10 
BULLETIN 996, U. S. DEPARTMENT OF AGRICULTURE. 
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 have produced 
lambs at a rate of 4.7 more per 100 ewes 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. 
The number of cases considered is so limited in this table that 
results might vary greatly with additional data in regard to the 
influence of grandparents upon number of lambs produced per 100 
ewes. There does not appear to be any connection of practical value 
between lamb production and the fact of sires and dams having 
been singles or twins. 
Table 5. — Effect of breeding on twin production of Southdown ewes in Government 
flock. 1 
Ewes' breeding. 
Number 
of ewes. 
Number 
of lamb- 
ings. 
Number 
of lambs 
dropped. 1 
Born twins: 
Sires twins, dams twins . . , 
Sires singles, dams twins . . 
Sires twins, dams singles . . 
Sires singles, dams singles . 
Average for twin ewes . . 
Born singles: 
Sires twins, dams twins . . , 
Sires singles, dams twins . . 
Sires twins, dams singles . . 
Sires singles, dams singles. 
Average for single ewes . 
12 
S4 
12 
134 
Per 100 
ewes. 
133 
142.9 
116.6 
142.5 
140.9 
14 
70 
21 
111 
157.1 
145.7 
109.5 
132.7 
136.2 
1 In a study of more than 10,000 sheep taken from the American Shropshire Sheep Record, Rietz and 
Roberts found twin ewes to have produced 144.1 lambs per 100 ewes, while singles produced 135.9 lambs per 
100 ewes. These data were obtained from flocks of variable management, however, which might in itself 
tend to make f of correlation between successive generations in numbers produced at a birth. See 
"Degree of Resemblance of Parents to Offspring, with Respect to Birth as Twins for Registered Shropshire 
Sheep," in Journal of Agricultural Research, Vol. JV, No. 6, Sept. 15, 1915. 
A safer way of appraising the possibility of increasing twin pro- 
duction by selection is to take into account the full records of female 
ancestors rather than a single birth in which the particular sire or 
particular dam was produced. 
VALUE OF TWIN LAMBS IN COMPARISON WITH SINGLES. 
Sheep raisers differ in their ideas of the desirable size of the lamb 
crop. At one extreme are ranchmen, chiefly interested in wool pro- 
duction, who consider twins as undesirable because feed conditions 
are unfavorable to a ewe's furnishing more than sufficient milk for 
one lamb. Even in such cases, however, it is always likely that a 
