Evaluation of sister chromatid exchanges in cattle reared in a radio active belt area of Southern Kerala

Abstract

A cytogenetic investigation on the effect of long-term. background radiation on cattle was carried out in this study. It involved the analysis of sister chromatid exchanges (SCEs) which was the most sensitive and quickest mammalian system to find out the effect of mutagens on genetic material. The technique standardized for sister chromatid differentiation (SCD) involved culturing of lymphocytes in RPMI-1640 medium and incorporation of 5-bromo-2-deoxy uridine (BrdU) at 20th hour of incubation. The cells were harvested at the end of 70th hour and the thionine stained~slides were exposed to UV light for one hour at a distance of one foot from the UV source. analysed for SCE.

Metaphase spreads showing SCD were Cattle reared in the four coastal wards of Chavara Panchayat (Kovilthottam, Cherusseribhagam, Kolangarabhagam and Kari thura) were taken as experimental group. Cattle from University Livestock Farm (ULF) , Mannuthy, which has no reports of background radiation, formed the control group. The mean SCE frequency per cell was found to be 1.536 ± 0.249 and 3.368 ± 0.273 for control and experimental groups, respectively. The range and number of SCEs/cell/generation for control animals were 0 to 5 and 0.768, respectively. In the experimental group it was 0 to 9 and 1.684. Thus an increase of 119.27 per cent in SCE frequency was recorded in high background radiation area when compared to that of control. The mean SCE frequencies for cattle of Kovilthottam, Cherusseribhagam, Kolangarabhagam and Karithura were 4 ± 0.966, 2.563 ± 0.584, 3.206 ± .411 and 3.389 ± 0.504, respectively and the SCE ranges were 0 to 7, 0 to 6, 0 to 7 and 0 to 9. There was no significant difference in SCE frequency among the four wards. The difference between SCE frequencies of Kovilthottam, Kolangarabhagam and Karithura to that of control was significant. This could be due to the effect of high background radiation on DNA and chromosomes. However, difference in SCE frequency between Cherusseribhagam and control was not significant. This could be due to non- homogenous distribution of monazite deposits in the coastal belt. Though the increase in SCE frequencies in Karithura, Kolangarabhagam and Kovilthottam were statistically significant, cattle reared in this area did not reveal any deviation in physiological and phenotypic performance. Thus this study indicates that SCE frequenc,y for cattle reared in Chavara panchayat with high background radiation was significantly higher than that of control group. This discloses the occurrence of chromosomal damage in this area though these cattle performed normally. This may be because of the repair mechanism or balanced by exchange mechanism during active replication of chromosomes.