RATE OF GROWTH OF CHICKS 



319 



eggs than pullet mothers. These eggs hatched into larger chicks which re- 

 tained their weight advantage to about 16 weeks of age. At 21 weeks of age, 

 chicks from pullet mothers approached the same mean weight as chicks from 

 hen mothers. In the light of these data and other data presented by Hays 

 (1928), chicks from hen mothers appeared to be superior to those from pullet 

 mothers only up to about four months of age. 



5. Relation of Early Growth to Future Vigor and Egg Production 



Table 7 presents data on the relation of body weiglit of pullets at four 

 weeks of age and at 21 weeks of age to vigor and to their later egg pro- 

 duction. Vigor in this case is measured by the mortality rate in the laying 

 houses during the first laying year for all pullets housed. This measure of 

 vigor was suggested by Hays and Sanborn (1928) in previous studies on the 

 same flock. Pullets were classed as small if they weighed less than .5 lb. at 

 four weeks of age and as large if they weighed .5 lb or over. At the age of 

 21 weeks the small group was made up of birds weighing less than 4.5 lbs. 

 and the large group of birds weighing 4.5 lbs. or more. Such a grouping is 

 purely arbitrary but furnishes a working basis in selecting pullets to be re- 

 tained for egg production purposes. 



Vigor 



Table 7 shows that the small pullets at four weeks of age exhibited a 

 higher mortality rate in the laying houses than the large pullets in each of 

 the five years reported. This consistent difference suggests superior vigor in 

 the large birds. However, when the weighted mean mortality rate is con- 

 sidered for the entire period, there is a difference of but 1.41 per cent in 

 favor of the large group. On the whole, these data, while not conclusive, sug- 

 gest the probability that rapid growth up to four weeks of age is associated 

 with superior vigor to some extent. 



Table 7. — Relation of Weight of Pullets to Mortality Rate in Laying Houses 

 and to Annual Egg Production. 



At 4 Weeks of Age 

 SMALL— UNDER .5 POUND LARGE— ..5 POUND OR OVER 



At 21 Weeks of Age 

 SMALI^UNDER 4.5 POUNDS LARGE— 4.5 POUNDS OR OVER 



