Effects Of Acute Heat Stress On Meat Quality And Peroxidation In Broilers Fed Different Sources Of Fat

The objective of this study is to investigate the peroxidative status and the change of meat quality in broilers under simulation of the acute heat stress. The cell culture technology was employed to simulate the acute heat stress in vitro. The results suggested that lipid peroxidation is one of the main reasons for the reduction of the meat quality under the condition of acute heat stress. In the development of lipid peroxidation, the signal transduction pathway of GSH/GSSG was activated. The high unsaturated fatty acid diet exaggerated peroxidation injury. Vitamin E could effectively remit the injury of the acute heat stress.Experiment 1. Effects of acute heat stress on meat quality and peroxidation in broilers fed different sources of fatThis experiment was designed to examine the effects of acute heat stress on meat quantity and preoxidative status in broilers fed different fat sources. Four hundred and eighty day-old Arbor Acres(AA) broilers were divided into 8 groups including normal temperature (negative control) and high temperature (positive control) that were given basal diet, as well as 5％tallow, 5％corn oil, 5％conjugated linoleic acid (CLA), 5％tallow+400mg/kg vitamin E, 5%corn oil+400mg vitamin E, 5％CLA+400mg/kg vitamin E. On day 42 d of age, the birds of the high temperature positive control groups were exposed to 38℃for 6 hours, and then parameters of meat quality and lipid preoxidation were examined.Results: The acute heat stress significantly decreased the pH of muscles and the water holding capacity of meat (P＜0.05). However, the shear force of meat was not significantly affected (P＞0.05) by the acute heat stress. Chicks fed corn oil had the lowest pH value and water holding capacity of meat among all the groups. Compared to the groups without vitamin E, the pH of muscles and the water holding capacity of meat of the groups that contained vitamin E had a good Conditions (P＜0.05). The activities of total superoxide dismutase (TSOD) and glutathione peroxidase (GSH-Px) of the serum, liver and muscle were significantly influenced by the acute heat stress (P＜0.05). Among all the groups, coil oil group showed the lowest activities of TSOD and GSH-Px (P＜0.05), followed by the positive control group, tallow group and CLA group. The activities of TSOD and GSH-Px of the groups with vitamin E were higher than other groups(P＜0.05). The activities of catalase (CAT) were similar among all the groups (P＞0.05). The changes in contents of malondialdehyde (MDA) of the serum, liver and muscle were opposite to those of the activities of TSOD and GSH-Px. It seems that coil oil group had the highest content of MDA and the groups with vitamin E had lower content of MDA than other groups (P＜0.05).Conclusions: Acute heat stress induced lipid peroxidation, hence degrading meat quality. During the acute heat stress, supplementation of corn oil aggravated the negative effects of acute heat stress. Contrary to the corn oil, CLA and tallow alleviated the heat stressful effects. Dietary supplementation of vitamin E could lighten the loss induced by heat stress and improved the meat quality. Heat stress might partially worsen meat quality due to lipid preoxidation.Experiment 2. Effect of different types of fatty acids on peroxidation of skeletal muscle satellite cells of broiler chicks exposed to acute heat stressThis experiment was conducted to compare the effects of different types of fatty acid on peroxidation of broilers' skeletal muscle satellite cells exposed to acute heat stress. Non-stress control groups A-R and acute heat stress groups A1-R1 were arranged in this experiment. All the groups contained the DMEM culture. Group A was without other elements. Groups B-E, G-J comprised Linoleic acid (LA), Conjugated linoleic acid(CLA), Palmitic acid(PA), or Stearic acid( SA)at 0.5mmol/L. Groups K-N, O-R respectively contained LA, CLA, PA or SA at 0.25mmol/L. With the above component, groups F, G-J and O-R were all comprised lg/L vitamin E.The element of groups A1-R1 were the same as that of the groups A-R respectively. Skeletal muscle satellite cells of 1 day-old Arbor Acres (AA) broilers were isolated and cultured, and culture fluids were changed when the cells were fusion. After 24h, groups A1-R1 were exposed to the atmosphere of 42℃for 3h.Results: Acute heat stress markedly increased the degree of lipid preoxidation and cells damage (P＜0.05). The glutathione (GSH) content in the cells were significantly decreased in heat stress exposed groups, and the lipid peroxidation process activated the GSH/GSSG signal transduction pathway. The content of lipid peroxidation and trypan blue dying rate of cells in groups contained LA were higher than those of other groups, and the cell proliferative activity was significantly lower than that of the other groups (P＜0.05). The degree ofpreoxidation of cells in groups with PA, SA, CLA was alleviated largely (P＜0.05). Addition of vitamin E markedly relieved the extent of cells damage by heat stress (P＜0.05). There were significantly interactions between heat stress and types of fatty acids, heat stress and vitamin E, heat stress and the dosage of fatty acids on the trypan blue dying rate, cell proliferative activity, the content of MDA and GSH (P＜0.05).Conclusions: Acute heat stress induced the lipid peroxidation process, leading to cells damage with the apoptosis. During the development of peroxidation stress, signal transduction pathway was actived. Under the acute heat stress, vitamin E could effectively reduced the degree of lipid peroxidation, alleviated the cell injury compared to groups without vitamin E. Additon of high dosage of unsaturated fatty acids leaded to more serious injures of cells the that of low level of unsaturated fatty acids. Contrary to the unsaturated fatty acid treated groups, low level of saturated fatty acids induced the more serious damage of cells.