| Holstein cows are cold-tolerant but not heat-tolerant,heat stress seriously affects the physiological state of the cows,resulting in reduced milk production and milk quality,increased morbidity,it has caused a huge blow to the breeding and dairy processing industries.At present,large number of farms are using spray-fan cooling system to cool down during heat stress period,although there have been many studies about the specific effects of heat stress on cows,but most of them do not specify the cooling method,and there are relatively few studies on cows in different lactation stages during heat stress period,so as to explore the changes in the environmental parameters of barn after using the spray-fan cooling system,and the physiological,milk production,blood biochemical indexes and other aspects of cows in different lactation stages after using the system during heat stress period are compared with the cows in different lactation stages during non-heat stress period,to provide a feasible reference for cooling strategies of dairy farms during heat stress period,to improve the efficiency of dairy farming and dairy cows welfare,this study carried out the following experiments.1.In this experiment,dividing all cows into four lactation stages according to days in milk: the late perinatal cows(0-21d),the early lactation cows(22-120d),the mid-lactation cows(121-200d),and the late lactation cows(201-305d).Randomly select 10 healthy multiparous cows(2-4 parity)with similar body condition,age and days in milk in each of the four stages of lactation,a total of 40 cows as the test objects.During the heat stress period(July-August)and the non-heat stress period(November-December),the environmental parameters of the barn were monitored for 20 days respectively,and the spray-fan cooling system was used to cool the barn during the heat stress period.Except for milk yield,the physiological indicators of cows are not tracked(Randomly select cows again each time when data is collected),feeding and management methods are based on the farm’s daily plan without manual intervention.a)After using the spray-fan cooling system,there is no significant difference between the temperature in the barn and outside the barn(P>0.05),humidity and wind speed in the barn increased extremely significantly(P<0.01),THI(Temperature-humidity index)increased significantly(P<0.05).The cooling system has a good control effect on the increase of temperature in the barn during the high temperature period in the afternoon(12:00 am-18: 00 pm),and it extremely significantly reduces(P<0.01)the maximum temperature in the barn.In the morning(08:00 am-12:00 am)and evening(20:00 pm-00:00 pm),the humidity increased due to spraying,so the cooling system performed relatively poorly,it can be considered to reduce the spray time or spray intensity in the morning and evening,and turn on all fans for ventilation and cooling.Without considering wind speed,THI has a certain deviation in accurately evaluating the level of environmental thermal stress.b)Compared with the non-heat stress period,rectal temperature and respiration rate of cows in each lactation stage increased extremely significantly(P<0.01)during heat stress period,rectal temperature respectively increased by 0.9 ℃,0.7 ℃,0.6 ℃,0.5 ℃,and respiratory rate increased by 32.9 times/min,29.1 times/min,29.3 times/min,28.8 times/min,late perinatal cows and early lactation cows are more affected by heat stress than midlactation and late lactation cows.The daily average yields of late perinatal cows,early lactation cows and mid-lactation cows were decreased extremely significantly during heat stress period than that during non-heat stress period(P<0.01),with a decrease of 9.17 %,18.97 %,and 13.23 %,there was no significant change in the average daily yield of late lactation cows(P>0.05).Heat stress leads to the decrease of milk production when the lactation starts of late perinatal cows and the decrease of peak milk yield of cows in each lactation stage.The milk fat percentage and ratio of milk fat to milk protein of all cows decreased extremely significantly(P<0.01),milk protein decreased significantly(P<0.05),somatic cell count(SCC)increased slightly but there was no significant difference(P>0.05).Compared with non-heat stress period,the incidence of hoof disease,ketosis,clinical mastitis,and subclinical mastitis of all cows respectively increased by 5.77 %,0.78 %,2.60 %,and 5.77 % during heat stress period.2.During the heat stress period,a day with high temperature and high humidity was randomly selected,in this study,it was the 9th day of the test period,in the non-heat stress period,the same time node was selected.Blood was collected from 40 cows whose milk production were tracked in test 1,determination of serum biochemical indexs including heat stress protein 70(HSP70),cortisol(Cor),8-isoprostaglandin(8-iso-PG),superoxide dismutase(SOD),glutamate dehydrogenase(GDH)total antioxidant capacity(T-AOC),haptoglobin(HPT),malondialdehyde(MDA),,non-esterified fatty acid(NEFA),the results are as follows:a)Compared with non-heat stress period,HSP70 and Cor of cows increased extremely significantly in each lactation during heat stress period(P<0.01),and 8-iso-PG of late perinatal cows and early lactation cows decreased significantly(P<0.05),there was no significant change in mid-lactation and late lactation cows(P>0.05).During heat stress period,the concentration of HSP70,Cor,8-iso-PG of late perinatal cows,early lactation cows mid-lactation cows have bigger change,late lactation cows change small,he results showed that the heat stress caused different degrees of stress response of cows in each lactation stage.Among them,the late perinatal cows,early lactation cows and mid-lactation cows were most affected by the heat stress.b)Compared with the non-heat stress period,the SOD activity of cows in each lactation stage during the heat stress period was extremely significantly higher(P<0.01),and the late perinatal cows had the largest increase.The T-AOC of late perinatal cows and early lactation cows was extremely significantly reduced(P<0.01),and the T-AOC of midlactation cows was significantly reduced(P<0.05),and there was no significant difference in late lactation cows(P>0.05),the concentration of MDA of early lactation cows and midlactation cows increased extremely significantly(P<0.01),the concentration of MDA of late perinatal cows increased significantly(P<0.05),and the MDA of late lactation cows showed no significant difference(P>0.05).The results show that the SOD activity increased in each lactation stage during heat stress period,lipid peroxidation increased,and the total antioxidant capacity declines.The late perinatal cows and early lactating cows are most affected by the heat stres,the imbalance of antioxidant system was the most serious,and late lactation dairy cows were less affected by heat stress.c)The GDH activity of cows in each lactation stage during heat stress period was extremely significantly higher than cows in non-heat stress period(P<0.01),mong them,late perinatal cowsand early lactation cows increased the most.The concentration of NEFA of late perinatal cows and early lactation cows was extremely significantly increased(P<0.01),NEFA of mid-lactation cows was significant Increased(P<0.05),there was no significant difference in late lactation cows(P>0.05).The concentration of HPT of late perinatal cows,early lactation cows and mid-lactation cows was extremely significantly increased(P<0.01),and there was no significant difference in dairy cows in the late lactation period(P>0.05).The results show that the health status of cows in each lactation stage was damaged to different degrees during heat stress period,among all cows,the health status of late perinatal cows and early lactation cows was lower than that of cows in other lactation stages.Conclusion:(1)The spray-fan cooling system has a good cooling effect in the high temperature period(12:00 am-18:00 pm),in the morning(08:00 am-12:00 am)and evening(20:00 pm ～ 00:00 pm)due to the excessive humidity caused by spraying,the cooling effect is not good.Therefore,it is expected to improve the cooling effect in high humidity time by reducing the spraying time or spraying intensity in the morning and at night,reducing the humidity in the room,and increasing the fan ventilation intensity at the same time.(2)Compared with the middle and late lactation cows,heat stress had a more serious effect on physiological indexs and milk yield of late perinatal cows and early lactation cows,at the same time,they has the highest level of heat stress,the antioxidant capacity was the most obvious reduction,the body health state damage was also the most serious.For all cows,milk fat percentage,milk protein,and ratio of milk fat to milk protein of all cows were seriously reduced,and the incidence of hoof disease,clinical mastitis and recessive mastitis increased obviously. |
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