Changes in the electrolytes of serum and urine with heat exposure in the bovine

Six mature Friesian bulls with an average body weight of 562 kg were kept - after a preparatory period - in a controlled climatic barn at 30 degrees C and 70% relative humidity for three weeks. They were fed 3.6 kg concentrates and 4 kg hay and water ad libitum. The rectal temperature remained unchanged under heat exposure. Na+, K+, and Ca++ increased in the blood serum, but decreased in the urine. Whereas PO4---increased in the serum and in the urine, the values for SO4--decreased in the serum and in the urine. The serum value for Cl- did not change, but the Cl- value decreased in the urine. The changes in the electrolyte metabolism at high environmental temperatures are important means of extending the discovery procedures for heat stress in cattle.