Mammary development and regression during lactation in goats in relation to milk secretion.

Mammary development was assessed in lactating goats using a combination of biopsy (for analysis of nucleic acids) and udder volumes (for determination of gross size). Single biopsies were shown to be highly representative of the composition of the whole gland provided that they were taken from carefully selected sites. Results indicated an increase in both milk yield and the size of the mammary cell population ( DNAt ) over the first three weeks of lactation. Yield, but not DNAt , continued to increase until peak lactation at around week eight. As milk yield fell between weeks eight and twenty-three the size of the cell population also decreased; beyond week twenty-three and until week thirty-six DNAt stabilized but yield continued to fall. It is concluded that the first part of the increase in milk yield during ascending (early) lactation in goats can be attributed to proliferation of secretory cells, but subsequently there is an increase in the amount produced by each cell. Likewise, declining lactation is initially characterized by a loss of cells, and yield per cell falls later.