|Gupta Satish K,|
Submitted to: Journal Of Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 1, 1994
Publication Date: N/A
Interpretive Summary: A major concern in the turkey industry is the failure of about 25% of all eggs placed in incubators to hatch. It is of significant importance to the breeder and hatchery operator to know if hatch failures are due to infertile eggs or embryonic deaths during incubation. While candling an egg after 10 days of incubation provides an estimate of the percentage of eggs with embryos that have developed for at least 3 days in the incubator, true fertility, that is, the percentage of eggs which actually were fertilized, is best determined in eggs prior to their incubation. In this study, the visual appearance of that area on the yolk which develops into a embryo (the blastodisc in infertile eggs and the blastoderm in fertile eggs) is described and categorized. Blastoderms were divided into 11 categories. The majority were a pale whitish nearly uniform color possessing a slightly more dense whitish coloration in their center. Other blastoderms deviated slightly from this appearance. In contrast, blastodiscs were divided into 6 categories and were characterized by a small, dense white, irregularly shaped area. These identifying characteristics of the blastoderm and blastodisc will assist hatchery operators and others in determining true fertility. Since differences between the blastoderm and blastodisc are often subtle, it was recommended that individuals initially work with eggs from virgin hens prior to attempting true fertility estimates on eggs from inseminated flocks.
Technical Abstract: The blastoderm (fertile) and blastodisc (infertile) of fresh laid eggs and eggs stored prior to incubation exhibit subtle but definable morphological variations. Such variations may make attempts to determine true flock fertility based on the appearance of the blastoderm/blastodisc difficult. The objectives of this study were to define and categorize such morphological variations and to determine if sperm influence the frequency distribution of the different categories. Eleven categories of blastoderms were defined on the basis of relative density and appearance of the area alba, area pellucida, area opaca, and the periblast. Blastodiscs were divided into 6 categories and were best differentiated from the blastoderms by the presence of vacuoles around the central dense area. Blastodiscs were also discernible from blastoderms on the basis of their overall dense white appearance. Differences in the frequency distribution of some of the blastodisc categories between virgin and inseminated hens may be due to the effect that supernumary sperm may have on the organization of the blastodisc (no fertilization but supernumary sperm present) or blastoderm (fertilized but failed to develop). It is recommended that before starting true fertility determinations, one should study the appearance of blastodiscs from virgin hens and then the blastoderm from inseminated hens in order to best appreciate the subtle differences in shape and density of the blastoderm/blastodisc structural components.