LACTATION STAGE-DEPENDENT CHANGES IN LEVELS OF TUMOR-NECROSIS-FACTOR CACHECTIN IN MILK

PROBLEM: Determination of lactation stage-dependent changes in levels of tumor neurosis factor (TNF) in milk. METHOD: Bioassay and immunoblo cking assay were used to identify and assay tumor necrosis factor (TNF ; mostly TNFalpha) in bovine milk at different stages of lactation. RE SULTS: TNFalpha levels in milk started to increase steadily after the onset of drying-off (weaning/involution), peaked at 4 to 6 wk prior to parturition and precipitously decreased to undetectable levels at par turition (colostrum). Thereafter, TNFalpha reappeared and maintained m idlevel concentration in the mature (normal) milk throughout the rest of the lactation cycle. Analysis of cells in mammary secretions by flo w cytometry revealed that elevated TNFalpha levels coincided with an i ncrease in macrophages in the secretion from the dry period. CONCLUSIO NS: These lactation stage-dependent changes in TNFalpha levels reflect differential effects that TNFalpha have on involution and prepartum r emodeling of the mammary gland of the dam and on gastrointestinal deve lopment and immunoregulatory function of the suckling.