Influence of hatcher holding times on several physiological parameters associated with the immune system of chickens.

Two experiments were conducted with broiler chicks to study the effects of posthatch holding time in the incubator on physiological and disease parameters. In each experiment, half of the chicks were removed shortly after hatching and half of the chicks were allowed to remain in the hatcher for an additional 30 hr. Bursa weights, hematocrits, total plasma protein, and blood glucose concentrations were measured at various times up to 35 and 28 days of age in Experiments 1 and 2, respectively. In addition, chicks hatched from eggs with one of two specific gravities (less than or equal to 1.065 and greater than or equal to 1.075) were tested in the second experiment. Spleen weights, heterophil:lymphocyte ratios and the influence of an aerosol Newcastle disease-Mycoplasma gallisepticum vaccine challenge were also measured in the second experiment. In Experiment 1, when chicks were held in the hatcher for an additional 30 hr, bursa weights were reduced through 8 days of age; however, they were significantly heavier by 21 days of age. In Experiment 2, both bursa and spleen weights were significantly reduced through 14 days of age when chicks were held in the incubator. Total plasma protein and glucose concentrations, hematocrits, and heterophil:lymphocyte ratios were all significantly higher for chicks held in the incubator. Chicks held in the incubator and then exposed to an aerosol vaccine challenge at 1 day of age had a significantly greater percentage of air sac lesions and the lesions were more severe at 28 days of age. Egg specific gravity had no influence on any of the parameters measured.(ABSTRACT TRUNCATED AT 250 WORDS)