WINTER CYCLF, AND WINTKH I'M'Sl'. 



!()' 



generally eliaraeterized hy partial or eomplete iiiiilt. Apparently nioilinf;-, 

 wliieh jueeedes the development, of a new growlli of feathers, is a phenome- 

 non initiated by a eessation of aetive funetioning of the rejjroduetive system. 

 A number of environmental intluenees as well as inherent feeimdity tluis 

 appear to' be eoneerned in the dilVerent pauses of the pullet laying year. The 

 sunj total of the winter })ause may or may not be represented by a continu 

 ous period of non-production. In other words, there may be several pauses 

 of four or more days with some production intervening. In these studies such 

 pauses have been added together and such individuals ])laeed in the san)e 

 class with birds whose pause is unbroken. 



The duration* of winter pause is recognized to be de])endent upon environ- 

 mental conditions such as hatching date, feeding and housing, weather con- 

 ditions, and all other influences that may affect the physical condition and 

 state of metabolism of the pullet. Since age at which .sexual maturity is 

 attained is modified by such controllable conditions as date of hatching, as 

 Hays and Sanborn (192+) point out, and since age when sexually mature 

 largely governs the time of beginning to lay, a complex relationship must 

 exist between age at first egg and winter pause. 



The presence or absence of winter pause depends upon inheritance, as 

 Hays (1924') points out. Pullets that exhibit a winter pau.se of a week or 

 more before March first are known to carry a dominant factor M, while 

 non-pause pullets are recessive and lack factor M. This factor is transmitted 

 equally by both males and females. In this connection, breeders should bear 

 in mind that genetically non-pause pullets may exhibit a winter pause 

 brought on by disease, abrupt changes of feed, moving to new quarters, and 

 other environmental influences largely within control of the poultryman. In 

 tlie breeding flock of the Massachu.setts Agricultural Experiment Station 

 extreme care has been exercised to keep environmental conditions constant 

 from year to year in order that inherited traits affecting fecundity may be 

 studied. 



Character of Birds Used 



This study includes all Rhode Island Red females, hatched from 1916 to 

 1021, on which pullet-year trapnest records are available. The flocks each 

 year are made up of all the daughters from each individual female whose 

 progeny was retained. Culling within the family has not been practiced. 

 The major portion of birds in each flock belong to the fecundity experiment. 

 There are, however, a limited number of birds bred for non-broodiness, some 

 lor intense broodiness, some for luitchai)ility, some for color, and a few 

 inbreds that arc included, l^ullet-year records alone are used in this study. 

 The heterogeneity of the flock can scarcely be considered as a factor a fleet- 

 ing the constants presented in this report. 



Two possible methods are open for attacking these questions in a large 

 population made up from nine years' breeding for fecundity. The first 

 method is the use of the coefficient of correlation. The second po.ssible mode 

 of attack is through the presentation of actual data by families tracing to 

 both foundation males and females through nine successive years. The possi- 

 bilities of the two methods may be briefly considered. 



* In a small percentage of the flock the pause begun Inte in February and sucn 

 birds did not resume laying until some time in March or later. In these cases, dura- 

 tion of pause is calculated when production is actually resumed. 



