Effect of parity and day of lactation on cell content in colostrum and milk of dairy cows

Fourteen cows, 7 at 1st and 7 at 2nd or 3rd calving, were considered. On day 0, 1, 3, 7, 30, 60 and 90 of lactation, colostrum and milk samples were taken. Each sample, obtained mixing morning and evening milkings, was tested for protein, fat, lactose, casein, urea, SCC (somatic cell count) and TBC (total bacterial count). Colostrum and milk somatic cells were isolated and immunocytochemically stained to identify epithelial cells, using an anti-cytokeratin antibody. After inspection by optical microscopy, the cytological slides were classified for increasing estimated percentage of epithelial cells over the total visible cells. Data were evaluated by ANOVA or 2 test. Results indicated that in most of the samples of the first week after calving the intact epithelial cells were very rare. By contrast, on days 30, 60 and 90, in many slides the epithelial cells, although generally less abundant than leukocytes, were a large part of the total cells. However, on days 0 and 1, high percentages of epithelial cells were more frequently present in colostrum of multiparous cows than primiparous ones (P<0.05). Furthermore, at parturition the total SCC was higher in the primiparous than multiparous cows (P<0.01), even if on days 0, 60 and 90 the primiparous cows had lower TBC (P=0.07) than the multiparous ones. Results suggest that milk total cell content is not merely a marker of mammary inflammation state and, like the content of epithelial cells, it may be influenced by different factors, including parity and lactation stages.