Energy Requirements and Feed of Dairy Cows under High Temperature Conditions
The gross efficiency of energy consumed and the productivity of dairy cows are affected by heat stress. In this report attempts were made to examine the energy requirements and feeding method of Holstein cows under high temperature conditions. To achieve this objective, energy balance trials were conducted under a temperature range of 18-36 ℃ using dry and lactating cows. The net energy requirement for maintenance of dry cows was 82.1 kcal/kg0.75・day in the range of 18-32℃ and it tended to increase by 5% at 36℃. The metabolizable energy requirements for maintenance (MEm) increased by 10% at 26 and 32℃. The increase in MEm tended to be lower in the case of highly metabolizable diets. The energy requirements of lactating cows increased under high temperature conditions. This increase seemed to be mainly caused by the increase in the MEm. There were no significant differences in the efficiency of conversion of ME partitioned to milk and body tissue among temperatures, and the efficiency was about 61%. It was observed that when the metabolizability of diets increased, the ME intake and the partition of gross energy to production in lactating cows increased whereas the heat increment which acted as a promoter of heat stress from the inner part of the body at high environmental temperatures decreased.