Abstract:
Proc, Aust, Soc. Anim, Prod. Vol. 18 THRESHOLD CONDITION SCORES OF MERINO EWES FOR IMPROVED AUTUMN LAMBING PERFORMANCE IN WESTERN AUSTRALIA J.M. KING*+, J.S. FISHER* and P.M. MURPHY* Condition score of Merino ewes was related to lambing performance during trials of a reproductive management package. Six hundred ewes on two farms were drafted into Test and Control groups. Test ewes 'were subjected to a synchronised joining programme, using testosterone-treated wethers, lupin grain supplement, ultra-sound imaging and separate feeding according to pregnancy status. Controls were not teased, separated, or given as much feed as the Test groups. The improved nutrition in the Tests significantly increased their condition by ~0.2 score at joining to a maximum 50.6 score prepartum in twinbearing ewes, compared with Controls. Test groups also had a significantly higher conception rate (7%), more lambs (25%) and heavier progeny at marking (40%) and weaning (60%). Three quarters of the increase in lamb marking above 75% (the State average) was due to survival of more twins; the increase in twinning was not significant. A ewe score of 2.1 prepartum was a prerequisite for 80% survival of twin lambs, whereas 1.9 was sufficient for 85% survival of singles, giving an overall mean of 1.9 (allowing 1.5 for empty ewes). The mean score in an undivided flock was estimated at 2.3, because single-bearing and empty ewes must be fed to excess to maintain the condition of twin-bearers. INTRODUCTION The contribution of nutrition to reproduction in the ewe is well recognised (e.g. Foot 1983), but the body condition appropriate to each stage is not. A live weight of 50 kg at joining and condition score 3 is advocated for Merino ewe flocks in agricultural areas of Western Australia (W.A.) by Croker and Kelly (1989). This condition should be maintained throughout pregnancy, but cannot be gauged by weighing after day 90 due to the increasing and variable size of the conceptus. We used scoring to provide the same gauge of body condition throughout the breeding cycle, and measured to the nearest half score (MLC 1983) rather than whole score which is the practice in W.A. (Suiter 1987). The aim of this paper is to relate the score of Merino ewes to their reproductive performance on farm, and identify the threshold scores below which there is a marked decrease in embryonic and lamb survival and growth. MATERIALSANDMETHODS Trials were duplicated on two farms in flocks of 600 Merino ewes, drafted alternately into Test and Controls. Ewes were mated in late November, for 26 days on Farm 1 and 41 days on Farm 2, using 3% rams. In the Test groups, oestrus was highly synchronised by the 'ram effect' using testosterone-treated wethers (Fulkerson et al. 1981) and a progesterone injection (Pearce and Oldham 1984). Lupin grain was fed (0.75 kg/hd/d) for ten days at joining to increase twinning rate. Test flocks were scanned once for pregnancy, using ultra-sound imaging 79 days after rams had been introduced, and sub-divided into single-, twin-bearing and non-pregnant ewes, Control ewes were not teased or separated. During the last two months of pregnancy and first month of lactation, cereal and lupin grain supplements were fed to maintain the Test pregnant ewes half a condition score above the Controls. Ewes were weighed at joining and lambs at marking and weaning. Ewes were also condition scored on six occasions between joining and weaning, The number of ewes raddled was determined after each of the first three oestrous cycles. * + school of Agriculture, The University of W.A., Nedlands, W-A, Present address: QDPI, P-0. Box 1054, Mareeba, Qld. 4880 6009. 272 Proc, Aust, Soc. Anim, Prod. Vol. 18 RESULTS Ewes of the same age and score in a commercial flock can have a wide range of mature body size, which detracts from the value of live weight as an indicator of body condition even without the confounding effect of pregnancy (Fig. 1). Fig. 1. Liveweight distribution of 3 year old ewes with condition score 2 prior to joining on Farm 1. Fig. 2. Mortality of twin but not single lambs was inversely related to condition score of ewes prepartum. At the start of the trial, the mean condition score of the ewes in the Test and Control groups within each farm was the same. It was maintained at that level in the Test groups throughout joining, as a result of the lupin supplement, but dropped significantly in the Controls as the pasture dried. The divergence in condition was mirrored in the conception and twinning rates, although the difference in twinning rate was not significant (Table 1). Table 1 Ewe scores at joining, and conception and twinning rates at scanning As a result of differential feeding during pregnancy, the mean score of Control compared with Test ewes 10 days prior to the start of lambing, was 0.2 lower in single-bearers and 0.4 to 0.7 lower in twin-bearers. When these scores were plotted against lamb mortality up to marking, the slope of the regression was significantly different from zero (PxO.02) for twins but not singles (Fig. 2). Twin-bearing ewes from Control groups failed to rear more than one lamb, whereas 60% of ewes from Test groups reared both lambs (Table 2). Lower lamb mortality in the Test groups resulted in 25% more lambs being marked than in the Controls; three quarters of the extra lambs marked were twins (Table 3). The marking percent for the Controls in 1989 was similar to that in -the commercial flocks from which they were derived in 1988. 273 Proc. Aust. Soc. Anim. Prod. Vol. 18 Table 2 Condition score of twin-bearing ewes prepartum and percent rearing two, one and no lambs Table 3 Lambs marked (as percent of ewes joined) in 1989 Lambs were weighed at marking on Farm 2.. The total weight of the Test progeny was 42% more than that of the Controls. The mean weight of the Test twins was the same as the mean of all the Controls, which were mainly singles (Table 4). At weaning, the difference in the ewe score and mean lamb weight between the two groups had disappeared (implying that the Control group was on better grazing than the Test). The extra weight of progeny weaned in the Test group had declined to 23% and was accounted for by the extra lamb numbers (Table 5). Table 4 Condition score of ewes and weight of lambs at marking on Farm 2 Significant difference between adjacent means on same line at ** P<O.Ol. Table 5 Condition score of ewes and weight of lambs at weaning on Farm 2 On Farm 1, the Test ewes remained in better condition than the Controls up to weaning, when the lambs were weighed for the first time. The heavier individual weight and higher number of lambs in the Test group produced a total weight of progeny which was 60% more than that of the Controls (Table 6). 274 Proc. Aust. Soc. Anim. Prod. Vol. 18 Table 6 Condition score of ewes and weight of lambs at weaning on Farm 1 DISCUSSION The lambing peak in the trial flocks was in the autumn which coincided with that for W.A. (Kelly and Lindsay 1987) and the proportion of lambs marked in the Control flocks was similar to the State average of 75% (ABS 1989). This figure is unlikely to be exceeded when rearing single lambs from either single or twin ovulations (Wilkins 1989). Three quarters of the improvement in lamb marking percent in the trials was due to the increased survival of twins. This increase was not associated with a significant rise in twin conception rate. A mean condition score, maintained at 2.4 throughout joining, achieved a 95% conception rate in a flock of Merino ewes. For 80% survival of twin lambs, the mean score of ewes prepartum needed to be at least 2.1. Mortality of twin lambs doubled if ewe condition score dropped to 1.6. Survival of singles (85%) was unaffected over this range, but lambs from ewes maintained at the lower scores during late pregnancy and lactation were 10% lighter at marking and 20% lighter at weaning than those from ewes with the higher scores. Therefore, a mean score of 1.9 is suggested for single lambing ewes peripartum. Non-pregnant ewes can be maintained at a score of 1.5. The overall mean score for a flock separated into twin-, single-bearing and non-pregnant ewes is calculated at 1.9 prepartum. If the ewes are fed as one flock the mean score has to be raised to 2.3, because twin-bearers fall 0.2 score below single-bearers. The condition scores suggested are more precise than those currently recommended in W.A. They are also lower, although there may be variations in scoring between operators. Such differences need to be minimised, because the condition of the ewe prior to lambing cannot be measured by weight and is critical for improving lambing performance in the State. ACKNOWLEDGEMENTS The project was funded by the AMLRDC and implemented on the farm of Mr. and Mrs. Gooding, Lake King and the University Farm, Wundowie. We are grateful to the UWA Animal Science Group and WA Department of Agriculture for support. REFERENCES ABS. (1989). Cat-No. 7221.5. Australian Bureau of Statistics, Perth. CROKER, K.P. and KELLY, R.W. (1989). W.A. Department of Agriculture, Bull. 4148. FOOT, J-2. (1983). In 'Sheep Production and Preventative Medicine', p-267, editor T.G. Hungerford. (The Post-Graduate Foundation in Veterinary Science: Sydney). FULKERSON, W. J., ADAMS, N. R. and GHERARDI, P. (1981). Appl. Anim. Ethol. 7:57 KELLY, R.W. and LINDSAY, D-R. (1987). J. Agric. W.A. 28: 99. M.L.C. (1983). 'Feeding the Ewe'. (Meat and Livestock Commission: Milton --Keynes). . PEARCE, D.T. and OLDHAM, C.M. (1984). In 'Reproduction in Sheep', p-261, editors D.R. Lindsay and D-T-Pearce. (Aust. Acad. Sci.: Canberra). SUITER, J.S. (1987). W.A. Department of Agriculture, Farmnote 40/87. WILKINS, J.F. (1989). Ph.D. Thesis, University of Western Australia. 275