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This article was published in 1967
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INSTITUTE OF INSPECTORS OF STOCK OF N.S.W. YEAR BOOK.
Clover Disease
E. R. TUOHY, B.V.Sc., Veterinary Inspector, Wagga Wagga
Clover disease is the name given to a condition in sheep characterised by inability to lamb, infertility, eversion of the uterus, and lactation among maiden ewes and wethers. It probably will not occur simultaneously in all of these dramatic forms, but often the first symptom seen is the most spectacular one, that of the ewe being unable to lamb, and consequently the condition is known as "Dead Lamb Disease".
The ewe makes little effort to deliver her lamb, about 30 per cent of the ewes being affected, resulting in losses of 15 to 20 per cent of ewes mated. Added to this is the loss of lambs due to the delivery being so prolonged that the lamb is born dead, or dies soon after birth.
Eversion (prolapse) of the uterus is also responsible for the deaths of ewes from septicaemia, following infection of the exposed uterus.
Perhaps the most serious effect of clover disease is infertility in the ewes, and this feature had its heaviest impact on flocks in Western Australia. The extent of this infertility, or failure to get in lamb, increases with continued grazing of affected pastures, and the ewes usually remain infertile even if transferred to natural pastures. Thus the effect of grazing affected pastures is cumulative. The effect of excess clover on the fertility of rams is not yet known.
There occurs a progressive decline in lamb-marking percentages, which from the combination of ewes' failure to conceive and lamb deaths, may result in only 20 per cent of lambs being marked to ewes mated. This alarming sign that a flock is affected may be the only indication of the disease, as the infertility, difficulty in giving birth, and prolapse of the uterus of the ewes may occur singly as symptoms, or in combination, on any affected property.
A minor but unusual manifestation of the disease is lactation in unbred ewes or wethers, with obvious secretion of milk in enlarged udders, and the development of "false bladders" in wethers, which may cause odd deaths.
Research has shown that Clover Disease is caused by chemical substances in the clover called oestrogens. These oestrogens resemble the female sex hormones produced naturally in the body by certain glands which control reproduction and allied functions. The continued intake of oestrogens from clover upsets the hormone balance controlling the various reproductive processes, and may produce abnormalities in sex organs and functions.
The disease was first recognised in sheep grazing subterranean clover in Western Australia in 1941, where drastic reduction in lambing percentages from 80 per cent to 20 per cent within three years of grazing clover, led to its discovery. At first the condition appeared to be restricted to Western Australia, where early conditions favoured clover dominance, but it has now been diagnosed in all southern States of the Commonwealth. Some symptoms of the disease have occurred among sheep grazing well balanced grass/clover pastures in both Western Australia and New South Wales, and other clovers, apart from subterranean clovers, such as Red Clover, can cause the condition. However, subterranean clovers have most oestrogenic activity and Dwalganup strain has a high potency, Marrar strain a moderate potency and Mount Barker strain a low potency.
At post-mortem examination, small cysts, ranging in size from a match head to a pea, may be found in the internal lining of the uterus of the ewe, and the udder and teats are enlarged. The size and number of these cysts appear to bear a relationship to the degree of infertility of the ewe. Old ewes, rather than young ewes, are likely to develop the condition, having consumed the clover for longer periods of time.
There is no treatment so that the empty ewes are best culled and fattened for slaughter.
Control of the disease presents problems but depends upon the prevention, if possible, of the ewes eating excessive quantities of clover whilst it is green. This excessive intake is most likely to occur in clover dominant paddocks, which should be mowed in strips, as the potency of the oestrogen is reduced by wilting of the clover, and is lowest in well-dried hay.
Ewes should not be allowed lush, clover grazing before or during mating periods. Avoid clover dominance in pastures by judicious grazing and application of fertilisers, and accelerate the phase of clover dominance which occurs during the early stages of the establishment of pastures.
Fortunately, most pastures in the improved areas of this district are now past this critical stage, but large acreages remain to be improved. The recommendation with these is to try to reduce the period of potent clover dominance by combined sowing with grasses and initial heavy applications of superphosphate.
Finally the value of some hay, or access to a grass paddock, to sheep "living in luxury", in a lush clover paddock, should not be under estimated, and it is considered significant that the sheep themselves will so vary their diet is given the opportunity.