A comparison of the subsequent production by Border Leicester X Merino ewes first joined as weaners or at 18 months of age.

Abstract

Proc. Aust. Soc. Anim. Prod. (1974) 10; 270 A COMPARISON OF THE SUBSEQUENT PRODUCTION BY BORDER LEICESTER X MERINO EWES FIRST JOINED AS WEANERS OR AT 18 MONTHS OF AGE R.N. TYRELL*, N.M. FOGARTY+, R.D. KEARINS**, and B.J. McGUIRK* Summary The performance of crossbred ewes which were pregnant after being joined at seven or nine months of age has been compared with that of ewes There was a tendency for pregnancy in first joined at 18 months of age. the young ewes to be associated with reduced bodyweight, fertility and wool This effect was not present in later production at 18 months of age. The results are discussed in the context of the value of a weaner years. joining strategy. I. INTRODUCTION It is common practice in New South Wales to first join Border Joining ewes as weaners Leicester x Merino ewes at 18-19 months of age. McGuirk, provides an avenue for increasing their lifetime lamb production. Bell and Smith (1968) suggested that this might be a desirable practice, although the long term effects of pregnancy in weaner ewes remained to be Cannon and Bath (1969) found negligible differences in the determined. subsequent production of two crossbred flocks, one of which was first joined at lo-11 months of age and the other at 20-21 months. This paper presents the results of an experiment conducted at Condobolin Agricultural Research Station, New South Wales, in which the subsequent production of ewes first joined at seven or nine months of age has been compared with that of ewes first joined at 18 months of age. II. MATERIALS AND METHODS The experiments reported in this paper form part of a larger project in which Border Leicester rams were backcrossed to Border Leicester x In Merino ewes having either a 50% or 75% Border Leicester component. 1968, 1969 and 1970, the twin ewe progeny of these matings was randomly The average allocated into two groups, one of which was joined as weaners. age of the ewes when joined was seven months in 1968 and 1969 and nine months in 1970. The remaining half of the twin ewe progeny each year was not The two groups were separjoined until approximately 18 months of age. Weaner ewes were ated only during the weaner joining and weaner lambing. ' teased with vasectomized rams for two weeks prior to joining in March. All joinings were to the equivalent of 3% of harnessed rams for a period of six weeks. 8 Ewes were weighed prior to joining, and lambs dropped and weaned by each ewe was recorded. old (22 months) and 2% year old (34 months) fleece shearing, which took place in June or July of each year old fleece weights were not collected for the at lambing the number of One and one half year weights were recorded at Two and one half year. 1970 group. * + ** Agricultural Research Station, Trangie, N.S.W., 2823. Agricultural Research Station, Cowra, N.S.W., 2794. Agricultural Research Station, Condobolin, N.S.W., 2877. 270 Bodyweights at joining, fertility and greasy fleece weights of ewes that gave birth to a lamb after being joined as weaners have been compared over successive years with ewes that were first joined at 18 months of age. III. RESULTS The mating and lambing performance of ewes joined as weaners is summarized in Table 1. The proportion of ewes mounted and raddled varied from 70.9% (1968) to over 90% (1969 and 1970). A significantly higher proportion of ewes from the 1970 group were pregnant after being joined as weaners compared to both the 1968 and 1969 groups (P < 0.05). However, the proportion of lambs weaned per ewe joined did not differ between groups due mainly to very low lamb survival in the 1970 group (22.7%). TABLE 1 Summary of weaner ewe joining and lambing performance Ewes which became pregnant as weaners tended to be heavier than ewes which did not become pregnant as weaners (Table 2). This difference was significant in 1970 (P * 0.05). Weaner pregnancy did not affect l+ year old joining bodyweight in the,1968 group but it was associated with lowered 1% year old bodyweights in both the 1969 and 1970 groups. These effects were not present at later joinings. TABLE 2 Bodyweight (kg) at joining of ewes which were first joined as weanexs or at 18 months of age 271 In both the 1969 and 1970 1% year old fertility of ewes which This effect was significant in 1970 pregnancy were not evident in later groups, there was a depression in the were pregnant as weaners (Table 3). (P < 0.05). Ill-effects due to weaner years. TABLE 3 Fertility (lambs born/ewe joined) of ewes which were first joined as weaners or at 18 months of age Weaner pregnancy was associated with reduced 1% year old wool production (Table 4). Differences were significant in both the 1969 and 1970 groups (P < 0.05). The 2% year old wool production of ewes in the 1969 group was also affected by weaner pregnancy (P < 0.05). TABLE 4 Annual greasy wool production (kg) of ewes which were first joined as weaners or at 18 months of age IV. DISCUSSION While the results varied somewhat between years, the 18 month fertility and greasy fleece weight of ewes pregnant as weaners were, on average, lower than for ewes first joined at 18 months of age. However, these adverse effects of weaner pregnancy did not persist beyond hogget performance. Similar results to these have been observed by both 272 et -Spencer - al. (1942) and Cannon and Bath (1969). When the performance of -all weaner joined ewes is compared with that of ewes first joined at 18 months of age, the gains from weaner joining are relatively small, with only 14 per cent lambs weaned. This gain is off-set by the adverse effects of weaner pregnancy on fertility and wool production at 18 months of age when the weaner joined group gave birth to nine per cent fewer lambs and produced an average of 0.26 lb less greasy wool. On the basis of the above figures a strategy of weaner joining would not be a worthwhile proposition. McGuirk, Bell and Smith (1968) demonstrated the importance of bodyweight to the success of weaner joining. The adverse effects of weaner pregnancy on l-8 month fertility would also appear to be related to bodyIn the two groups in which weaner pregnancy depressed 18 month weight. bodyweight (1969 and 1970) the fertility at the 18 month joining was also reduced. On the other hand, the 18 month bodyweight of the ewes in the 1968 group was not depressed by weaner pregnancy, nor was their fertility. Thus, if the practice of weaner joining is to be exploited, nutritional management should be examined as perhaps the key factor by which conception rates can be improved and subsequent production effects alleviated. v. ACKNOWLEDGEMENT We would like to thank Dr B.J. Res tall for his advice and assistance during the preparation of this paper. VI. REFERENCES CANNON, D-J., and BATH, J.G. (1969). Aust. J. exp. Agric. Anim. Husb. 2: 477. McGUIRK, BTJ., BELL, A-K., and SMITH, M.D. (1968). Proc. Aust. Soc. Anim. Prod. 7: 220. SPENCER, D.A., SCHOTT, R-G., PHILLIPS, R.W., and AUNE, B. (1942). J. Anim. Sci. - 27. 1: - 273