All animals were fed, ad libitum, a low quality chopped hay (i.e. 28%
fiber, 4% crude protein), thus simulating the natural quality of forage
available during periods of drought. To ensure that most food was
consumed the hay was chopped into short pieces. Food and water
containers were located outside and in front of each metabolic cage to
minimize spillage. They were cleaned daily with de-mineralized water.
The animals fed on the same batch of hay throughout the entire
experimental period. Each animal adapted to, and fed, the low quality
forage for a period of threeweeks before being housed in the metabolic
cages. Food was provided in trays at the front of each cage and the daily
consumption recorded. During preliminary trials and experimental
periods, food was offered at twice the previous day's level of ad libitum
intake. The moisture content of the forage (generally less than 12%) was
measured daily. Thus, the amount of preformed water consumed was
calculated, and an accurate measure of dry matter intake determined.
Each animal was then further acclimated to their designated environmental
control chamber and forage diet for one additional week. After
the acclimation period, measurements of food intake and dry matter
digestibility were made daily for a further 18–21 days. The same
procedures were followed for animals subjected to a temperature of
22 °C and to the alternating heat load (22 °C and 40 °C,12-hour cycle).An
8–10 day resting period was allowed for each animal that came out of
one experimental treatment before being used in the next treatment.