8 
BULLETIN 996, U. S. DEPARTMENT OF AGRICULTURE. 
ewes not dropping twins. In our experimental flocks, however, 
ewes have never been discarded on that account, although some ewes 
have been kept to advanced age that might have been disposed of 
one or two seasons earlier if it had not been for their marked prolifi- 
cacy. The figures given in Table 3 for ewes over 6 years old may, 
therefore, have been to a slight extent affected by selection. The 
data given include nine years' records. The ages are those at time 
of lambing and not at time bred. Only ewes producing lambs are in- 
cluded in this table. 
Table 3. — Effect of age of ewes on number of lambs dropped in experimental flocks. 
Age of ewes. 
Cases of 
lambing. 
Number 
of lambs 
dropped. 
Age of ewes. 
Cases of 
lambing. 
Number 
of lambs 
dropped. 
Years. 
2 
79 
63 
67 
62 
Per 100 
ewes. 
111.4 
123.8 
143.3 
143.5 
Years. 
6 
49 
35 
22 
8 
Per 100 
ewes. 
161.2 
3 
142.8 
4 . 
8 
113.6 
5 
9 
162.5 
TWIN PRODUCTION AS AFFECTED BY BREED OF EWE. 
Evidence as to inheritance of fertility makes it appear that vari- 
ous breeds or strains have each an inherited limit of fertility and that 
the obtaining of the full possibility in any one season will be deter- 
mined by the extent to which the conditions and management favor 
the full utilization of the inherited capacity. 
Records of actual returns from 189 flocks representing 9 breeds for 
the seasons of 1919 and 1920 were obtained by the Animal Husbandry 
Division through the kindness of breeders who reported. The aver- 
age number of lambs in proportion to ewes, lambing in the spring, is 
shown below, also the separate record of the 2-year-old ewes drop- 
ping lambs the first time) and the highest flock average reported for 
each breed. The table gives the average of the two seasons' reports. 
The high return for the breed is for a single season. 
Table 4. — Record of lamb crops, by breeds, from 189 flocks. 
[Average of seasons 1919 and 1920.] 
Flocks. 
2-year-old ewes. 
Aged ewes. 
Total ewes. 
Highest flock. 
Breed. 
Ewes. 
Number 
oflambs 
dropped. 
Ewes. 
Number 
oflambs 
dropped. 
Ewes. 
Number 
oflambs 
dropped. 
Ewes. 
Number 
oflambs 
dropped. 
Xu ir>be r. 
26 
11 
IS 
27 
26 
16 
25 
16 
24 
Xumber. 
215 
40 
96 
138 
549 
91 
167 
84 
1S6 
Per 100 
ewes. 
146 
145 
144 
143 
139 
135 
134 
123 
111 
Xumber. 
566 
106 
214 
378 
S57 
190 
402 
184 
667 
Per 100 
ewes. 
163 
161 
156 
153 
14S 
148 
154 
149 
125 
Xu77iber. 
7S1 
146 
310 
516 
1,406 
281 
569 
268 
853 
Per 100 
ewes. 
158 
157 
152 
151 
144 
144 
148 
141 
Xumber. 
6 
11 
6 
6 
6 
23 
6 
8 
9 
Per 100 
ewes. 
200 
191 
Oxford 
200 
Southdown 
200 
200 
200 
183 
Tunis 
Rambouillet 
200 
177 
