PRINCIPLES OF LIVESTOCK BREEDING. 5 



early maturity in growth that has been one of the characteristics for 

 which the domestic animals have been most carefully selected. 



Under favorable conditions hogs, sheep, cattle, and horses mature 

 at remarkably early ages. Females usually become mature a little 

 earlier than males under the same conditions, but the difference is 

 not great. Boars and sows have been known to breed as early as 

 3 months, bulls and heifers at 4 months, rams and ewes at 5 months, 

 and stallions and mares at 12 months. It is not, however, considered 

 advisable to breed animals until some time after sexual maturity 

 has begun, in order to avoid interference with their development. 

 Moreover, the young will not obtain so good a start as they should 

 unless the dam has nearly finished her own growth. It has also been 

 asserted that the offspring of a very young sire are apt to be unthrifty, 

 but there seems to be little evidence for this belief. Sows may usually 

 be bred without harm at about 8 months, permitting their offspring 

 to be born just a year from their own birth. Ewes are often bred 

 at 7 months to lamb at a year, but under ordinary conditions a thrifty 

 flock can not be maintained unless breeding is deferred until a year 

 later. Heifers may usually be bred at 15 months, which means 

 calving at 2 years of age. Most fillies can be bred at 2 years and 

 practically all by 3 years. Limited use of males may be begun at 

 about these same ages. 



FREQUENCY OF SERVICE. 



The number of females which can be served by a mature male 

 varies greatly under different circumstances. Most care seems to be 

 necessary with the stallion, in which fertility rapidly declines after a 

 number of daily services. Eighty mares is about the limit of the 

 number which should be served by one stallion in a season. With 

 careful handling a single bull may be used with 60 or 70 cows, a single 

 ram with even more than 100 ewes, and a single boar with 30 or 40 

 sows. Under range conditions the numbers are much less. One 

 bull may run with 20 to 30 cows and one ram with 40 to 70 ewes. 



The principal effect of too frequent service on a mature male seems 

 to be temporary sterility. Daily service by a vigorous stallion was 

 found by Lewis, of the Oklahoma experiment station, to be accom- 

 panied with a rapid decrease in both the number and vitality of the 

 sperm cells. It is a common belief that fertilization by the weakened 

 sperm cells, formed after excessive service, will result in unthrifty 

 young, but the experimental evidence does not support this view. 

 O. Lloyd-Jones and F. A. Hays, of the Iowa experiment station, made 

 extensive experiments on rabbits to test this question. After too 

 frequent service they found a marked decline in the percentage of 

 pregnancies induced and ultimately a decline in the size of litters, 



