| The aim of this research was to search methods to alleviate heat stress in dairy cattle. The difference between endotoxin concentration,MDA concentration,activity of SOD and GSH-Px in plasma of diary cattle in winter and summer were conduct investigated.On this basis,dairy goats with indwelling catheters in aportal vein, mesenteric vein, carotid artery were used as a model to investigate where the endotoxin in portal vein comes from,the effect of heat stress on the net absorbtion of endotoxin across MDV and PDV,plasma flux,,MDA,TAP,SOD,GSH-Px,CAT flux,and the relationship between gastrointestinal permeability changes and oxidative stress in heat situation.Then Three Saanen dairy goats with indwelling catheters in the portal vein, and carotid were used to investigate the effect of yeast culture,VE supplement on dry matter intake, rectum temperature and respiration frequency,net absorbtion of endotoxin across PDV,and the concentration of endotoxin in portal vein and carotid in heat situation,the dynamic changes of concentration of MDA,TAP,SOD in portal were also investigate.At last,dairy cattles were used to investigate the effect of yeast culture and selenium yeast supplement on dairy cattles subjected to heat stress. The main research contents and results are as follows:1,The investigate about the effect of heat stress on blood endotoxin level and anti-oxidation level in dairy cattle16 healthy Holstein cows were divided into the summer group (in August) and winter group (12 months), each treatment with eight repetitions, a cow each repetition.Summer, when the dairy cow-house temperature and humidity index (THI)> 72 up to 15 consecutive days, winter, when the cow-house THI<72 up to 15 consecutive days,15mL jugular vein blood was taken.endotoxin level in plasma, Superoxide Dismutase (SOD), total antioxidant activity (TAP), glutathione peroxidase (GSH-Px) activity, and malondialdehyde (MDA) content in plasma were detected. The results show that:in summer, cow plasma endotoxin, MDA content was highly significantly (p<0.01)higher, SOD activity was highly significantly (p<0.01) lower, TAP and GSH-Px activity was significantly (p<0.05) lower than in winter. 2,Effect of heat stress on endotoxin and redox flux across mesenteric-drained and portal-drained viscera of dairy goatThree Saanen first lactation dairy goats were surgically fitted with indwelling catheters in the portal vein, the mesenteric vein and carotid. After 3-week recovering the goats were subject to a 6-day experiment stage. On the third day of experiment stage, all the goats were blood sampled 6 times from 8.00 to 20.00 at 2-hr interval. Room temperature was controlled at 24℃during recovering and the first 5 days of experiment stage. On the 6 day of experiment stage, all the goats were blood sampled 12 times from 8.00 at 2-hr interval, and room temperature was adjusted to 35℃at the beginning of the day and kept for 24 hr. With the prolonged heat stress, plasma flux rate in portal and mesenteric vein kept on decreasing, while plasma endotoxin concentration in arterial, portal and mesenteric venous kept on increasing. Net absorption of endotoxin across MDV and PDV began increasing after 4-hr exposure in heat environment. Average net absorption of endotoxin (EU/hr) across MDV and PDV in heat stress group during the whole period of heat stress increased by 279.05% and 227.92% compared to thermo-neutral group. Plasma concentration of GSH-Px and CAT in mesenteric and portal vein, and that of SOD in mesenteric vein, increased significantly during heat stress. Plasma concentration of TAP in mesenteric vein at different time of exposure in heat environment in heat stress group did not differ from the mean value in thermo-neutral group group, while that in portal vein at different time of heat exposure in heat stress group was always lower than the mean value in thermo-neutral group. Main conclusions were:1) net absorption of indotoxin in portal vein is mainly from Non- mesenteric tissues both in heat stress and in thermo-neutral condition; 2) Heat stress may lead to the significant decrease of plasma, TAP, SOD, GSH-Px, and CAT flux across PDV and MDV, and the significant increase of indotoxin flux across PDV and MDV; 3) the increase of gastrointestinal permeability in dairy goats during heat stress may not be induced by the increase of oxidative stress.3,The research about the effect of Supplementary feeding yeast culture, VE on dairy goats in heat stress situation Three Saanen (first lactation,average body weight 30 kg)dairy goats were surgically fitted with indwelling catheters in the portal vein,and carotid.3*3 Latin square experimental design was used.The three treatments were control group(C, fed basal diet),VE group (VE,on the base of basic diet each goat was supplementary fed 100IU VE per day), yeast group (Y, on the base of basic diet each goat was supplementary fed 15 grams of yeast culture per day).Each experiment lasted 4 days,4-day interval between the two. Yeast and vitamin E were fed at 8:00 every morning.After recovered,the goats were housed in single-cage in temperature-controlled room, the ratio of concentrate to roughage is about 5:5, record feed intake. The indoor humidity was controlled and maintained at 55% in all the experiment period,the temperature was 35℃during 08:00-20:00,24℃during20:00-08:OO.The 4th day of each exeperiment PAH was infused at 13:00 pm,2 hours later blood was taken,and then blood was taken at intervals of 1 hour,last for 12 times, rectum temperature and respiration frequency were measured at interval or 2 houes.During the interal of two trial, the indoor humidity was 55%, the temperature was 24℃.The results showed that: among the treatments,the plasma flow rate, dry matter intake was no significant difference (P> 0.05). rectum temperature and respiration frequency during the heat stress period and the whole term of the deal, the difference is not significant (P> 0.05), but in thermoneutral zone, the average rectal temperature of C group was significantly (p<0.05) higher than the VE group, and in thermoneutral zone,at different time points, the average rectal temperature of C group were significantly (P <0.01) higher than the VE group and Y group.the average respiration rate in thermoneutral zone, there was no significant difference (P> 0.05) among the treatments, but at some individual time points, C group was significantly (p<0.05) or very significantly (P<0.01) higher than the VE group and Y group. The net absorption of endotoxin, throughout the trial period, each time point, C group was the highest, VE was the lowest, Y group was middle; During heat stress period, the average net absorption of endotoxin,, C group was significantly (P<0.01) higher than the VE group and Y group; In thermoneutral zone, on average, three treatments were not significantly different (P> 0.05); the average of the whole term, C group was significantly (P<0.01) higher than the VE group, the difference between Y group and the other two groups were not significant.the average SOD activity concentrations of portal vein plasma,in heat stress period, C group was significantly (P<0.01) higher than the VE group and Y groups; In thermoneutral zone, on average, C group was significantly (p<0.05) higher than the VE group; The average of the whole term, C group was significantly (P<0.01) higher than the VE group and Y group.TAP concentration of portal vein plasma, each time point of the entire trial period, C group was the lowest, VE group was the highest, Y group was the middle; In heat stress period, the average, C group was highly significantly (P<0.01) lower than the VE group,was significant (p<0.05) lower than the Y group, Y group was significantly (P <0.01) lower than the VE group; In thermoneutral zone, on average,C group was significantly (p<0.05) lower than the VE group, the differences betweenY group and C group, Ygroup and VE Group were not significant (P> 0.05); the whole term,on average, C group was significantly (P<0.01) lower than the VE group, Y group was significantly (p<0.05) lower than the VE group, the difference betweenY group and C group was not significantly (P> 0.05).each time point of throughout the trial period, MDA concentration of the portal vein plasma, C group was the highest, VE group was the lowest, Y group was the middle; in heat stress period, on average, C group was highly significantly (P<0.01) higher than the VE group and Y group, Y group was highly significantly (P<0.01) higher than the VE group; in thermoneutral zone, C group was highly significantly (P<0.01) higher than the VE group and Y group,there was no significant difference (P> 0.05)betweenVE group and Y group; the whole term,on average, C group was highly significantly (P<0.01) higher than the VE groups and Y group, Y group was highly significantly (P<0.01) higher than the VE group. Experiment Conclusion:during heat stress, supplementary feeding VE, yeast culture could reduce rectal temperature, endotoxin concentrations in portal vein and carotid arteries, the net portal absorption of endotoxin and oxidative damage.4,The study about the effect of supplementary feeding yeast culture and yeast selenium on alleviating heat stress in dairy cows In this study, single-factor experimental design was used.Forty eight during d 120 to d 200 after postpartum, health, milk yield were 18kg to 22kg Holstein dairy cows in mid-lactation, which have similar milk yield, lactation period and parity,were divided randomLy into four groups, each treatment with six repetitions, two cows each repetition.:Se-Y group (on the base of basal diet,0.3g selenium yeast was added per kilogram of dry matter), YC group (on the base of basal diet,4g yeast culture was added per kilogram of dry matter), C group (fed the basal diet) and Se-Y+YC group (on the base of basal diet,4g yeast culture and 0.3g selenium yeast was added per kilogram of dry matter). The total experimental time were 47 days, include 7 days of preliminary experimental period and 40 days of formal experimental period.During the formal experiment period the temperature and relative humidity were recorded every two days, dry matter intake,rectal temperature and respiratory frequency were measured every 10 days. every 10 days milk yield was measured, every 20 days, milk composition were analysed, every 10 days 15mL blood was taken from Jugular vein for the analysis of plasma MDA, endotoxin content and SOD, GSH-Px activity. The results show that:in the formal experiment period, According to temperature and humidity index of, dairy cattle had been in a heat stress condition.The experiment group than the control group had increased in milk production, in which Se-Y group increased 5.67%(p> 0.05), YC group increased 2.06%(p> 0.05), Se-Y+YC group increased 8.25%(p<0.05); milk fat and lactose content among different groups were no significant difference (p> 0.05), but milk protein content of each experiment group were increased to some extent, in which Se-Y group, YC group, Se-Y+YC group than the control group,the rate of milk protein were increased by 4.0%(p> 0.05),7.7%(p<0.05) and 9.6%(p<0.05).The rectal temperature of experiment group was lower than the control group, in which Se-Y group was 0.33℃(p> 0.05)lower than control group, YC group was 0.27℃(p> 0.05)lower than the control group, Se-Y+YC group was 0.47℃(p<0.05)lower than the control group. Respiratory rate and dry matter intake among the treatments were no significant differences. GSH-Px activity concentration, Se-Y group, Se-Y+YC groups was significant (P<0.01) higher than YC group, C groups. SOD activity levels among the treatments were no significant difference (p> 0.05). Plasma MDA concentration, A, Se-Y+YC group was highly significantly (p<0.01) lower than C group, YC group was significantly (p<0.05 lower than C group. Plasma endotoxin concentrate, Se-Y group, YC group, Se-Y+YC group was highly significantly (P<0.01) lower than C group, the other three groups had no significant difference (P> 0.05).Study result:during heat stress period, added yeast culture in the diet can significantly increase the cows milk protein content and significantly reduce the blood MDA content, highly significantly low blood endotoxin concentration; during heat stress period, added yeast selenium in the diet can significantly increase Cows blood selenium content and glutathione peroxidase activity,highly significantly decreas blood MDA content and endotoxin concentration;during heat stress period, yeast seleniumand the combined effects of yeast culture can significantly increase milk yield and milk protein content, significantly low rectal temperature, significantly increase blood selenium content and glutathione peroxidase activity, significantly reduce MDA content in blood and endotoxin concentrations. Their combined effects was more effective than each of their separate application.In summary, heat stress caused decreased anti-oxidation function of dairy cows, increased plasma endotoxin levels. Enhance the body's antioxidant capacity, supplementary feeding yeast culture, can reduce the absorption of endotoxin in the heat stress situations, thus to some extent mitigate the impact of heat stress on dairy cows.
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