Effects Of Thermal Changes In Four Seasons On Physiological And Biochemical Indexes Of Perinatal Cows

Modern high-yielding dairy cows experience severe metabolic stress during the transition period between late gestation and early lactation to meet the high energy and nutrient requirements of the fetus or the mammary gland,and additional thermal stress during this time has more serious adverse implications on metabolism and welfare.The effect of warm environment on lactating cows has been widely reported,but its effect on perinatal cows is seldom studied.The research of finding out the comfortable thermal environment of the cow during the transition period is even less.In this experiment,during the trial period of spring?4-5mon?,summer?7-9mon?,autumn?10-11mon?,winter?12-1mon?,the respiratory frequency,heart rate and rectal temperature?RT?of 335 prenatal and 315 postpartum Holstein cows were measured.The plasma of 97 prenatal and 101 postpartum Holstein cows were collected and their biochemical indexes were determined.The purpose of this study was to find out the comfortable range of thermal environment for perinatal cows in southern China.The main contents and results are as follows:1.Effect of thermal environment on physiologica indexes of perinatal cowsThe results showed that there were significant difference of respiratory frequency and rectum temperature in four seasons of perinatal cows?P<0.05?.The respiratory frequency and RT in summer were significantly higher than that in the other three seasons.The respiratory frequency and RT of dairy cattle were significantly correlated with THI?P<0.05?or extremely significant positively correlated with THI?P<0.01?.The results showed that respiration frequency and RT could be used as sensitive indicators of perinatal cows response to thermal environment.Perinatal cows have a lower respiratory frequency in the summer than in the mid-lactation cows,but the rectal temperature is higher than that of the lactating mid-lactation cows.2.Effect of thermal environment on biochemical indexes of transition dairy cowsThe results showed that the total antioxidant capacity?T-AOC?of perinatal dairy cows and mid-lactation dairy cows decreased in summer and autumn.High temperature and humidity aggravated oxidative stress in perinatal dairy cows and mid-lactation dairy cows.3.Effect of thermal environment on immune indexes of transition dairy cowsThe immune indexes in the blood of the four seasons perinatal cows and mid-lactation cows in the same experimental group were determined.Overall the results showed that the immunosuppressive degree of the perinatal cows in the summer was increased,the immune ability of the mid-lactation cows was higher than that of the perinatal cows,except in summer.4.Effect of thermal environment on endocrine indexes of transition dairy cowsThe endocrine indexes in plasma of four seasons perinatal cows were determined.The results showed that the secretion of progesterone and cortisol from perinatal cows increased in summer and winter,And there were significant differences among the four seasons?P<0.05?.The concentrations of plasma T₄ and PRL were lower in summer and autumn.It shows that summer is not suitable for calving and oestrus of perinatal cows.5.Determination of the comfortable thermal environment range for transitional dairy cowsBased on the regression analysis of the respiratory frequency of the perinatal cows with THI,the range of the comfortable thermal environment for transition dairy cows was preliminarily established.The upper limit of comfortable thermal environment of THI for transitional dairy cows is between 59-64;the lower limit of comfortable thermal environment of THI for prenatal dairy cows is between 50-52;and the lower limit of THI for postnatal dairy cows is between 49-50.