Evaluation of Stover management practices or ameliorative strategies on the utilization of tanniferous feeds by ruminants
Boitumelo, Wame Shaimane
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Seven experiments which hcluded one fieIdlagronomy, four in vitro and two in vivo triais were carrieci out to (i) determine the optimum time of harvesbng and storage methods that preserved the nutritive quality of make and sorghum stovers, Ci) examine strategias for enhancing the u-tion of high tannin feeds (bird-resistant (BR) sorghum stover supplemented with forage legumes Ws) with vaqing tannin concentrations) by using ameliorants (polyethylene glycol MW 40ûû (PEG-4000), urea or sulphur). It was determhed tbat nutritive value was significamly (P0.00 1) innuenceci by crop type, perhd of harvest and storage method. The highest nutrient content was recorded at 2 weeks (-2 weeks) before physiological dead ripe s%age of grain and when the stover was harvested irnmediately after grain harvest and stored under ahade. Addition of ameliorants significantly improved DMD and gas production in vitro. Urea and sulphur were as effective as PEG in alleviating the antinutritive effects of high tannin in feeds. The optimum levels of PEG required to alleviate the anti-nunitive effects of CTs varied with forages. Nevertheless, a ratio of 21 (PEG: CT) was found to be optimum for the deviation ofthe adverse effects of CTs. Forage Iegumes with hi& concentrations of CT- when used as supplements to BR sorghum stover, depressed animal performance (feed intake, growth and growth eficiency). The response assumed both a hear and quadratic pattern, suggesting a threshold point beyond which respoose decreased. sesban 15019, Desmodium intorfum and Acacia angusfissima) with different nutntionai attn'butes at 1:2 or 2: 1 ratio signiIicantiy improved gas and ammonia production in vitro. This there is potentiai for improving- the utibtion of some forages that would nody pose problerns (e.g. R angusrssihn) îfused by themseLves. It was possible to assas the reactivity (biologicd activity) of tannins by reacting them with PEG and relating it to radial ciifEsion assay @rotein precipitation assay). Resuits showed a high correlation (r = 0.87, Fc0.01) between PEG-CT reactions and radiai &ion assay, thus indicating that PEG-CTs reaction may be an effdve method of indexing tannin reactivity.
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