FERTILITY 91 



89. Age and fertility. The fertility of animals is 

 influenced by age. Young animals that have not yet 

 reached maturity are generally less fecund than mature 

 individuals. There is also some evidence to show that 

 old mature animals are more prolific than younger mature 

 animals. It is highly probable that skillful feeding and 

 management may result in a significant increase as age 

 advances. 



90. Relation of age to fertility in swine. At the 

 Missouri Experiment Station, the author has had under 

 investigation the relation of the age of animals to their 

 breeding powers. The animals used in this experiment 

 have been swine, and the general plan has been to divide 

 the sows into three groups according to age. Group I 

 is composed of very young sows from four to five months 

 of age; group II of half mature sows about eighteen 

 months of age ; and group III of mature sows from twenty- 

 four to thirty months old. The young immature sows 

 of group I have been bred at the first appearance of 

 puberty, which in well-fed sows is from four to five months 

 old. The female offspring of the immature sows are 

 again bred at the first appearance of he'at, and this will 

 be continued indefinitely. A number of interesting 

 phenomena have been observed, but only those results 

 which throw light on the relation of age to the fertility 

 of the mother are recorded here. 



91. Influence of age of sow on size of litter. In 

 the Missouri experiment described above, there have 

 been to date (1913) twenty-six litters from immature 

 sows. The average number of pigs to the litter has been 

 four and eight-tenths. From the half mature sows, 

 eight litters have resulted in an average of six and three- 

 tenths to a litter. The average number of pigs in six 



