoli proceed to quiescence, r qa ¼ rate at which quiescent alveoli are reactivated to become active secretory alveoli, and r qs ¼ rate at which quiescent alveoli proceed to senescence.…”