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摘要
The present study was conducted to investigate the effects of dietary supplementation of chromium methionine (CrMet) on performance, immune responses, and stress status of broiler chicks subjected to heat-stress conditions. A total of 450 day-old Ross 308 broiler chicks were randomly distributed between 5 replicate pens (15 birds each) of 6 experimental treatments according to a 2 x 3 factorial arrangement of treatments including 2 temperature conditions (thermoneutral and heat stress) and 3 supplemental Cr levels (0, 500, and 1,000 mu g/kg as CrMet). For induction of heat stress, the house temperature was set at 35 +/- 2 degrees C from 15 to 42 d of age. Results showed that the chicks subjected to heatstress condition had lower (P < 0.01) feed intake, BW gain, and deteriorated (P < 0.05) feed conversion values compared with those kept in the thermoneutral house. Dietary supplementation with CrMet increased (P < 0.01) feed intake and improved (P < 0.01) weight gain and feed efficiency. There were significant Cr level x temperature interactions, so that inclusion of CrMet into the diets was more effective in heat-stressed chicks. Exposure to heat stress sup-pressed (P < 0.01) cutaneous hypersensivity response to phytohemagglutinin-P injection at 30 d of age, and dietary supplementation of 500 mu g Cr/kg induced (P < 0.05) this response, with the greater impacts in heat-stressed chicks, resulting in a significant (P < 0.01) Cr x temperature interaction. Antibody responses against Newcastle and infectious bronchitis disease viruses were diminished (P < 0.01) in heat-stressed chicks. Dietary inclusion of CrMet improved (P < 0.05) antibody responses to different immunostimulants, and this effect was more pronounced in heat-stressed chicks. Exposure to heat stress caused a significant (P < 0.05) decrease in the proportion of helper (CD4(+)) T lymphocytes and increased cytotoxic (CD8(+)) T lymphocytes, resulting in a decreased (P < 0.01) CD4(+) to CD8(+) ratio in peripheral blood circulation. Supplementation of CrMet to heat-stressed chicks modulated (P < 0.01) plasma corticosterone level. The present findings indicate that dietary CrMet supplementation could alleviate heat-stress-induced growth retardation in broiler chicks. Moreover, supplemental CrMet modulated suppressive effects of heat stress on cellular and humoral immune responses.
- 出版日期2015-7
