The effects of roughage quality, physical form and presentation with a wheat based diet on the performance of lot fed lambs.

Abstract

THE EFFECTS OF ROUGHAGE QUALITY, PHYSICAL FORM AND MODE OF PRESENTATION WITH A WHEAT BASED DIET ON THE PERFORMANCE OF LOT FED LAMBS G.C. FILE* Summary Diets of whole wheat with either lucerne or oaten hay were fed to 180 second cross lambs (18 weeks old) in store condition. The two hays were fed either mixed with the wheat or separately to it and were offered in either milled or long form. Neither physical form nor mode of presentation of the roughage affected lamb performance. However, a high percentage of hay was wasted when fed in the long form. Lambs supplemented with lucerne hay had a mean liveweight gain of 166 g hd-ld-'; this was significantly higher than the mean liveweight gain of 131 g hd-id-l achieved by those lambs supplemented with oaten hay. I. INTRODUCTION Lot feeding of weaner lambs permits the producer to finish lambs for market, irrespective of seasonal conditions. Early marketing achieved bylot feeding removes otherwise unproductive stock and alleviates grazing pressure at a time when pasture is generally in short supply. This should lead to an improved productivity of the remaining stock. The use of feedlotting needs to be an integral part of a farming programme without extensive outlay on yards or on machinery to mill and mix grains and roughages normally provided.' Suitable yards for lot feeding are generally available or can be cheaply constructed. However, the purchase of a hammermill-mixer unit is a major item of expense for an opportunist feed lot venture. This expenditure could be avoided if lamb performance was not greatly reduced by feeding grain and roughage in an unprocessed form. The present study was undertaken to assess whether physical form and method of presentation of two roughages added to a wheat based diet affected food intake and rate of gain of lambs in a feed lot. II. MATERIALS AND METHODS One hundred and ninety five second cross lambs (Dorset Horn x Border Leicester/Merino) of mixed sex were divided into 13 equal groups using sex and live weight as a basis for restricted randomisation. Groups had a mean live weight of 23.3 kg (1 0.3) and lambs ranged in age from 16 to 20 weeks. One group was slaughtered at the commencement of the experiment so an estimate of initial carcass weight could be calculated for the remaining groups. In a 3 x.2 factorial design with two replicates the 12 .groups were randomly allocated to diets of whole wheat (13.9% C.P., 92% D.M.) with lucerne hay (20.0% C.P., 94% D.M.) or oaten hay (4.6% C.P., 95% D.M.) roughage offered in three ways: either fed separately to the * N.S.W. Department of Agriculture, Drought Research Unit, Veterinary Research Station, Glenfield, N.S.W. 2167. 437 wheat in a long or milled form or milled and fed mixed with the wheat (70% wheat, 30% roughage). On a group basis lambs were fed on increasing amounts of wheat and ad lib. roughage during a ten day introductory period. For the remainder of the experiment feed was offered ad lib. from self feeders and hay racks. All wheat was supplemented with 1.3% NaCl and 1.5% CaC03. This was achieved by adding it in layers to the wheat in the self feeders (where fed separately) or adding it to the mixing unit (where fed mixed. Milling and mixing were accomplished with an 'All Bulk'* hammermill-mixer unit fitted with a 15 mm screen. Lambs had continuous access to feed, a fresh batch being given every second day. Residues and group-intakes were measured weekly. Spoilt feed was replaced and an estimate of hay wastage from hay racks was made by drying and weighing all hay on the ground during two five day periods. Lambs were-dosed at three weekly intervals with 'Nilverm r+ to minimise helminth infestation and with 500,000 I.U. vitamin A, 500 I.U. vitamin E and 2 mg Se (as NaSe03) at the commencement of feedlotting. They were held in yards provided with adequate feeder space, fresh water and a limited amount of cover. An outbreak of enterotoxaemia during the second week of the experiment resulted in six deaths. Immediate vaccination of the lambs prevented any further losses. Lambs were weighed at weekly intervals and it was intended to slaughter each group when its mean live weight reached 35 kg. This realised with all lambs supplemented with lucerne hay. However, an early completion of the trial due to heavy rain did not permit this the slower growing lambs supplemented with oaten hay andthey were slaughtered when their mean live weight was approximately 33.6 kg. fasting live weight did not differ significantly from those of the lucerne supplemented lambs. Final live weight (after 12 h fasting) cold carcass weight (after 20 h at 4*C) were recorded. was with Their and All calculations were based on the entire period that lambs spent in the feed lot. Liveweight gain and carcass gain results were analysed by least squares analysis of variance for a randomised complete block with unequal numbers of sheep per plot. Intake data and food conversion data were analysed by randomised complete block analysis of variance. The significance of difference between individual mean values was estimated by Duncan's Multiple Range Test at the 5% level. III. RESULTS Lambs on all three lucerne hay supplemented diets reached a marketable weight in 57 days compared to 66 days taken by those supplemented with oaten hay. This is reflected in their significantly higher rates of liveweight gain (P40.01) and carcass gain (PxO.05). Method of preparation and presentation of the roughage did not affect rate of gain of lambs in this experiment (Table 1). The four groups offered free access to either wheat or roughage all ate similar amounts of wheat. Within these groups the lambs on lucerne hay consumed significantly more roughage (PqO.05) than those on oaten hay; the ratio of wheat to roughage eaten being 58:42 for lucerne hay *Dalgety Australia Limited. + I.C.1, Australia Limited. 438 supplemented diets and 71:29 for oaten hay supplemented diets. Lambs tended to eat more wheat (PcO.05 with lucerne hay, N.S. with oaten hay) when offered milled and mixed with roughage than when alone. Food conversion ratio (FCR) was not significantly affected by type of hay or method of presentation. However, FCR values for those lambs being fed diets where the hay was milled or milled and mixed tended to be higher than for those being fed hay in the long form. It was estimated that 32% of the lucerne hay.and 43% of the oaten hay fed was wasted from the hay racks. Poorly designed hay racks and damp conditions accentuated this wastage. TABLE 1 IV. DISCUSSION (a) Scientific The more acceptable performance of lambs fed lucerne hay supplemented diets as compared to those supplemented with oaten hay is due to the higher intakes (Table 1) of the more digestible lucerne hay diets (File, unpublished data). The higher protein level of the lucerne hay may have induced these higher voluntary intakes although intake of wheat was not affected by hay quality. 439 It has been shown that the prevention of selection of the more digestible portion of a roughage by milling results in increased FCR values (Reynolds and Lindahl 1960; Beardsley 1964; Hale and Brent Theurer 1972). This type of trend was present although it was not significant. Intake of the milled and mixed diets (within hay types) was significantly higher than those where the grain was fed separately to the roughage. This higher intake was not reflected in an improved rate of gain; However, FCR values although higher, were not significantly different. The main constituent of the increase in intake was increased wheat consumption (PqO.05 with lucerne supplemented diets, N.S. with oaten hay supplemented diets) while roughage intakes remained constant. .With free-access lambs ate 58:42 wheat lucerne ration. An enforcement of a 70130 ration may have caused metabolic upsets by affecting rumen environment or changing the end products of digestion. (b) Practical Using values based on $83/tonne for wheat, $7O/tonne for lucerne hay and $35/tonne for oaten hay it was estimated that the cost of feed/head in this experiment to produce a marketable carcass was $4.80 for all diets where a free choice was permitted. If the wheat and roughage were fed mixed then the cost was estimated to be $5.60/bead. Although costs for the oaten hay diets (after adjusting for lower valued carcasses) were similar to those of lucerne hay diets, the oaten hay fed lambs remained in the feed lot for an extra nine days. Labour costs associated with this extended period may detract from the use of poorer quality roughage. Cost of long hay wasted from hay racks was higher for lucerne hay than for oaten hay and if wastage was included in the feed cost estimation it made long hay as expensive as the 70130 mixture. Reduction of wastage by improved hay rack design would reduce costs considerably. Capital investment, machinery depreciation and high labour costs associated with the milling and mixing process all make long hay a more economical proposition. This and the fact that liveweight gains were not affected by physical form or method of presentation suggest that there is no physiological or economic justification for the use of a hammermill-mixer unit in the type of enterprise described. v. ACKNOWLEDGEMENTS This work was supported by a grant from the Australian Meat Research Council. Valuable assistance was given by Mr K. McCarthy and Mr G. Williams, whose contributions are gratefully acknowledged. VI. REFERENCES BEARDSLEY, D.W. (1964). Journal of Animal Science. 23 : 239. HALE, W.H. and BRENT THEURER, C. (1972). 'Digestive Eysiology and Nutrition of Ruminants Volume 3 - Practical Nutrition'. (Church : Oregan State University Press). REYNOLDS, P.J. and LINDAHL, I.L. (1960). Journal of Animal Science. 19 - : 873. 440