The effect of porcine somatotropin (pST) on production parameters, carcass and meat quality characteristics of pigs

Thesis (MScAgric)--University of Stellenbosch, 2005.

ENGLISH ABSTRACT: Porcine somatotropin (pST) is a naturally occurring protein (hormone), secreted by the pituitary gland of young pigs and is one of the major growth regulating factors. High levels of pST is found in circulating blood of young animals, resulting in the partitioning of nutrients into lean tissue and bone growth. Supplying an exogenous source of pST should increase the deposition of lean muscle and bone and decrease the deposition of fat in the older (above 60 kg) pig. To ascertain whether pST would have a positive influence on production- and meat characteristics in the South African scenario for pigs slaughtered at a high bodymass, a trail was conducted. For group housed animals pST had no significant effect on the following parameters: feed intake, calculated cumulatively on a weekly basis, ADG, live weight, carcass weight, carcass length, ham length or chest depth, intramuscular fat area, muscle depth and colour measured with a Hennessey probe and waterbinding capacity. However, when the FCR of pigs in this investigation were calculated, there was a significant (p<0.05) influence by sex and pST detected. Boars converted their feed to live weight better than barrows and gilts from week ten onwards. Boars had an increased FCR when treated with pST. A significant increase was found in muscle area and a significant decrease in extra muscular (back fat) area of boars and barrows. A significant pST (p< 0.05) effect (3 mm reduction) was seen for backfat depth measured by the Hennessey probe and the intrascope. Porcine somatotropin significantly (p<0.05) increased the muscle area of the loin-cut for all animals. The area covered by subcutaneous fat of boars and barrows were significantly (P<0.05) reduced by pST treatment, with no effect detected for gilts (p>0.05). Porcine somatotropin treatment increased the muscle percentage and decreased the extramuscular fat percentage in such a way that the differences between sexes was reduced. Thus, more uniform fat-muscle distribution between carcasses was obtained by pST treatment. Control animals had a significantly higher pH24 than pST treated animals (P=0.049). Lower values were found for animals receiving pST for L* (p=0.016), a* (p=0.002) and b* (P=0.016). The effect on b* (yellow-blue range) in the M longissimus thoracis of pST treated animals showed slightly (but significantly) less yellow and more green compared to control animals (p=0.016). This combined with the lower L* values (brightness) indicates that pST treated animals had a significantly darker colour meat compared to the control animals. Individually housed animals showed no significant differences for the following characteristics: live weight, carcass weight, head, trotters, shoulder, middle back, middle belly, loin belly, thigh, fillet, carcass fat and kidney. Whereas pST caused a significantly lower percentage of the middle back of boars and barrows, but not in gilts, pST could only precipitate a lower percentage (11.18%) loin back of treated animals (p=0.026) v.s. control animals (12.05%). A trend (p>0.1) was detected for percentage bone in the middle back, with the pST treated (14.17% vs. 13.18%) animals having more bone than that of control animals. pST animals had a higher percentage (p=0.024) skin (5.04%) than the control animals (4.28%). This study shows that there is no negative effect of pST on meat quality characteristics and carcass composition, in fact there is less variation between carcasses obtained from different sexes treated with pST. The producer can bring heavier animals to the market with a reduced backfat percentage and a greater percentage meat with the help of pST.

AFRIKAANSE OPSOMMING: Vark somatotropien (pST) is ‘n natuurlike hormoon wat deur die pituitêre klier in die brein afgeskei word by klein varkies en is een van die belangrikste hormone betrokke by groei regulering. Hoë vlakke van pST kom voor in die bloed van jong varkies, dit veroorsaak dan die verspreiding van nutriente in die liggaam van die varkie sodat dit meer vleis en beengroei toon en minder vet deponeer. Namate die varkie volwasse word neem die bloedvlakke van pST af en begin die liggam meer vet deponeer ten koste van proteien groei, terselfde tyd begin die seksuele kenmerke ontwikkel. Die toediening van ‘n eksterne bron van pST behoort die groei van been en vleis te bevoordeel in ouer diere (bo 60 kg). Vir die doeleindes van die ondersoek wou ons bepaal of pST ‘n positewe effek het op groei en vleiskwaliteitseienskappe van varke wat in Suid Afrikaanse kondisies gebruik word en teen ’n hoër liggamsmassa as gewoonlik geslag word. Vir varke wat in groepe behuis was was daar geen effek op die volgende eienskappe nie: voer inname weekliks bepaa, gemiddelde daaglikse toename, liggaamsmassa, karkasgewig, karkas lengte, ham lengte, bors diepte, intrmuskulêre vet en spierdikte bepaal met ‘n Hennessey sonde asook waterbindigs vermoë. Bere het egter ’n beter voeromsettings faktor gehat as burge en soggies, maar as pST toegedien is het hulle voeromsettingsfaktor toegeneem. ’n Betekenisvolle (p<0.05) toename in spier area van alle diere, met ’n gesamentlike afname in onderhuidse vet area van bere en burge (nie soggies nie) is gevind. ’n Betekenisvolle afname (3 mm) in rugvetdikte is gevind by diere wat met pST behandel is. Hierdie effekte is so in die lewe gebring dat die verskil tussen die geslagte minder prominent is en karkasse meer uniform is. Betekenisvolle hoër pH24 waardes is gevind by kontrole diere as by pST behandelde diere (p=0.049). L* (p=0.016), a* (p=0.002) en b* (p=0.016) waardes was betekenisvol laer vir pST behandelde diere as vir kontrole diere. Die effek op b* waardes (geel-blou reeks) in die M. longissimus thoracis van behandelde diere was in so ‘n mate dat die vleis ietwat minder geel en meer groen was in vergelyking met die kontrole diere (p=0.016), saam met laer L* waardes (helderheid) is ‘n indikasie van ietwat donkerder vleis van behandelde diere. Individueel behuisde diere het geen betekenisvolle effek getoon vir die volgende parameters nie: liggamsgewig, karkasgewig, kop, voete, skouer, middel rug, middel maag, lende maag, dy, haas en niere. ‘n Betekenisvolle laer persentasie middel rug is gevind in bere en burge, maar nie vir soggies nie, maar in die lende rug is ‘n betekenisvolle effek gevind vir alle diere (11.8% vir pST en 12.05% vir kontroe , p=0.026). ‘n Neiging (p>0,1) is gesien vir die hoeveelheid been in die middle rug van diere behandel met pST (14.17% vs. 13.18%) Dier met pSt behandel het’n betekenisvol hoer persentasie vel as kontrole diere gehat (5.04% vs. 4.28%, p=0.024. Die resultate van die ondersoek bewys dat daar geen negatiewe effekte van pST op vleis- en karkaseienskappe is nie, daar is self minder variasie tussen karkasse van verskillende geslagte. Die boer kan swaarder diere bemark met minder rugvet en meer vleis met behulp van pST.

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