WINTER CYCLE OF EGG PRODUCTION IN THE RHODE 

 ISLAND RED BREED OF THE DOMESTIC FOWL 



By H. D. GooDALE, 

 Massachusetts Agricultural Experiment Station 



INTRODUCTION 



The winter cycle of egg production is one of the internal factors 

 concerned in determining total production. It was first recognized by 

 Pearl and Surface in Barred Plymouth Rocks. They state (7, p. gg- 

 100) : ^ 



It will undeniably be advantageous, in studying certain phases of the problem of 

 egg production, to endeavor to use a time unit which conforms to the natural 

 periodicity displayed by hens [italics are mine — H. D. G.]. . . . 



The plan followed at the present time in the investigations in progress at the 

 Maine Station breaks the laying year up into four parts. The first of these includes 

 the months of November, December, January, and February. Broadly speaking, 

 this is the period of winter laying and is so designated. . . . 



The justification for the conclusion that this division of the year is in general a 

 natiu-al one and corresponds to a real cyclical periodicity in egg production is in con- 

 siderable measure to be found in the facts regarding mean monthly egg production 

 and variation in this character set forth in this and the preceding section of the paper. 

 The winter-laying period is a period characterized by rapid increase in mean pro- 

 duction associated with a relatively equally rapid decrease in variability, both 

 absolute and relative. In this period a large part of the flock falls in the A compo- 

 nent of the monthly distributions (see p. 142). This laying period is, strictly speak- 

 ing, not a part of the natural or normal reproductive cycle of the hen. Egg laying 

 in this part of the year is something which diu^ing domestication has been added on, 

 as it were, to the natural reproductive activity of the wild Callus. It is a result of 

 "forcing" or special stimulation. From the evolution standpoint, egg production 

 in these months is a comparatively recent acquisition. Such being the case, the 

 greater variability observed in winter laying is only what would be expected. 



The limits of this artificial winter cycle of egg production are fairly well defined. 

 It begins with the beginning of the laying year. Its other limit is marked by the 

 slacking up in egg production, which occurs in February (see Fig. i). This slacken- 

 ing up in February, which appears to be a characteristic of egg production, generally, 

 is to be explained, we believe, chiefly if not entirely as the result of the ending of 

 the winter cycle by the majority of birds which have laid during the early winter. 

 Such birds rest for a period at about this time before beginning the spring laying 

 cycle. Of cotu-se it must be understood that these statements are made only with 

 reference to what might be called the general or average course of events. Particular 

 birds may form exceptions in their laying. Many birds, of course, have no proper 

 winter cycle of laying at all. They begin to lay for the first time in January or Feb- 

 ruary, and keep on laying without any large break straight through the spring cycle. 



' Reference is made by number (italic) to " Literature cited," p. 574. 



Journal of Agricultural Research, Vol. XII, No. 9 



Washington, D. C. Mar. 4, 1918 



mf Key No. Mass. — 3 



38324°— 18 3 (547) 



