EFFECTS OF DIETARY LEVELS OF VITAMIN-A ON THE EGG YIELD AND IMMUNE-RESPONSES OF LAYING HENS

This research, which was designed and carried out as two consecutive e xperiments, investigated the effects of four different levels (0, 4,00 0, 12,000, and 24,000 IU/kg) of vitamin A supplementation on egg yield , plasma vitamin A levels, and immune responses of laying hens. Transm ission of maternal immunity to their descendants was also studied. In the first experiment, egg yield, blood vitamin A levels, and various p arameters of the immune system such as T lymphocyte levels in the peri pheral blood, plasma cell counts in the spleen, and antibody titers ag ainst Newcastle Disease Virus (NDV) in the sera were investigated for a l-yr period. A total of 864 Hisex-brown laying hens were used in thi s experiment. The chicks were reared as commercial flocks until the 18 th wk of age. No significant differences occurred among the parameters of the different diet groups. In the second experiment, maternal immu nity was assessed in the chickens, supplied by hatching the eggs from hens in the first experiment. Maternal immunity was assayed by using t he parameters as in Experiment 1. For this purpose, both blood and tis sue samples were taken on the 2nd, 7th, and 10th d posthatch. Vitamin A supplementation had no significant effects on maternally, derived an tibody titers or histologic structure of the lymphoid organs.