Abstract:
THE INFLUENCE OF SHEARING ON THE GROWTH AND ECONOMIC VALUE OF CARRY-OVER LAMBS J. P. DRINAN* and B. D. FERGUSON Summary Dorset Horn x Border Leicester-Merino lambs born in July-August 1963 and May-June 1964 were shorn lo-12 weeks before slaughter. An equal number were not shorn. Averaged over both years, shorn lambs were 10.8 kg heavier at slaughter (P < (0.01) in February, and had 4.9 kg heavier carcases (P < 0.05). The net economic return from shorn lambs was lower than from unshorn lambs, though this difference was not significant. I. INTRODUCTION Carry-over lambs are commonly shorn to stimulate their growth rate and to protect them against grass seed infestation and blowfly strike. This experiment was designed to investigate the influence of shearing on lamb growth and economic return from meat and wool. II. MATERIALS AND METHODS The experiment was conducted under commercial conditions in the Berriquin Irrigation District of New South Wales. Dorset Horn x Border Leicester-Merino lambs born in July-August 1963 and in May-June 1964 were used. On November 19, 1963 and November 9, 1964 the lambs were weaned and divided into two groups (Shorn and Unshorn), balanced for sex and liveweight. Within each group, lambs were further classified as being Heavy or Light according to whether their liveweights were above or below the group mean. On December 4, 1963 and November 16, 1964 one group was shorn and the other crutched and wigged. The lambs were weighed on four occasions and the weights corrected by addition of individual wool weights. At slaughter on February 20, 1964 and February 26, 1965 individual carcase weights, grades and values, and average skin values were obtained. III. RESULTS Shorn lambs grew faster (P < 0.01) (Figure 1), were heavier at slaughter (P < 0.01) and had heavier carcase wei(rhts (I? < 0.05) (Table 1). There was no difference in carcase grade between the two groups. Net carcase values were higher for Shorn lambs. The lower net value of wool and skins from Shorn lambs (P < 0.01) contributed to their lower net economic return (Table 1). GNew South Wales Department of Agriculture, Agricultural Research Station, Trangie. -f-New South Wales Department of Agriculture, Finley. Fig. l.-The relative growth rates of Light Shorn (0) and Unshorn (0 ) lambs and Heavy Shorn ( A ) and Unshorn (A) lambs in 1963 and 1964. There was a significant shearing x weight interaction for net economic return, such that Heavy Unshorn lambs were more valuable than Heavy Shorn lambs, and Light Unshorn lambs were less valuable than Light Shorn lambs (Figure 2). IV. DISCUSSION The differences in liveweight gain between Shorn and Unshorn lambs in this experiment are considerably larger than those reported by Tucker (1964), yet Unshorn lambs retained an advantage in net economic return. This advantage persisted despite blowfly strike of four Unshorn lambs in 1964, which reduced their average carcase weight to 1.9 kg below the mean of their group. As the lambs grazed irrigated paspalum/white clover pastures, grass seed problems were not encountered in either year. 191 Fig. 2.-Carcase values and net economic return from Light Shorn (0) and Unshorn ( l ) lambs and Heavy Shorn ( n ) and Unshorn (A) lambs in 1963 (-) and 1964 (--). In addition to the lower net value of their wool and skin, the Shorn lambs were penalised because a greater number of their carcases were heavier than the economic optimum for carcase value. However, the carcases of Light Shorn lambs weighed less than the optimal 20.3 kg so that they were more valuable than those of Light Unshorn lambs. In terms of net economic return, this advantage was 192 TABLE 1 Number of lambs, and means each production measurement Unshorn lambs in each year of for Shorn and 'EPrice obtained by grower at -tAfter deduction of shearing for the Unshorn group. Wool *Total value of carcase -I- skin abattoir. costs of 23 cents/head for the Shorn group and 5 cents/head was sold on the property. -I-- wool - shearing costs. reduced but was still enough to justify shearing lambs that were lighter than the mean. In practice, lambs are sold in even groups as they reach finished liveweight. Therefore, shearing will only be useful when the faster growth rates lead to an economic advantage which more than compensates for the lower net value of wool and skins. In such a case, maximum advantage would be obtained by shearing all lambs and then slaughtering them as they reach the carcase weight giving maximum net economic return. It is difficult to predict this weight which varied from 20.2 kg in 1963 to 22.1 kg in 1964 due to market fluctuations. V. ACKNOWLEDGMENTS The co-operation of Mr. A. W. Wessel, 'Pinewood', Berrigan, is gratefully acknowledged. Thanks are also due to Mr. I. D. Killeen, New South Wales Department of Agriculture, Agricultural Research Station, Leeton, for advice and criticism. VI. REFERENCE T UCKER , M. J. ( 1964). Shearing carry-over lambs. Agricultural Gazette of New South Walea 75: 1318. 193