216 SWINE 



then he should not be overworked. One service per day 

 is considered to be sufficient when used for a considerable 

 length of time. When used continuously the whole year, 

 this is too much. In emergency cases, for a short period 

 of time, two or even more services per day may be al- 

 lowed in the case of a vigorous animal, provided he is 

 allowed to rest before and afterwards. 



The Dam. — A sow is useful and should remain in the 

 herd as long as she can produce and raise a large litter. 

 A mistake is very often made by retaining young sows 

 year after year and selling the older ones. It is argued 

 that after producing a litter the sow will make profitable 

 gains, which is naturally very true, and that she can be 

 put in market condition along with the litter to good ad- 

 vantage. While this is true, she is also developing into 

 a more valuable breeding animal. When young sows are 

 being kept year after year the practice of selection, as dis- 

 cussed in Chapter 8, is very largely lost because good in- 

 dividuals do not appear in large enough numbers so that 

 an entirely new breeding herd of good sows can be se- 

 lected year after year. Furthermore, all good appearing 

 individuals are not good breeders because they do not 

 produce large litters, may not give sufficient milk to 

 nourish their litters, may not be good mothers to care for 

 them after farrowing, etc. Thus a mature sow that has 

 been tried should be kept in the herd as long as possible. 

 This can be done with profit, especially when two litters 

 per year are being produced. 



BREEDING THE SOW. 



The period of heat is the time at which a sow is in sea- 

 son and ready to be bred. It usually occurs about every 

 twenty-one days and, if a sow is not bred, lasts for two or 

 three days. The methods employed for serving a sow are 



