Influence of day in milk and parity on milk and plasma IgA in dairy cows

Seven primiparous (PR) and 7 multiparous (MU) Fresian cows were studied for 3 months after calving. Cows calved between January and February 2010. On day 0, 1, 3, 7, 30, 60 and 90 of lactation, milk yield was recorded, milk and blood samples were taken. Milk samples were obtained mixing morning and evening milkings and then tested for total bacterial count. Skimmed milk and plasma were tested for IgA by ELISA. Maximum daily milk production was observed on day 30 for MU cows (43.3 l/d) and on day 60 for PR ones (40.5 l/d). On day 0, 60 and 90 total bacterial count was lower in milk from PR cows (P=0.06. Concerning milk and plasma IgA, in both groups highest levels were found at calving. The day after parturition IgA concentrations dramatically decreased in both plasma and milk, remaining at low levels for the rest of the study period. On calving day plasma IgA was higher (P<0.01) in PR than in MU cows (137 vs 46.4 µg/ml), whereas milk IgA was lower (P<0.01) (640 vs 782 µg/ml). Milk IgA was positively correlated to plasma IgA (P<0.01) during the first month of lactation, and negatively related to bacterial count (P<0.05) after the first month. In conclusion, this study gives a description of the pattern of IgA in plasma, colustrum and milk of dairy cows during the first months of lactation and its relation to milk bacterial count and parity.