WINTER CYCLE AND WINTER PAUSE 



IN RELATION TO WINTER AND ANNUAL 



EGG PRODUCTION. 



By F. A. HAYS and RUBY SANBORN 



IXTRODUCTION 



Winter cycle is represented by a period of continuous egg laying during the 

 winter season. February 28 or 29th is arbitrarily chosen as the closing date 

 of the winter period. A distinct cessation of laying before the end of Febru- 

 ary may be assumed to mark the end of the winter laying cycle. Just what 

 length of pause should be chosen to mark the end of the winter laying cycle 

 is purely arbitrary. Goodale (1918) suggested that a ten-day cessation of 

 laying is sufficiently small to mark the end of the winter cycle. In the studies 

 reported here, a four-day interval is considered as a winter pause because, in 

 the flock studied, such a pause generally means the omission of one clutch* 

 of eggs. The omission of one clutch of eggs really marks a distinct break 

 in the functioning of the reproductive system and probably represents the 

 termination of a laying cycle. Pauses due to broodiness or to injury or dis- 

 ease are not considered, and only pauses occurring between November 1 and 

 February 28 or 29 are classed as winter pauses or as marking the end of the 

 winter cycle. 



Winter cycle may further be defined as total days from dkte of first egg 

 to a pause of four or more days, the pause being considered only between 

 the dates November first and March first. Winter cycle length can therefore 

 be determined only for the pause class of birds, as Goodale (1918) pointed 

 out. Winter cycle is probably inherited as a recessive, according to Goodale 

 (loc. cit.) ; but he failed to discover a relationship between number of eggs 

 laid in the winter cycle and duration of winter pause. 



Winter pause may be defined as the period when egg production ceases, 

 following the termination of the winter cycle and previous to the initiation 

 of the spring laying cycle. Pearl (1912) and Goodale (1918) make reference 

 to winter pause in relation to fecundity. Pearl (loc. cit.) found that the 

 winter cycle in Barred I'lymouth Rocks was characteristically terminated l)y 

 a cessation of production. Goodale (loc. cit.), on the other hand, observed a 

 cessation of production previous to March first in but a part of a Rhode 

 Island Red flock. Goodale (1922) states that winter pause is due in part 

 to inherited characteristics and in part to environmental conditions. He dis- 

 covered a rather intimate relation between the time of beginning to lay in 

 the fall and the appearance and duration of the winter pause. 



Winter pause is usually associated with the shedding of some feathers, or 

 partial molt, as Hays (1924) suggested. Furthermore, a cessation of pro- 

 duction during broodiness or at any other time during the hiying year is 



* The term "clutch" refers to the number of eggs laid on successive days, which 

 js more or less characteristic of the individual hen. 



