Effects Of Heat Stress On Growth,production Performance And Blood Biochemical Indexes Of Cows And Calves During Dry Milk Period

The dry period is a crucial stage in the process of cow production.During this period,the fetus grows rapidly in the parent body,and the breast tissue also grows and develops.Cows exposed to heat stress during the dry period will produce less milk during the subsequent lactation process,resulting in impaired immune function and affecting the health and growth performance of the calves.Therefore,this paper is to study the effects of heat stress on the production,growth performance and blood biochemistry of cows and calves during dry period based on the test and research of the production performance of cows in dry period(summer calving,Heat stress,HT group),calve conditions,the blood routine examination and plasma biochemical indexes of dry cows within 1 week before parturition,1,7,14,28 and 56 days after delivery and calves before colostrum,3,7,14,28 and 56 days after feeding colostrum,comparing cows without heat stress during dry period(autumn calving,Cooling,CL group).The results are as follows:1.Determination of heat stress and its effect on cow rectal temperature in dry periodThe cowshed temperature-humidity index(THI)in summer and autumn were 71.64±0.43 and 63.01 ±0.10,respectively,showing significant difference(P<0.01).Rectal Temperature(RT)in dry period in summer and autumn was 39.02±0.19 and 38.95±0.01 degrees,respectively(P<0.01).The above results indicated that cows have been exposed to heat stress during the summer experiment,which can be used to evaluate the effects of heat stress on cows in dry period.2.Effects of heat stress on the performance of cows productionHeat stress in dry period has no significant effect on the colostrum Brix(P>0.05),but the qualified rate of cows colostrum in dry period decreased by 19.23%.The average milk production in the whole lactation period of the HT group was 34.89±0.57kg,and that in the CL group was 41.78±1.16kg.Heat stress in dry period had no significant effect on the average butterfat rate,milk protein rate and SCC(Somatic cell count)in the whole lactation cycle(10 lactation months)(P>0.05),but the milk protein rate and SCC in the HT group in the first lactation month were significantly higher than those in the CL group(P<0.05).3.Effects of heat stress on growth performance of calves.There was no significant difference in calf birth weight between summer and autumn(P>,0.05),and the 2-month weaning weight HT group I was significantly higher than the CL group(P<0.05).The body length of calves in the HT group at birth was not significantly different from that in the CL group(P>0.05),but the body height and chest circumference in the HT group at birth were significantly higher than those in the CL group(P<0.01).There was no significant difference in body height between the two groups at weaning(P>0.05),and the calf body oblique length and chest circumference in HT group were significantly higher than those in CL group(P<0.05).4.Effects of heat stress on blood biochemistry in cows.Heat stress in dry period significantly increases the dry cow monocyte percentage(P<0.01),and then early lactation average white blood cell count,neutrophil count decreased significantly(P<0.05),which leads to the average hemoglobin count,average RBC deposited,average red blood cell volume,the average amount of red blood cells,hemoglobin,platelet volume,and platelet distribution width significantly decreased(P<0.01),the average percentage of mononuclear cells and average red blood cell hemoglobin concentration significantly rise(P<0.05).Compared with CL group,1 d HT group in lactation average amount of red blood cell hemoglobin significantly reduce(P<0.05)in lactation 7 d monocyte percentage increase significantly(P<0.05),mammary 14 d monocyte percentage significantly increase(P<0.01),and the average red blood cell volume and the average red blood cell hemoglobin significantly decreased(P<0.05)in lactation 28 d of red blood cells deposited and platelet count decreased significantly(P<0.05),positive platelet pressure significantly reduced(P<0.01),on the 56d of lactation,the average HGB concentration increase significantly(P<0.01),the hematocrit,mean RBC volume,mean platelet volume and platelet width decrease significantly(P<0.01),and the platelet ocrit decreased significantly(P<0.05).Heat stress environment significantly affected the secretion of gonadotropin-releasing hormone in dry cows,resulting in a significant decrease in plasma tumor necrosis factor-α(P<0.01)and immunoglobulin G concentration(P<0.05).During the experiment,the average value of heat stress protein 70 in the blood of HT group was significantly different from that of CL group(P<0.01),indicating that dairy cows in HT group were affected by heat stress.After heat stress,the average values of corticotropin(ACTH),growth hormone(GH),and tumor necrosis factor-α(TNF-α)decreased significantly(P<0.05).In contrast,the average concentrations of lipid peroxides(LPO)and GnRH increased significantly,and the average contents ofβ-hydroxybutyric acid(BHBA)and insulin(Insulin)increased significantly(P<0.01).Compared with CL group,HT group in lactation 1 d BHBA significantly increased(P<0.05)in lactation 7 d of Hsp-70 increase significantly(P<0.05)in lactation 14 d significantly increase(P<0.05),Insulin ACTH decreased significantly(P<0.05),mammary 28 d BHBA,SOD and Hsp-70 concentration increased significantly(P<0.05),IgG significantly reduced(P<0.05),mammary 56 d BHBA,Hsp-70 and LPO concentration increased significantly(P<0.05).5.Effects of heat stress on plasma biochemistry in calves.The neutrophil count,neutrophil percentage,red blood cell count,hemoglobin count and hematocrit of calves born after heat stress in dry milk period increased significantly(P<0.01),monocyte percentage significantly increased(P<0.05).However,the absolute value of lymphocytes,the percentage of lymphocytes,platelet count and platelet deposited average decreased significantly(P<0.01).Compared with CL group,the percentage of neutrophils in HT group increased significantly(P<0.01)at 3 days old,while the absolute value of lymphocytes,mean erythrocyte hemoglobin and mean erythrocyte hemoglobin concentration decreased significantly(P<0.05),while lymphocyte percentage,platelet count and platelet pressure decreased significantly(P<0.01).When the 7 days of age,neutrophil percentage significantly increased(P<0.01),the absolute value of lymphocytes decreased significantly(P<0.05),and the percentage of lymphocytes decreased significantly(P<0.01).Within 14 days of age when the neutrophil count was significantly increased(P<0.05)and neutrophil percentage significantly increased(P<0.05),and the lymphocyte absolute value decreased significantly(P<0.05)and lymphocyte percentage significantly decreased(P<0.01),neutrophil percentage appear when 28 days of age significantly increased(P<0.01),red blood cell count,erythrocyte pressure hemorrhage red protein count increases significantly(P<0.05),Lymphocyte absolute value,platelet count and platelet deposited significantly reduced(P<0.05),lymphocyte percentage significantly decreased(P<0.01),neutrophil counts when 56 days of age,red blood cell count,erythrocyte deposited and hemoglobin count were significantly increased(P<0.01),neutrophil percentage increase significantly(P<0.05),lymphocyte percentage decreased significantly(P<0.05),red blood cell,platelet count and platelet distribution width positive pressure significantly reduced(P<0.01).The average value of Hsp-70 in the blood of calves exposed to heat stress during the dry milk period was significantly increased(P<0.01).Interferon y(IFN-y),GnRH,Insulin and LPO decreased significantly(P<0.05),ACTH decreased significantly(P<0.01),and Cortisol,GH and TNF-α concentrations increased significantly(P<0.05).Compared with CL group,TNF-αbefore feeding colostrum HT group significantly increased(P<0.05),in the age of 3,ACTH decreased significantly(P<0.05)and LPO significantly lower(P<0.01),when the age of 7,ACTH and TNF-α significantly reduced(P<0.05),Hsp-70 significantly increased(P<0.05),the age of 14,ACTH decreased significantly(P<0.05),Hsp-70 was significantly increased(P<0.05),the age of 28,SOD and TNF-α significantly increased(P<0.05),LPO significantly decreased(P<0.05),IFN-ysignificantly decreased(P<0.05),and IgG and GH significantly increased(P<0.05)at the age of 56 days.In summary,when THI>68,heat stress occurred in cows,which significantly increased the rectal temperature of dairy cows,decreased the qualified rate of colostrum and milk yield during lactation,significantly increased SCC,in the first lactation month,and affected the blood routine indexes and plasma biochemical indexes of cows and calves in different degrees.In short,heat stress during dry milk not only significantly reduced the production performance of postpartum cows but also broke the balance of energy metabolism and oxidative stress of cows and calves,affected hormone secretion and reduced immune function.