Feeding Of Ewe Flock During Pregnancy

Press, Volume XCIX, Issue 29234, 18 June 1960, Page 9

Feeding Of Ewe Flock During Pregnancy

t' WE and lamb mortality, at lambing and during the first week after birth, is probably the greatest single source of economic loss in sheep in New Zealand, according to Dr. L. R. Wallace, chief nutrition officer at the Ruakura animal research station. He told the Ruakura farmers’ conference this week that the magnitude of this loss was governed to a considerable extent by the birth weight of lambs.

Dr. Wallace said that at Ruakura in each of three years - a group of Romney ewes had been mated to Southdowns and the ewes run together as a single flock till five weeks before lambing was due to begin. They had then been divided into three groups. One was grazed on abun-

dant pasture and the ewes gained on average about 5R> i week. The second group* on a somewhat lower plane of feeding gained about 2|lb a week while the third group was grazed very hard indeed and actually lost condition. , ‘ l

Among single lambs it had been found that losses tended to be concentrated among the very heavy lambs. Over the three years the death rate at birth and during the first week thereafter was only 3.3 per cent, for lambs of about average size of 9 to 111 b but more than 30 per cent, for the heaviest lambs weighing 131 b or more and the lightest weighing 71b or less.

In twin lambs losses were concentrated among the lighter sets. Over the three years death rate among twins at birth and during the first week was 7.3 per cent.

for those of more than 71b weight but 28 per cent, for those weighing 71b or less. “It will be clear that from the point of view of lambing mortality a very high level of feeding prior to lambing should be avoided, for it is apt to result in a proportion of very big single lambs which 1 ewes have difficulty in delivering. ... On the other hand a very-low level of nutrition must also be avoided for thia will result in an unduly high proportion of light-weight twins which tend to be born weak and which are apt to die through failure to get a drink, from exposure or from mismothering during the first fefw days after birth.” During each of the three years at Ruakura lamb losses were lowest among the lambs from ewes which had been fed only moderately well during the pre-lambing period. It was perhaps worth recording that although the intermediate level of feeding reduced the birth weight of single lambs by an average of only l-10th lb as compared with those from ewes on a high plane of nutrition, it was effective in reducing the proportion of single lambs weighing more than 111 b from 13 to 5 per cent.

Dr. Wallace referred to work that he had done at Cambridge with Dr. John Hammond and to other work in Scotland which showed that the level of nutrition during the first three months of pregnancy had little effect on

the growth of the developing lamb.

Discussing the effect of the level of feeding upon the growth of lambs after birth, Dr. Wallace said that the lambs from all three groups had grown equally well at,Ruakura. At Lincoln College, Professor I. E. Coop had also found that a high level of nutrition during pregnancy which increased birth, weight by about 0.51 b had little, if any, influence on the rate of growth and the weaning weight of the lambs irrespective of the level of nutrition after lambing. Small Differences ' Whatever the explanation for this it could, he thought, be taken as established that differences in plane of nutrition before lambing which produced only small differences in birth weight usually had little or no effect on the subsequent growth rate of either single or twin lambs. Dr. Wallace said that wool growth was, of course, affected by the level of feeding during pregnancy. In the Ruakura trials over three seasons the average fleece weights of ewes moderately well fed before lambing were only about l-10th lb less than for the high plane ewes, but the very low level of feeding reduced fleece weights by an average of 0.61 b. In trials at Lincoln, Professor Coop had shown that 14 weeks of differential feeding before lambing produced differences in fleece weight averaging about lilb.