Changing Dietary Cation-antion Balance For Dairy Cows & The Evaluation Of Thermal Environment

With the milk production increasing and the climate becoming warmer and warmer, the heat stress of dairy cows has become more and more serious. This thesis studies the influence of dietary cation-anion difference and its administration time on lactation performance, the effect of season on milk production, and the relation of thermal environment and physiological reaction, hoping that it can provide a theoretical basis for dairy cow management at hot summer in Wuhu and other southern areas.This thesis is divided into three parts. In the first section, selected Holstein cows which were health at mid-lactation and random assigned them into two groups, and analyzed the effect of DCAD on lactation performance in summer. Two treatments were all fed on basical diet supplementing (B) cation salt every morning or (A) noadditives, the control. Milk yield in B increased by 0.82%, 3.09%, 9.69% on the seventh, fourteenth, twenty-first day respectively, and the differences between groups were significant (P < 0.05 ). Milk fat, protein were not affected by the time of DCAD supplement. The results indicated that DCAD had an important effect on the lactation performance of Holstein cows at mid-lactation.In the second section, collected the date of milk yield of Holstein dairy cows from Jan 2004 to Dec 2004 in Wuhu, and discussed the effect of season on milk production. In Wuhu, the milk yield decreased about 2%, 8%,13% in May, June and August respectively. During long-term hot season, the difference of milk yield decreased to 0.47 kg per kg milk yield, So we drew a conclusion that it was essential to strengthen the management of high yield dairy cows at hot summer.In the third section, analyzed the relation and the regressions of respiration rate(RR), rectal temperature(RT), mean skin temperature(mTs) and dry-bulb temperature(DBT), and wet-bulb temperature(WBT) respectively. The regressions of RR, RT and mTs on dry ball temperature was 4.15 times/min, 0.14°C, 0.09°C,and on wet ball temperature was 1.1 times/min(WBT < 23)and 6.5 times/min(WBT≥ 23), 0.22°C 0.17°C respectively. The effective temperature could be expressed by RR or RT as follows:RR=0.1DBT+0.9WBT, RT=0.34 DBT+0.66WBT. This indicated that WBT had more important effect on RR or RT, and the coefficient of WBT for high yield dairy cows should be improved.