The feeding value of morphologically different wheat straws.

Abstract

Proc. Aust. Soc. Anim. Prod. Vol. 17 THE FEEDING VALUE OF MORPHOLOGICALLY DIFFERENT WHEAT STRAWS W.J. WALES*, P.T. DOYLE*, and G.R. PEARCE* 479 Wheat straws and stubbles are generally regarded as poor quality roughages as they are low in readily available energy and protein and may be lacking in other essential elements. Sheep grazing on stubbles are able to maintain body weight for several weeks only (Mulholland 1987) and if fed for extended periods may die (Franklin et.al. 1967). However, there is considerable variation in the physical and chemical characteristics of straws and stubbles. These result from genetic and environmental influences and the interactions between these. The magnitude of genetic and environmental effects are poorly defined. The aim of this study was to determine the extent to which differences in the characteristics of wheat straw from one cultivar could effect feeding value. Wheat stubbles (cv. Millewa) were sampled from a range of environments within Victoria. Three straws (WSl, WS2 and WS3) which represented the middle and extremes in the range of in vitro organic matter digestibility (IVOMD) were selected, harvested and fed to crossbred Merino sheep (8 sheep per straw). The wheat straws were described in terms of the percentage of leaf and stem components and the IVOMD of these and their organic matter intake (OMI) and apparent digestibility (OMD) which were measured during a 33 day experiment (see Table 1). Table I. Characteristics, intake and digestibility of the straws #Calculated from leaf sheath and leaf blade IVOMD value The percentage of straw dry matter in leaf and stem fractions differed (P<O.O5). The leaf fractions had higher IVOMD values than the stems for each straw. The higher percentage of leaf in WSl and WS2 contributed to higher IVOMD values of these straws. OMl was higher (P<O.O5) in WSl and WS2 than WS3 and these straws had higher percentages of leaf components. Despite the differences (P(O.05) in the OM1 between WSl and WS3 there were no differences in the OMD of the straws. Pronounced differences under the controlled laboratory conditions occumed between IVOMDs of the whole straw although these differences were not reflected in the OMDs under the conditions of the gastro-intestinal tract. Morphological composition of wheat straws can be an important determinant of OMI and thus may have a major influence on the feeding value. FRANKLIN, M.C., McINNES, P. and BRIGGS, P.K. (1967) Aust. J. Exp. Agric. Anim. Husb. L: 206-212. MULHOLLAND, J.G. (1987) Proc. 2nd International Symposium on the Nutrition of Herbivores (&SAP) pp. 25-26. *School of Agriculture and Forestry, University of Melbourne, Parkville, Vic.3052