| The experiment was carried out to investigate the roles and mechanisms of grape seed extract (GSE) in attenuating heat stress of beef cattle. Forty healthy Simmental×Native cattle with the similar age and weight (410±6.0kg) were randomly divided into4groups (10cattle per group), and assigned to four diets: control group (CON, basal diet), chromium nicotinate group (CN, basal diet+chromium nicotinate (33mg/d·cattle)), grape seed extract group (GSE, basal diet+GSE (650mg/d·cattle)), chromium nicotinate and grape seed extract group (CN+GSE, basal diet+chromium nicotinate (33mg/d·cattle)+GSE (650mg/d·cattle)). The experiment lasted35d including7d adaptation period. The daily feed intake per cattle was accurately recorded during the experiment. The cattle were weighed on d1and d28. Blood samples were collected from jugular vein on d1, d14and d28. On d29before feeding,6cattle were randomly selected from each group to be slaughtered, and the samples of jejunal epitheliam, liver and longissimus dorsi were collected.The results showed that the average daily gain and dry matter intake of cattle were significantly increased by supplementing CN, GSE or both CN and GSE (P<0.05). Villus height of jejunal mucosa of cattle in groups of GSE and CN+GSE was significantly higher than that of cattle in CON group (P<0.05), however, there were no significant difference in the villus height between CON group and CN group (P>0.05). Villlus width of jejunal mucosa of cattle was significantly increased by supplementing CN, GSE or both CN and GSE (P<0.05). The number of goblet cells and lymphocytes in jejunal mucosa were not affected by supplementing CN, GSE or both CN and GSE, however, there were a tendency of rising for these iteThe concentration of total protein in serum of cattle was significantly increased by supplementing GSE or both CN and GSE(P<0.05), and the activity of alanine transaminase in serum of cattle was significantly decreased (P<0.05). When compared to CON group, the concentrations of growth hormone, glucose, triglycerides and the activity of alkaline phosphatase in serum of cattle in groups of CN, GSE or CN+GSE were significantly greater (P<0.05), and the concentrations of blood urea nitrogen, cortisol, insulin and high-density lipoprotein cholesterol in serum of cattle were significantly less (P<0.05). The concentration of cholesterol in serum of cattle in groups of CN or CN+GSE was significantly greater than that of cattle in CON group (P<0.05). The trypsin activity in jejunum of cattle in groups of CN, GSE and CN+GSE was higher than that of cattle in CON group (P<0.05). The amylase activity in jejunum of cattle was significantly increased by supplementing GSE or both CN and GSE (P<0.05), however, the amylase activity was not affected by supplementing CN (P>0.05). The lipase activity in jejunum of cattle was not affected by supplementing CN, GSE or both CN and GSE, however, there was a tendency of rising.Supplementing CN, GSE or both CN and GSE significantly increased the activities of glutathione peroxidase, catalase and total superoxide dismutase in serum and liver of cattle (P<0.05), and significantly decreased the concentrations of malondialdehyde and8-hydroxydeoxyguanosine (P<0.05). The concentration of interleukin10(IL-10) in serum, jejunum and muscle, and the mRNA expressions of peroxisome proliferator-activated receptor-y and peroxiredoxin1in muscle of cattle were significantly increased by supplementing CN, GSE or both CN and GSE (P<0.05). The concentrations of tumor necrosis factor a, IL-6and IL-1β in serum, jejunum and muscle, and the mRNA expressions of heat stress protein70and toll-like receptor4in muscle, and inducible nitric oxide synthase in liver of cattle in groups of CN, GSE and CN+GSE were significantly less when compared to CON group (P<0.05).Overall, GSE can effectively attenuate the responses of cattle induced by heat stress. The present study also shows that the main reasons for the attenuated heat stress by supplementing GSE were attributed to the increased antioxidant capability and reduced levels of inflammatory cytokines in blood and tissue of cattle. Therefore, GSE can be used to anti-heat stress additive in the ruminant production in regions of high temperature and humidity. |
