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Accueil du site → Doctorat → Royaume-Uni → 1990 → Factors influencing the nutritive value of barley straw for ruminants

University of Reading (1990)

Factors influencing the nutritive value of barley straw for ruminants


Titre : Factors influencing the nutritive value of barley straw for ruminants


Université de soutenance : University of Reading

Grade : Doctor of Philosophy (PhD) 1990

Barley straw is an important source of feed for sheep in the semi-arid areas of west Asia with a Mediterranean climate. In temperate areas of Europe only a proportion is fed to ruminant livestock, principally cattle. Rainfall was found to increase the height of barley crops and decrease straw leaf proportions. Straw from temperate climates was shown to have 10-20 g less digestible dry matter (DM) 100 g DM$\sp-1$ than straw from semi-arid areas. Variety strongly influenced straw digestibility at particular locations. Agronomic practices had no important effect whilst grazing at the tillering stage had variable effects on straw quality. Taller varieties had less leaf blade and more stem, the most digestible and least digestible fractions in the straw respectively. Later heading or later maturing varieties contained more leaf. Average increase in straw yield in semi-arid areas was 93 kg ha$\sp-1$ for each unit increase in straw digestibility but grain yield was reduced by 35 kg ha$\sp-1$. Feeding trials with sheep fed unsupplemented straw showed that organic matter intake (OMI) could range from 31.0 to 45.9 g/kg M$\sp0.75$ day$\sp-1$ and organic matter digestibility (OMD) from 43.0 to 47.7% depending upon variety. Supplementation with either barley grain or cottonseed cake had variable effects on straw OMI and OMD suggesting the presence of variety x supplementation interactions. Harvesting using a combine produced straw with higher feeding value than traditional hand harvesting which is still practised in west Asia. Treatment with aqueous ammonia and sodium hydroxide (5 g 100 g straw DM$\sp-1$) improved the leaf sheath fraction of barley straw more than leaf blade or stem. Ammoniation to improve nutritive value is likely to be less effective with straw from semi-arid climates which contains more leaf blade. Cell wall phenolic levels explained differences in digestibility between alkali-treated and untreated straws but not between straws of different varieties. Comparison of variety effects on straw digestibility with variety x environment interactions demonstrated some stability for straw feeding value in barley. However breeding for these will require development of rapid methods for predicting feeding quality. Within the barley/sheep farming system practiced in semi-arid areas of west Asia the selection of barley varieties with superior grain yield and straw quality could have an important impact on sheep production.

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