Environment and Management II

The impact of maternal flock age and incubation on embryo metabolism was studied to understand late incubation overheating and mortality in Ross 308 embryos. Fresh broiler hatching eggs (n = 45) were obtained from commercial breeder flocks at 3 ages: Young (Y): 25 to 34 wk, Peak (P): 35 to 45 wk, Old (O): 46 to 54 wk of age), stored for 2 to 4 d at 18°C and 73% RH, then incubated for 14 d at 37.5°C and 56% RH. At 15 d of incubation (E15), 12 fertile eggs per flock age were placed individually in metabolic chambers and subjected to one of 4 machine temperatures (MT; 36.0, 36.5, 37.0, or 37.5°C) until E21.5. The O2 consumption, CO2 production and eggshell temperatures (EST) were recorded and embryonic heat production (EHP) calculated and used as an indicator of embryonic metabolism. At E21.5, quality was assessed using chick weight, length, pipping and hatching times. Data were analyzed by the Proc Mixed procedure of SAS at P < 0.05 significance level. Relation­ ships among MT, parent flock age, EHP and EST were determined by regression. There were no differences in daily O2 consumption, CO2 production or EHP between maternal flock ages or MT. Daily EST was not affected by flock age. The EST at 37.5°C was higher than all other MT treatments except at E20 where it was not different from 37.0°C MT. The daily EST at 37.0°C MT was also higher than the daily EST at 36.5°C and 36.0°C, while 36.5°C had higher daily EST compared with 36.0°C MT. The MT showed a strong positive linear relationship with EST (R2 = 0.89) but there was no relationship between EST and EHP. Egg weight and chick weight increased as flock age increased. There was no effect of flock age on chick length or pipping time but hatching time was shorter for 37.0°C MT compared with all other temperatures. In conclusion, MT had a much greater effect on embryo development than maternal flock age in Ross 308 embryos.