MEASUREMENT OF THE WINTER CYCLE IN THE EGG 
PRODUCTION OF DOMESTIC FOWL 1 
By Raymond Pearl, 
Biologisty Maine Agricultural Experiment Station 
In a series of papers the writer and his associates (2, 6, g ) 2 have shown 
that there are to be distinguished definite cycles in the egg-laying activi¬ 
ties of the fowl. The two most striking and definite of these cycles we 
have called, respectively, the “winter” and the “spring” cycles, these 
terms being used because of the seasonal incidence of these periods of 
laying activity. In the writer's studies on the inheritance of fecundity 
(4, 5, 7, 8) in the fowl he has used as an index of the innate fecundity of a 
bird its pullet-year “winter production,” defined as the number of eggs 
produced before March 1 of the bird's pullet year—i. e., the first March 1 
following the individual’s birth. The reasons why this measure of 
productivity rather than some other was chosen for the work have been 
fully set forth in earlier papers and need not again be gone into here. It 
may suffice to say that, by all the tests which it has so far been possible 
to apply, this index of fecundity has proved very satisfactory in practice. 
The results which one obtains with it are duplicated in every essential 
particular if one uses the longer period of one year, but genetic differences 
in fecundity are more strongly emphasized in the shorter period, with a 
corresponding gain in the precision and certainty of the Mendelian 
analysis. 
It has never been contended, however, in any of the writer's work that 
winter production, as above defined, was anything more than an index 
or indicator of innate fecundity. It is logically obvious that the only 
perfect measure of total fecundity would be some direct function of total 
fecundity. All that the writer’s work has shown regarding the point 
here under discussion is that winter production is a good indicator, all 
things considered, of a fowl's innate fecundity capacity. It is not a 
perfect indicator, but that it is a good one is confirmed not only by 
the experience of this laboratory but also by that of other workers 
(j. 3.10). 
In the course of the writer's investigations regarding this character, 
studies have been made of various other fecundity indicators besides 
winter production. The thought occurs to one that possibly under other 
environmental conditions than those prevailing in Maine winter produc- 
1 Papers from the Biological Laboratory of the Maine Agricultural Experiment Station, No. 89. 
2 Reference is made by number to "Literature cited," pp. 436-437- 
Journal of Agricultural Research, 
Dept, of Agriculture, Washington, D. C. 
ay 
Vol. V, No. 10 
Dec. 6, 1915 
Maine—6 
(429) 
