The effects of drying temperature on chemical composition and nutritive value of some tropical fodder shrubs

Abstract

The effects of drying temperature on chemical composition and nutritive value of leaves of the shrub legumes Acacia angustissima (Miller) Kuntze, Calliandra calothyrsus Meissn and Leucaena leucocephala (Lam.) de Wit were determined in two studies in Zimbabwe. In the first study, the effects of shade-, sun- and oven-drying leaves on chemical composition and protein precipitation capacity of tannin extracts were studied. Drying method affected (P<0.01) chemical composition, with cell wall polysaccharides increasing from shade drying to oven drying. Calliandra calothyrsus leaves had the highest total phenolics, tannin phenolics and the lowest N content. About 40% of phenolics in L. leucocephala were non-tannin compared to less than 15% in A. angustissima and C. calothyrsus. Extractable proanthocyanidins and their capacity to precipitate protein were affected (P<0.01) by drying method; extracts from shade-dried leaves were 10% and 20% more reactive than extracts from sun- and oven-dried leaves, respectively. The relative degree of polymerisation of the proanthocyanidins was higher (P<0.01) for oven-dried (1.44) leaves compared to shade-dried (1.01) and sun-dried (1.00) leaves. Drying temperature influences the nutrient–polyphenolic interactions in A. angustissima, C. calothyrsus and L. leucocephala leaves and these interactions have important implications for feed evaluation protocols and for use of these leaves in ruminant feeding systems. The second study considered the effects of feeding sun-dried or fresh leaves of the three shrub legumes as supplements to native pasture hay on nutrient intake and digestion by goats. Feeding the fresh or dry leaves made no difference in terms of dry matter intake and digestion, and N digestion. This offers farmers flexibility in terms of feeding strategies, as they can feed the browse in any form that suits their farm situation. Increasing the level of C. calothyrsus in the diet increased faecal N. Nitrogen retention was lower for animals fed with C. calothyrsus compared to those fed with the other browses.