VIGOR IN PRODUCTION-BRED FLOCKS 



By F. A. Hays, Research Professor of Poultry Husbandry, and 

 Ruby Sanborn, Research Assistant in Poultry Husbandry. 



Introduction 



In pedigree breeding for iiigii fecundity the question of vigor is of para- 

 mount importance because the mortality rate tends to become higher as egg 

 production increases. Without question, tiie complex physiological process of 

 egg lajing places the pullet under a severe test for vigor which may or may 

 not shorten her life. Poultrymen and biologists are not familiar with the vast 

 array of factors concerned, but the foniier are very eager to know how high 

 vigor may be detected in the living bird. 



High vigor may be defined as the possession of all those necessary qualities 

 or characteristics that make possible a long and productive life in the hen. 

 A number of common physical characteristics are made use of in culling 

 operations, but just how mucli weight should be attached to these has never 

 been demonstrated. 



Pearl (1911) points out that adult mortality may be considered as an index 

 of general vitality and constitutional vigor, and presents mortality records in 

 the laying houses for a period of nine years. 



Lippincott (1921) states that there are certain characteristics that are cor- 

 related with that maximum efficiency of all organs termed constitutional vigor 

 l)ut that these characters are relative rather than absolute. He makes ref- 

 erence to breed characters, head characters, body characters, etc. 



Dryden (1921) emphasizes the fact that a hen may not inherit high vigor 

 and that such a hen may break down under the strain of higii production. 

 This worker lays sijiecial stress on the value of high vigor as a necessary con- 

 comitant of inherited high fecimdity. 



Bittenbender (1922) suggests that both males and females should be selected 

 for constitutional vigor and vitality, and that vitality, type and e^g produc- 

 tion are very closely correlated. Such body characters as type of head, beak, 

 eyes, comh, body, breast, legs and toes may be used as indices of vigor. 



Rice and Botsford (192-5) write: "The use of strong, vigorous birds is 

 essential, as it means better fertility and hatchability, and less mortality in 

 chicks." These writers consider the head of the fowl as the best guide in 

 selection for vigor. 



At the present time there is need for well substantiated evidence on the 

 relation of specific characteristics to vigor. 



As the measure of vigor for these studies, mortality rate in the laying 

 bouses for a 365-day period has been used. This period begins when the 

 pullets are housed at about 150 days of age and covers the pullet laying year 

 only. Those families having the lowest mortality rate during the pullet laying 

 year are thus considered to be the most vigorous. 



In this bulletin consideration is given to two general groups of conditions 

 aflFecting mortality in the laying houses: namely, those that may be controlled 

 l)y methods of management, and those that may be controlled by methods of 

 breeding. In the first class may be mentioned age of mothers and hatching 

 dates; in the second group belong age at first egg, weight at first egg, per- 

 sistency, production, etc. Knowledge of the relation of conditions or char- 

 acteristics to mortality rate is useful to poultrymen in developing a manage- 

 ment and breeding program to combine high fecundity and low mortality. 



