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. 
