Thesis (MScAgric) -- University of Stellenbosch, 2002. / ENGLISH ABSTRACT: Experiment 1: Two studies were conducted to research the effect of divergent selection for multiple rearing ability on carcass weight, mutton production, meat quality and carcass characteristics of similar-aged Merino sheep. Data of 114 19-month-old Merino sheep, 40 ewes and 74 rams were used in this study. The study was done in two parts over 2 years. Only rams (52) were slaughtered over a two-week period in study A. Twenty-two rams and 40 ewes were slaughtered over a three-week period in study B. The sheep were descended from two selection lines that have been divergently selected for maternal multiple rearing ability since 1986. In brief, ewe and ram progeny of ewes rearing more than one lamb per joining (i.e. that reared twins at least once) were preferred as replacements in the high (H) line. Descendants of ewes that reared fewer than one lamb per joining (i.e. that were barren or lost all lambs born at least once) were preferred as replacements in the low (L) line. In study A the mean (±SE) slaughter weight of H line rams . were 12% heavier (P<O.OI) than that of L line contemporaries. A corresponding difference (P<O.OI) of 13% was found for carcass weight Adjustment for the higher live weight by analysis of covariance ofH line rams resulted in most of the line differences being eliminated (P>0.05). The difference between the weight of the loin retail cut remained significant (P<O.OI) in favour of the H line (1.64±0.04 vs. 1.37±0.08 kg, respectively). Skin weight (3.93±0.15 vs. 3.34±0.07 kg respectively; P<O.OI) and skin thickness (2.28±0.1l vs. 1.97±0.06 mm respectively; P<0.05) were greater in L line rams than in H line contemporaries. Rams in the L line also had heavier (P<0.05) trotters than the H line (l.05±0.03 vs. 0.96±0.02 kg respectively). In study B there were no interaction between line and sex and the data were pooled to present the main affects of sex and line. In study B the mean (±SE) slaughter weight of H line animals was 7% heavier (P=0.05) than that of L line contemporaries (44.02±0. 7 vs. 41.2±1.2 kg, respectively). A corresponding difference (P<0.05) of 11% was found for carcass weight between the two lines (pooled sexes) (l6.1±0.3 vs. 14.4±0.5 kg, respectively). There was no difference in the tenderness of the meat between the two selection lines but L line animals tended (P<0.16) to have more tender meat than H line contemporaries. Adjustment for the higher live weight of H line animals by analysis of covariance resulted in most of the line differences being eliminated (P>0.05). Hindquarter weight still remained significantly (P<O.OI) in favour of the H line after correction for live weight. Meat of L line animals was healthier based on their PUF A/SF A ratio. Experiment 2: This experiment was conducted to quantify the effect (noted in the first experiment) of selection for and against multiple rearing ability in Merino sheep on m. longissimus dorsi postmortem pH profiles. Data of 20 Merino sheep (10 rams and 10 ewes) were used. The sheep were slaughtered at a commercial abattoir. After slaughter pH was measured at 45 min, 2, 4, 8, 10, 12, 16, 20, 24, 33 and 48 h post slaughter, respectively. The pH was measured on the right side of each carcass in the m. longissimus dorsi between the 1st and the 6th lumbar vertebrae. The m. longissimus dorsi between the 1st and the 6th lumbar vertebrae of the left side was used for meat quality analysis. The initial pH of H line animals tended to be higher than that of L line contemporaries. At 48 h post-slaughter the pH of L line was higher (P<0.05) compared to that of H line animals. The meat of H line animals was tougher (99.79±3.58 vs. 88.32±3.38, P<0.05) than that of L line contemporaries, but there were no differences in the other meat quality characteristics. A higher initial pH (found in the first experiment, with a similar tendency in the second experiment) could indicate a lower susceptibility to stress in the H line. Experiment 3: An experiment was done to compare the meat-production potential between Merino and South African Mutton Merino (SAMM) ewes with increasing age. Slaughter data of . 653 Merino and SAMM ewes were used. Animals were slaughtered between 220 and 2719 days of age, which encompassed a range of slaughter weights from 27 to 100 kg. The ewes were differentiated according to age, 219 ewes being younger than 600 days and 416 being older than 600 days at slaughter. Young SAMM ewes had 10% heavier carcass weights than young Merino ewes and the difference was 47% between mature ewes. Mean maximum carcass weights of 33.44 and 22.65 kg were derived for the SAMM and Merino, at respective age of 2100 and 1900 days. SAMM ewes had a 47% thicker fat depth. Although Merinos were earlier maturing than the SAMM ewes, the latter breed had more subcutaneous fat at the mature stage. Experiment 4: The fourth experiment examined the effect of breed and sex on the carcass composition, yield of retail cuts, fat depth and chemical composition of meat from 35 South African Mutton Merino (SAMM) (17 rams and 18 ewes) and 61 Dormer (21 rams and 40 ewes) sheep. As there was no breed x sex interaction, the data were pooled to present the main effects of breed and sex. There were no differences in slaughter and carcass weight between Dormer and SAMM sheep. Dormers' had more fat (kidney, back fat depth) than SAMM sheep. The eye-muscle area of the Dormers' was 13% larger than that of the SAMM sheep. Rams were heavier (64.86±0.85 vs. 44.55±0.74 kg) than the ewes at slaughter. All the traits that were recorded, were heavier or higher in rams (P<0.05). After adjustment for higher live weight of the rams, the proportion of neck retail cut from the rams was higher than that from ewes and the proportion of hindquarter weight from the ewes was higher (P<0.05) than that from rams. After adjustment for the higher live weight of the rams, the moisture (75.35±0.37 and 73.35±0.37%) and lipid (2.68±0.33 and 3.80±0.33%) contents differed significantly (P<0.05) between the rams and ewes, respectively. With the significantly higher SFA value of the SAMM sheep and higher MUF A value of the Dormer sheep, meat from Dormer sheep could be regarded as healthier from a human prospective than that from SAMM sheep. Experiment 5: A study was done to test an ultrasound scanner (used on pigs) for the prediction of subcutaneous backfat and m. longissimus dorsi depth on Merino (52 rams), SA Mutton Merino (17 rams and 18 ewes) and Dormer (21 rams and 40 ewes) sheep. The sheep were scanned with an ultrasound scanner to predict the backfat and eye-muscle depth on the live animal. All animals were slaughtered to measure the true values of the fat depth and eye-muscle depth (25 and 45mm from the midline at the 13th rib). Overall regression equations over breeds (SAMM and Dormer, pooled breeds), and lines (H and L line Merinos, pooled lines) were obtained. Compared to previous research, the correlations between scanned values and true values were comparatively low (r = 0.07 - 0.25). Evidence from the literature suggested higher correlations of r = 0.53 - 0.56. Higher correlations could be achieved in older and fatter animals. The fact that the operator had no experience of scanning sheep could also have contributed to the low correlations. / AFRIKAANSE OPSOMMING: Eksperiment 1: Twee studies is gedoen om te kyk na die invloed van seleksie vir meerling grootmaakvermoe by Merino's op karkas-, vleiseienskappe en vleiskwaliteit is. Data van 114 19 maand oue Merino skaap, 40 ooie en 74 ramme is in die studie gebruik. Die studie is gedoen in twee dele oar 'n tydperk van twee jaar. Slegs ramme (52) is geslag oor 'n tydperk van twee weke in studie A. Twee en twintig ramme en 40 ooie is in studie B geslag oor 'n pericde van drie weke. Merino-ooie en -ramme afkomstig van 'n hoe (Il-lyn) en lae (L-lyn) lyn geselekteer vir rneerling grootmaakverrnoe is gebruik in 'n studie wat oor twee jaar uitgevoer is. Die twee lyne is intensief geselekteer vir en teen meerling grootmaakverrnoe vanaf 1986. Ram- en ooi-nageslag wat afkomstig is van ooie wat een of meer keer tweelinge in haar lewe per lam kans groot gemaak het is gebruik vir die H-lyn, terwyl ram en ooi nageslag afkomstig van ooie wat een of minder as een lam per lamkans groot gemaak het is gebruik vir die L-Iyn. In studie A is 52 rarnme (42 H-Iyn en 10 Llyn) geslag en slag- en karkaseienskappe is bestudeer. In ondersoek B is 22 ramme (16 l-l-lyn en 6 L-lyn) en 40 coie (34 H-Iyn en 7 L-Iyn) gebruik. Slag-, karkas- en vleiseienskappe is bestudeer. In ondersoek A is gevind dat die slagmassa van die Il-Iyn ramme 12% hcer en die karkasmassa 13% hcer is as die van die L-lyn ramme. Na kovariansie ontleding van die swaarder slagmassa van die H-Iyn diere, was die pote (1.05±0.03 vs. 0.96±0.02 kg; P<0.05) en velie swazrder (3.93±0.15 vs. 3.34±0.07 kg; P<O.Ol) en die velle dikker (2.28±0.11 vs. 1.97±0.06 mm; P<0.05) by L-Iyn diere as by H-lyn diere. Die groothandel lende snit van die H-Iyn diere was swaarder (1.64±0.04 vs. 1.37±0.08 kg; P<0.05) as die van L-Iyn diere. By studie B was daar geen interaksie tussen lyn en geslag nie, dus is die data verpoel om die betekenisvolheid van die hoofeffekte van lyn en geslag weer te gee. 'n Sewe persent hoer slagmassa is by H-Iyn diere waargeneem (44.02±0.7 vs. 41.20± 1.2 kg; P<0.05). 'n Ooreenstemmende verskil van (P<0.05) 11% is gevind in karkas massa tussen die twee lyne (16.1±0.3 vs. 14.4±0.5 kg). Daar was geen veskil in taaiheid van die vleis nie, maar diere van die H lyn se vleis het geneig (P<0.06) om taaier te wees. Na die kovariansie ontleding met massa as kovariant was die boude (P<O.OI) van die H-lyn diere en die lende (P<O.OI) groothandel snit van die ooie swaarder, verder was die verskille dieselfde as in ondersoek A Die vetsuurresultate toon dat net by die verhouding tussen die poli-onversadigde en vesadigde vetsure (PUF A/SF A) 'n verskil tussen die Iyne was. Die vetsuur resultate dui daarop dat die Llyn diere gesonder vleis vir menslike voeding het as die van die H Iyn diere. Eksperiment 2: In 'n tweede eksperiment is gekyk wat die invloed van seleksie vir meerling grootmaakvermoe by Merino skape op post mortem m. longissimus dorsi pH profiele is. Daar is gebruik gemaak van 20 Merino skape (10 ooie en 10 ramme), 10 H lyn en 10 Llyn diere. Die skape is geslag by 'n kornrnersiele abattoir. Die pH metings is geneem, 45 min, 2, 4, 6, 8, 10. 12, 16, 20, 24, 33 en 48 uur na slag. Die pH is geneem in die m. longissimus dorsi van die regter sy tussen die 1ste en 6de lumblale werwels. Die linker kant is gebruik vir vleiskwaliteits toetse Die pH lesing van H lyn diere wat 45 min na slagting geneem is het hoer geneig as in Llyn, terwyl pH lesings van die Llyn diere 48 h na slagting hoer was. Die vleis van die H lyn diere was taaier (99.79±3.58 vs. 88.32±3.38; P<0.05) as die van die Llyn diere, maar daar was geen verskille in die ander vleiskwaliteits toetse nie. Die hoe begin pH kan daarop dui dat die H lyn skape minder spanning voor slag ervaar he! Eksperiment 3: Die invloed van ouderdom op vleis produksie potensiaal, slag en karkasmassa en vetdikte by Suid Afrikaanse Vleis Merino (SAVM) en Merino ooie is ondersoek. Data van 635 Merino en SAVM ooie is gebruik. Die ooie was tussen 220 en 2719 dae oud met slagting en slagmassas wat gewissel het tussen 27 en 100 kg. Die ooie is opgedeel ten opsigte van ouderdorn. Die jong groep was ooie wat jonger as 600 dae oud was en die die res was bestempel as die ou groep. Die karkas massa van die jong SAVM ooie was 10% hcer as die van die Merino ooie en by die ou groep was die verskil 47% Ouer SAVM ooie het 52% dikker vet as die Merino ooie gehad. Merino ooie het 'n maksimum karkas massa van 22.65 kg op 'n ouderdom van 1900 dae gehad terwyl SAVM ooie 'n maksimum karkas massa van 33.44 kg op 'n ouderdom van 2100 dae gehad he! Al is die Merino 'n vroer ryp skaap as die SAVM, het die SAVM meer vet as volwasse dier. Eksperiment 4: In die experiment is gekyk na die effek van ras en geslag op slagmassa, karkasmassa, vleiseienskappe asook chemiese en vetsuur samestelling van die vleis van SAVM en Dormer skape. Slagdata van 61 Dormers' (21 ramme en 40 ooie) en 35 SAVM's (17 ramme en 18 ooie) is gebruik, Daar was geen interaksie tussen ras en geslag nie en dus is die data verpoel om die invloed van die hoof effekte (ras en geslag) te toets. Geen verskille is in die slagmassa tussen die Dormers en SAVM gevind nie. Die vet (onderhuids en niervet) van die Dormers was meer en die oogspier oppervlakte was 13% groter as die van SAVM skape. Ramme was swaarder (64.86±0.85 vs. 44.55±0.74 kg) as die ooie met slag. Na kovariansie ontleding van swaarder slagmassa van die ramme was die groothandel nek snit van die ramme swaarder (P<0.05) as die van die ooie en die boude van die ooie swaarder (P<O.Ol) in vergelyking met die van die ramme. Die voginhoud van vleis vanaf ramme was hoer (77.35±0.37 vs 75.35±0.37) as die van die coie. Ooie het 'n hcer persentasie vet in die vleis van die 11113de ribsnit gehad (2.68±0.33 vs. 3.80±0.33 %) Volgens die vetsuur analises het SAVM diere 'n hoer persentasie versadigde vetsure en die Dormers 'n groter persentasie mono-onversadigde vetsure gehad. Dit kan 'n aanduiding wees dat vleis vanaf Dormer skape gesonder is vir menslike gebruik. Eksperiment 5: Hierdie studie is gedoen om 'n ultraklank apparaat (gebruik by varke) te toets vir voorspelling van onderhuidse vet en oogspierdiepte by skape. Daar is gebruik gemaak van 52 Merino ramme (42 van die H-lyn en 10 van die Llyn), 61 Dormer skape (21 ramme en 40 ooie) en 35 SAVM skape (17 ramme en 18 ooie). Die vetdikte en oogspierdiepte op die lewende diere is bepaal met 'n ultraklank apparaat, waarna die diere geslag is en die werklike waardes direk op die koue karkas gemeet is. Regressie vergelykings is opgestel om korrelasies tussen ultraklank waardes en werklike waardes te kry. In hierdie proef was die korrelasies tussen geskatte en werklike waardes swak (r = 0.07-0.25). Beter korrelasies is egter weI deur ander navorsers gekry (r = 0.53- 0.56) Beter korrelasies kan in ouer en vetter diere verkry word. Die feit dat die operateur nie baie ondervinding met die skandering van skape gehad het nie kon bydrae tot die swak korrelasies.