Recent developments in the genetic evaluation of dairy animals have concentrated on using the desirable properties of the test-day model to genetically evaluate milk production (Ptak and Schaeffer, 1993). This methodology results in a single breeding value for each animal reflecting its level of daily milk production, adjusted for the many environmental influences and the shape of the lactation curve. Papers by Dijkstra et al. (1997) and Pollott (2000) have attempted to statistically model milk production throughout lactation in terms of the underlying biology, rather than by the more common empirical methods (see Masselin et al., 1987 for a review). Daily milk yield throughout lactation can be thought of as the result of three processes; mammary cell differentiation in pregnancy and early lactation, cell death (apoptosis) throughout lactation and the secretion rate of differentiated mammary cells (Figure 1).
Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 2002. Session 1, , 1.39, 2002
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