Injury at birth affects lamb survival

Press, Volume CXV, Issue 33874, 20 June 1975, Page 16

Injury at birth affects lamb survival

Injury to the central nervous system suffered by lambs at birth looks like being a major factor not only in deaths of lambs at birth, but also in the few days after lambing in stormy conditions, and it may also have a longer term effect on body growth and wool production in later life where the damage at birth is less severe and the animal survives.

These are the conclusions that can be drawn from research work, done over the last six years, by a former New Zealand veterinarian who has been on the staff of the veterinary school at Sydney University for 14 years. He is Mr K. G. Haughey, who was formerly senior veterinarian with the Ashburton Veterinary Club. Mr Haughey is senior lecturer in veterinary medicine and stationed at the university’s farming property at Camden, outside Sydney.

His work in Australia, which has been supported by the Australian Wool Corporation, the Reserve Bank of Australia and the New South Wales Graziers’ Association, has been on perinatal lamb mortality — the death of lambs shortly before, during and within seven days after birth.

Mr Haughey says that his interest in such lamb deaths developed while he was with the Ashburton club and he acknowledges the encouragement he was then given by people associated with the club. Last week he reported on his Australian work to the annual seminar of the New Zealand Veterinary Association Sheep Society held in Palmerston North. In New Zealand, Mr Haughey said while in Christchurch recently, about seven to 15 per cent of all lambs born died at birth or within the first week after birth. In Australia the corresponding figure was about 25 per cent.

Over the years there had been piecemeal research into the causes of these deaths, and the result had been that only about 20

per cent of them could be accounted for.

The rest of the lambs died during birth, presumably because of the birth process, or in the next two or three days and a big number of these fell into the group known as the mismothering, exposure and starvation complex, the main feature of which was that they had not suckled.

There was good reason for lambs dying under cold conditions soon after birth, said Mr Haughey, but some people had felt that there might already be something wrong with lambs that died under such conditions and which predisposed them to this fate. Consequently in 1970, he had started looking at the brain and spinal cord of all lambs that died during birth, or within a week of birth.

In his paper Mr Haughey said that a reluctance, to examine the central nervous system had been a notable sin of omission in the past. “I can say this with impunity as I have been one of the guilty parties. Indeed if there is an award for the world record number of lambs autopsied for least effect I should be a unanimous recommendation,” he added. “We

have now amended our ways ..”

Mr Haughey said that practically all lambs that died during birth showed damage to their brain and/or spinal cord. Of the big starvation, mismothering and exposure complex, which accounted for up to 65 per cent of deaths in some flocks, a very high proportion of these lambs also had damage to their brain and/or spinal cord. These findings, he said, led to the development of the hypothesis that these injuries were caused by the birth process. Experiments had been set up which demonstrated this to be so.

The next question was clearly if they had these injuries did they affect their chances of survival. A further series of experiments had been set up and as a result they had been able to show that these injuries were of great significance in this context. “The conclusion that we arrived at from all of this work is that injury to the brain and/or spinal cord is the greatest single cause of perinatal lamb mortality,” he said.

“We now know what the problem is. We think that now with autopsies and laboratory examinations we can account for about 90

per cent of lamb deaths. It has given us an understanding of the problem. Everyone has been severely handicapped in proposing a solution as they had not known what about 80 per cent of the deaths were due to.”

Mr Haughey said that they were also interested in the possibility that lambs less severely affected at birth and which survived might develop residual handicaps that could affect their subsequent growth or their wool production.

On two occasions, he said that the body growth of sheep born of artificially delayed births had been temporarily and significantly depressed compared'to their controls during periods of low feed availability. “The latter result suggests that residual handicaps derived from birth injury are a component of within-flock and betweenanimal variability in productive performance,” he said.

In their experimental work Mr Haughey said that the brain injury had been artificially induced, without reference to all of the factors involved in the field, and was not as severe as that produced naturally. They had now acquired more "than 100 ewes that had lost lambs at birth on at least half of four lambings and they had another comparable flock of ewes that had not lost a lamb in four lambings. The factors involved in lambing were the duration of the birth, how vigorous it was, the size of the lamb and the size of the ewe’s pelvis.

There was evidence that in some flocks the size of the pelvis of ewes was important in relation to lamb survival, but in others it was not. In other circumstances it looked as though the lamb’s body size and the process it had to go through at birth was the most important factor. There were genetic and nutritional factors that affected the size of the lamb.

There was not enough information yet on the whole issue of pelvic size and whether or not it was an inherited factor.

At the present time Mr Haughey said that no solution of the problem could be offered. But the work does raise some interesting points. One would be the desirability of assisting ewes to lamb with consequent damage to the lamb affecting its chance of survival soon after lambing and also po;l sibly its later productivity. It could well give support to the concept of easy care lambing flocks. And it might raise some doubts about the comparisons of sheep for productivity. Mr Haughey said that they had also looked at the perinatal mortality in calves, foals and piglets with results similar to those for lambs. The conclusion was that the greatest single cause in domestic species was the injury of the brain and/or spinal cord at birth.

“The experimental evidence supports the hypothesis if injury is severe at

birth the lamb will die at birth or very shortly after, if it is less severe it impairs the lamb’s sucking drive so that it is likely to die under cold conditions, and there is the possibility that if the injuries are less severe the animal may survive birth but still develop residual handicaps that will affect its growth and wool production in later life.” Mr Haughey said that in their experimental work some 700 lambs had been subjected to experimental procedures and many ewes had also been killed.