RELATIONSHIP OF INCUBATION HUMIDITY AND FLOCK AGE TO HATCHABILITY OF BROILER HATCHING EGGS

The present study was conducted to determine the effect of incubation humidity (different wet bulb temperature at same dry bulb temperature) on hatchability and embryonic development with respect to flock age. All eggs in Experiment 1 were collected from a flock of broiler breeders over a 4-day period every 4 wk from 28 to 64 wk of age. On the day following the 4th day of collection, half the eggs were placed in an incubator at a wet bulb temperature of 28.3 +/- .5 C, and the remaining half were placed in an incubator at a wet bulb temperature of 30.0 +/- .5 C. The dry bulb temperature was 37.5 C in all cases. A second experiment was conducted with eggs collected from 34- and 66-wk-old flocks. Incubation conditions were the same as in Experiment 1 with a 2 x 2 factorial arrangement of treatments in a completely randomized design. When pooled across breeder age in Experiment 1, hatchability of fertile eggs was increased and early embryonic mortality was decreased by the 28.3 C wet bulb temperature. The improvement was most evident when the flock was young. Data from Experiment 2 suggest that the reduced early embryonic mortality was due to increased water loss in the 34-wk-old flock in the lower wet bulb temperature treatment during the first 3 days of incubation, which presumably increased oxygen influx. When the flock was older, there was evidence of lower hatchability in some larger eggs due to lower wet bulb temperature. The data suggest that lower incubation wet bulb temperature overcomes barriers to water loss and vital gas diffusion, which are evident in small eggs from young flocks but not present in larger eggs from older flocks.