Factors Influencing Periparturient Neutrophil Function in Dairy Cows

Many diseases and conditions of economic importance in dairy cattle occur most commonly during the immediate postpartum period. Kehrli et al1 found neutrophil function to be impaired during this period. These authors described periparturient depression of random migration, bacterial ingestion, chemiluminescence, iodination and cell-mediated cytotoxicity. In this study, heifers which had postparturient intramammary infections also suffered the most severe peripartum alteration of neutrophil function. This supports the contention that neutrophil function is an important element in the first-line defense of the body against bacterial infection. Impaired neutrophil function during the periparturient period may contribute to the peculiarly high incidence of bacterial infections during this period.1 The incidence of disease in periparturient cows is further influenced by other factors, including parity and the occurrence of retained fetal membranes (RFM). Epidemiological studies have linked advancing parity to an increasing incidence of several disorders. Thus the lactational incidence risk of retained fetal membranes and ovarian cysts increased with advancing parity in a study of over 61,000 lactations in a population of Finnish Ayrshires.2 A separate study found that advancing age of dairy cows was associated with increased incidence of retained fetal membranes and mastitis. Retained fetal membranes, in turn, predispose to a host of other reproductive disorders including metritis, silent heat and undiagnosed infertility2 and mastitis.4,5 Even when controlling for the effects of specific, diagnosed diseases, advancing parity was associated with reduced reproductive efficiency. These authors speculate that this may be related to subclinical reproductive tract lesions. In itself, RFM is relatively innocuous. The retained membranes are unsightly, often fetid, and aesthetically objectionable for many milkers, but the effect of uncomplicated RFM on the cow is minimal. The major significance of RFM is in the mediation of more severe conditions. Thus, cows which have suffered retention of fetal membranes are at significantly increased risk for developing metritis2,3,7, ketosis3, mastitis2,4,5 and even subsequent abortion in the following pregnancy.2 Schukken, Erb and Smith5 studied the relationship between RFM and mastitis in a population of commercial dairy cows. They found that cows which retained the fetal membranes were at a higher risk (relative risk= 1.5) of developing mild mastitis, and at a much higher risk (relative risk = 5.4) of developing severe mastitis with systemic manifestation than were cows not retaining the membranes. A further finding was that longer duration of placental retention was associated with greater likelihood of mastitis. In a follow-up study in a hospital-based population, this group confirmed these results.4 These authors speculate that the relationship between retained placenta and mastitis is mediated by deficient peripartal peripheral neutrophil phagocytic activity. In 1984 Gunnink proposed that deficient neutrophil activity was a factor in the pathogenesis of RFM in cattle.8-10 He showed that circulating leukocytes from cows with RFM showed diminished chemotactic responses to cotyledon suspensions in vitro.8 He further demonstrated that this impaired chemotactic response existed before parturition9 and that it persisted at least 10 days into the post-partum period.10 Heuwieser and Grunert11 have also reported impaired neutrophil migration in cows which retained fetal membranes. We therefore designed experiments to determine whether periparturient neutrophil function was influenced by parity of the cow or by RFM as part of a project aimed at illuminating pathophysiological factors with epidemiological observations.