BRIEF COMMUNICATION: The effect of re-milking following extended non-milking periods on the proliferation and apoptosis of mammary epithelial cells in dairy cows

In dairy cows, the increase in milk yield from parturition to peak lactation is attributed to an increase in the secretory activity of mammary epithelial cells (MECs) (Capuco et al. 2001). However, following peak lactation, there is a decline in milk production, which is attributed to the loss of MECs by programmed cell death or apoptosis (Capuco et al. 2001). The role of involution and the factors that regulate it in the bovine mammary gland are not well understood. Previous studies have characterised the process of involution in the bovine mammary gland by determining whether involution is reversible following an extended milk stasis. Involution was fully reversible following seven days of non-milking (Dalley & Davis 2006), but was only partially reversible following longer non-milking intervals (Noble & Hurley 1999; Singh et al. 2012). The aim of this study was to determine if the apoptosis and proliferation of MECs is reversible with resumption of milking following extended nonmilking intervals in pasture-fed cows.