| Objective: The heat stress of dairy cows refers to the high-temperature stimulation of cows that exceed their body temperature regulation ability,causing non-specific response of the body.The heat stress can cause metabolic disorders,decline in production performance,and weakened immunity,thus seriously affecting the health of dairy cows.With the global warming,the impact of heat stress on dairy cows has become increasingly serious,causing huge losses to the development of dairy industry.In the measures to prevent and control heat stress,feed additives are increasingly favored by people because of their advantages such as low dosage,significant effect and convenient use.The purpose of this study is to develop a formula of anti-heat stress feed additives for dairy cows and evaluate its anti-inflammatory and antioxidant abilities,as well as its effects on production performance,energy metabolism and immune status of dairy cows,in order to find a feed additive that can alleviate heat stress of dairy cows.Method: In an intensive pasture with 1,000 dairy cows in daqing city,heilongjiang Province,26 healthy cows lactating for 173±13 days were selected.And they were divided into two groups,control group and feeding group,with 13 cows in each group..In the feeding group,300 g of feed additive per head(mainly composed of vitamin E,chromium methionine,glucose,magnesium oxide,urea,etc.)was mixed with the basal diet,and the control group was fed with basal diet and 300 g of corn.The composition of the basal diet was based on the diet of the cattle farm and was fed in a fully mixed diet(TMR)with free accessed to water.The feed additives were mixed in a portion of TMR and fed once a day at 5:00.Blood was collected before feeding and milked for 30 minutes.The experiment was divided into feeding period of 35 days and stopping feeding period of 7 days.The milk yield of 26 heads was measured before the start of the experiment,and the milk yield was recorded on the 7th day,the 14 th day,the 21 st day,the 28 th day,the 35 th day and the 7th day after the end of the experiment.The milk fat rate,milk protein rate,fat egg ratio and urea nitrogen content were measured by the milk composition analyzer.The analyzer measured milk fat percentage,milk protein rate,fat egg ratio,and urea nitrogen content.10 ml of blood was collected from the tail vein on the 0th,5th,10 th,15th,20 th,25th,and 30 th day of the test period.After natural coagulation,centrifuged at 4000 r/min for 10 min at room temperature,and the supernatant was placed in EP.Inside the tube,it was stored in the refrigerator for inspection.At the end of the experiment,the collected serum was tested for physiological and biochemical indicators.The indicators were Superoxide dismutase(SOD),Glutathione peroxide dismutase(GSH-PX),Malondialdehyde(MDA),free fatty acid(NEFA),?-hydroxybutyrate(BHBA)and stress protein70(HSP70),albumin,globulin,immunoglobulin G(IgG)and immunoglobulin M(IgM).Results: 1.The feed additive could alleviate the heat stress of cows,and the difference of HSP70 in blood of cows in the feeding group was extremely significant on the 10 th and 20 th days(P<0.01),which was lower than that in the control group.The difference between day 5 and day 30 was significant(P<0.05).2.The feed additive used in this test could increase the milk production by 2.28 kg/d during heat stress.3.The feed additive could optimize the quality of the milk.The milk fat percentage of the feeding group during feeding was significantly higher than that of the control group(P<0.05).4.The feed additive could improve the antioxidant capacity of lactating dairy cows.The difference of SOD in the blood of the feeding group was extremely significant at 10 th,15th,20 th,25th and 30 days(P<0.01),and the MDA of the blood was 15 in the blood.The difference between 20 and 30 days was extremely significant(P<0.01),which was significantly lower than that of the control group on the 10 th day(P<0.05).5.The feed can reduce the occurrence of energy metabolism disorders in dairy cows and improve the health of dairy cows.The BHBA and NEFA in the blood of the feeding group were lower than those in the control group,and the BHBA in the blood of the feeding group was significantly different at the 5th,10 th,and 20 th day(P<0.01),which was lower than that of the control group.NEFA was significantly different at 10 d and 20 d(P<0.05).6.There were no significant differences in blood globulin,white egg ratio,total protein,IgG and IgM.In summary,the feed additive has the effects of improving production performance,alleviating the symptoms of heat stress in cows,and improving metabolism of the body.Results: 1.Feeding the additive can reduce the heat stress state of the cow.2.This feed additive can increase lactation output and milk fat composition of dairy cows during lactation period.3.This feed additive can improve the antioxidant level of dairy cows,thereby improving the health level of dairy cows.Therefore,this feed additive has a certain protective effect on the heat stress of lactating cows. |
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