Studies on lambs from lines genetically selected for low and high copper status 1. Differences in mortality

Publisher Website
Google Scholar
Abstract
Mortality and its causes were studied during two consecutive years in a total of 934 lambs. The lambs were from two lines of sheep genetically selected for low (L) and high (H) concentrations of copper (Cu) in plasma within an interbred Scottish Blackface × Welsh Mountain population and from unselected Scottish Blackface (B) and Welsh Mountain (W) breeds. The lambs grazed improved hill pastures. Half of the lambs in each line or breed were given an oral Cu supplement by 7·5 weeks of age.Mortality from birth to 24 weeks in H was less than half that in L; mean proportional mortalities were L 0·28, H 0·12, B 0·37 and W 0·07, with a similar distribution in each year. Swayback accounted proportionately for 0·26 deaths in year 1, but proportionately for only 0·02 in year 2. The majority of other losses involved a variety of microbial infections.Genetic type (W < H < L < B) was a major determinant of, and Cu supplementation a protection against, swayback and non-swayback losses. For non-swayback losses L lambs were about twice (P < 0·01) and B lambs about four times (P < 0·001) more vulnerable than H and W lambs respectively. Unsupplemented lambs were more than twice as vulnerable to non-swayback causes of death in the 1st year (P < 0·05) and four times as vulnerable in the 2nd year (P < 0·01) as were Cu-supplemented lambs. There were no cases of swayback in supplemented lambs even though Cu treatment was in some lambs as late as 7·5 weeks after birth.Such marked differences in mortality rate, particularly between the selected lines, had not been apparent in the 5 years preceding pasture improvement, suggesting a genotype × environment interaction affecting survival.The results provide the first definitive evidence that decreased resistance to infection is a clinical consequence of ovine Cu deficiency in the field, amenable to control by Cu treatment and genetic selection.