8 MASS. EXPKRIMKXT STATION RULLETIX 20S 



Part 3. — The Inheritance of Persistency 



High persistency has been reported by Hurst (1921) to be inherited as a reces- 

 sive trait in White Leghorns and White Wyandottes. He measured high persis- 

 tency by the ability to lay at the rate of 30 per cent from July 1 to the close of the 

 la\ing year, no birds being considered high in persistency unless they laid for at 

 least 50 days after July 1. This period would end on August 19 as the earliest 

 date, losing Hurst's dividing age between early- and late-maturing birds at 

 270 days, the absolute length of the biological laying year for the highly persistent 

 birds would be about 9 months or 270 days. 



Hays and Sanborn (1926) report that the Massachusetts Station flock shows two 

 general classes with respect to duration of the laying year — those laying for less 

 than 315 days and those laying for more than 315 days. Hays (1927a) presented 

 evidence to indicate that the ability to lay for 315 days or more depends upon a 

 dominant autosomal gene P. 



This part of the report isconcerned with the ability of dams to transmit persisten- 

 cy to their daughters. The obvious weakness of such a study lies in the fact that 

 genetic records of the sires are not available. In a general way, however, the data 

 will be useful to show whether or not selection of dams alone for duration of 

 biological year increases the length of laying year in resulting daughters. 



Twelve generations of daughters consisting of 231 1 individuals are included from 

 427 dams that had been retained in the flock for two or more full laying years. 

 These dams are the birds that have already been considered in Parts 1 and 2. 

 They are divided into three classes with respect to duration of their biological year. 

 In tabular form are presented the number of dams and daughters concerned, 

 together with the daughters' mean annual persistency records and their mean 

 annual egg records and the mean annual egg record of the dams. 



T.ABLE 2 — REI .\TI0N OF THE LENGTH OF BIOLOGICAL Ve.\R OF DaMS TO ThEIR 



Annual Egg Production and to their Daughter's Annual Persistency, 

 Annu.\l Egg Production, and Laying House Mort.\lity. 



Length of 

 biological year 

 of dams 



Under 315 days 



From 31.S to 365 days 159 



Over 365 days 242 



Table 2 show^s that in the selection of breeders emphasis was laid on length of 

 biological year so that the number of dams concerned in the low class is small, and 

 the majority fall in the group with a biological year greater than 365 days. The 

 mean annual egg records of the dams are also closely associated with the length 

 of the biological year. 



Daughters' annual persistency includes the productive perioil from first pullet 

 egg either to the onset of a 30-day cessation of production after March 1 or to the 

 end of the 365-day laying year. It is evident that this method of calculating per- 

 sistency does not take cognizance of the actual persistency of birds that lay beyond 

 the 365-day period. The difference in mean annual persistency of classes 1 and 2 

 is 5.58+3.84, and of classes 2 and 3 is 5.15 + 1.62. The data therefore show no 

 significant difference in the mean annual persistency of daughters from dams with 

 a biological year of less than 315 days and those from dams with a biological year 



