Incubation relative humidity effects on allantoic fluid volume and hatchability

Four incubation trials were conducted to evaluate the effects of incubation RH on hatchability, allantoic fluid volume, and embryo weight. In Trial 1, White Leghorn eggs were incubated at a RH of 55 or 69% and a dry bulb temperature of 37.8 C and hatchability was determined. In Trial 2, hatchability and allantoic fluid volume were determined (Day 14 of incubation) for eggs incubated at 43, 55, or 69% RH. In Trial 3, allantoic fluid volumes and embryo weights were determined on Days 10, 12, 14, and 16 of incubation for eggs incubated at 40, 55, or 70% RH. In Trial 4, hatchability, allantoic fluid volumes, and embryo weights were determined on Days 13, 14, and 15 of incubation for eggs incubated at 40, 55, or 70% RH from hens 34 and 49 wk of age. There were no differences (P > .05) in hatchability between eggs incubated at 55 or 69% RH in Trial 1, or among eggs incubated at 43, 55, or 69% RH in Trial 2. In Trial 4, hatchability was highest for eggs from 34-wk-old hens incubated at 55% RH. In Trial 2, percentage egg weight loss per day of incubation (.68, .55, and .40%) and projected 19-d weight loss (12.9, 10.45, and 7.6%) decreased significantly with increased incubation RH of 43, 55, and 69%, respectively. Allantoic fluid volume (as a percentage of initial egg weight) on Day 14 of incubation significantly increased with the increase in RH; 13.86, 15.45, and 17.93% for RH of 43, 55, and 69%, respectively. In Trial 3, allantoic fluid volume peaked on Day 14 of incubation and volume increased or decreased with corresponding incubation RH; 14.05, 16.25, and 19.44% for RH of 40, 55, and 70%. In Trial 4, allantoic fluid volume was greatest on Day 13 of incubation and volume increased or decreased with corresponding incubation RH 13.38, 16.91, and 18.68% for eggs from 34-wk-old hens and 11.12, 13.77, and 16.59% for eggs from 49-wk-old hens. Eggs from 49-wk-old hens had lower allantoic fluid volumes, but higher initial egg weights due to greater percentage egg weight loss during incubation. Incubation egg weight loss in different RH appears to result from the corresponding depletion of the allantoic fluid reservoir.