Influence of exogenous estradiol on the concentration of antitrypsin, albumin, N-acetyl-beta-D-glucosaminidase and somatic cells in milk of cows at various lactation stages.

Estradiol benzoate (0.02 mg/kg of body weight) was injected (i.m.) daily to 13 ovariectomized cows in their first or third lactations during early (60-90 days), mid (140-200 days) and late (240-300 days) lactation. The majority of the udder quarters were free of bacteria throughout the experiment. Signs of clinical mastitis were observed after 9-19 days of treatment in cows at mid and late lactation. This was accompanied by a decrease in milk yield, an increase in milk somatic cell count (MSCC) and increases in milk concentration of antitrypsin and serum albumin (as indicator of increased permeability); and milk NAGase activity (as indicator of epithelial cell damage or release of the enzyme from phagocytes). NAGase activity was first to increase and on some occasions was not accompanied by an increased MSCC. The response was either absent (first lactation) or relatively mild (third lactation) in cows at the early stages of lactation. The intensity of the inflammatory response increased with advancing lactation stage. Generally, the response of cows in the third lactation was greater than that of cows in the first lactation at a corresponding stage of lactation. Three cows which received the control treatment with vehicle alone showed no changes in any of the parameters except a slight decrease in antitrypsin. All inflammatory indicators correlated negatively with quarter milk production; milk NAGase activity was superior in this respect (r = -0.75). All correlation coefficients were generally higher after, rather than before the hormone treatment.