Thesis (MScAgric)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: One of the reasons why meat supply does not meet human demand is that man has
concentrated on utilising relatively few animal species as a source of meat. Development of
unconventional livestock, such as goats, is advocated as a means of increasing global meat
production and consumption. Although South Africa possesses large numbers of domestic
ruminants, meat consumption has been limited mainly to sheep and cattle. Goats are used to
a lesser extent. This is partly attributed to a general belief that goat meat is inferior to mutton
and beef.
Numerous contradictions regarding comparative goat and sheep growth, carcass
characteristics and meat composition exist in literature. Concepts involved with most of the
contradictions includes average daHy gain (ADG), dressing percentage, carcass weight
distribution and organoleptic characteristics, especially tenderness, juiciness and flavour,
particularly as pertaining to animals reared/grown under intensive/feedlot conditions.
Therefore this project was undertaken to obtain more information on the growth, carcass and
organoleptic characteristics, as well as meat chemical compositions of Boer goat (BG) kids in
comparison with South African Mutton merino (MM) lambs, reared under feedlot conditions.
Thirty-two BG kids and 32 MM lambs were used for this investigation. All the animals were
castrated and weaned before entering the feedlot. Two pelleted diets (fed to 16
animals/species) with either a low (LE; 8.9 MJ/kg OM) or a high (HE, 10.9 MJ/kg OM)
metabolisabie energy level were fed individually, ad lib for either 28 or 56 days. Feed and
water intake, ADG and feed conversion efficiencies (FCE) were monitored. During the last week of the feeding trial, 12 BG kids and 12 MM lambs were used to evaluate the digestibility
of the two diets.
After either 28 or 56 days, the animals were slaughtered and the carcasses dissected into
South African commercial cuts. The m. semimembranosus and 8-9-10-rib cut of each carcass
was dissected for determination of chemical composition, drip loss, cooking loss, shear force
values and colour measurement. The m. gracilis was dissected from the hind leg of the
carcass and used for sensory evaluation.
MM's had significantly higher AOG's than BG's (e.g. MMHE56: 0.281; BGHE56: 0.162
kg/day). Within a diet there was no difference (P>0.05) in FCE between BG's and MM's and
only the MM's FCE differed between the LE and HE diet (e.g. BGLE28: 7.65; BGHE28: 6.37;
MMLE28: 8.73; MMHE28: 5.56 kg feed/kg weight gain). BGLE digested dry matter (OM),
crude protein (CP) and energy more efficiently and had a higher energy retention than MMLE.
The two diets had the same ME-value for the goats, which confirms that goats perform equally
well on a lower quality feed as their contemporaries on a higher quality feed. Neither species,
nor diet affected nitrogen retention. The BG had a 49 % lower (P<0.01) water intake per kg
weight gain than the MM on both the high and low energy diets. Both species had a lower
(P<0.01) water intake on the high than on the low energy diet. Furthermore, the BG had a
daily water intake of only 171 ml/kgo.75 compared to the 302 ml/kgo.75 of the MM.
The weight of the liver, empty stomach, head and feet (as a percentage of empty body weight)
were higher in goats than in sheep. The MM's had significantly heavier skins, probably due to
wool growth. Both kidney fat and gastro-intestinal tract (GIT) fat increased with age. The
animals slaughtered after 56 days in the feedlot had significantly longer and deeper carcasses
than their contemporaries slaughtered after 28 days. Within a diet and slaughter age, the MM
had significantly broader and deeper carcasses than the BG's. BG's had significantly less
weight per unit carcass length, and thus more slender carcasses than MM's. Diet had no
significant influence on the carcass weight distribution of the goats. However, MM's had
heavier carcasses (LE: 19.87 vs. 15.28 kg; HE: 24.01 vs. 17.05 kg) and proportionally heavier
ribs and buttocks than BG's.
Neither diet nor slaughter age influenced the proximate analysis of the m. semimembranosus,
but MM's had significantly lower moisture values than BG's. In the 8-9-10-rib cuts BG's had
significantly more moisture and protein and lower fat and energy values than MM's. OM, fat
and energy values increased with an increase in slaughter age in both species. BG's had
significantly higher concentrations of 11 of the 18 measured essential amino acids in their 8-9-
10-rib cuts than the MM's. Gaat carcasses had higher Ca, K, Mg, Na and P-Ievels than sheep
carcasses, regardless of the diet fed. There was a tendency for goat's m. semimembranosus
to have a lower Fe-content than that of sheep. BG carcasses had a lower carcass cholesterol content than that of lamb (66.77 vs. 99.28
mg/100g, respectively). Palmitic (C16:0), stearic (C18:0) and oleic (C18:1 n9) acid comprised
the greatest proportions of fatty acids in both the m. semimembranosus and 8-9-10-rib cut for
both species. On a LE-diet there was no significant difference between the saturated fatty
acid (SFA) to unsaturated fatty acid (UFA) ratio of goat meat and lamb. However, on the HEdiet,
lamb had a significantly higher SFA:UFA ratio than chevon (m. semimembranosus: 0.842
vs. 0.689; 8-9-10-rib cut: 1.407 vs. 0.892). Organoleptically, a difference was noted between
chevon and lamb. Each has a specific species flavour, which was not influenced by energy
level of the diet. BG meat was perceived to be stringier than that of the MM, but there was no
significant difference in Warner-Bratzler shear force values. Tenderness declined with age in
both species and there was also a tendency for goat meat to be less juicy than lamb. Chevon
had a more pronounced aftertaste than lamb. No objective differences could be distinguished
between the colour of the cooked chevon and lamb. There was a tendency for fresh lamb to
have a higher a*-value (redness) than chevon. Although diet did not influence drip loss, drip
loss increased with an increase in slaughter age. Only after 56 days did the MM's m.
semimembranosus have a significantly higher drip loss than the BG's (LE: 4.84 vs. 3.43%;
HE: 4.72 vs. 3.32%). In the m. semimembranosus of both species, cooking loss increased
with an increase in slaughter age.
Since diet did not influence the growth, carcass weight distribution, water holding capacity,
colour, shear force values or organoleptic qualities of chevon, BG's may be finished on a diet
with a lower ME-value than that usually formulated for sheep, without a reduction in
performance. This may render a direct economic advantage for BG feedlot finishing. Meat
from young feedlot goats is not inferior to that of lamb and it has a higher protein percentage
and lower fat percentage. Therefore, it can be considered as a healthy food commodity,
especially among low-income groups or people wishing to consume a low calorie diet. / AFRIKAANSE OPSOMMING:
'n Vergelykende analise van nutriëntverbruik en vleiskwaliteisparameters van
Boerbokke en Suid-Afrikaanse Vleismerino's:
Een van die hoofredes waarom die vraag na vleis die aanbod oorskrei, is die feit dat die mens
tot op hede net op 'n paar dierspesies as bron van vleis gekonsentreer het. Benutting van niekonvensionele
spesies, soos bokke, kan aanbeveel word ten einde die globale vleisproduksie
en -verbruik te verhoog. Ten spyte van die feit dat Suid-Afrika oor baie gedomestikeerde
herkouerspesies beskik, is vleisverbruik in die verlede tot hoofsaaklik skape en beeste beperk.
Bokke is tot 'n mindere mate gebruik. Dit kan gedeeltelik toegeskryf word aan die algemene
siening dat bokvleis ondergeskik aan skaap- en beesvleis is.
Verskeie teenstrydighede ten opsigte van vergelykings tussen bokke en skape se groei,
karkaseienskappe en vleissamestelling bestaan in die literatuur. Teenstrydige resultate ten
bpsigte van gemiddelde daaglikse toename (GOT), uitslagpersentasie, karkasgewigverspreiding
en organoleptiese eienskappe (veral taaiheid, sappigheid en geur) van diere
afgerond onder intensiewe/voerkraal-toestande, kom veral voor. Hierdie projek is vervolgens
uitgevoer ten einde meer inligting ten opsigte van die groei, karkas- en organoleptiese
eienskappe, sowel as die chemiese samestelling van die vleis van Boerbok (BB) lammers in
vergelyking met Suid-Afrikaanse Vleismerino (VM) lammers, onder voerkraal-toestande
grootgemaak, te verkry.
Twee-en-dertig BB lammers en 32 VM lammers is vir hierdie studie gebruik. AI die diere is
gekastreer en gespeen voor hulle in die voerkraal geplaas is. Twee verpilde diëte (gevoer
aan 16 diere/spesie) met óf 'n lae (LE, 8.9 MJ/kg DM) óf 'n hoë (HE, 10.9 MJ/kg DM)
metaboliseerbare energievlak is individueel, ad lib, vir óf 28 óf 56 dae aan die diere gevoer.
Voer- en waterinname, GOT en voeromsettingsdoeltreffendheid (VOD) is gemonitor. Gedurende die laaste week van die voedingsproef is 12 BB'e en 12 VM's gebruik ten einde
die verteerbaarheid van die twee diëte te bepaal.
Na 28 of 56 dae is die diere geslag en die karkasse in Suid-Afrikaanse kommersiële snitte
verdeel. Die m. semimembranosus en 8-9-10-rib snit van elke karkas is verwyder vir bepaling
van chemiese samestelling, drupverlies, kookverlies, skeurwaardes en kleurbepaling. Die m.
gracilis is uit die agterbeen uitgehaal en vir sensoriese evaluering gebruik.
VM's het betekenisvolle hoër GOT's as BB'e (bv. VMHE56: 0.281; BBHE56: 0.162 kg/dag)
gehad. Binne 'n dieet was daar geen verskille (P>0.05) in VOD tussen BB'e en VM's nie en
net die VM's se VOD het tussen die LE- en HE-dieet verskil (bv. BBLE28: 7.65; BBHE28:
6.37; VMLE28: 8.73; VMHE28: 5.56 kg voer/kg gewigstoename). BBLE het die droë materiaal
(DM), ruproteïen (RP) en energie meer effektief verteer en het 'n hoër energieretensie as
VMLE gehad. Die twee diëte het dieselfde ME-waarde vir die bokke gehad, wat bevestig dat
bokke net so goed op 'n laer kwaliteit voer presteer as op 'n dieet van 'n hoër kwaliteit.
Stikstofretensie is nie deur spesie of dieet beïnvloed nie. Die BB het 'n 49% laer (P<0.01)
waterinname per kg massatoename op beide die HE- en LE-dieet gehad. Beide spesies het
'n laer (P<0.01) waterinname op die hoë as die lae energie dieet gehad. Verder het die BB
ook 'n daaglikse waterinname van slegs 171 ml/kg075 gehad in vergelyking met die 302
ml/kgO.75van die VM.
Die gewig van die lewer, leë pens, kop en pote (as persentasie van leë liggaamsgewig) was
hoër vir bokke as vir skape. Die VM's se velle was betekenisvol swaarder, waarskynlik as
gevolg van wolgroei. Beide niervet en kanaalvet het toegeneem met 'n toename in
slagouderdom. Die diere wat na 56 dae in die voerkraal geslag is, het betekensivol langer en
dieper karkasse gehad as dié na 28 dae. Binne 'n dieet en slagouderdom, het die skape
breër en dieper (P<0.05) karkasse as die bokke gehad. BB'e het betekenisvol minder gewig
per eenheid karkaslengte en dus maerder karkasse as VM's gehad. Dieet-energievlak het
geen betekenisvolle effek op die verspreiding van karkasgewig by bokke gehad nie. VM's het
egter swaarder karkasse (LE: 19.87 vs. 15.28 kg; HE: 24.01 vs. 17.05 kg) en proporsioneel
swaarder ribbes en boude as BB'e gehad.
Dieet of slagouderdom het nie 'n betekenisvolle effek op die chemiese samestelling (vog, vet,
proteïen en as) van die m. semimembransous gehad nie, maar VM's het laer (P<0.05)
vogwaardes as BB'e gehad. In die 8-9-10-rib snit het BB'e betekenisvolle hoër vog en
proteïen, maar laer vet- en energiewaardes as VM's gehad. In beide spesies het DM, vet en
energiewaardes toegeneem met 'n toename in slagouderdom. BG'e het 'n betekenisvolle
hoër konsentrasie in 11 van die 18 gemete essensiële aminosure in hul 8-9-10-rib snitte
gehad in vergelyking met VM's. Bokkarkasse het ook hoër Ca, K, Mg, N en P-vlakke as
skaapkarkasse gehad, ongeag die dieet. Daar was 'n neiging vir die bok m.
semimembranosus om 'n laer Fe-inhoud as dié van die skaap te hê. BB-karkasse het 'n laer cholesterol-inhoud as skaapkarkasse (66.77 vs. 99.28 mg/100g, onderskeidelik) gehad.
Palmitiensuur (C16:0), steariensuur (C18:0) en oleïensuur (C18:1n9) het die grootste
proporsies van die vetsure in beide die m. semimembranosus en 8-9-10-rib snit van beide
spesies uitgemaak. Op 'n LE-dieet was daar geen verskil tussen die versadigde (SFA) tot
onversadigde (UFA) vetsuur-verhouding van bok- en skaapvleis nie. Op 'n HE-dieet het
skaapvleis egter 'n betekenisvol hoër SFA:UFA-verhouding as bokvleis gehad (m.
semimembranosus: 0.842 vs. 0.689; 8-9-10-rib snit: 1.40 vs. 0.892, onderskeidelik).
Organolepties is 'n verskil tussen bok- en skaapvleis gevind. Elkeen het 'n spesifieke
spesiegeur, wat onafhanklik van die dieet was. Bokvleis is waargeneem as meer veselrig as
skaapvleis, maar daar was geen verskil in Warner-Bratzler skeurwaardes nie. In beide
spesies het sagtheid afgeneem met 'n toename in ouderdom en daar was 'n neiging vir
bokvleis om minder sappig as lamsvleis te wees. Bokvleis het ook 'n meer pertinente
nasmaak as lam gehad. Geen objektiewe verskil kon tussen die kleur van gekookte skaapen
bokvleis onderskei word nie. Daar was egter 'n tendens vir vars lamsvleis om 'n hoër a*-
waarde (rooiheid) as bokvleis te hê. Alhoewel dieet nie 'n invloed op drupverlies gehad het
nie, het drupverlies toegeneem met 'n toename in slagouderdom. Slegs na 56 dae het die VM
se m. semimembranosus 'n hoër (P>0.05) drupverlies as dié van die BB getoon (LE: 4.84 vs.
3.43%; HE: 4.72 vs. 3.32%, onderskeidelik). In die m. semimembranosus van beide spesies
het kookverlies toegeneem met 'n toename in slagouderdom.
Aangesien dieet nie 'n effek op die groei, karkasgewig-verspreiding, waterhouvermoë, kleur,
skeurwaardes of organoleptiese eienskappe van bokvleis gehad het nie, kan BB'e op 'n dieet
met 'n laer ME-waarde as wat normaalweg vir skape geformuleer word, afgerond word,
sonder om 'n verlaging in produksie te verwag. Dit mag 'n direkte ekonomiese voordeel vir
afronding van BB'e in die voerkraal inhou. Vleis van jong voerkraalbokke is nie
minderwaardig teenoor die van skape nie e-n dit het 'n hoër proteren- en laer vetpersentasie.
Dus kan bokvleis as 'n gesonde voedselbron gesien word, veralonder lae-inkomste groepe of
mense wat 'n lae kalorie-dieet wil inneem.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/52060 |
| Date | 12 1900 |
| Creators | Sheridan, Rouxlene |
| Contributors | Hoffman, L. C., Ferreira, A. V., Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Science. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | xii, 127 p. |
| Rights | Stellenbosch University |
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