HATK OK LAY INC AM) V.GG I'HODUCTION 189 



12. (.'orri'ldfiim lUtxcicii .liiininl l''.<l<i Ixtcoril (iitd A'<7 Winter Rule. 



Net wiiittM- rate lias been considered one measure of intensity or rati" 

 of layinii. There yet remains to be studied the relation between winter 

 rate and annual egfT yield. A correlation table has been constructed for 

 the entire population and tlie followinp,- constants have been arrived at: 



Xiunhrr of birds 2528 



-Mean annual egg" record 182. 9() 



Annual egg record standard deviation ±-t2.83 

 Mean net winter rate 68.27 



Winter rate standard deviation ±8.81 

 Coefficient of correlation +.4769 ±.0104 



A rather intimate correlation exists between net winter rate and annual 

 production. As a criterion for predicting annual egg production, net 

 winter rate is superior to any other thus far considered. This fact would 

 seem to indicate that the rate of laying up to March first is an index to 

 the probable rate throughout the year. 



D. ANNUAL RATE OF LAYING 



Annual rate is taken as a long-time measure of intensity. The time 

 interval employed in calculating the rate for each individual is the persist- 

 ency interval or period from first pullet egg to complete molt. The mean 

 time interval for the 1916 flock is 248 days, and the maximum time interval 

 was in the 1922 flock with 330 days. For mean persistency of other flocks, 

 see Massachusetts Agricultural Experiment Station Technical Bui. 9. An- 

 nual rate is a gross representation of the percentage of time in the produc- 

 tion year that each bird actually laid. The relation of annual rate to hatch- 

 ing date, age at first egg and weight at first egg is first considered, and 

 finally the relation of annual rate to annual production. 



13. Correlation JietiCeeii Hatrhini/ hate and Annmd Rate. 



Date of hatching is known to l)e of considerable practical importance. 

 In previous publications it has been shown to influence age at sexual 

 maturity, winter pause, and annual persistency, as well as rate of growth. 

 It is therefore desirable to know if hatching date shows any influence upon 

 annual rate. The population over the ten-year period was tabulated in a 

 correlation table which gave the constants below: 



Number of birds 2560 



Mean hatching date (Apr. 18) 4.29 



Hatching date standard deviation ±2.26 



Mean annual rate 57.57 



Annual rate standard deviation ±9.57 



Coefficient of correlation +.0318 ±.0133 



The mean annual rate above shows that the birds averaged to lay 57.57 

 per cent of the time between first egg and the onset of complete molt. 

 This population of 2560 individuals had a mean annual egg production of 

 181.59. Simple calculation of the time interval shows it to be 315 days. 



