Abstract
A model for comparing resistance to Salmonella Enteritidis was evaluated in different broiler breeds. The recruitment and phagocytic activity of peritoneal macrophages were assessed in three different broiler breeds (A, B and C) which are farmed world-wide. Assessment was performed after three days of intraperitoneal (i.p.) administration of 3% Sephadex G-200 (10 ml), initiated at twenty-one days of age, followed by contact with i.p. live S. Enteritidis (10 ml, 1.2 x 10(8) colony forming units/ml) for 45 min. Assessment included determination of the number of i.p. macrophages recruited, the number of i.p. phagocytized S. Enteritidis cells per macrophage, the levels of degranulated i.p. beta-glucuronidase and beta-galactosidase, and the count of surviving S. Enteritidis cells. Confirmation of the significance of the model was obtained by comparing resistance to field infection by S. Enteritidis in the three broiler breeds. The recruitment of i.p. macrophages in response to challenge with Sephadex and S. Enteritidis was significantly higher (P < 0.05) in birds of breed A (mean cumulative i.p. macrophage count, in 10 fields of microscopic slide smear magnified at x1,000, was equal to 81.7), compared to recruitment in birds of breed B (33.3) or breed C (41.2). The mean number of phagocytized S. Enteritidis cells per i.p. macrophage in birds of breed A (2.68) was significantly higher (P < 0.05) than in breed B (0.83) and insignificantly higher (P > 0.05) than in breed C (2.35). In addition, the highest level of recruitment and phagocytic activity of macrophages, in birds of breed A, was associated with a higher significant mean i.p. beta-glucuronidase activity (10,425.5 units/ml) than in breed B (3,438.2 units/ml) or breed C (3,356.94 units/ml) (P < 0.05). Moreover, birds of breed A demonstrated a higher mean i.p. beta-galactosidase activity (2.225 units/ml) than birds of breed B (0.852 units/ml) or breed C (1.852 units/ml) (P > 0.05). The higher level of recruitment and activity of i.p. macrophages and the higher rate of degranulation of i.p. enzymes in breed A were associated with a greater number of surviving i.p. S. Enteritidis cells. In response to outbreaks of S. Enteritidis in the field, the average mortality was significantly higher in flocks of breed A (3.2%) than in flocks of breed B (1.2%) or breed C (0.96%) (P < 0.05). These data provide an indication of the significance of the model in reflecting the differences in resistance of S. Enteritidis of broiler breeds reared in a farm environment.