Effects of immunocastration on the nutrient responses, carcass traits and meat quality of growing pigs (Sus crofa domesticus)

Needham, Tersia (2014-12)

Thesis (MScAgric)--Stellenbosch University, 2014.

Thesis

ENGLISH ABSTRACT: Increased consumer awareness has motivated the industry to find alternative methods to surgical castration for controlling boar taint and aggression in male pigs. Immunocastration has been identified as a solution, however; little research has been done into the nutritional requirements of immunocastrated pigs. Thus the objective of this study was to determine the optimal protein levels for immunocastrated pigs with regards to growth performance, carcass traits and yields as well as meat quality when supplemented with or without ractopamine hydrochloride (RAC). The study involved 120 male pigs following a 2 x 2 x 3 factorial design. The main effects evaluated were sex (immunocastrated versus entire), RAC supplementation (0 versus 10 mg/kg and dietary balanced protein level (7.50 {low}, 9.79 {medium} and 12.07 {high} g lysine/kg). Vaccination occurred at 16 and 20 weeks of age and from 20 weeks each pig was allocated to one of the balanced protein diets with RAC supplementation at either 0 or 10 mg/kg for the last 28 days of growth. Slaughtering occurred at 24 weeks at which time carcass traits were measured and carcasses were processed, commercial cuts were weighed, deboned and trimmed into muscle, bone and fat portions which were then weighed individually. Immunocastration increased the average daily gain, average daily feed intake, feed conversion ratio (FCR) and backfat deposition after the second vaccination. The FCR was improved by RAC supplementation, with the best FCRs seen at the medium and high balanced protein diets. Immunocastration and RAC increased live weight at slaughter and calliper backfat thickness but no differences were seen for the dressed hot carcass weight or Hennessey Grading Probe backfat thickness. Supplementation of RAC increased the percentage of the hot carcass weight, comprising of the shoulder, hindquarter, loin and belly, as well as the shoulder muscle, hindquarter muscle and loin muscle percentages, while decreasing the fat percentage of the belly and hindquarter. Chemical composition analysis of the Longissimus thoracis (LT) muscle indicated differences (p ≤ 0.05) for crude protein content but they were considered biologically negligible. The cooking loss of the LT was decreased by immunocastration and feeding medium protein. Feeding RAC decreased the a* and b* colour values and increased the Warner Bratzler shear force (WBSF) values, resulting in less red and less tender meat. Entire males fed low dietary protein had the lowest L* values, while entire males fed medium protein diets had the highest L* values. Immunocastrates fed the low protein diet had the most tender meat, whereas immunocastrates fed the high protein diet had the least tender meat. Immunocastration decreased the androstenone levels to below 0.5 μg/g fat and although it did not significantly affect the testicle size, it influenced the morphology and increased the lightness (L*), yellowness (b*) and decreased the redness (a*) of the testicle’s cut surface colour. The results from this study indicated that the balanced dietary protein requirements for immunocastrates differ both with and without RAC supplementation and thus the correct dietary protein level needs to be provided so that growth performance and leanness is not compromised. The return per carcass can also be improved by supplementing RAC, owing to improved cutting yields and lean yields of carcasses. Together, immunocastration, RAC supplementation and the correct balanced protein diet may allow pig producers to efficiently produce heavier male carcasses without boar taint while conforming to the animal welfare expectations of the consumer. However, an incentive for producers in terms of immunocastration needs to be provided by the possible modification of the current carcass classification system so that heavier immunocastrated male carcasses are not penalised.

AFRIKAANSE OPSOMMING: Die toename in verbruiker bewustheid het die bedryf gemotiveer om alternatiewe metodes vir chirurgiese kastrasie te vind, terwyl beergeur en aggressie in manlike varke beheer word. Immunokastrasie is geïdentifiseer as ʼn moontlike metode, maar min navorsing is egter tot dusver gedoen om die optimale proteïen vlakke vir hierdie immunokastrate te bepaal. Min is ook bekend oor die groei prestasie, karkas-eienskappe, opbrengs asook vleiskwaliteit van immunokastrate as raktopamien hidrocholoried (RAC) tot die dieet bygevoeg word. ʼn Studie is gevolglik gedoen met 120 manlike varke in ʼn 2 x 2 x 3 faktoriaal ontwerp. Die hoof effekte wat geëvalueer was, is geslag (immunogekastreerd of intakt), RAC byvoeding (0 of 10 mg/kg) en gebalanseerde proteïenvlak (7.50 {lae}, 9.79 {medium} en 12.07 {hoë} g lisien/ kg). Inenting het plaasgevind op 16 en 20 weke ouderdom en van 20 weke was elke vark toegeken aan een van die gebalanseerde proteïen diëte met RAC byvoeding teen 0 of 10 dpm vir die laaste 28 dae van groei. Diere is geslag op 24 weke ouderdom, waartydens karkaseienskappe gemeet was. Die karkasse is vervolgens opgesny en die kommersiële snitte geweeg. Die snitte is verder verwerk en spier, been en vet is afsonderlik geweeg. Immunokastrasie het die gemiddelde daaglikse toename, gemiddelde daaglikse voerinname, voeromsetverhouding (VOV) en rugvet dikte verhoog na die tweede inenting. Die VOV is verbeter deur RAC byvoeding, met die beste VOVs waargeneem op die medium en hoë gebalanseerde proteïen diëte. Resultate het getoon dat beide immunokastrasie en RAC gelei het tot ʼn toename in lewendemassa by slag asook vernier rugvetdikte, alhoewel daar geen verskil tussen warm karkasmassa of Hennessey Grading Probe (HGP) rugvetdikte was nie. Aanvulling van RAC verhoog die skouer, agterkwart, lende en pens uitgedruk as persentasie van die warm karkasmassa. Die massa, uitgedruk as persentasie van warmkarkasmassa, van die skouerspier, agterkwartspier en lendespier is ook verhoog terwyl pensvet verlaag het. Chemiese analise van die Longissimus thoracis (LT) spier het aangedui dat die ru-proteïen inhoud verskil (p ≤ 0.05) alhoewel die verskille wat gevind was waarskynlik nie biologiese waarde het nie. Die persentasie kookverlies van die LT is verlaag deur immunokastrasie en die middel proteïenvlak-dieet. Die byvoeding van RAC het die a* en b* kleurwaardes verlaag en die Warner-Bratzler-shear-force (WBSF)-waardes verhoog, wat gelei het tot minder rooi vleis asook minder sagtheid. Intakte varke wat ʼn lae proteïen dieet gevoer was, het die laagste L* waardes getoon terwyl intakte varke wat ʼn middel proteïenvlak-dieet gevoer was die hoogste L* waardes getoon het. Immunokastrate wat ʼn lae proteïen-dieet gevoer was, het die sagste vleis gelewer, maar immunokastrate wat ʼn hoë proteïen-dieet gevoer was, het die taaiste vleis gelewer. Immunokastrasie het die konsentrasie androstenoon tot onder 0.5 μg/g vet verlaag en alhoewel dit geen betekenisvolle effek op testikel grootte gehad nie, het dit die morfologie van die testikel geaffekteer asook die ligheid (L*) en geelheid (b*) verhoog en die rooiheid (a*) van die gesnyde testikel oppervlakte verlaag. Die resultate van hierdie studie dui daarop dat die gebalanseerde proteïen vereistes vir immunokastrate verskil vir immunokastrate met en sonder RAC byvoeding. Dit is dus belangrik dat die korrekte proteïenvlak en aminosuur samestelling gevoer moet word vir die spesifieke dier onder beskouing ten einde groeiprestasie en maerheid te maksimeer. Die opbrengs per karkas kan ook verbeter word deur die byvoeding van RAC, as gevolg van die verbeterde snit-opbrengs en maer-vleis opbrengs van karkasse. Die kombinasie van immunokastrasie, RAC aanvullings asook die korrekte gebalanseerde proteïen-dieet skep die moontlikheid aan varkprodusente om swaarder beerkarkasse doeltreffend te produseer sonder die teenwoordigheid van beergeur terwyl daar terselfdertyd aan die verbruiker se dierewelsyn-wense voldoen word. Die insentief vir die produsent is egter nog afwesig en daarom is dit nodig dat die klassifikasie stelsel hersien moet word ten einde te verseker dat daar nie teen immunogekastreerde diere op die slaglyn gediskrimineer word nie.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/95767
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