Temperatures continuously higher and lower than the standard incubation temperature by 3°C from embryonic d 16 until embryonic d 18.5 result in differential effects on embryonic development, the hatching process, and embryonic metabolism. Embryos in the high-temperature group were forced into a state of malnutrition by the temperature treatment, as reflected by reduced embryo growth and yolk consumption, resulting in a significantly lower chick weight at hatch. In addition, altered air cell and blood gases as well as a retarded hatching process further indicated reduced growth of embryos exposed to higher incubation temperatures during the latter part of incubation. In addition, hatchability was significantly reduced by the high-temperature treatment due to higher embryonic mortality during the treatment period and the hatching process. Levels of blood glucose, lactate, liver glycogen, plasma triglycerides, and nonesterified fatty acids indicated an altered carbohydrate and lipid metabolism for the high-temperature group. Although the hatching process of embryos exposed to lower incubation temperatures was also significantly retarded, their embryonic development and growth were strikingly similar to those of the control group.

We first tried to monitor the critical points for eggshell breakage in different logistic chains. Second, we examined whether there was a difference in eggshell strength among eggs produced in different housing systems. Finally, we developed a model to investigate the relation between eggshell strength and the likelihood of an egg cracking during handling and grading. Four logistic chains with different housing systems (battery cages, furnished cages, aviary, and free-range), all housing Bovans Goldline chickens in their mid-lay (45 wk), were compared. In every chain, a randomized set of 1,500 eggs was sampled, and the strength was defined. At every critical point in every logistic chain, the eggs were reexamined for breakage. The classic and furnished cage systems showed the highest percentage of breakage directly at point of lay (6.73 and 10.72%), whereas the other systems showed lower breakage (1.94% in the aviary and 1.99% in the free-range system). Further, in the logistic chain, grading and packing of the eggs generated the second highest percentage of breakage (from 1.50 to 2.65%). Breakage due to transportation ranged from 0.16 to 2.65%. There was a significant difference among the eggshell strength (shell stiffness and damping ratio) of eggs from chickens in different housing systems, showing eggs from chickens in the aviary system to be stronger than cage eggs (classic and furnished) and free-range eggs to be weaker than the other eggs. A significant correlation was found between eggshell strength and the likelihood of breakage in the production chains. In conclusion, it was first shown that, besides the laying, packing of the eggs is a critical point in the logistic chain of consumption eggs; second, the strength of the eggs in the different housing systems differed, and, finally, the eggshell stiffness and damping ratio of consumption eggs are an acceptable measure for rapid eggshell quality assessment and could provide a good predictive value for eggshell breakage in all types of table egg production chains.

No abstract