Developing a model for feedlot production of Boer goat slaughter kids

Van der Merwe, Daniel Andre (2015-12)

Thesis (MSc)--Stellenbosch University, 2015.

Thesis

ENGLISH ABSTRACT: In this study, the effects of energy content of the feedlot diet as well as the length of the production period were investigated for Boer goat slaughter kids. The kids were housed in individual pens on the Elsenburg experimental farm, Western Cape, South Africa. Boer goat castrate kids were weaned at approximately 18 weeks of age (weighing 22.2 ± 3.5 kg) and were randomly allocated to one of three trial diets that varied in energy content; namely a low, medium and high energy diet (11.3, 12.0 and 12.7 MJ ME/ kg feed respectively) which were supplied ad libitum. The goats were further randomly allocated to one of five slaughter groups that were slaughtered at five week intervals at a commercial abattoir. The first group of goats was slaughtered at the start of the trial in order to serve as a baseline reference. During the study the effects of dietary energy content, and time spent in the feedlot were investigated for the feedlot production and slaughter characteristics of Boer goat kids. Additionally the effect of the energy content of the feedlot diets on the sensory and chemical properties of goat meat were evaluated. During the production period individual feed intake and live weight gain were monitored on a weekly basis. It was observed that live weight of the goats increased throughout the production period. Quadratic functions were used to describe the change in average daily gain and dry matter intake of the goats during the feeding period. Goats that were fed the low and medium energy diets exhibited higher daily gains (P= 0.02) and dry matter intakes (P< 0.01) than goats on the high energy diets. Dietary energy content and age of the animal in the feedlot did not influence the feed conversion ratio to produce a unit of live weight. A linear function was used to model the growth of the goats during this production period. The goats were not able to reach the point of inflection on the growth curve. Therefore the sigmoidal growth curve could not be plotted which could have been modelled by a function similar to the Gompertz model. Dressing percentages of the carcasses varied throughout the production period for all the diets, with goats on the low energy diet having the lowest dressing percentage (45.8%; P= 0.04). The energy content of the trial diets had no effect on the yield of the offal components and retail cuts of the carcass. Generally it was observed that the yields of the hindquarter and neck cuts decreased whilst that of the forequarter increased with the age of the goats at slaughter. The degree of carcass fatness increased with time spent in the feedlot, with the majority of fat being deposited in the abdominal cavity, rather than in the subcutaneous fat depot. Dietary energy content was expected to influence the levels of intramuscular fat, which in turn would affect the eating quality of the meat. However, the levels of energy in the diets fed to goats did not influence the tenderness, juiciness or the aroma and flavour profiles of the goat meat as observed during descriptive sensory analysis of the meat by a trained panel. Chemical analysis of the cooked meat samples also showed that the levels of intramuscular fat did not vary between the samples, resulting in the lack of differences detected between treatments in the sensory evaluation.

AFRIKAANSE OPSOMMING: In hierdie studie is die effek van die energie-inhoud van die voerkraal dieet, tesame met die lengte van die produksie tydperk, vir Boerbok lammers ondersoek. Die lammers is in individuele kampies gehuisves op die Elsenburg proefplaas, Wes- Kaap, Suid-Afrika. Die gekastreerde Boerbok lammers is gespeen op ’n ouderdom van ongeveer 18 weke (gewig van 22.2 ± 3.5 kg) en is ewekansig toegewys aan een van die drie proefdiëte waarvan die energie-inhoud gewissel het; naamlik 'n lae, medium en hoë-energie dieet (11.3, 12.0 en 12.7 MJ ME / kg voer onderskeidelik) wat ad libitum verskaf is. Die bokke is verder lukraak toegewys aan een van vyf slag groepe, wat met vyf weke tussenposes by ’n kommersiële abattoir geslag is. Die eerste groep bokke is aan die begin van die proef geslag om sodoende as basislyn verwysing te dien. Tydens die studie is die effek van die verskil in energie-inhoud van die dieet en die tyd wat in die voerkraal gespandeer is, op die voerkraal produksie en slag eienskappe van die Boerbok lammers ondersoek. Daarbenewens is die effek van die verskil in energie-inhoud van die voerkraal dieet op die sensoriese en chemiese eienskappe van bokvleis geëvalueer. Tydens die produksie periode is individuele voerinname en liggaamsgewig toename op ’n weeklikse basis gemonitor. Dit is waargeneem dat die liggaamsgewig van die bokke tydens die hele produksie tydperk toegeneem het. Kwadratiese funksies is gebruik om die verandering in die gemiddelde daaglikse toename tydens die voerperiode, sowel as die droëmateriaal inname van die bokke te beskryf. Bokke wat die lae en medium-energie diëte gevoer is, het hoër daaglikse toenames (P = 0.02) en droë materiaal inname (P< 0.01) as bokke op die hoë-energie dieet getoon. Die voeromset verhouding benodig om ’n eenheid lewendige gewig te produseer is nie beïnvloed deur die energie-inhoud van die dieet, of die ouderdom van die bokke in die voerkraal nie. ’n Lineêre funksie is toegepas om die groei van die bokke gedurende die produksie tydperk te modelleer. Die groei van die bokke kon nie die infleksiepunt van die groeikurwe bereik nie. Dus kon die sigmoïdale groeikurwe nie getrek word nie, wat deur ’n funksie soortgelyk aan die Gompertz model gemodelleer kon word. Uitslag persentasies van die karkasse het l regdeur die produksie tydperk varieër vir al die diëte; bokke op die lae-energie dieet het die laagste uitslagpersentasie gehad (45.8%; P = 0.04). Die energie-inhoud van die proefdiëte het geen effek op die opbrengs van die afval komponente en handelsnitte van die karkasse gehad nie. Oorhoofs is dit waargeneem dat die opbrengs van die agterkwart en neksnitte afgeneem het, terwyl dié van die voorkwart toegeneem het met slag ouderdom. Die vetheidsgraad van die karkas het toegeneem met tyd spandeer in die voerkraal, met die meerderheid van die vet gedeponeer in die buikholte, eerder as in die onderhuidse vetlaag. Daar is verwag dat die energie-inhoud van die dieet die vlakke van binnespierse vet sal beïnvloed, wat op sy beurt ‘n effek op die eetkwaliteit van die vleis sal hê.. Teenstrydig met verwagtinge het die vlakke van energie in die dieet van die bokke geen invloed gehad op die sagtheid, sappigheid of die aroma en geur profiele van bokvleis nie, soos waargeneem deur middel van beskrywende sintuiglike analise van die vleis deur 'n opgeleide paneele. Chemiese ontleding van die gaar vleismonsters het ook geen verskillein die vlakke van binnespierse vet tussen die verskillende monsters getoon nie, wat gelei het tot daar geen verskille tussen die behandelings in die sensoriese evaluasie waargeneem is nie.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/97903
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