Milk and plasma IgG levels in primiparous and multiparous cows, during the first week of lactation

Bovines are born agammaglobulinemic and achieve immune protection by transport of colostral immunoglobulins into the bloodstream through intestinal epithelium. This transfer depends on initial permeability of intestinal mucosa and transcytotic mechanisms mediated by receptors. Despite immunoglobulin transfer ceases within 48 hours after birth, receptors persist into adulthood. In bovine colostrum/milk the predominant immunoglobulin is IgG (subclasses IgG1 + IgG2), which mainly derives from maternal blood. During the first week of age, interaction between ingested IgGs and intestinal receptors stimulates intestinal mucosa thickness and villi length of the newborn. During the first week of lactation, colostrum/milk and blood IgGs were analysed in 7 primiparous and 7 multiparous Fresian dairy cows, in order to identify factors affecting their level. All cows were fed a total mixed ration ad libitum. On day 0, 1, 3 and 7 of lactation, milk yield and composition were determined and colostrum/milk and blood samples were tested for IgG1 and IgG2 by ELISA. Data were analysed by the PROC MIXED RM method of SAS. Colostrum/milk yield ranged between 11.5 and 34.7 L/d, without differences between primiparous and multiparous cows, throughout the study period, but protein and casein were higher (P<0.05) in colostrum/milk of multiparous ones, from day 1 to 7. By contrast, on parturition day, fat (95.4 vs. 58.8 g/L, SE=9.35, P<0.01) and urea (0.81 vs. 0.65 g/L, SE=0.04, P<0.05) were higher in colostrum of primiparous cows. In both groups, maximum levels of IgGs were observed at parturition. Total IgG was twice higher in colostrum of primiparous cows (2.47 vs. 1.26 g/L, SE=0.30, P<0.05), but this difference was entirely due to IgG2 (1.20 vs. 0.37 g/L, SE=0.15, P<0.01), whereas colostrum IgG1 did not differ between groups.. In both groups, colostrum/milk IgG1 correlated (P<0.05) negatively with milk yield and positively with milk protein. In primiparous cows, colostrum/milk IgG2 correlated (P<0.01) negatively with milk yield and positively with milk urea. Maximum levels of blood IgGs were observed at parturition, without differences between groups. Results suggest that milk yield, protein and urea, parity and distance from parturition are all factors affecting the level of IgG in colostrum and milk. Results suggest that IgG1 and IgG2 are transferred from maternal blood into milk through different processes and the efficiency of IgG2 transfer seems to decrease with parity.