UNCORRECTED PROOFS JSFA1907.2003/330 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Journal of the Science of Food and Agriculture J Sci Food Agric 84:000–000 (online: 2004) DOI: 10.1002/jsfa.1907 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 Ruminal degradation of tannin-treated legume meals TF Mart´ ınez, ∗ FJ Moyano, M D´ ıaz, FG Barroso and FJ Alarc ´ on Departamento de Biolog´ ıa Aplicada, ´ Area de Zoolog´ ıa, CITE II-B, Universidad de Almer´ ıa, E-04120 Almer´ ıa, Spain Abstract: The inefficiency of protein utilisation by ruminants fed protein concentrates (based on legume meals) causes serious economic loss and environmental damage owing to their rapid hydrolysis and deamination in the rumen. Thus efforts aimed at slowing the ruminal fermentation of such feeds are needed, and recent studies have observed potentially positive effects of tannins on ruminant nutrition under certain circumstances. Tannins are a complex group of naturally occurring plant polyphenols characterised by their ability to bind with proteins. This property of tannins is considered responsible for the decreased ruminal digestibility of forages both in vivo and in vitro. Under that perspective, commercial tannic acid was added at three proportions (10, 25 and 50 g kg -1 on a dry matter basis) to four different legume meals (horse bean, kidney bean, soybean and pea), and the effect on in situ dry matter and crude protein ruminal disappearance was assessed. The results confirmed the dose-dependent (although not persistent after 48 h) slowing of in situ digestibility, this effect being significant at the highest tannin treatment when compared with untreated samples. Scanning electron microscopy revealed that soybean seed endosperm cell walls were protected from digestion by the ruminal microbiota, while the digestion of starch granules was relatively unaffected by tannic acid. Electrophoresis of the protein fractions confirmed the lower digestibility of tannin-treated seeds as well as the relative lack of alteration of the electrophoretic profile of individual proteins. Implications for the digestion of concentrates in ruminants are discussed.  2004 Society of Chemical Industry Keywords: concentrate feeds; ruminant digestibility; bypass protein; tannins; scanning electron microscopy INTRODUCTION Dietary protein ingested by ruminants is extensively degraded by the micro-organisms in their rumen. 1 The rapid conversion of protein to ammonia and its subsequent absorption across the rumen wall before being eventually excreted as urea leads to inefficient nitrogen utilisation in ruminants. 2 Under this perspective the identification and quantification of compounds and/or factors able to reduce ruminal degradation of protein, increasing its outflow to the small intestine, has been a main research topic during the last 25 years. Great interest is currently being shown in exploring the potential of tannins to protect plant proteins from ruminal degradation, mainly after the banning of meat and bone meals in the EU. Tannins have traditionally been considered as antinutritive factors for ruminant and non-ruminant animals owing to their ability to complex with macromolecules, mainly proteins, 3 this interaction being responsible for a reduced bioavailability of nutrients. In recent years, however, tannins have become a matter of interest in ruminant nutrition because of their potentially useful effects on dietary protein utilisation, mainly related to forages 4,5 but also to concentrates. 6 The chemical bases of the tannin–protein interactions, highly dependent on pH, 7 as well as the particular anatomy and physiology of the ruminant digestive tract, are responsible for this change in the perception of polyphenols in ruminant nutrition. 8 Therefore current research efforts are focused on identification of the factors involved in the slower fermentation of tannin-rich forages and concentrates so that ruminant feeds can be improved. Scanning electron microscopy (SEM) gives direct evidence of digestive phenomena taking place in the rumen. This technique is a useful complement to in vivo and in vitro digestibility studies. Although not quantitative, SEM offers qualitative information about the interaction of ruminal micro-organisms and seed structures during digestion processes. Most of the studies carried out using this technique have focused on cereal seeds, and to a lesser extent on legume seeds. On the other hand, SEM studies have been mainly used to assess the effect of formaldehyde and micronisation 9,10 as procedures aimed at manipulating the degradability of seeds in the rumen. Nevertheless, the influence of tannins on the ruminal digestion ∗ Correspondence to: TF Mart´ ınez, Departamento de Biolog´ ıa Aplicada, ´ Area de Zoolog´ ıa, CITE II-B, Universidad de Almer´ ıa, E-04120 Almer´ ıa, Spain E-mail: tomas@ual.es (Received 27 March 2002; revised version received 13 April 2004; accepted 17 June 2004)  2004 Society of Chemical Industry. J Sci Food Agric 0022–5142/2004/$30.00 1