OVULATION IN THE DOMESTIC FOWL 



Richard M. Fraps 



Agricultural Research Service, U.S. Department of Agriculture 

 Beltsville, Maryland 



Observations and experiments on many species have contributed much to 

 our knowledge of various aspects of ovarian development and ovulation in 

 birds. The common domestic fowl is, however, the only avian species for 

 which we have today any fairly substantial and coherent perspective — incom- 

 plete though this may be in many respects — of processes directly and in- 

 directly involved in ovulation. 



A number of arguments might be advanced for the seemingly dispropor- 

 tionate concern with ovulation in the fowl, including such things as this bird's 

 ready availability, adaptability to experimental conditions and procedures, 

 and possession of convenient external indices of gonadal function (65). But 

 in addition to these obviously desirable attributes, the domesticated hen 

 continues to ovulate over much of the year, she does so in definite patterns 

 so arrayed as to constitute recurring cycles of considerable experimental 

 significance and, not least in importance, the time of most ovulations may be 

 predicted with a high degree of accuracy. 



With good cause the hen thus deserves its favored position in the study of 

 ovulation in birds. Nevertheless, a sound knowledge of the physiology of 

 ovulation in birds can scarcely be based on any single species, and it is 

 regrettable that so Httle is known regarding these complex and undoubtedly 

 diversified phenomena among other species, and more particularly in wild 

 birds exhibiting restricted breeding seasons. This broader comparative know- 

 ledge seems all the more desirable in view of the suspicion that the domestic 

 hen has been so highly selected for egg production that her reproductive 

 processes can no longer be regarded as representative of birds generally and 

 of wild birds more specifically. 



It is true that broody and incubation behavior have been greatly reduced 

 in many contemporary breeds of fowl, but the same can be said of those wild 

 species, such as the American cowbird and the European cuckoo, in which 

 brood parasitism has become established. It is also true that processes 

 responsible for follicular growth, maturation and ovulation proceed more 

 intensively in the contemporary domestic fowl than in her wild forebears, but 

 this can hardly be held to signify any qualitative change in underlying 



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