H. A. RAGAN, P. L. HACKETT, B. J. MCCLANAHAN AND W. J. CLARKE 
921 
Farrowing Performance 
An extensive statistical analysis of the far- 
rowing performance of the animals ingesting 
^^Sr has been previously published. Except for 
weaning weights of offspring from the original 
625 /iCi/day dams, there were no differences 
in liter size, percentage of stillborn, birth 
weights, or weaning weights between control 
and animals ingesting up through 625 jiiCi/day. 
The lower weights of 625 jitCi/day offspring 
were probably due to the severe radiation ef- 
fects produced in the dams resulting in reduced 
lactation during the nursing periods and to the 
accumulative radiation effects on the neonates. 
Farrowing parameters in the Fl generation 
dams, ingesting 0 through 125 ftCi/day, were 
mdistinguishable, with the exception of larger 
litters in the 25 ftCi/day group. The reason for 
this difference is not apparent. 
Original sows of the 3,100 jU,Ci level failed to 
aurvive the gestation period, and 625 ftCi/day 
offspring died before sexual maturity, so that 
there are no Fl nor F2 generations, respec- 
tively, in these groups. 
It is important to note that the lowest level 
fed these swine (1 ftCi/day) results in a body 
burden approximately 5 times higher than the 
International Commission for Radiation Protec- 
tion body burden limits for occupational expo- 
sure in man,^ and is 2,000 times greater than 
the highest ^°Sr level ever reported in Ameri- 
can diets.'* Even at levels 125 times these values, 
there were no adverse affects noted on farrowing 
performance. 
Life Span Effects 
Currently there are 78 swine still alive that 
were assigned to the original study. These in- 
clude thirty-two controls, twenty-eight 1 /xCi off- 
spring, eleven 5 fxCi offspring, and two 25 /nCi 
original sows and five of their offspring. The re- 
sults of cumulative mortality data, though in- 
complete at this time, indicate increased deaths 
in original pigs of the 625 and 125 /xCi/day 
groups after 1 and 5 years, respectively, and 
possibly after 10 years in the 25 /xCi/day 
group.i'^ Cumulative mortality in the offspring 
of the 1, 5 and 25 /u,Ci/day groups was not sig- 
nificantly greater than control values through 9 
years of age. The high mortality rates in the 
125 and 625 /aCi/day groups were due to the ex- 
treme stresses placed on the hematopoietic sys- 
tem by ^"Sr. The vast majority of deaths, or 
cases requiring euthanasia, in all groups over 5 
years of age were due to uterine tumors or 
faulty dentition. 
The mortality rates in the uterine milk expo- 
sure study are extremely interesting. The ani- 
mals that have received ^^'Sr exclusive of the 
gestation period, that is only during the nursing 
period and then by feeding, had a 70% mortal- 
ity by 36 months of age, whereas those exposed 
to "°Sr in utero, nursing, and by subsequent 
feeding experienced only a 22% death loss over 
the same time period. The one death in the 
group exposed in utero only, was a non-radia- 
tion related acute necrotizing pancreatitis. 
Osseous Lesions 
Radiographically, there were no definitive le- 
sions at ingestion levels less than 125 /iCi/day. 
At 125 /uCi/day, radiolytic areas became appar- 
ent in the mandible after approximately 4 years 
of ""Sr ingestion. The same was true of 625 jU,Ci 
offspring taken off ^°Sr feeding and allowed to 
survive 2 to 3 years. In these higher dose levels, 
there occurred rather severe periodontal osteo- 
necrosis resulting in early loss of teeth and/or 
suppuration. These observations were not sur- 
prising since greater than 30% of the ®^Sr 
body burden was located in the skull,^^ par- 
tially due to a greater ''^Sr deposition per gram 
of bone in this area.^^ 
Histologically, the ^°Sr induced bone lesions 
consisted of irregular calcification and an in- 
crease in resorption cavities, reactive bone, and 
fibrosis, progressing to severe osteonecrosis at 
ooSr levels of 625 )LcCi/day and above. A de- 
tailed analysis of histologic changes by dose lev- 
els has not been made at this time due to dimin- 
ished bone effects at the lower dose levels. As 
the 1, 5, and 25 /nCi/day groups accumulate a 
greater radiation dose, a difference may be de- 
tectable if the survival time is sufficiently long. 
Although a high incidence of bone tumors 
was predicted as an end result of ^<'Sr feeding, 
this has not proved to be true. Only seven ani- 
mals in the chronic toxicity study have devel- 
