Eggs from breeder flocks of different ages, have a difference in composition. As a result, embryonic energy utilisation and heat production are different. This is worth taking into account to optimise incubation settings, thus achieving high hatchery
performances and good chick quality.
By Ampai Nangsuay, Bas Kemp and Henry van den Brand, Wageningen University, the Netherlands, Ron Meijerhof, Poultry Performance Plus, the Netherlands, Yuwares Ruangpanit, Kasetsart University, Thailand
During incubation, nutrients in the egg are converted to energy for embryonic development and growth. Due to limited oxygen supplies during the first seven days, an embryo uses mainly carbohydrates as an energy source. After day seven when functional organs for oxygen uptake are developed, yolk fat is used as the main energy supply. These biochemical processes produce heat as a by product and as a result embryonic heat production (HP) increases during the incubation period. As the balance of HP and heat transfer during incubation affects embryo or eggshell temperature (EST), changes in embryonic HP can affect EST. EST can in turn affect hatchability, chick quality and later life performance.
Different breeder ages
Embryonic HP is affected by the origin of the egg. For example, it is known that older breeders produce larger eggs, which produce more heat during incubation. However, in case the egg size is the same, but eggs of different breeder ages are used, it is unclear to which extent HP is affected. Therefore, two experiments with different breeder ages and different egg sizes were performed to investigate effects on embryonic energy utilisation and embryonic HP.
In the first experiment, eggs from Ross 308 broiler breeders at 29 and 53 weeks were used. Within each breeder age, eggs were selected for two weight classes at 57-61 or 66-70 gram. Eggs were incubated in single stage incubators at a commercial hatchery. EST till day 18 of incubation was maintained in all treatments at 37.8 ± 0.2°C. Set point of the hatcher was 36.5°C for all treatments. Egg weight, yolk weight and albumen weight were determined, whereas body weight, residual yolk (RSY) and yolk free body mass (YFBM) were measured at pulling time at 516 to 518 hours after start of incubation. Amount of fat, protein and carbohydrates in yolk, albumen, RSY and YFB were analysed and energy content was calculated. Based on these analyses, energy utilisation and efficiency of energy utilisation (EYFB) were determined.
|Energy utilisation (kJ) = [Albumen (kJ) + Yolk (kJ)] – RY (kJ).
|EYFB (%) =
|Albumen (kJ)+Yolk (kJ)–RY (kJ) x 100
Egg weight difference
Because we selected within each flock age on egg size, egg weight was almost the same between flock ages, but higher for the large eggs (see Table 1). Although egg weight differed by almost 7 g between small and large eggs within the young flock (29 weeks), this difference was not seen in yolk weight. At similar egg size, older breeders (53 weeks) produced eggs with about 3-4 g more yolk than younger breeders. In the old flock, a difference in yolk weight was also seen, where large eggs had an almost 2 g higher yolk weight than small eggs. Amount of albumen was higher in the large eggs than in small eggs and in the young flock compared to the old flock. When we look to the energy content of the albumen, yolk and total egg, the same pattern as in yolk and albumen weight can be seen. Particularly the yolk is mostly determining the energy content of the egg. Very interesting results were found in hatchlings. Although fresh yolk weight differed 3-4 g between young and old flock, this difference disappeared at hatch. Chicks of young and old flocks of each egg size had the same RSY weight. Comparable results were found for YFB weight at hatch. Again no differences between small eggs of young and old flocks were found and the same holds true for the large eggs. However, this does not mean that the chicks did not differ. Chicks of the old flock had the same YFBM within each egg size, but the body composition differed, meaning that chicks from the old flock had more fat and protein and less water deposited in the body.
Efficiency of energy
The amount of energy used by embryos strongly reflected the amount of energy in fresh yolk. Again, in the young flock no difference between small and large eggs was found in energy utilisation. In old flocks this difference was shown, with higher values for the large eggs particularly. As indicated above, not all the energy of the egg is deposited in the chick, but part is lost during the incubation process. Although again the same pattern among the four egg origins was found, these differences were shown to be not significant. The most interesting result is probably demonstrated by the efficiency of energy utilisation (EYFB); amazingly this was the same for all the four egg classes. This means that with the different origin of eggs the amount of energy deposited in the chick varies, but the efficiency of the process is not influenced by the origin of the egg.
Yolk size determining
Based on the data from this experiment a strong correlation between fresh yolk weight and energy utilisation was calculated (Figure 1). It can be concluded that yolk size strongly determines the energy utilisation regardless of egg size and breeder age. On the other hand, it also suggests that yolk size is the main determinant of embryonic HP during incubation. Because of that we conducted a second experiment. In this experiment again eggs of Ross 308 broiler breeders aged 29 and 53 weeks were used. In both flocks eggs of 58 to 61 gram were selected. Eggs were incubated in climate respiration chambers at an EST of 37.8°C and oxygen consumption and carbon dioxide production were determined continuously. Based on these measurements the HP of embryos was calculated. Indeed, a 15% higher HP at day 18 of incubation in eggs from the 53 weeks old flock compared to the 29 weeks old flock was found (Figure 2).
In conclusion, eggs from old flocks contain more energy due to more yolk, have a higher energy utilisation and produce more embryonic HP than eggs of young flocks. Therefore, the origin of the eggs is worth taking into account to optimise incubation settings for high hatchery performances and good chick quality.
[Source: World Poultry magazine Vol 30 nr 3, 2014]