A Model to Describe Growth Patterns of the Mammary Gland During Pregnancy and Lactation

¹ Department of Animal Nutrition, Wageningen Agricultural University, PO Box 338, 6700 AH Wageningen, The Netherlands
² Institute of Grassland and Environmental Research, North Wyke Research Station, Okehampton, Devon EX20 2SB, United Kingdom
³ Institute of Grassland and Environmental Research, Plas Gogerddan, Aberystwyth, Dyfed SY23 3EB, United Kingdom
⁴ Department of Animal and Poultry Science, University of Guelph, Guelph, ON, Canada N1E 3L2
⁵ Purina Mills Inc., PO Box 66812, St. Louis, MO 63166-6812
⁶ Centre for Dairy Research, University of Reading, Reading RG6 2AT, United Kingdom

Extensive proliferation and death of cells in the mammary gland occur during pregnancy and lactation. In this study, a mechanistic model was developed that yielded a single equation to describe the pattern of mammary growth of mammals throughout pregnancy and lactation. The model contains a single pool, which is the cell population of the mammary gland; one influx, representing cell proliferation; and one efflux, representing cell death. The parameters of the equation lend themselves to direct physiological interpretation. The model fitted data on mammary gland DNA adequately and can be related to current knowledge on factors and inhibitors of mammary gland growth. A unique definition of the parameters of the model can be difficult because of the high degree of variation among animals, an improper number of observations, or timing, as indicated by analyses of simulated data. The model can also be applied to the study of the entire lactation curve. The widely applied gamma equation and the equation that was developed in this study were compared using weekly production data from dairy cows. The new model performed well, particularly when a sharp peak in milk production occurred. The model has the advantage of providing, for the first time, a simple biological description of the lactation curve that can be used to discriminate changes in lactational performance that are associated with experimental treatments.

Key Words: modeling • mammary gland • lactation

Submitted on July 22, 1996
Accepted on February 6, 1997

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