8 MASS. EXPERIMENT STATION BULLETIN 411 



Relation of Annual Variability in Egg Weight to Winter Pause 



Winter pause, as used in these studies, includes a cessation of egg laying for 

 eight or more days between November 1 and March 1 of the pullet laying year. 

 Both time of onset and duration of pause are believed to be affected by environ- 

 mental influences. Evidence was presented in 1924 by Hays, indicating that a 

 major inherited factor for pause was operating. Data were presented later 

 (Hays, 1936) to indicate that the minimum period of non-production associated 

 with inherited winter pause was about eight days. Lerner and Taylor (1939), 

 using White Leghorns, confirmed the observations from this laboratory on Rhode 

 Island Reds. These workers used a cessation in laving of seven or more days 

 between November 1 and March 1 as winter pause. 



The Rhode Island Red females used in these studies were grouped into the 

 "pause" class if they had shown a cessation in egg production of eight or more 

 successive days between November 1 and March 1. Those individuals which 

 did not exhibit a winter pause were grouped into the "non-pause" class. 



The standard deviation in egg weight for the first twelve months of laying 

 was calculated on 273 individuals with winter pause and showed a mean annual 

 variability in egg weight of .99 grams with a standard deviation of .029. The 

 corresponding figures for a population of 145 birds without winter pause were 

 1.03 ± .041 grams. The difTerence between the two populations amounted to 

 only .04 + .05 grams, which has no significance. These data furnish some evi- 

 dence that winter pause bears no relation to variabilitv' in egg weight during the 

 first laying jear. 



Relation of March Variability in Egg Weight to Winter Pause 



March variability in egg weight for 412 "pause" birds was .77 grams with a 

 standard deviation of .018; and for 337 "non-pause" birds, .72 ± .019 grams. 

 The difTerence was .05 + .026 grams and has no significance. These data indi- 

 cate that the presence or absence of winter pause has no effect on the variability 

 in egg weight during the month of March. 



Relation of Annual Variability in Egg Weight to the Broody Instinct 



Goodale, Sanborn and White (1920) have shown the broody instinct to be in- 

 herited, and these observations were confirmed by Hays (1924) and many other 

 workers. Hays and Sanborn (1934) presented data covering a 22-year period, 

 indicating that Rhode Island Red pullets average to lose about fifteen laying 

 days at each broody period. Jull (1940) reported that 494 non-broody Rhode 

 Island Reds averaged 204.78 eggs compared with 179.65 eggs for 447 broody 

 birds. 



In breeding operations there is a constant attempt to eliminate the broody 

 instinct from the fiock. This procedure has been efTective in reducing the inci- 

 dence of broodiness during the first laying year to as low as 2 percent, but never 

 in completely eliminating the broody instinct in any breed. 



In this study it is desirable to know whether the presence or absence of the 

 broody instinct affects the variability in egg weight. The population was divided 

 into broody and non-broody on the basis of their first-year records, and the 

 variability in egg weight records studied. 



The mean annual variability in egg weight for 10 broody birds for the first 

 laying jear was .70 ± .106 grams; and for 383 non-broody birds, the figure was 

 .99 + .024 grams. The difference in the variability of the two groups was 

 .29 + .108 grams and is of doubtful significance. 



