Effect of Incubation Dry-Bulb and Wet-Bulb Temperatures on Time of Hatch and Chick Weight at Hatch

Abstract

In two experiments, broiler hatching eggs were incubated under conditions that permitted comparison of dry-bulb (DB) and wet-bulb (WB) temperatures. The experiment covered both the setter (1 to 17 days) and hatcher (18 to 21.5 days) phases.In Experiment 1, DB temperatures of 37.2 and 37.5 C and WB temperatures of 28.3 and 30.0 C from 1 to 21.5 days were compared in a 2 by 2 factorial design that extended through both the setter and hatcher phases. Overall, chicks hatched earlier under the higher of the DB conditions and the lower of the WB conditions. There was a significant DB by WB interaction, attributed to the early hatching effect of a lower WB temperature being more pronounced at the higher DB temperature. Increased chick weight was recorded at the higher WB temperature.In Experiment 2, the DB temperature in the setter phase (D1) and the hatcher phase (D2) as well as the WB temperature in the setter phase (W1) and hatcher phase (W2) at the same levels as in Experiment 1 were compared in a 2 by 2 by 2 by 2 factorial design. Time of hatch was decreased by the high Dl temperature, but no other main effect was observed.Regression analysis showed interactions of Dl by D2, Dl by W1, Dl by W2, and W1 by D2 for the intercept as well as for the linear and quadratic components of the response. The W1 by W2 interaction was significant for the intercept and for the linear component. The D2 by W2 interaction was significant for the intercept only. These interactions were interpreted to be caused by the relative effects of DB temperature on rate of metabolic water production and the water-vapor pressure within the egg as well as by the effect of WB temperature on the moisture and concentration gradient between the egg and incubator.Chick weight at time of hatch was affected by the time of removal from the incubator. Chick weight was also directly related to time of hatch and to the holding time within the incubator.