FLUSHING TO INCREASE LAMB YIELDS. 9 



the ages of the rams at the time of service. The results did not show 

 any connection between age of sire and number of twins among 

 his "get." 



Overworked or run-down condition of a ram may result in a smaller 

 lamb crop through a lack of numbers or of vitality of the sperm cells 

 in the seminal fluid. Such a lack is most likely to occur in the case 

 of ram lambs running in a flock with the ewes, and it would be more, 

 likely to result in ewes not getting in lamb than in a decreased number 

 of twins. Though improbable, it is possible that a ewe might pro- 

 duce two ova and have one of them fail to become fertilized because 

 of a lack in the number or vitality of the sperm cells. 



BREEDING FOR TWIN LAMBS. 



It appears quite logical to suppose that the proportion of twin 

 births in a flock can be increased by selecting, for breeders, rams and 

 ewes themselves born as twins. However, the facts do not bear 

 out such a supposition. This does not preclude the possibility of 

 increasing lamb yields by breeding, but selection for this purpose 

 should be based on average yields of different strains rather than on 

 records of individuals. 



The fact that a ram was born as a single or as a twin can not reason- 

 ably be expected to have any relation to the number of twins among 

 his offspring. The function of the sperm cells of the male is to 

 fertilize the ova produced by the female, and under ordinary condi- 

 tions the number and strength of the sperm cells is many times greater 

 than actually needed. 



It is reasonable, however, to expect a son of a ewe that is a regular 

 producer of twins to transmit some or all of his dam's capacity to 

 his daughters. Any ewe's inheritance of capacity for bearing twins 

 must therefore be traced through the prolificacy records of her female 

 ancestors. 



In the breeding of the bureau's purebred Southdown flock, records 

 have been obtained of 458 cases of lambing which include only ewes 

 that have dropped lambs at least three times. A few of the ewes 

 had eight or nine lambing records. The relation of the production 

 of these ewes, the fact of their having been born as single or twin 

 lambs, and also whether their sires and dams were born as singles or 

 twins are shown in Table 5. It must be remembered that the fact of a 

 ram or a ewe having been born as a single or twin is in itself an 

 incomplete record of the dam's productive capacity. 



As shown in the table twin-born ewes were found to be 4.7 per cent 

 more prolific than those born singles. The highest record, however, 

 is from ewes born as singles with both parents twins, and the second- 

 highest record is for single-born ewes by single sires from twin dams. 



