878 
GENETIC AND BIOLOGICAL EFFECTS OF RADIATION 
Table III. — The Mortality and Survival Time of Burros and Swine Exposed to Daily Doses of "Co Gamma Radia- 
tion until Death 
Daily Dose 
(R) 
No. of 
Animals 
Exposure Rate 
(R/min.) 
Av. Weight 
(Kg) 
Mean Surv. 
Time (days) 
Mean Cumu- 
lative Lethal 
Dose (R) 
Ref. 
No. 
Swine 
100 
60 
0.55 
58 
22 
2,220 
16 
100 
32 
0.47 
46 
56 
5,600 
17 
50 
10 
0.55 
66 
206 
10,250 
26 
Burros 
100 
10 
0.8 
180 
23.3 
2.330 
27 
50 
10 
0.8 
180 
30.3 
1,570 
28 
25 
10 
0.8 
180 
63.0 
1,675 
28 
conditioning exposure the LDsooo had in- 
creased by a factor of 1.64 (Table IV) above 
that for nonconditioned swine.- The apparent 
radioresistance was evident at 61 days and 107 
days after exposure. Recovery from radiation 
injury in sheep measured by the same tech- 
nique was approximately 70% at 30 days after 
irradiation.^^ 
Genotype 
The influence of genotype on the response of 
animals to irradiation has long been recog- 
nized.1^21 From 2 experiments involving three 
breeds of swine exposed to daily doses of 100 R 
until death,!^ it was concluded that the mortal- 
ity response (Figure 3) was influenced by ge- 
netic and physiologic factors other than those 
associated with breed definition. Environmental 
factors and nutrition in early life may con- 
tribute substantially to the variation in the 
mortality curve for swine. 
Age and Size 
The high correlation between age and size 
of swine less than 1 year old limits independent 
interpretation of either of these variables rela- 
tive to influence on radiation response. The 
LD50/30 for young pigs appears to be less than 
Table IV. — Thirty-Day Mortality of Swine before and 
after Conditioning Exposure (CE) to 1 Mvp X-rays* 
CE (R) 
Days after 
CE 
LD50/30 
(R) 
Recovery 
% 
Mean Survival 
Time of 
Decedents 
( days ) 
0 
399 
15.6 
240 
3 
282 
51 
16.3 
266 
7 
306 
66 
13.3 
265 
20 
654 
196 
11.3 
♦Nachtwey, Ainsworth, and Leong.= 
that for swine 8 to 9 months old,^^ but the data 
are not adequate for valid comparisons. In view 
of the range of LD50/30 listed for various experi- 
ments (Table I), it is of interest to note the 
similarities in data from different laboratories 
for swine of the same breed, age and size ex- 
posed to X-rays and gamma-rays at dose rates 
of similar magnitude.^-^ 
LATE EFFECTS 
Late effects of mixed gamma-neutron and 
X-irradiation were studied in swine throughout 
their life span.^^ The swine were exposed to 
bomb radiation at 4 months of age (LD50/30 was 
486 rads).* Thirty percent of the swine were 
survivors of a second radiation dose of X-rays 
(350 rads plus) 2* when they were approximate- 
ly 8 months old. The total combined dose for the 
swine ranged from 15 to 850 rads (Table V) . 
Visible clinical changes were similar in the 
irradiated and control swine except for ap- 
parent unilateral atrophy of the musculature 
(Figure 4) in some of the irradiated individuals 
Table V. — Number of Swine per Dose Exposed to Bomb 
Radiation and X-rays 
Number of Swine 
Dose (rads) 
Total 
Males 
Females 
Controls <1 
35 
23 
12 
15 
8 
5 
3 
75 
7 
3 
4 
250 
10 
5 
5 
380 
9 
7 (D* 
2 
425 
10 
4 
6 
(3) 
480 
5 
2 
3 
535 
5 
5 (1) 
0 
600 
7 
5 (5) 
2 
(2) 
730** 
10 
5 (4) 
5 
(5) 
*( ) — Number of swine 
bomb exposure. X-ray dose 
**Mean dose (range 695 
reirradiated with X-rays 
was approximately 68% 
to 850 rads). 
4 months after 
of total dose. 
