FERTILITY IN RHODE ISLAND REDS 5 



2. Relation Between Age of Breeding Stock and Fertility 



Curtis and Lambert (1929) studied the effect of age of birds on fertility. Their 

 data showed that cockerels mated to hens gave a greater duration of fertility 

 from a single mating as well as a larger number of fertile eggs than did cockerels 

 mated to pullets. Cocks mated to hens gave a slightly greater duration of fertility 

 but slightly fewer fertile eggs than did cockerels mated to pullets. Cocks mated 

 to hens gave a higher fertility record than cockerels mated to pullets but the 

 number of fertile eggs from the older parents was smaller. 



Jull (1935) reported on fertility in White Leghorns, Rhode Island Reds, and 

 Barred Plymouth Rocks from mating cockerels to pullets, yearlings, and two- 

 year-olds. In the Leghorns fertility declined slightly with an increase in the age 

 of the females. With Rhode Island Reds fertility was essentially identical in 

 pullets and in yearlings, with a slight decline in the two-year-olds. In the Barred 

 Plymouth Rocks highest fertility appeared in the two-year-olds, and pullets 

 showed the lowest fertility. In crossbreeds fertility was greater in the pullets 

 than in the yearlings. 



A study has been made on the effect of age of parents on fertility for the period 

 from 1922 to 1936. In these studies all inbred and outbred matings have been 

 eliminated. The data are divided into the late- and earh-hatched groups. The 

 data for 1926 are omitted as indicated in Section 1. 



The relation of age of male to fertilit}^ may be considered first. It will be noted 

 (Table 2) that the mean fertility from cockerels in the late-hatched group was 

 82.94 percent and in the early-hatched group, 82.73 percent. Yearling males 

 gave a mean fertility of 71.88 and 58.29 percent respectively in the two groups. 

 Two-year-old males had a mean fertility of 68.94 and 30.84 percent. Males 

 three years old or over showed a mean fertility of 24.06 and 30.40 percent. An 

 ideal set-up for testing the effect of age, either of males or females, on fertility 

 would include a large group of males mated to the same group of females, be- 

 ginning when the birds were twelve months old and continuing until they were 

 four or five years old. The number of birds in these tests, however, appears to 

 be adequate to indicate a definite decline in fertility of males with increasing age. 

 Jull (1935) found that White Leghorn and Rhode Island Red males had higher 

 fertility as cockerels than as yearlings. 



Another very significant fact indicated by Table 2 is that cockerels gave the 

 same fertility in the eaily-hatched group as in the late-hatched group, while 

 yearling and older males showed a very significant lowering of fertility by earlier 

 hatching. It is evident, therefore, that the cockerels were in a more active state 

 of sexual function than older males, even under rather severe weather conditions. 



Fertility in females of different ages is recorded in Table 2 under mean of classes. 

 In the late-hatched group, yearling females had a significantly higher fertility 

 than pullets when mated to males of any age. These data are not in agreement 

 with those of Jull (1935), but Jull does not report hatching dates. In the early- 

 hatched group, however, pullets showed a significantly higher fertility than year- 

 lings; but when the eight yearlings that were mated to very old males are omitted, 

 the fertility records of pullets and yearlings do not differ significantly. The 

 group of 52 two-year-old hens appears to have been fully equal to the younger 

 birds in fertility, but the number is too small to carry any particular significance. 

 These data suggest that the fertility of females of all ages is less affected by weather 

 conditions than is the fertility in males. 



The effects on fertility of mating birds of different ages should also be con- 

 sidered. In both groups cockerels gave the highest fertility when mated to 



