Effect of dietary supplemental levels of vitamin A on the egg production and immune responses of heat-stressed laying hens.
Two experiments were conducted to evaluate the effect of vitamin A supplementation of a commercial layer diet on the laying performance and immune function of heat-stressed hens. In Experiment 1, two different levels of vitamin A supplementation (3,000 and 9,000 IU/kg) were used to investigate the laying performance and antibody titer against Newcastle disease virus (NDV) of heat-stressed hens. Results showed that the high level of vitamin A supplementation (9,000 IU/kg) had a beneficial effect on the feed intake and laying rate of heat-stressed hens (P < 0.05), compared with the control group (3,000 IU/kg). The antibody titers were not influenced by the level of vitamin A (P > 0.05). In Experiment 2, the effect of four levels of vitamin A (3,000, 6,000, 9,000, and 12,000 IU/kg) on the antibody titer to NDV and T lymphocyte proportion was studied. The experimental birds were exposed to a high temperature (31.5 C) 15 d after NDV vaccination (Treatment 1) or immediately (Treatment 2). The results showed that the egg weight was increased (P < 0.01) by the high levels of vitamin A supplementation (6,000 and 9,000 IU/kg), but feed intake, laying rate, and body weight loss were not (P > 0.05). In Treatment 1, vitamin A had no significant effect on antibody titers against NDV in normal or hot environments but increased (P < 0.01) the proportion of alpha-naphthyl acetate esterase (ANAE)-positive cells. Vitamin A supplementation had a significant effect on NDV antibody titer and ANAE-positive cell proportion in Treatment 2 (P < 0.01). The results of the present study suggested that vitamin A supplementation in commercial layer diets to layer chickens under heat stress was beneficial to laying performance and immune function.
Lin
H
H
Department of Animal Science, Shandong Agricultural University, Taian, P R China. hailin@sdau.edu.cn
Wang
L F
LF
Song
J L
JL
Xie
Y M
YM
Yang
Q M
QM
D000821:Animal Feed; D000818:Animals; D000914:Antibodies, Viral / Q000097:blood* / Q000187:drug effects; D002645:Chickens / Q000276:immunology / Q000502:physiology*; D019587:Dietary Supplements; D004305:Dose-Response Relationship, Drug; D004306:Dose-Response Relationship, Immunologic; D004531:Eggs; D005260:Female; D018882:Heat Stress Disorders / Q000276:immunology / Q000503:physiopathology / Q000662:veterinary*; D006358:Hot Temperature / Q000009:adverse effects*; D018655:Lymphocyte Count / Q000662:veterinary; D009522:Newcastle disease virus / Q000276:immunology*; D010058:Oviposition / Q000187:drug effects; D013601:T-Lymphocytes / Q000276:immunology; D014801:Vitamin A / Q000008:administration & dosage*
D000914:Antibodies, Viral; D014801:Vitamin A