Thesis (MScAgric)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: This research study consists of three investigations with regard to ostrich (Struthio camelus var. domesticus) production, meat quality and the processing of ostrich meat into a value added meat product. The first study was conducted in order to establish whether the gradual replacement of soybean oilcake meal with cottonseed oilcake meal (CSOCM) as a protein source in the diet of slaughter ostriches would affect ostrich growth performance and meat quality. A total of 105 ostriches were divided into five feeding groups according to the CSOCM inclusion level: Control (0% CSOCM), 3%, 6%, 9% and 12% CSOCM, and fed with experimental diets from 6 to 13 months of age. As a result of feeding CSOCM, the final live weight and the average daily gain significantly increased in the 12% CSOCM group compared to the other treatment diets. The proximate composition, cholesterol content, mineral and fatty acid profile of the meat remained unaffected. Considering all the results, CSOCM may be used as an alternative protein source to soybean oilcake meal in ostrich nutrition, resulting in decreased feed costs. Secondly, a descriptive sensory analysis, together with chemical and physical measurements, was performed to determine whether the manipulation of the fatty acid composition in the fan fillet (Iliofibularis muscle) as a result of feeding CSOCM would be detected on a sensory level. Two levels of CSOCM were investigated; 0% as a control and 9% CSOCM. No significant differences were found for the physical measurements (cooking loss (%) and shear force) as well as for the pH and proximate composition of the raw fan fillet. The Control group presented a higher (P<0.05) mono-unsaturated fatty acid (MUFA) content in the cooked fan fillet whereas the 9% CSOCM group showed a favourable increased (P<0.05) poly-unsaturated fatty acid (PUFA) content when compared to the cooked Control samples. As a result, the poly-unsaturated:saturated fatty acid (PUFA:SFA) ratio in the 9% CSOCM group was also higher (P<0.05). No differences (P>0.05) were found between the treatments for the n-6:n-3 (omega 6 to omega 3) ratio. The 9% CSOCM group had a more intense beef aroma, had a higher level of initial and sustained juiciness as well as increased tenderness (P<0.05). Inclusion of 9% CSOCM resulted in a favourable cooked ostrich fan fillet. Finally, the effect of feeding CSOCM on a processed ostrich meat product was investigated. Fan fillet (Iliofibularis muscle) from 13 month old birds receiving no cottonseed oilcake meal (Control) or 9% cottonseed oilcake meal (9% CSOCM) was used. Olive oil was used as a replacement for pork fat, and warthog (Phacochoerus africanus) meat was used to replace commercial pork meat in the production of a semi dry sausage, cabanossi. Olive oil was included at three levels (0%, 1% and 2%). Six treatments were investigated: Control 0% olive oil, Control 1% olive oil, Control 2% olive oil, 9% CSOCM 1% olive oil, 9% CSOCM 2% olive oil en 9% CSOCM 2% olive oil. The Control and 9% CSOCM ostrich meat did not differ significantly in chemical composition nor fatty acid profile. After smoking and drying the fat content in the cabanossi containing 0%, 1% and 2% olive oil averaged 7.2%, 7.45% and 8.65% respectively. Processed meat products containing less than 10% fat are classified as a low-fat meat product. Olive oil is a mono-unsaturated vegetable oil containing mainly Oleic acid (C18:1n9c), and low quantities of saturated fatty acids and polyunsaturated fatty acids. Total mono unsaturated fatty acids in the cabanossi increased from 47.0% to 73.0% of total fat, whilst total saturated fatty acids and total polyunsaturated fatty acids decreased from 40.6% to 19.9% and 11.6% to 6.6% respectively as olive oil increased from 0% to 2%. The inclusion of olive oil at 2% resulted in cabanossi with increased (P<0.05) tenderness, juiciness and cured red meat colour, all factors that appeal greatly to the consumer. Overall flavour was not adversely affected by the inclusion of olive oil. This investigation indicated that the use of CSOCM had no negative effect on the production performance of ostriches whilst a 9% CSOCM inclusion level resulted in meat that was found to be favourable by a trained sensory panel. Furthermore, the use of CSOCM as a feed component also had no negative effect on a processed product (cabanossi) derived from the meat obtained from the birds fed this feed component. The CSOCM used in this investigation had low levels of gossypol (10 to 20ppm) and more research is required on the effect of the use of CSOCM with higher levels of gossypol on the production performance of ostriches. / AFRIKAANSE OPSOMMING: Die studie het bestaan uit drie ondersoeke met betrekking tot volstruis (Struthio camelus var. domesticus) -produksie, -vleiskwaliteit en die vervaardiging van waarde-toegevoegde geprosesseerde volstruis-vleisprodukte. Die doel van die eerste studie was om vas te stel of die geleidelike vervanging van sojaboonoliekoekmeel met katoensaad-oliekoekmeel (CSOCM) as ‘n proteïenbron in die voeding van volstruise, die groeipersentasie en vleiskwaliteit van die Iliofibiularis spier (fan fillet) sal affekteer. ‘n Totaal van 105 volstruise is verdeel in vyf voedingsgroepe volgens die katoensaad oliekoekmeel insluitingsvlak: Kontrole (0% CSOCM), 3%, 6%, 9% en 12% CSOCM. Die onderskeie voedingsgroepe was van ses tot 13 maande ouderdom op die eksperimentele voere geplaas. Die resultate het aangedui dat die voëls in die 12% CSOCM behandelingsgroep ‘n betekenisvolle (P<0.05) toename in finale lewende massa asook gemiddelde daaglikse toename gehad het. Die proksimale samestelling, cholesterol-inhoud, mineraal- en vetsuursamestelling van die vleis was nie geaffekteer deur die insluiting van CSOCM nie. Die CSOCM kan dus wel as ‘n alternatiewe proteïenbron in die voeding van volstruise gebruik word. Laasgenoemde bevinding kan ook lei tot verlaagde voerkostes, aangesien CSOCM heelwat goedkoper is as sojaboon-oliekoekmeel. Die tweede deel van die studie was van ‘n chemiese asook sensoriese aard. ‘n Beskrywende sensoriese analiese is uitgevoer om vas te stel of die manipulering van die vetsuursamestelling in die volstruis fan fillet as gevolg van die CSOCM sensories waargeneem kan word. Die chemiese en fisiese eienskappe van die vleis is ook ondersoek. Twee vlakke van CSOCM inhoud is ondersoek; 0% (as kontrole) en 9% CSOCM. Geen betekenisvolle verskille is gevind vir die fisiese vleiskwaliteit (kookverliespersentasie en taaiheid), asook vir die proksimale samestelling en pH van die fan fillet nie. Die gekookte fan fillet van die Kontrole behandeling het ‘n betekenisvolle (P<0.05) toename in mono-onversadigde vetsure (MUFA) getoon en die 9% CSOCM het ‘n voordelige toename in poli-onversadigde vetsuur-inhoud (PUFA) gehad. Die poli-onversadigde tot versadigde vetsuurverhouding (PUFA:SFA) was as ‘n gevolg ook betekenisvol hoër. Geen verskille (P>0.05) is opgemerk in die omega-6 tot omega-3 poli-onversadigde vetsuurverhouding (n-6:n-3) nie. Met betrekking tot die sensoriese eienskappe het die 9% CSOCM ‘n meer opvallende beesvleis aroma, hoër vlakke van aanvanklike sappigheid en ook sagter vleis in vergelyking met die kontrole behandeling gehad (P<0.05). Insluiting van 9% CSOCM het gelei tot ‘n gekookte volstruis fan fillet van voornemende kwaliteit. Laastens is daar ondersoek ingestel op die vervanging van varkvet met olyfolie in die vervaardiging van ‘n volstruis cabanossi. Chemiese asook sensoriese analises is uitgevoer op die gedroogde en gerookte volstruis cabanossi. Vir die vervaardiging van laasgenoemde produkte is die fan fillet van 13 maande oue voëls van die Kontrole (0% CSOCM) en 9% CSOCM behandelings gebruik. Addisioneel tot die volstruisvleis is daar ook vlakvarkvleis (Phacochoerus africanus) gebruik om die kommersiële varkvleis te vervang. Olyfolie was ingesluit teen drie vlakke (0%, 1% en 2% van die totale mengsel). Ses behandelings was ondersoek: Kontrole 0% olyfolie, Kontrole 1% olyfolie, Kontrole 2% olyfolie, 9% CSOCM 1% olyfolie, 9% CSOCM 2% olyfolie en 9% CSOCM 2% olyfolie. Daar was geen verskille (P>0.05) in die chemiese en vetsuursamestellings van die Kontrole en 9% CSOCM volstruisvleis nie. Na die droging en rooksiklus was die gemiddelde vet-inhoud van die 0%, 1% en 2% olyfolie cabanossi monsters onderskeidelik 7.2%, 7.45% en 8.65%. Geprosesseerde vleisprodukte met ‘n vet-inhoud van minder as 10% word in die kommersiële vleisindustrie na lae vet vleisprodukte verwys. Olyfolie is baie ryk aan MUFA, veral Oleïensuur (C18:1n9c) en dit bevat ook lae hoeveelhede SFA en PUFA. Die totale MUFA inhoud in die cabanossi het toegeneem van 47.0% tot 73.0% terwyl die totale SFA en PUFA onderskeidelik afgeneem het van 40.6% tot 19.9% en 11.6% tot 6.6%, met ‘n olyfolie toename van 0% tot 2%. Die insluiting van olyfolie teen 2% het gelei tot ‘n sagter cabanossi wat meer sappig was met ‘n meer opvallende rooi gekuurde vleiskleur, wat almal eienskappe is wat dié produk meer aantreklik maak vir die verbruiker. Hierdie studie het aangedui dat CSOCM geen negatiewe effek gehad het op die produksie van volstruise nie. Volstruisvleis van die behandelingsgroep wat CSOCM teen 9% van die dieet ontvang het, het wel vleis geproduseer wat as aanvaarbaar aanskou was deur ‘n opgeleide sensoriese paneel. Die gebruik van CSOCM as ‘n voerbestandeel het ook geen negatiewe effek gehad op ‘n geprosesseerde produk (cabanossi) gemaak van die volstruisvleis nie. Die CSOCM wat in die huidige studie gebruik is, het baie lae vlakke van gossypol (10 – 20dpm) gehad en verdere ondersoek is noodsaaklik om die effek van CSOCM met hoër vlakke van gossypol op die produksie van volstruise te bevestig.

Thesis (MScVoedselwet)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: Two experiments were conducted in order to manipulate the physical and chemical properties and shelf life of ostrich meat. Experiment 1: The effect of dietary fish oil rich in n-3 fatty acids on the organoleptic, fatty acid and physicochemical characteristics of ostrich meat. The diet of four ostrich groups (15 birds per group), approximately 3 months of age (ca. 41 kg live weight) grazing a predominantly oats pasture, was supplemented with a diet containing 6.7% fish oil. The birds received a supplement of either 0 (diet 1), 800 (diet 2), 1600 (diet 3) or 2400 g (diet 4) DM/day resulting in the consumption of 0 (diet 1), 14.5 (diet 2), 29 (diet 3) and 43.5 (diet 4) g fish oil per day. The ostriches were slaughtered at 10 months of age (ca. 70 kg live weight). An increase in the amount of fish oil consumed was found to have had statistically no significant effect on the sensory characteristics of the M. iliofibularis, although there was a tendency towards an increase in ‘fishiness’, for both aroma and flavour. However, increased concentrations of fish oil had a significant effect on the aroma and flavour of the abdominal fat pads. The muscle pHf and muscle lightness (L*) reflected a significant reduction with increased fish oil levels. The increased feed intake, on the other hand, had no effect on the chemical composition (moisture, protein, fat and ash content) of the meat. The fatty acid profile of both fat and meat was affected by the consumption of fish oil. The SFA concentration increased, while the PUFA concentration decreased, with an increase in feed intake. The MUFA concentration remained constant for all four groups. Experiment 2: The effect of dietary vitamin E and the type of packaging on the sensory quality, physicochemical composition and shelf life of ostrich meat. Two groups of ostriches (35 birds per group; ca. 3 months old) were fed diets containing either 40 mg/kg feed vitamin E (control) or 150 mg/kg feed Vitamin E for nine months. The birds were slaughtered at 12 months of age. The effect of different the levels of vitamin E and heat shrink treatment of vacuum packaging material on the shelf life of refrigerated (0°C) ostrich M. flexor cruris lateralis, was evaluated over 81 days. Vitamin E and heat shrink treatments were found to have had no significant effect on the sensory characteristics; off-meat aroma, sourness, juiciness and mealiness. Rancidity was found to be slightly more pronounced (although not statistical significant) in the vitamin E and heat shrink groups than in the feed control and vacuum-packed groups. A significant decrease in the organoleptic quality of the meat, over a 40 day shelf life period, was observed. The pH and muscle tenderness showed a significant reduction with increased storage time. The purge loss in the package increased over time with no change in muscle drip loss. The colour, conjugated dienoic acid and fatty acid content showed no significant changes over time or with regards to treatment. The total viable counts and coliform numbers in the muscle increased over time, with the coliforms being slightly suppressed by the inclusion of vitamin E in the diet. A microbiological safe shelf life of 40 days at 0°C was obtained. / AFRIKAANSE OPSOMMING: Twee eksperimente is uitgevoer om die fisiese en chemiese eienskappe, asook die rakleeftyd van volstruisvleis, te manipuleer. Eksperiment 1: Die effek van visolie, ryk aan n-3 vetsure, op die organoleptiese, vetsuur- en fisies-chemiese eienskappe van volstruisvleis. Die dieet van vier groepe volstruise (15 voëls per groep), ongeveer 3 maande oud (ca. 41 kg lewende massa) wat ‘n hawer weiding bewei het, is aangevul met ‘n byvoedingsmengsel wat 6.7% visolie bevat en in toenemende hoeveelhede vir die groepe volstruise gevoer is. Die voëls het ‘n aanvulling van 0 (dieet 1), 800 (dieet 2), 1600 (dieet 3) of 2400 g (dieet 4) DM/dag ontvang wat gelei het tot ‘n inname van 0 (dieet 1), 14.5 (dieet 2), 29 (dieet 3) en 43.5 (dieet 4) g visolie per dag. Die volstruise is op ‘n ouderdom van 10 maande geslag (ca. 70 kg lewende massa). ‘n Toename in die hoeveelheid visolie ingeneem, het geen statisties betekenisvolle effek op die sensoriese eienskappe van die M. ilifibularis gehad nie, alhoewel daar ‘n tendens was vir ‘n toename tot ‘n ‘visagtige’ aroma en smaak. ‘n Toename in die konsentrasie visolie het egter ‘n betekenisvolle effek op die ‘visagtige’ aroma en smaak van die abdominale vet neerslae gehad. Die spier pHf en spier ligtheid (L*) het ‘n betekenisvolle afname met toename in voer inname getoon. Die verhoogde olie inname het egter geen effek op die chemiese samestelling (vog-, proteïen-, vet- en asinhoud) van die vleis gehad nie. Die vetsuurprofiel van beide die abdominale vet neerslae en die vleis is deur die inname van visolie verander. Die versadigde vetsuurkonsentrasie het verhoog terwyl die poli-onversadigde vetsuurkonsentrasie verlaag het met ‘n toename in rantsoenvlakke. Die mono-onversadigde vetsuurkonsentrasie het egter konstant gebly vir al vier groepe. Eksperiment 2: Die effek van vitamien E en die tipe verpakking op die sensoriese kwaliteit, fisies-chemiese samestelling en rakleeftyd van volstruisvleis. Twee groepe volstruise (35 voëls per groep, ongeveer 3 maande oud) het voere oor ‘n tydperk van nege maande ontvang wat 40 mg vitamien E/kg voer (kontrole) of 150 mg vitamien E/kg voer bevat het. Die voëls is op 12 maande ouderdom geslag. Die effek van die verskillende vlakke van vitamien E en hitte-behandeling van die verpakkings materiaal op die rakleeftyd van verkoelde (0°C) volstruis M. flexor cruris lateralis, is oor 81 dae geëvalueer. Vitamien E en die hitte-behandeling het geen betekenisvolle effek op die organoleptiese eienskappe (af-vleis aroma, suurheid, sappigheid en melerigheid) gehad nie. Galsterigheid was ‘n bietjie meer gedefinieerd (anie-betekenisvol) in die vitamien E en hitte behandelde groepe as in die rantsoen kontrole en vakuum verpakte vleis. ‘n Betekenisvolle afname is waargeneem in die organoleptiese kwaliteit van die vleis oor ‘n 40 dae rakleeftyd periode. Die pH en taaiheid van die spier het betekenisvol afgeneem met ‘n toename in bergingsperiode. Die drup verlies tydens verpakking het ook oor tyd toegeneem, terwyl geen verandering in die analitiese drup verlies van die spier verkry is nie. Die kleur, gekonjugeerde dieensuur en vetsuursamestelling het geen verandering oor tyd of ten opsigte van behandeling getoon nie. Die Totale Lewendig Seltelling en coliforme het toegeneem oor tyd, terwyl die coliforme deur die byvoeging van vitamien E tot ‘n mate onderdruk is. ‘n Mikrobiologies veilige rakleeftyd van 40 dae is verkry.

Thesis (MScAgric (Animal Sciences))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The purpose of this study was to evaluate the production of slaughter ostriches in a grazing environment at different levels of supplementary feed. Two grazing trials were conducted. In the first trial, one group of finisher ostriches (six months old) was put into a feedlot and received a complete finisher diet. The other four groups were allowed to graze lucerne pasture (stocking rate of 15 birds/ha) with 1500, 1000, 500, and 0g supplementary feed/bird/day. Pasture production and intake were measured. There was no difference (P >0.05) between the end mean live weights of the feedlot ostriches and those two grazing groups receiving 1500 or 1000g supplementation. The average daily gain (ADG) of the group receiving 1000g supplementation was lower (P <0.05) than the ADG of the group receiving 1500g supplementation, but all three groups reached a mean target slaughter weight of 95kg within the 154 days of the study. Therefore, pastures together with the correct supplementation (at least 1000g/bird/day) can replace complete feeds in the finishing phase of slaughter ostriches and can play an important role in the production of these birds. For lucerne intake, a quadratic relationship (P <0.01) was found between pasture dry matter (DM) intake (g/bird/day) and supplementary feed intake (g/bird/day). The maximum lucerne intake level (1692.8g/bird/day) was achieved at 619.6g supplementary feed/bird/day. In the second grazing trial, finisher ostriches were allowed to graze lucerne pastures at two different stocking rates (10 and 15 birds/ha) while receiving either 0 or 800g supplementary feed/bird/day. Ostriches receiving supplementation had higher (P <0.05) mean end live weights than ostriches receiving no supplementation. Ostriches receiving supplementation reached a mean target slaughter weight of 95kg within the timespan of the trial, but ostriches receiving no supplementation did not. Stocking rate had no influence on mean end live weight of the birds. An interaction (P <0.05) was found between the level of supplementation and stocking rate for ADG of the birds. Stocking rate influenced ADG only for birds receiving no supplementation. As stocking rate increased, ADG of birds receiving no supplementation declined. Results of the pasture data indicated an increasing level of replacement of grazed lucerne DM by supplementary feed as the trial progressed and this was more pronounced at the higher stocking rate of 15 birds per hectare. A high stocking rate seems to have had a gradual depressing effect on lucerne DM production, while the less severe levels of defoliation at a lower stocking rate promoted lucerne DM production. A digestibility trial was conducted with mature ostriches (12 months old) to investigate the effect of supplementation on intake and digestibility of nutrients, as well as to investigate the substitution effect that ostriches may display when they receive supplementary feed in addition to grazing. The same dietary treatments as in the first grazing study were given to ostriches while they were kept in metabolism crates. These diets were also fed to 20-week old roosters to obtain energy values for these diets for roosters. These energy values would be used to predict ostrich energy values for the same diets by means of a regression equation. For the roosters, each diet treatment was mixed with 50% maize to prevent digestive disorders and ensure maximum feed intake. Ostriches started to substitute supplementary feed for pasture when supplementation was supplied at levels higher than 62% (i.e. 1000g supplementary feed/bird/day) of total feed intake. For each increase of 100g in supplementary feed intake, pasture was replaced at a rate of 4.9%. Higher (P <0.05) total feed intakes were reached by ostriches if they grazed lucerne pastures and received supplementation than if they grazed pasture alone. Pasture grazing alone had lower (P <0.05) dry matter digestibility (DMD) and apparent metabolizable energy (AME) values for both ostriches and roosters than if pastures were supplied with a supplement. A significant stepwise regression could not be computed for the prediction of ostrich AME values from rooster AME values. The economics of different feeding systems (extensive versus intensive) were evaluated with an economic analysis, which was based on the same materials and methods and results of the first grazing trial. A margin above feed cost (MAFC) analysis was performed to evaluate the economic viability of the different feeding systems. The present value (PV) of the MAFC for the pasture-based system with 1000g/bird/day supplementation was only 8.3% lower than that of the feedlot system over a period of six years, while the PV of the cost of the same pasture-based system was 78.4% lower than that of the feedlot system. Birds finished on lucerne pasture with 1000g supplementation led to a saving of 57% in feeding costs if compared to a feedlot system. A sensitivity analysis of the MAFC revealed that the pasture-based system was less sensitive to changes in feeding costs than the feedlot system. Therefore, the unique circumstances of each ostrich producer will play a role in the decision whether to raise ostriches in a feedlot or on pastures. / AFRIKAANSE OPSOMMING: Die produksie van slagvolstruise in ‘n ekstensiewe weidingsstelsel met verskillende vlakke van aanvullende voeding is gedurende hierdie studie ge-evalueer. Twee weidingsstudies is uitgevoer. In die eerste studie is een groep afrondingsvolstruise (ses maande oud) in ‘n voerkraal geplaas en ‘n volledige afrondingsdieet gevoer. Die ander vier groepe is op besproeide lusernweiding geplaas (teen ‘n weidigtheid van 15 voëls/ha) en het onderskeidelik 1500, 1000, 500 en 0g aanvullende voeding/voël/dag ontvang. Weidingproduksie en -inname is gemeet. Daar was geen verskil (P >0.05) tussen die eindgewigte van die voerkraal volstruise en dié van die weidende voëls wat onderskeidelik 1500 en 1000g aanvullende voeding ontvang het nie. Die gemiddelde daaglikse toename (GDT) van die groep weidende voëls wat 1000g aanvullende voeding ontvang het was laer (P <0.05) as die GDT van die groep weidende voëls wat 1500g aanvullende voeding ontvang het, maar al drie hierdie groepe het ‘n gemiddelde teiken slaggewig van 95kg bereik binne die 154 dae van die studie. Weiding, tesame met die korrekte aanvullende voeding (van ten minste 1000g/voël/dag) kan volvoer rantsoene in die afrondingsfase van slagvolstruise vervang en kan dus ‘n belangrike rol speel ten opsigte van die produksie van hierdie voëls. Vir lusern inname is ‘n kwadratiese passing (P <0.01) tussen weiding droë materiaal (DM) inname (g/voël/dag) en aanvullende voeding inname (g/voël/dag) gevind. Die maksimum lusern inname (1692.8g/voël/dag) is bereik wanneer voëls 619.6g aanvullende voeding/voël/dag ingeneem het. In die tweede weidingsstudie, is afrondingsvolstruise (6 maande oud) toegelaat om lusern te bewei teen twee verskillende weidigthede (10 en 15 voëls/ha) en het ook 0 of 800g aanvullende voeding/voël/dag ontvang. Volstruise wat aanvullende voeding ontvang het, het hoër (P <0.05) gemiddelde eindgewigte bereik as volstruise wat geen aanvullende voeding ontvang het nie. Volstruise wat aanvullende voeding ontvang het, het ook die teiken slaggewig van 95kg bereik binne die tydsduur van die studie, terwyl die volstruise wat geen aanvullende voeding ontvang het nie, nie daarin kon slag nie. Weidigtheid het nie ‘n invloed (P >0.05) gehad op die eindgewigte van die voëls nie, maar ‘n interaksie (P <0.05) is gevind tussen vlak van aanvullende voeding en weidigtheid wat GDT van die voëls betref. Weidigtheid het GDT beïnvloed slegs vir volstruise wat geen aanvullende voeding ontvang het nie. Soos die weidigtheid van die voëls wat geen aanvullende voeding ontvang het nie, toegeneem het, het die GDT van hierdie voëls afgeneem. Ontleding van die weidingsdata het ‘n toenemende vlak van verplasing van die weiding met aanvullende voeding getoon soos die studie gevorder het en dit was meer merkbaar by die hoër weidigtheid. Die hoër weidighteid het ook gelei tot ‘n geleidelike afname in lusern DM produksie, terwyl die minder aggressiewe vlakke van ontblaring by die laer weidigtheid lusern DM produksie bevorder het. ‘n Verteringsstudie is gedoen met volwasse volstruise (12 maande oud) om die invloed van aanvullende voeding op inname en verteerbaarheid van nutriente te toets, asook om die substitusie effek wat volstruise mag toon wanneer hulle aanvullende voeding ontvang op weiding, te ondersoek. Dieselfde dieet behandelings as in die eerste weidingsstudie is vir die volstruise gegee terwyl hulle in metabolisme kratte aangehou is. Hierdie diëte is ook aan 20-week oue hane gevoer om die energie waardes van die diete vir hane te verkry. Hierdie energiewaardes sal dan gebruik word om volstruis energiewaardes te voorspel vir dieselfde diëte met behulp van ‘n regressie vergelyking. Vir die hane is elke dieet gemeng met 50% mielies om inname te handhaaf en spysverteringsstoornisse te voorkom. Volstruise het weiding begin verplaas met aanvullende voeding sodra die vlak van aanvullende voeding hoër as 62% (d.i. meer as 1000g aanvullende voeding/voël/dag) van die totale inname van die voëls was. Vir elke 100g toename in aanvullende voeding, word weiding verplaas teen ‘n tempo van 4.9%. Weiding, tesame met aanvullende voeding, het gelei tot hoër totale droë material (DM) voerinnames by volstruise as wanneer weiding alleen beskikbaar was. Wanneer weiding alleen voorsien was, was daar laer (P <0.05) verteerbaarhede van DM en waarskynlike metaboliseerbare energie (WME) waardes vir beide volstruise en hane as wanneer die weiding voorsien word met aanvullende voeding. Geen betekenisvolle stapsgewyse regressie kon gevind word om volstruis energie waardes uit hoender energie waardes te voorspel nie. Die ekonomie van verskillende sisteme (ekstensief versus intensief) is in hierdie studie vergelyk en is gebaseer op dieselfde materiaal en metodes en resultate van die eerste weidingsstudie. ‘n Marge bo voerkoste analise is gebruik om die ekonomiese lewensvatbaarheid van die sisteme met mekaar te vergelyk. Die huidige waarde van die marge bo voerkoste van die weidingssisteem waar 1000g aanvullende voeding gevoer word was 8.3% laer as dié van die voerkraal sisteem oor ‘n periode van ses jaar. Daarteenoor was die huidige waarde van die koste van dieselfde weidingssisteem 78.4% laer as dié van die voerkraal sisteem. Die weidingssisteem waar volstruise 1000g aanvullende voeding ontvang het, het ‘n besparing van 57% in voerkoste getoon wanneer dit met die voerkraal volstruise vergelyk is. ‘n Sensitiwiteitsanalise van die marge bo voerkoste het getoon dat die weidingssisteem minder sensitief is vir wisselende voerkoste as die voerkraal sisteem. Die unieke omstandighede van elke produsent sal ‘n rol speel in sy keuse om volstruise op weiding of in ‘n voerkraal af te rond.