Mammary immunoglobulin transfer rates following prepartum milking

Colostrum formation is thought to occur slowly over an extended period (4 wk) prepartum. Furthermore, colostrum formation is highly variable among cows in total volume, IgG₁ concentration, and mass obtained at first postpartum milking. Recent work has suggested that a rapid transfer of IgG₁ to secretions may occur if animals are milked prepartum. Our objective was to establish the concentration, mass, and mass transfer rates of IgG₁ in multiparous Holstein cows (n = 11, parity = 3.6 ± 1.1) milked prepartum (−74 to −1 h) and again around 4 h postpartum. Blood concentrations of IgG₁ were very low (<1 mg/mL) in 7 cows at prepartum milking and did not decline following prepartum milking. Cows showed variability in the capacity to recover total volume, IgG₁ concentration, and IgG₁ mass. Three groupings of cows were considered based on the time between the 2 milkings (prepartum + 4 h postpartum): long-time (−74 to −54 h, n = 3), medium-time (−25 to −17 h, n = 4), and short-time (< −13 h, n = 4) groups. The average rates of transfer of these groups were 1.4 ± 0.8, 3.0 ± 1.3, and 25.1 ± 15.8 g/h, respectively. The data indicate that a longer time between prepartum and postpartum milking is not a main factor in IgG₁ secretion transfer. Furthermore, because blood concentrations did not change after prepartum milking and the mass of blood plasma IgG₁ was not sufficient to account for the mass occurring in postpartum colostrum, a source of IgG₁ other than blood circulation appears to be present during colostrogenesis.