10 MASS. EXPERIMENT STATION BULLETIN 307 



The mode of inheritance of intensit> has been reported by Hays and Sanborn 

 (1927b). Two dominant genes I and I' are concerned. Hens carrying gene I 

 alone ha^•e an average winter clutch size greater than 2 but less than 2.6. Gene 

 r gives a clutch size of about 2.6. Both genes together increase the clutch size 

 up to 3 or more eggs throughout the winter season. There is no sex linkage for 

 clutch size. Improvement in clutch size has been made possible through the 

 use of breeding stock showing the ability to la\" large numbers of eggs in succession 

 throughout the winter season. The minimum winter clutch size for breeders 

 should be 3 eggs, and males should be constanth selected for the ability to trans- 

 mit large clutch size to their daughters. 



l]'i)iter Pause 



Winter pause or the cessation of laxing for four cr more da>s between Novem- 

 ber 1 and March 1 of the pullet year reduces the number of eggs laid in a year. 

 The simple correlation between length of pause and annua! production is re- 

 ported bj" Hays and Sanborn (1926b) to be — .2107 + .0176, and the net cor- 

 relation was given as — .5487 + .0128 (Hays and Sanborn, 1927b). The fact 

 is very evident, therefore, that the appearance and duration of the pause exercises 

 a very significant influence on the number of eggs laid. 



The data from this station point rather definitely to both inheritance and 

 environment as responsible for winter pause. There is very great difficulty in 

 separating the two causes, and this retards progress in eliminating pause from the 

 flock. The fact that, in full sisters hatched on the same date and housed together, 

 some exhibit pause and some lack it, rather strongly suggests that inheritance 

 is concerned. Furthermore, the average duration of pause per family has been 

 reduced b> selection even though the proportion of birds without the four-day 

 pause has not significanth- changed during the last twenty years. There appears 

 to be one dominant factor M concerned in hereditary pause, as Hays (1924) 

 points out. The logical procedure in eliminating this character consists in the 

 constant selection of pause-free breeders and in hatching and housing under 

 optimum conditions at all times. 



Broodiness 



Brood\' periods represent periods when production ceases. On the average, 

 each broody period occasions a loss of about fifteen days of egg production. 

 Hays and Sanborn (1926a) reported that, of the original flock hatched in 1912, 

 89.6 per cent were broody during the first la\ing year. As the experiment has 

 progressed the percentage of brood\' birds has greatK' decreased, reaching a mini- 

 mum of 11.7 per cent in 1932. Along with the decrease in percentage of broody 

 birds there has occurred a high reduction in number of broody periods per broody 

 individual. For example, the 1913 flock averaged 5.4 periods per individual 

 broody bird, while the 1923 flock averaged but 1.9 periods per broody bird. 

 Hays (1933b) presents definite experimental evidence showing that degree of 

 broodiness measured by number of broody periods depends on inheritance. 



The presence of broodiness has been shown by a number of workers to greatly 

 reduce egg production. Jull (1932) reports that 494 non-broody Rhode Island 

 Red birds averaged 204.78 eggs, compared with 179.65 eggs for 477 broody 

 birds. Ha\s (1933b) reported that 267 birds in a non-broody line averaged 

 209.81 eggs, while 259 birds in a broody line averaged 179.02 eggs. The net 



