Effects of breeder age and oxygen concentration during incubation on embryonic heat production and development, and post-hatch chick performance.

Nutrients in the egg and oxygen diffused through the eggshell and membranes are two important factors affecting the metabolism and growth of avian embryos (WILSON, 1997; WANGENSTEEN and RAHN, 1970). The composition of the egg is influenced by breeder age (Marion et al., 1960) and similar sized eggs of an old compared to young breeder flock showed a higher yolk size and consequently higher energy content (NANGSUAY et al., 2013). To optimise nutrient use and development during the incubation and post-hatch period, embryos originating from different breeder ages that differ in their initial nutrient availability might therefore require different oxygen concentrations during incubation. To test this hypothesis, the current study investigated effects of breeder age and oxygen concentration during incubation on embryonic metabolism and development, and post-hatch chick performance. Similar sized eggs of a young (29 weeks) or old (53 weeks) Cobb 500 breeder flock were incubated at 3 oxygen concentrations (17%, 21% or 25%) from day 7 of incubation until 6 hrs after emergence from the eggshell. Egg composition at set, embryonic weight and heat production during incubation and post-hatch performance until 7 days of age was evaluated. Results showed that eggs of the old compared to the young flock were 1.2 g heavier and had 3.9 g more yolk (P < 0.01). No interactions between breeder age and oxygen concentration were found for the characteristics described below. Embryonic heat production was significantly higher from ED14 until ED18 with a higher oxygen concentration (P < 0.05). Yolk-free body mass at 6 hours after hatch was only affected by oxygen concentration, where the 21 and 25% treatment showed a higher weight than the 17% treatment (P < 0.01). This difference disappeared at 7 days of age (P > 0.10). Body weight and relative intestine weight at 7 days of age was higher in chickens of the old compared to the young breeder flock (P < 0.05). Other relative organ weights were not affected by the treatments (P > 0.05). FCR was affected by the oxygen concentration during incubation; the 17% treatment had the highest FCR and the 21% treatment had the lowest FCR, whereas the 25% treatment was intermediate (P < 0.05). Although the higher yolk weight of the eggs of the old compared to the young flock probably increased the energy content and nutrient availability for the embryo, this did not result in a higher metabolic rate or development when oxygen concentration was increased during incubation. This suggests that other factors such as the development and functionality of the yolk sac membrane and/or CAM may limit embryonic metabolism and development. The higher post-hatch growth of chickens of the old compared to the young breeder flock might be related to differences in physiology or development of supply organs, such as the intestines. Embryonic development was positively influenced by a higher oxygen concentration during incubation, but this effect disappeared in the post-hatch period. A higher O₂ concentration during incubation did improve the nutrient efficiency for post-hatch growth until day 7 of age, expressed by a lower FCR. [ABSTRACT FROM AUTHOR]