TRACE ELEMENTS IN ANIMALS 141 



groups as equal as possible, were fed with mineral mixtures, 

 made up into licks, the four mixtures containing respectively 

 copper, cobalt, manganese or boron in the same amount. These 

 were made available to the ewes on the various farms early in 

 December, and by lambing time about the beginning of April 

 practically all the licks had been consumed. As a result it was 

 found that of the lambs born from ewes which received minerals 

 with copper 1-34 per cent were affected with swayback as 

 compared with 13-1 per cent of the lambs from ewes which 

 received minerals without copper and 15-2 per cent where no 

 minerals were supplied. While this experiment indicates that 

 the addition of a small amount of copper to the diet of the ewes 

 is effective in preventing swayback, it does not follow that the 

 vegetation on which the ewes normally feed in swayback areas 

 is necessarily deficient in copper. As Dunlop points out, the 

 presence of excess of lead or other minerals may render the 

 copper unavailable and it may not be absorbed in adequate 

 quantity from the gut. 



The favourable effect of feeding copper to pregnant ewes had 

 also been demonstrated by Bennetts and Chapman (1937) in 

 Australia and was confirmed in further work by Dunlop, Innes, 

 Shearer and Wells (1939), but although it seems clear that the 

 addition of copper to the diet is an effective preventive of sway- 

 back, it would be premature to assume that the disease is 

 actually due to copper deficiency. It has already been pointed 

 out that copper similarly prevents scouring of cattle, which, as 

 we have seen, is due to poisoning by excess of molybdenum. At 

 present therefore we cannot rule out the possibility that sway- 

 back may be due to poisoning by lead or some other metal, and 

 that copper has a similar action in preventing the disease as it 

 has in preventing molybdenum poisoning of cattle on teart lands. 

 It may be significant that at least two of the areas in which 

 swayback occurs, north Derbyshire and the Mendips, are areas 

 in which lead occurs in sufficient quantity to be mined. It 

 should also be observed that the symptoms in goats supposed by 

 Sjollema to be suffering from copper deficiency are quite different 

 from those of swayback. One might expect the symptoms pro- 

 duced in two such nearly related species as sheep and goats by 

 deficiency of the same element to be similar. 



