The Rhythm In Deep Body Temperature And Dietary Cation-Anion Difference In Lactating Dairy Cows

The rhythms in deep body temperature is a sign which indicates the homoiothermal animal is in the healthy status. There are the diurnal fluctuations in body temperature, respiration rate, and acid-base balance of lactating dairy cows under summer condition. The acid-base status of lactating dairy cows was affected in hot humid weather. During the hot part of the day, blood and urine pH were higher, and blood pCO2 and the content of HCO3" were lower, which suggested respiratory alkalasis. During the cooler part of the day, blood and urine pH fell, and the content of blood HCO₃was lower, which suggested compensated metabolic acidosis. The research aimed at determing the effects of dietary cation-anion difference and administration time-dependent on performance acid-base and mineral status under summer condition in mid and high-yielding dairy Cows.The first part of this research studied administration time-dependent influence of dietary cation-anion difference on performance acid-base and mineral status under summer condition in mid-yield dairy cows Ten mid-lactation Holstein cows were assigned randomly to A or B, A was control, which was feed basic diet and DCAD equal 32.4 mEq/100g DM. The total of salt in A concentrate was added to the morning concentrate of B. The results indicated that administration time-dependent of dietary cation-anion difference significantly influenced the performance of heat-stress dairy cows. Intake of DM and 4% FCM increased 16.7% (P<0.05) and 19.4% (P<0.01), respectively; Expect of NFC (P<0.01), milk fat protein lactose and rough mineral were not altered by administration time of dietary cation-anion difference; Blood samples taken from the caudle vein at 14:00 indicated that blood Na K and Ca and blood pH carbon dioxide partial pressure and HCO3' concentration were not altered by the administration time, Blood base excess increased in B, but the difference between groups was not significant. Urine pH was increased (P<0.05) ,and the excretion of urinary Na K and Cl had the tendency to be raised. And the urine strong ion difference (SID=Na⁺+K⁺-Cl^-) was decreased.The second part of this research studied the effects of dietary cation-anion difference and administration time-dependent on milk yield rectal temperature, respiration rate and blood and urinary parameters. Sixteen high-lactation Holstein cows were assigned randomly to A,B, and C. A was control, which was feed basic diet; on the base of A,B was added 30g K2CO3 to the concentrate of breakfast; C was added 15gK2CO3and 20gNaHCO3 to each the concentrate of breakfast and lunch on the base of A. The dietary cation-anion difference of A,B, and C is 42.3, 47.16, and 52.45mEq/100g DM, respectively. The results indicated that DCAD and administration time-dependent influenced the performance of heat-stress dairy cows. Milk yield of B and C increased 8.9% and 10.4%, respectively. Rectal temperature of B was lower than A and C during the experiment, and measured values at 15:00 and 23:00 lower significantly( P<0.05 ). Respiration rate is not significant in A, B, and C during experiment. The results of caudal artery blood gas measured at 5:30 indicated that blood bicarbonate and TCO₂ of C increase significantly. Base excess was negative value in A and B, and B lower significantly than A. The results of blood gas measured at 14:00 different insignificantly. The results of caudal vein serum ions indicated that serum concentration of Ca²+ decrease significantly compared with A. Urinary parameters different insignificantly, but urine pH was increased by DCAD. The analysis of typic periods indicated that rectal temperature , respiration rate and the level of decrease in yield in B were lower significantly during continuous hot summer, and implied that the improvement of physiological parameters and performance benefit from the fitting DCAD and administration time-dependent.