tailieunhanh - FACTORS CONTRIBUTING TO YOLK RETENTION IN POULTRY: A REVIEW

Immunosuppression significantly decreases the ability of young poultry to respond effectively to standard vaccinations, and also predisposes them to infection by other specific pathogens. How- ever, sub-clinical immunosuppression is often not readily appar- ent to the farmer, and therefore a common “silent” cause of significant economic losses. Pathogens causing such infectious disease conditions are termed “erosive” for site productivity (Shane, 2004). In contrast, major pathogens with high death rates and rapid spread such as NDV, IBDV or HPAI, although ge- nerically termed “catastrophic” diseases, cause lower economic losses in the longer term than the lower-level but more pervasive and widespread erosive pathogens do | REVIEW ARTICLE Pakistan Vet. J. 24 1 2004 FACTORS CONTRIBUTING TO YOLK RETENTION IN POULTRY A REVIEW K. A. Khan S. A. Khan A. Aslam M. Rabbani1 and . Tipu Department of Pathology and department of Microbiology University of Veterinary and Animal Sciences Lahore Pakistan ABSTRACT Yolk retention and yolk sac infection is considered as an important cause of death in chicken as well as in guinea fowl duck turkey quail and goose. The factors which slow down the rate of yolk absorption and may in turn lead to yolk retention are discussed. Yolk sac infection of bacterial origin is most important among these factors. Other factors which may contribute include posthatch starvation type of initial feed brooding temperature prolonged exposure to hatcher environment and size of birds. Key words Yolk retention poultry yolk sac infection. INTRODUCTION During incubation extraembryonic membranes encircle the yolk substance and constitute the yolk sac which is attached to gut of the chick by yolk stalk. Just before hatching the yolk sac is pulled from the egg cavity to abdomen of chick as an extension of intestine. Residual yolk comprises 20-25 of body weight at hatch but within the first week of life it becomes negligible in size Ramnoff 1960 . There are certain factors that affect yolk absorption and in turn may lead to its retention. Once bacteria get entry to yolk other factors favour rapid bacterial growth and these include the fact that the yolk contains a lot of fat and water favoured nutrients for bacteria. In addition the yolk sac is maintained at the temperature of the hatcher and then at the chick s body temperature which are the ideal temperatures for multiplication of certain bacteria Anonymous 2000 . So yolk retention due to any cause may lead to yolk sac infection. YOLK RETENTION a Incidence Incidence of yolk retention and yolk sac infection is widely reported in literature. Anjum 1997 stated that it was the commonest cause of early chick mortality in Pakistan. .