Genetic parameters were estimated for 2403 purebred Landrace pigs ever a two year period, representing 21 sires. The traits studied included average daily gain, age adjusted to 91 kg, ultrasonic measurements of backfat at the midback and loin positions, total and adjusted total ultrasonic backfat and corresponding carcass backfat measurements. Least squares analyses were used to estimate and adjust for the effects of sex, season and sex by season interaction. Heritabilities and genetic correlations were calculated for all traits using both half and full-sib estimates. Adjusted age and adjusted total ultrasonic backfat measurements were found to be the nest appropriate predictors of carcass value. Estimates of heritability for adjusted age and adjusted total ultrasonic backfat were 0.24±0.10 and 0.26±0.10 based on half-sib and 0.56±0.07 and 0.41±0.06 from full-sib analyses. Genetic correlations between these two traits were -0.07±0.28 and -0.01±0.10 based on the two respective methods. The total phenotypic correlation was -0.01±0.02. A selection index example was developed from half-sib estimates of the genetic parameters and economic factors were estimated from fixed and variable costs for adjusted age and the Canadian market index system. / Land and Food Systems, Faculty of / Graduate

Digitized by Kansas Correctional Industries

Thesis (PhDAgric)--Stellenbosch University, 2006. / ENGLISH ABSTRACT: The South African pork industry is characterised by low slaughter weights when compared to the rest of the world. This inevitably leads to a smaller number of kilograms produced per unit fixed cost and subsequently the efficiency of production is reduced. A study was conducted with 189 pigs representing three sex types (boar, gilt and castrate) and five commercial genotypes. Pigs entered into the trial at an age of 10 weeks and an average live weight of 27.5±2.5kg. Treatments were according to slaughter weight ranging between 62 and 146kg. Production and carcass characteristics, meat quality and processing characteristics and sensory attributes were assessed. Production characteristics assessed included live weight gains, intake, P2 backfat thickness and feed conversion ratio. Main observed effects were associated with slaughter weight and its interaction with sex type. Rates of change in parameters measured were described. Growth and feed conversion ratio were described using linear models while cumulative feed intake was described using 2nd order polynomials. Carcass characteristics assessed included carcass weight, dressing percentage, carcass length, ham length, ham circumference, chest depth, backfat thickness measurements, muscle depth, eye muscle area, subcutaneous fat area, intramuscular fat area as well as ratios of eye muscle to subcutaneous and intramuscular fat area. The main statistical differences observed were for slaughter weight. Significant sex type differences were observed for dressing percentage and some fat and muscle depth measurements. Meat quality characteristics assessed included colour measurements, tenderness, drip loss and water holding capacity. Main differences observed were for slaughter weight. Carcass yields were assessed in terms of absolute and percentage yields of commercial cuts as well as yield of processable lean meat. In terms of the absolute and percentage yields of the commercial cuts, the main statistical differences observed were for slaughter weight. Changes in cut yield with increased slaughter weight are described using regression analysis. In terms of yields obtained for processable lean meat, the main statistical differences observed were for slaughter weight. Sex type differences were only observed for percentage belly and topside processable lean meat and percentage brine uptake of belly bacon, whole gammon ham and topside gammon. Genotypic differences were observed for percentage yield of processable lean meat of the neck and whole gammon and percentage fresh to smoke losses of back bacon and whole gammon ham. Sensory attributes were assessed using gammon ham, belly bacon and fresh loin. Observed slaughter weight differences were inconsistent and did not appear to change with an increase in slaughter weight. Once meat was processed, most sensory differences were no longer observed. Increased slaughter weight generally led to increased juiciness and decreased tenderness. It is therefore concluded that the current South African pig genotypes have the ability to maintain high growth rates for a much longer time and therefore can be slaughtered at a higher weight without detrimental effect on production efficiency, carcass and meat quality characteristics, yields of commercial and processable lean meat, processing characteristics and ultimately sensory characteristics of the meat produced. / AFRIKAANSE OPSOMMING: Die Suid-Afrikaanse varkbedryf word gekenmerk deur relatiewe lae slagmassas in vergelyking met die res van die wêreld. Dit lei onvermydelik tot ‘n kleiner aantal kilogramme vleis geproduseer per eenheid vaste koste. ’n Studie is gevolglik gedoen met die doel om die tempo’s van verandering van sekere produksie-, karkas-, vleis- en proseseringseienskappe te kwantifiseer ten einde die optimale slagmassa te bepaal wat vir alle rolspelers in die bedryf tot voordeel sal wees. Die studie is gedoen met 189 diere wat vyf kommersiële genotipes en drie geslagstipes (beer, sog en kastraat) verteenwoordig het. Varke is op ’n ouderdom van 10 weke met ’n gemiddelde lewende massa van 27.5±2.5kg in die proef opgeneem. Behandelings was volgens slagmassa en het gevariëer van 62 tot 146kg. Produksieparameters en karkas-, vleiskwaliteits-, en proseseringseienskappe sowel as sensoriese eienskappe, is ëvalueer. Produksieeienskappe wat ëvalueer is sluit in: groei, inname, P2 rugvetdikte en voeromset-verhoudings. Hoofeffekte wat waargeneem is, was vir slagmassa en interaksies van slagmassa met geslag. Tempo van verandering in die parameters gemeet, is beskryf. Groei en voeromsette is beskryf deur die passing van ‘n linieêre model terwyl kumulatiewe voerinname beskryf is deur ‘n 2de orde polinoom. Karkaseienskappe wat ëvalueer is, sluit in: karkasmassa, uitslagpersentasie, karkaslengte, hamlengte, hamomtrek, borsdiepte, rugvetdikte, spierdiepte, oogspieroppervlak, onderhuidse vet-, binnespierse vetoppervlak en verhoudings van oogspier- tot-vetoppervlakke. Die hoof statistiese effekte wat waargeneem is, was vir slagmassa. Betekenisvolle geslagsverskille is waargeneem vir uitslagpersentasie en sommige, vet- en spierdieptemetings. Genotipiese verskille is waargeneem vir sommige vetmetings. Vleiskwaliteiteienskappe wat beoordeel is, het kleur, drupverlies, waterbindingsvermoë en sagtheid ingesluit. Hoofeffekte waargeneem was vir slagmassa. Karkasopbrengste is ëvalueer in terme van absolute en persentasie opbrengste van kommersiële snitte sowel as prosesseerbare maer vleis. In terme van absolute en persentasie opbrengste van kommersiële snitte, was meeste van die variasie beskryf deur slagmassa. Tempo van verandering in die persentasie opbrengste van die snitte word beskryf. In terme van opbrengste vir proseseerbare maer vleis is die hoof statistiese verskille waargeneem vir slagmassa. Geslagverskille is waargeneem vir persentasie streepspek en binneboud maer vleis opbrengs vir prosesering en persentasie pekelopname van streepspek, heel varkboud ham en binneboud ham. Genotipe verskille is waargeneem vir persentasie opbrengs van maer vleis vir prosesering van die nek en heelboud en persentasie vars-tot-klaar-gerook verliese van rugspek en heelboud hamme. Sensoriese eienskappe is ëvalueer vir twee geprosesseerde en een vars snit. Slagmassa-effekte was nie konstant nie en parameters het klaarblyklik nie verander soos slagmassa verander het nie. Sodra vleis geprosesseer is, het die meeste sensoriese verskille verdwyn. Beide sappigheid en taaiheid het toegeneem met ‘n toename in slagmassa. Dit kan dus aanvaar word dat, gegewe die huidige Suid Afrikaanse genotipes, dit moontlik is om swaarder karkasse te produseer sonder noemenswaardige nadelige effekte op karkas-, vleis-, opbrengste-, prosesering- en sensoriese eienskappe van varkvleis.