Genetic and Environmental Factors Affecting the Development of Avian Embryos

Abstract

An avian embryo is amenable to a variety of manipulations at almost every stage. Its overall rate of growth as well as the development of individual structures and organs can be drastically altered by different environmental factors. Disturbances in development may be caused by factors either located within the egg or acting through the outer environment. People who are not primarily concerned with hatchability problems and incubation techniques frequently pay little attention to some of the important factors which have a definite influence on the development of the embryo. This often leads to erroneous conclusions, and makes the reproduction of data difficult. For workers concerned with studying the norm of development or exploring the causal factors in developmental anomalies, it is of the utmost importance to standardize both material and experimental conditions in order to obtain some harmony in the development of an embryo. The purpose of this manuscript is not to review extensive literature in avian development, but to acquaint researchers and teachers of biology with the roles played by genetics and various extrinsic environmental factors in the development of early embryos, The material is discussed under the following headings: 1. History of the breeder stock. a. Genetic background b. Diet of the breeders c. Diseases d. The age of the layers 2. Preincubation storage environment. a. Length of preincubation storage b. Storage temperature c. Humidity level d. Turning of eggs e. Gaseous environment 3. Incubator environment. a. Incubator temperature b. Humidity level during incubation c. Turning of eggs during incubation d. Gaseous environment during incubation 4. Physical and oviposital conditions of the eggs. a. Shell porosity and thickness b. Egg weight c. The time of the day when the egg is laid d. Jarring of eggs 5. Optimal conditions for using avian eggs for experimental studies.