Effects Of Heat Stress On Performance,Ruminant And Lying Behavior Of Different Lactating Dairy Cows

In summer,the excessive heat accumulated in the cow's body cannot be completely dissipated,and heat stress is extremely likely to occur.The cows in different lactation stages have different physiological metabolic states,and the degree of heat stress affects them is different.In order to determine the specific changes of cows in different lactation stages under heat stress,45 lactating cows Containing early,middle,and late lactating cows were selected to study the Impact of heat stress on rectal temperature,respiratory rate,milk production,milk composition,blood biochemical indicators,ruminant behavior and lying behavior.The test results are as follows:1.under non-heat stress conditions,RT of cows was around 38.5?,and RR was less than 50 beats / min.On mild heat stress levels,RT of cows in each lactation stage is at least 39?,and RR is about 70 beats / min.On moderate heat stress levels,RT of cows in each lactation stage can reach 39.8?.RR is higher than 90 beats / min.With the deepening of heat stress,RT and RR of cows in the three lactation stages increased significantly(P <0.05).RT and RR of cows were significantly positively correlated with the THI(P <0.05).Each additional unit of THI increased RT of each lactating cow by 0.1055?,0.0916?,0.0962?,RR increased by 3.8408,3.7292,and 3.504 times.Therefore,compared with middle and late lactating cows,heat stress has a greater effect on RT and RR of early lactating cows.2.Under non-heat stress,the rumination time of cows is about 550min/day,the rumination time is about 230 min during the day,and the rumination time is about 320 min at night.Mild heat stress significantly reduced the daily rumination time,daytime rumination time and night rumination time of early lactation cows(P <0.05),and with the increase of heat stress,Rumination time was further significantly reduced(P <0.05).Moderate heat stress significantly reduced daily rumination time and daytime rumination time in mid-lactation and late lactation cows(P <0.05).Therefore,it was concluded that early cows High temperature is more sensitive,and heat stress has the most severe effect on rumination time in early lactation cows.3.Under non-heat stress,the standing time of early,middle and late lactating cows is about 800 minutes per day and the standing frequency is about 10 times per day.There is no significant difference in standing time and number of standing cows at different lactation stages(P > 0.05).In the early lactation period,the standing time was significantly increased at moderate heat stress level(P <0.05),and the standing frequency was significantly increased at the mild heat stress level(P <0.05).There was no significant change in standing frequency(P> 0.05);Compared with non-heat stress,there was no significant change in standing time in heat-stressed late lactating cows(P> 0.05),and the standing frequency was significant at moderate heat stress levels Increased(P <0.05).Therefore,heat stress has a greater effect on standing time and standing frequency of cows in early lactation than in middle and late lactation.4.Compared with the non-heat-stressed cows,the milk production of the heat-stressed cows in each lactation stage cows significantly decreased(P <0.05).Under non-heat stress,the milk production growth rate of the early lactation cows was 4.68%,and the decline rates of the middle and late lactation cows were 6.56% and 8.8%.The milk production decline rates of early,middle,and late dairy cows were 13.9%,20.66%,and 20.1% in summer,so the change rates of milk in early,middle,and late milking cows were 18.58%,14.1%,and 11.3%,heat stress has the greatest impact on milk production in early lactation cows.Due to heat stress,the content of lactose and non-fat solids in milk of early lactation cows decreased significantly(P <0.05),and the content of glucose and free fatty acids in blood decreased significantly(P <0.05).The casein content in milk of mid-lactation cows decreased significantly(P <0.05),the total protein content in blood decreased significantly(P <0.05),the urea nitrogen content in blood increased significantly(P <0.05).When the temperature rises,the body's fat metabolism is weakened,carbohydrate metabolism is enhanced in early lactation cows.And protein metabolism is enhanced in mid-lactation cows.In summary,when cows experience heat stress,the rectal temperature and respiration rate of cows increase significantly,production performance decreases significantly,and rumination and lying behavior decrease significantly.Among them,heat stress has the most serious impact on cows in early lactation.In the actual production process,we must pay close attention to the heatstroke prevention and cooling of the early lactating cows in the early summer.