Abstract:
EARLY NUTRITION AND LIFETIME REPRODUCTIVE PERFORMANCE OF EWES T. F. REARDON* and L. J. LAMBOURNE* Summary Groups each of approximately 100 Merino ewe lambs were given either good nutrition (grazing) in their first year (HH) or were subjected to poor grazing on native pastures between the ages of 6 weeks and 9 months (LH), or 9 months and 14 months (HL). At all other times between birth and 7 years of age the ewes ran together on improved pasture. Differences in Iiveweight resulting from the treatments diminished with time but small liveweight differences persisted until 7 years of age. Only in the first year's lambing was there any difference between groups in the number of dry ewes when 25% of HL ewes were dry. At the third and subsequent lambings the twinning rate of the HH ewes was higher than that of the HL and LH. I. INTRODUCTION Coop and Clark (1955) recorded the lifetime performance of ewes subjected to different nutritional treatments in early life, and relatively mild undernutrition from 0 to 12 months of age affected of dry ewes but not the twinning rate, whilst severe undernutrition 18 months affected twinning rate but not the number of dry ewes. Corriedale found that the number from 4 to The aim of the experiment reported in this paper was to compare the lifetime production of Merino ewes subjected to a period of poor nutrition between either 6 weeks and 9 months or 9 months and 14 months of age. Only the effects on liveweight and reproduction are reported here. II. MATERIALS AND METHODS A total of 320 fine wool Merino ewe lambs born in September/October 1958 were randomized into three groups at six weeks of age. One group (LH) with their mothers were thereafter run on native pasture (low plane) until June 1959. The other two groups (HH, HL) were run together on the best available improved pasture (high plane) until June 1959. All lambs were weaned earl y in March 1959. On June 25, 1959, the low plane lambs were transferred to high plane and at the same time one of the high plane groups (HL) was transferred to low plane until all were shorn at the end of November. All groups have run together since then except for a short period during lambing in 1962. The ewes were joined as one flock with Merino rams in April/May of each year from 1960 to 1964. The ewes were lambed in yards and ewes and new lambs were identified twice daily. In 1962 each group lambed in a separate paddock. . * C.S.I.R.O., Pastoral Research Laboratory, Armidale, N.S.W. t Present Address: C.S.I.R.O., Division of Animal Physiology, Cunningham Laboratory, St. Lucia, Queensland. 106 Fig. l.-Group mean liveweights of HH (-), LH (- -) and HL (.... . ...) ewes from six weeks to 34 months of age. (X: Change in nutritional treatments, S: End of nutritional treatments.) III. RESULTS AND DISCUSSION Mean liveweights of the three groups from six weeks of age to 34 months of age are shown in Figure 1. Subsequent liveweights are shown in Table 1. The LH group made substantial compensatory weight gains when placed on improved pasture at 9 months of age. The HL groups suffered considerable weight loss when placed on native pasture at 9 months of age and were slow to compensate when they returned to improved pasture 5 months later. The percentage of ewes that failed to lamb in each year is given in Table 2. There were no differences between the groups except in 1960 when a quarter of the HL ewes did not produce a lamb. The HL ewes were considerably lighter when joined though this may not be the only relevant factor in their poor performance. Esplin, Madsen and Phillips ( 1940) found that even when the livcTABLE 1 Mean liveweight (kg) of each group * Value not significantly different (P = 0.05) from that above or below it. + * Bracket encloses values not differing significantly (P = 0.05). 107 Number of ewes TABLE 2 NOT lambing per 100 ewes present * ** P<O.OOS TABLE 3 Percentage of ewes lambing that produced twins weight of ewes poorly fed between 6 and 12 months of age had, by 18 months of age, caught up with that of control ewes there were still differences in the percentage of ewes failing to lamb at 2 years of age. In addition to the short-term effect on percentage of dry ewes there have been long-term effects on twinning rate (see Table 3) expressed as the percentage of ewes lambing that had twins. In each year from 1962 to 1964 the HH ewes had a higher twinning rate than the LH ewes and a higher twinning rate than the LH and HL ewes considered together. The difference between the HH * and HL ewes in 1964 is not significant. Though there appear to be consistent differences between LH and HL ewes, these differences are not significant in any one year nor when all years are considered together. The effects reported here have been produced by relatively mild degrees of undernutrition applied for relatively short periods. They suggest one reason for the usually low twinning rate of Merinos and also pose an interesting problem as to the physiological mechanisms involved. IV. ACKNOWLEDGMENTS Mr. D. B. Muirhead, now with the Australian Meat Board, was responsible for the running of the experiment in its early months. Mr. A. F. Gray and Mr. A. Ferris, Pastoral Research Laboratory, Armidale, have been responsible for the care of the animals and the collection of lambing records respectively. V. REFE' RENCES C OOP , V. R. (1955). The influence of method of rearing as hoggets on the life-time productivity of sheep. New Zealand Journal of Science and Technology LARKE , I. E., and C E SPLIN A37: 214. , A. C., M ADSEN , M. A., and P HILLIPS , R. W. (1940). Effects of feeding ewe lambs during their first winter. Utah Agricultural Experiment Station Bulletin 292. 108