Yahav, S., Institute of Animal Science, ARO, Volcani Center, P.O. Box 6, Bet Dagan, 50250, Israel

At high ambient temperature (T(a) = 35°C) weight gain and feed intake declined significantly. At 15°C weight gain was similar to that at 25°C, at the cost of increased feed intake. Under diurnal cyclic temperature, weight gain and feed intake were significantly lower than in the average corresponding temperature. In all treatments the turkeys' body temperature (T(b)) was at the lower level of normothemia known for broiler chickens at a similar age. The blood system compensated for changes in T(a) by increasing hematocrit, hemoglobin concentration and heart muscle weight at low T(a), and by plasma expansion and increased panting at high T(a). Plasma (T3) concentration was positively correlated with feed intake and weight gain.