The effects of continuous low level gamma irradiation (Co⁶⁰) on the reproductive ability of the Spanish goat

Abstract

This study was conducted to obtain data on the effects of low level continuous gamma irradiation at levels of 0, 2R, 7R, 30R and 40R per 20 hour day for the lifetime of the individual. Twelve males and 11 females were randomly assigned to each of the control, first 30R and 40R groups which were placed on experiment April 30, 1965. Twelve males and 12 females were assigned to each of the control, second 30R, 7R, and 2R groups and placed on experiment September 30, 1965. A median death time (MDT) of 56 and 50 days was observed for the 40R males and females, respectively. The MDT was the same (80 days) for both males and females in the first 30R group but in the second 30R group it was 101 and 86 days for the male s and females, respectively. The MDT for the 7R males will be much longer than for the females. As of April 1, 1967, two 7R males and 8 females have died of irradiation sickness resulting in a MDT of 348 days for the females. In this study the female appears more sensitive to irradiation than the male when longevity is evaluated but probably the least sensitive reproductively. The ability of females to survive in a given irradiation environment was the only definite impairment to female reproduction. All females that lived long enough produced consecutive kid crops with the exception of two females in the first 30R group. One female in the second 30R group gave birth to a set of twins and 8 others were pregnant at exitus, having conceived shortly after being placed in the irradiation environment. All 7R females completed one gestation, however, eight females died prior to the time allowable for completion of the second gestation period. The other four 7R and all 2R females have completed their second gestation period and are apparently pregnant for the 3rd time. The irradiated kids in the first kid crop were somewhat smaller. However, there were no differences observed in the birth and weaning weights of the kids born as a result of the second gestation period. The effects of irradiation on male reproduction has varied with the level of exposure. Total sperm production (TSP) started declining after 7 weeks of irradiation in the 40R and both 25R groups reaching essentially aspermia by the 18th week. A decline in sperm motility and percent alive occurred along with the drop in TSP. Percent normal sperm started declining on week 9 and reached a low on week 12, after which they recovered slightly before aspermia was reached. The three most predominant types of abnormal sperm in order of greatest magnitude were coiled tails, tailless heads, and protoplasmic droplets. The TSP started declining on weeks 11 and 16 and by the 22nd week the average sperm per ejaculate was only 5% and 40% of the control numbers; and by the 62nd week 7% and 26% for the 7R and 2R groups, respectively. Motility and percent normal sperm declined gradually from week 14 for the 7R and week 18 for the 2R groups. However, the percent live sperm was significantly lower than the controls in the 7R group from the 18th week but did not become significantly less in the 2R group until the 53rd week. It has thus been concluded from the data presented, that small daily doses of continuous irradiation of 2R/day and above, will significantly reduce the quality of the semen produced by male Spanish goats. The adult male Spanish goat, like the adult male albino rat appears to be more sensitive than the female to daily exposures of low level irradiation over extended lengths of time.