THE BREEDING OF CHICKENS 



163 



use of what he tcrinwl the Uci)r()(JuctivL' Index, which lie 

 l)r(ii)(ise(l as a nieasure of the net reproduetive abiUty of 



Fig. 81 



70 



GO 

 z: 

 o 



h60 

 o 



§40 



h30 



20 

 J 

 "10 







Oo, 



APR, MAY 



MONTH 



.SEPT. OCT. 



Comparison of pullet and yearling production of Leghorns at the Vine- 

 Land International Egglaying and Breeding Contest during the years 1910- 

 191S. 



various matings. This Reproductive Index (IvI) is as 

 follows: 



Number of chicks alive at end of the third week after hatching X 100 



RI = 



Total number of days from the day when this mating began to the 

 day when the last egg from this mating began its incubation. 



It is not altogether clear just what is meant by " the day 

 when this mating began." Obviously the mating must have 

 been made some days before the first eggs were saved in order 

 that fertility might be established. "The day the first egg 

 saved was laid" would possibly be a clearer statement. 



The results of his studies based on the records of 1114 

 matings, shown in Tables XXII and XXIII, clearly indicate 

 that for the stock he was breeding, the first was the best 

 breeding year for I)oth cockerels and pullets. It indicates 

 further that the decline in reproductive ability with advanc- 

 ing a"-e was more rapid for males than for females. 



Pearl specifically states that only well-matured young 



