141 
normal birth weight which is fairly uniform for all healthy animals of a given size 
and breed. It is also undoubtedly true that the birth weight may be greatly influenced 
by the conditions affecting the mother. 
'The nutrition of the embryo, which will be largely dependent upon the condition 
of the mother during pregnancy, will probably he a determining factor in fixing the 
birth weight It is also possible that the condition of the mother during the period 
leading up to the ripening of the egg will influence the nutrition of the embryo, and 
consequently the birth weight of the young. 
During a period of four years the writer kept accurate records of the birth weight 
of lambs from a small flock of sheep. These birth weights were studied in connection 
with the size and condition of the parents, tiie sex of the offspring, and other im- 
portant conditions. Careful records of the subsequent growth of the young were 
also made and important differences noted. One of the subjects of investigate in was 
the possible influence of the increased size or breed of the male upon the birth weight 
of the young. The breeding ewes in this experiment were native sheep purchased 
in the vicinity of the ^Missouri Experiment Station. The rams represented three 
breeds, the Hampshire, Shropshire, and Delaine Merino. In summing up the results 
of the entire experiment it was found that the average birth weight of 41 half-blood 
Hampshire Iambs was 7.8 pounds; of 33 half-blood Shropshire lambs, 8.4 pounds, 
and of 36 half-blood Merino lambs, 7.7 pounds. The average weight of the Shrop- 
shire rams used in this investigation was 195 pounds; of the Hampshire rams. 185 
pounds; and of the Merinos, 142 pounds. These weights have no constant relation 
to the birth weights of their offspring. Not only was this true in individual cases, 
but it also seemed to be true that males of the larger breeds did not produce young 
having a greater birth weight than rams of the smaller breed-. 
By comparing the birth weight of lambs with the weight of the mothers it was 
found that the birth weight of lambs varied directly with the weight of mother. 
This is shown in the following table: 
Relation of weight of dam to birth weight of lamb. 
Weight of dams. 
Below 90 pounds. 
90 to 100 pounds.. 
100 to 110 pounds 
110 to 120 pounds 
120 to 130 pounds 
Average 
Number 
birth 
of 
weight 
lambs. 
of all 
lambs. 
Founds. 
8 
7.2 
6 
7.1 
22 
7.5 
32 
7.9 
23 
8.3 
From this table it would seem that the birth weight of the young has a constant 
relation to the weight of the mother. 
It may be well in this connection to ask what significance the birth weight may 
have in the development of the young animal. To determine this point, the records 
of the growth after birth for periods of six to nine weeks were carefully tabulated, 
and these are indicated in the subjoined table: 
Relation of birth weight f<> subsequent growth 
Birth weight of lamlis 
Average Average 
10 pounds and above 
9 to 10 pounds 
8 to 9 pounds 
7 to 8 pounds 
Below 7 pounds 
Average 
weekly 
weeklv 
Number 
length of 
gam. in- 
gam, ex- 
of lambs. 
feeding 
eluding 
cluding 
period. 
birth 
birth 
weight. 
weight. 
Weeks. 
Pounds. 
Pounds. 
i 
8. 55 
■VI 
4.5 
- 
6. 05 
0.0 
4.2 
14 
7.33 
3.7 
2.5 
13 
9. 03 
3.4 
2.3 
6 
7. 06 
2.62 
1.7 
This table shows that so far as these observations extend the size of the young at 
birth has a very important relation to the subsequent growth of the young animal. 
Large birth weights were in everv case favorable to lanre gains and vigorous growth, 
