The effect of supplementing untreated, urea-supplemented and urea-ammoniated wheat-straw with maize-meal and/or fish-meal in sheep

Supplementation of untreated, urea-supplemented or urea-ammoniated wheat-straw diets with sources of readily fermentable energy (maize-meal; 0 and 20% of the total diet) and rumen-undegradable protein (fish-meal; 0 and 5% of the total diet) was investigated in a 3x2x2 factorial experiment, involving an intake and in vivo digestibility trial with 48 adult S.A. Mutton Merino wethers. Straw dry matter (DM) intake on ammoniated wheat-straw diets was 27 and 22% higher ( P ≤0,01) than on untreated and urea-supplemented diets, respectively. No significant difference was found between the latter treatments. The inclusion of 5% fish-meal stimulated ( P ≤0,01) straw DM intake by 13% relative to the control diets without fish meal. Incorporation of the 20% maize-meal supplement alone, or in combination with 5% fish-meal, did not result in any further improvement in straw DM intake. The apparent digestibility of organic matter (OM), cell-wall constituents (CWC), acid detergent fibre (ADF) and hemicellulose was higher ( P ≤0,01) on the urea-ammoniated wheat-straw diets than on either the untreated wheat-straw diets or the urea-supplemented wheat-straw diets. No differences were obtained between the latter treatments. The apparent OM digestibility of the wheat-straw diets was improved by the inclusion of 5% fish-meal and/or 20% maize-meal. Apparent digestibility' of CWC and ADF was not particularly affected by the inclusion of fish-meal or maize-meal. Combined supplementation of the straw diets with both 5% fish-meal and 20% maize-meal tended to suppress the apparent digestibility of CWC and ADF. Apparent hemicellulose digestibility of the wheat-straw diets was increased ( P ≤0,01) by 4,5% due to the inclusion of maize-meal. Apparent nitrogen (N) digestibility and N-balance was involved in significant ( P ';;0,01) three-factor interactions. Urea supplementation improved ( P ≤0,01) N-digestibility compared to untreated wheatstraw diets. Urea ammoniation similarly improved N-digestibility in relation to untreated wheat-straw with or without supplementary maize-meal. The apparent N-digestibility of urea-supplemented wheat-straw tended to be higher than on urea-ammoniated wheatstraw, but the only significant ( P ≤0,01) difference occurred between the diets without maize-meal and/or fish-meal. Nitrogen balance was generally improved in sheep receiving diets containing urea-ammoniated wheat-straw, and fish-meal alone or combined with maize-meal. No significant differences in N-balance were found between the untreated wheat-straw diets and corresponding ureasupplemented wheat-straw diets. Aanvulling van onbehandelde, ureum-aangevulde en ureum-geammoniseerde koringstrooidiete met bronne van maklik fermenteerbare energie (mieliemeel; 0 en 20% van die totale dieet) en rumen nie-degradeerbare proteien (vismeel; 0 en 5% van die totale dieet) is ondersoek in 'n 3X2x2-faktoriaaleksperiment met 48 volwasse SA Vleismerinohamels. Strooi droe materiaal (DM)-inname op die geammoniseerde strooidiete was onderskeidelik 27 en 22% hoer ( P ≤0,01) as op onbehandelde en ureum-aangevulde diete. Geen betekenisvolle verskille het tussen laasgenoemde diete voorgekom nie. Die insluiting van 5% vismeel as aanvulling het strooi DM-inname met 13% bo die onaangevulde kontrole gestimuleer. Slegs mieliemeel of mieliemeel in kombinasie met vismeel as aanvulling het geen verdere verhogings in strooi DM-inname veroorsaak nie. Die skynbare verteerbaarheid van organiese materie (OM), selwande (SW), suurbestande vesel (SBV) en hemisellulose was hoer ( P ≤0,01) op ureum-geammoniseerde koringstrooidiete as op onbehandelde of ureum-aangevulde strooidiete. Geen verskille het tussen laasgenoemde diete voorgekom nie. Die insluiting van 5% vismeel en/of 20% mieliemeel afsonderlik as aanvulling, het skynbare OM-verteerbaarheid verbeter. Die skynbare verteerbaarheid van SW en SBV is tot 'n mindere mate deur die insluiting van vismeel of mieliemeel beinvloed. Gesamentlike aanvulling met 5% vismeel en/of 20% mieliemeel het geneig om die skynbare verteerbaarheid van SW en SBV in koringstrooidiete te onderdruk. Skynbare hemisellulose verteerbaarheid van die koringstrooidiete is met 4,5% deur die insluiting van mieliemeel verhoog. Skynbare stikstof (N)- verteerbaarheid en N-balans was betrokke by betekenisvolle ( P ≤0,01) driefaktor-interaksies. Ureum-aanvulling het skynbare N verteerbaarheid verhoog ( P ≤0,01) in vergelyking met ooreenstemmende onbehandelde koringstrooidiete. Ureum-ammonisering het ook skynbare N-verteerbaarheid verhoog by die dieet wat geen aanvulling ontvang het nie, en by die dieet wat 20% mieliemeel ingesluit het. Die skynbare N-verteerbaarheid van ureum-aangevulde koringstrooi het hoer geneig as op ureum-geammoniseerde koringstrooi, met slegs die verskil tussen die diete wat geen mieliemeel of vismeel ingesluit het nie, betekenisvol ( P ≤0,01). Stikstofbalans was in die algemeen beter op diete wat ureum-geammoniseerde koringstrooi ingesluit het, en op diete waarby vismeel alleen of in kombinasie met mieliemeel ingesluit is. Geen betekenisvolle verskille in N-balans is verkry tussen onbehandelde koringstrooidiete en ooreenstemmende ureum-aangevulde diete nie. Keywords : Urea-ammoniation, supplementation, intake, digestibility, nitrogen balance.