Effects of Long Term Storage on the Egg, Embryo and Chick

When most people think of a chicken egg, they think of something nutritious to eat. From an avian embryo’s point of view the egg provides the same function. At the time the egg is laid, if the oöcyte has been successfully fertilised, almost all of the nutrients required for the embryo to grow and develop are enclosed within the egg. There are two main elements missing; one is oxygen and the other is heat. The importance of both of these factors in embryonic growth and development are addressed elsewhere in this book (see French, 2002; Ar and Deeming, 2002). In most commercial poultry breeding operations, hatching eggs are produced by flocks of breeders housed in barns. Male and female broiler breeders are housed together so that natural mating can occur, while turkey breeder hens are housed separately from the toms and therefore must be artificially inseminated. Most broiler breeder eggs are laid in nests and collected by mechanical belts while turkey breeder eggs are still hand-collected. Irrespective of the method of insemination or egg collection, once the eggs are collected they are stored in on-farm cool stores, usually for a few days, until they can be transported to the hatchery. This is done as daily egg transport from the breeder farms to the hatchery would be inefficient. Once transported to the hatchery, the eggs are again stored in large egg stores. Egg storage at the hatchery usually occurs for two reasons. First, hatching eggs are stored until enough eggs are available to fill large incubator racks. Second, stock-piling of eggs occurs in anticipation of fluctuations in egg production or demand for broiler chicks during the production year. Storage of fertile eggs both on farm and at the hatchery occurs at temperatures below 21 C. This can prevent the growth of bacteria, but the main purpose is to stop development of the very young embryo. After oviposition, temperature is the primary catalyst which influences embryonic development (see French, 2002). As assessed by microscopic embryonic staging methods (Eyal-Giladi and Kochav, 1976), storage of fertile Single Comb White Leghorn eggs for various lengths of time at 14 C stopped all observable embryonic development (Table 1; Fasenko et al., 1992). Using a similar microscopic staging technique developed for turkey embryos (Gupta and Bakst, 1993), it was shown that turkey embryonic development during storage for 3, 7 or 14 days at 15 C continued from Stage 7 (the stage most common at the time of lay) to a Stage of 8, and then ceased (Bakst and Gupta, 1997). The minimum temperature above which embryonic development occurs (physiological zero) has been reported at two different levels. Edwards (1902) reported the minimum temperature for embryonic development to be 21 C, while Funk and Biellier (1944) found this minimum temperature to be 28 C. Previous researchers have hypothesised that the minimum temperature for embryonic development is not the same for all developing tissues of the early growing embryo (Kaufman, 1948). Therefore the objective of storing eggs at temperatures well below physiological zero is to prevent abnormal growth of the embryo which could occur if eggs were held at temperatures between physiological zero and normal incubation temperatures of 37.5 C. The generally accepted optimal range for hatching egg storage in the industry is between 14 and 18 C. Different storage temperatures and conditions are recommended depending on the length of storage (See reviews by Proudfoot and Hamilton, 1990; and Meiijerhof, 1992). AVIAN BIOLOGY RESEARCH 2 (1/2), 2009 73–79