1. Factors affecting broiler breeder performance. 4. The interrelationship of some reproductive traits;McDaniel;Poult. Sci.,1981
2. The influence of time of oviposition and egg shell quality on hatchability of eggs from broiler breeder hens;McDaniel;Poult. Sci.,1977
3. The effect of egg shell quality on hatchability and embryonic mortality;McDaniel;Poult. Sci.,1979
4. Specific gravity test for monitoring eggshell quality;Loeffler,1987
5. The age of embryonic mortality was determined according to guidelines based on: Hodgetts, B., 1988. The timing of major embryonic events. Hatch Handout #7. A.D.A.S. The only departure from this classification of embryonic death was that it was assumed that no clearly visible signs of blood could be seen until 3 days of incubation. Embryos reported as dying in the first 2 days of incubation only include those identified when the eggs were broken open after 6 days of incubation. Because the eggs tended to be too mixed up to spot small quantities of blood, all possible Day 1–2 dead embryos found in the eggs unhatched after 21 days of incubation were classified as Day 1–3 dead embryos. Cracked, upside down and slightly contaminated eggs containing dead embryos were broken open and the age of death recorded. Some studies of embryonic death do not record the age of embryonic death of any such eggs. The pipped embryos are chicks that have pipped the egg shell. All hatchability, fertility and age of embryonic death data are expressed as a percentage of total eggs set. The “spread” was calculated as the percent fertility minus the percent hatch. The total chicks hatched for the thick or thin shelled eggs was calculated by counting the number of unhatched thick or thin eggs and subtracting that number from the number of thick or thin eggs originally set in the incubator. Because the thick and thin eggs were mixed together in the same hatcher tray, it was not possible to determine the number of cull chicks from each type of egg. The hatchability, fertility, and age of embryonic death data for the thin and thick egg shells were grouped according to the ages of the breeder flocks at the time that the eggs were set in the incubator. The age groupings were 30.0–34.9, 35.0–39.9, 40.0–44.9, 45.0–49.9, 50.0–5479 and 55.0–59.9 weeks of age. The data for each age grouping was analyzed separately, using an analysis of variance in which shell thickness and hatchery were fixed effects. Since no significant hatchery effects were observed, the results are presented only for the thick and thin shells. Significance was accepted at the 5% confidence level.