Effect of induced molting in laying hens on production and immune parameters.

A total of 600 commercial strain (DeKalb) Single Comb White Leghorn hens, 80 wk of age, were used in this study to determine the effects of different induced molting programs on production and immune parameters. The hens were randomly divided into four treatment groups (three experimental and one control) of 150 hens each. The hens in the first treatment group were fed a layer ration containing 20,000 ppm of zinc for 5 d, and received a reduced photoperiod of 8 h/d for 5 d (Zn group). In the second group, feed was withdrawn for 10 d, the photoperiod was reduced to 8 h/d and oyster shell and water were provided for ad libitum consumption. At Day 11, hens consumed corn and oyster shell ad libitum until Day 30 and at Day 31, hens were returned to a full feed layer ration and received 16 h of light/d [California treatment (CAL group)]. In the third treatment, light was reduced to 8 h/d, and oyster shell was provided for ad libitum consumption until Day 60. Feed and water were removed for the first 2 d and on Days 4, 6, and 8. On Days 3, 5, 7, and 9, hens were fed 45 g of feed per hen. On Day 10 until Day 60, hens were fed 90 g/hen and at Day 61, hens were returned to the layer ration ad libitum and received 16 h of light/d [on-again, off-again program (ON-OFF group)]. The last group served as controls (CONT). Body weight, egg production, egg size, internal egg quality, shell weight, and mortality were determined. Total circulating leukocytes, differential leukocyte counts, and antibody production were also measured. The results demonstrated that induced molting significantly increased egg production from 64% to 77 to 83%, Haugh units from 80.4 to 85.9 to 87.3, and shell weight from 5.3 g to 6.3 to 6.4 g when compared to CONT. The body weight of the molted hens decreased significantly to 84.8, 74.5, and 88% of the initial body weight for Zn, CAL, and ON-OFF groups, respectively. The total circulating leukocytes was significantly lower in molted hens than in CONT hens. Differential leukocyte counts were affected by all induced molting programs and the heterophil to lymphocyte ratio was significantly increased, reaching 0.61, whereas that of CONT was only 0.20. Antibody production was largely unaffected by any of the induced molting programs