Effect of feed composition and sex on feedlot performance, carcass characteristics and profitability of Dorper lambs

Hanel, Emma Claire (2022-04)

Thesis (MScAgric)--Stellenbosch University, 2022.

Thesis

ENGLISH ABSTRACT: The Dorper is the most numerous of the meat sheep breeds in South Africa. However, the early maturity of the breed and its tendency to deposit localised fat at an earlier age, typically requires them to be slaughtered at a lower live weight when compared to later maturing breeds. These characteristics tend to be enhanced under favourable environmental conditions, such as intensive feeding systems. Most feedlot operators discriminate against Dorper’s and are reluctant to finishing them owing to their slaughtering at a lower live weight or having their grade negatively affected, thereby reducing the income potential. There is limited literature describing the effect of diet and sex on the performance and profitability of feedlot finished Dorper lambs. The objectives of this two-part study were to determine the effect of treatment (diet) and sex on overall feedlot production parameters of Dorper lambs. Part two considered the effect of diet and sex on carcass characteristics and overall profitability parameters. Eighty-four Dorper lambs were randomly allocated to one of seven treatment groups (1=control, 2=low-energy, 3=high-protein, 4=high-protein + low-energy, 5=high-fat + low- starch, 6=high-fat + low-starch + high-protein, 7=control + β antagonist), comprising 12 animals each- 6 ram and 6 ewe lambs in a 2 x 7 factorial design. Treatment yielded a significant (P ≤ 0.05) effect on performance for most of the measured parameters (dry matter intake, number of feedings, final weight, liveweight gain, average daily gain and feed conversion ratio), while the effect of sex was limited, and the interaction of treatment and sex was significant for feed conversion ratio (P = 0.01) only. Findings of this study show the lambs final weight was significantly the highest for Treatment 4. Moreover, these animals yielded superior performance for liveweight gain and ADG across all groups in both ram and ewe lambs (P ≤ 0.05). Although, not significant, rams on average yielded numerically slightly superior performance compared to ewe lambs across the measured parameters. Treatment 1 yielded the best feed conversion in both rams and ewes, suggesting that the standard feedlot diet resulted in the most efficient growth, while Treatment 7 was shown not effective in improving feedlot performance for all the recorded parameters. Findings of Part two, investigating the main effects on carcass characteristics, show that Diet yielded a significant (P ≤ 0.05) effect on most of the measured parameters (final weight, warm and cold carcass weights, warm and cold slaughter percentage, feed cost, carcass value and margin above specified costs) while the effect of sex was limited. The interaction of diet and sex was significant (P ≤ 0.05) for the difference in slaughter percentage between warm and cold carcasses and the margin above specified cost only. The highest (P ≤ 0.05) final weights of Treatment 4 lambs corresponded to the highest carcass weights and thus the highest carcass value/revenue being achieved. Additionally, this group yielded superior performance for these parameters in both ram and ewe lambs (P ≤ 0.05). Although, not significant, rams on average yielded slightly superior performance compared to ewe lambs across the measured parameters. While Treatment 7 yielded the highest slaughter percentage, with the ewes being the highest of all groups (P ≤ 0.05), Treatment 1 yielded the highest numeric margins over specified costs (R/head and R/kg), along with the lowest FCR, suggesting the correlation between margin and efficiency of growth. Apart from improving slaughter %, Treatment 7 was shown not effective in improving the recorded parameters. Results from this study indicate that diet played a significant role in most of the measured parameters on Dorper lambs. Differences were also evident between the sexes. Notable differences and wide variation in the data, indicates that further research is required to reduce individual variation and ensure that all animals, both rams and ewes, yield positive returns from the feedlot finishing.

AFRIKAANSE OPSOMMING: Die mees algemene vleisskaapras in Suid Afrika is die Dorper. Die vroeë volwassenheid van hierdie ras en die geneigdheid om op ‘n vroeë ouderdom gelokaliseerde vet neer te lê, veroorsaak dat hulle op ‘n laer lewendige massa geslag moet word in vergelyking met ander rasse. Hierdie eienskap is geneig om onder gunstige toestande, soos tydens intensiewe voerkraalsisteme, te vererger. Die meeste voerkraalbestuurders diskrimineer dus teen die Dorper en is huiwerig om hulle te af te rond. Dit is weens die gevolglike laer slaggewig en swakker gradering wat gewoonlik die inkomste verlaag. Beperkte literatuur wat die effek van dieët en geslag op prestasie en winsgewindheid van Dorper voerkraallammers beskryf is beskikbaar. Die doelwit van hierdie tweeledige studie was om vas te stel wat die effek van dieët en geslag op voerkraal produksieparameters van Dorper lammers is. Deel twee van die studie het die effek van dieet en geslag op karkaseienskappe en winsgewendheid ondersoek . Vier-en-tagtig Dorper lammers is ewekansig in een van sewe behandelingsgroepe (1= kontrole, 2= lae energie, 3= hoë proteïen, 4= hoë proteïen + lae energie, 5= hoë vet en lae stysel, 6=hoë vet + lae stysel + hoë proteïen, 7= kontrole groep +β-atagonis) in ‘n 2 x 7 faktoriaal ontwerp ingedeel. Elk van die groepe het uit 12 lammers (waarvan 6 ooi- en 6 ramlammers per groep) bestaan. Hoofeffekte was dieet en geslag. Dieet het ‘n betekenisvolle effek op die prestasie van die meeste voerkraalparameters insluited DMI, aantal voedings, finale massa, lewendige massatoename, GDT en VOV getoon, terwyl die effek van geslag beperk was. Slegs die interaksie tussen behandeling en geslag was betekenisvol (P = 0.01) vir VOV. Die bevindings van die studie toon dat die finale lewenede massa van die lammers die hoogste met behandelingsgoep 4 was. Hierdie groep het ook verbeterde (P ≤ 0.05) prestasie vir totale lewende massatoename en GDT teenoor alle ander behandelingsgroepe van beide ooie en ramme getoon. Alhoewel nie statisties betekenisvol nie, het ramme numeries ‘n hoër prestasie in groeiparameters teenoor ooie getoon. Behandeling 1 het die beste VOV aangeteken wat daarop dui dat die standaard voerkraaldieet tot die mees effektiewe groei gelei het, terwyl behandeling 7 nie tot verbeterde voerkraalprestasie vir alle groeiparameters gelei het nie. Die bevindings van deel twee van die studie toon dat dieet ‘n betekenisvolle effek op die meeste meetbare slag- en ekonomiese parameters (finale massa, warm en koue karkasmassas, warm en koue uitslagslagpersentasie, voerkoste, karkaswaarde en marge bo spesifieke koste) gehad het. Die effek van geslag was egter beperk. Dieët en geslagsinteraksie vir uitslagpersentasie was slegs betekenisvol (P ≤ 0.05) tussen die warm en koue karkasse sowel as marge bo spesifieke koste. Die hoogste (P ≤ 0.05) finale massa van behandelingsgroep 4 se lammers korreleer met die hoogste karkasmassa en lei dus ook na die hoogste karkas waarde/ inkomste van hierdie groep. Ten opsgte van hierdie parameters het behandeling 4 ook vir beide geslagte beter (P ≤ 0.05) prestasie behaal. Alhoewel nie statisties betekenisvol nie, het ramme, in vergelyking met ooie, gemiddeld ‘n beter prestatsie oor die meetbare parameters behaal. Behandeling 7 het die hoogste uitslagpersentasie gelewer, met ooie die hoogste (P ≤ 0.05) van al die groepe. Behandeling 1 het tot die hoogste numeriese marge bo spesifieke koste (R/kop and R/kg) asook die beste VOVgelei, wat daarop dui dat daar ‘n korrelasie tussen marge en effektiwiteit van groei is. Benewens vir die verbetering van uitslagpersentasie, was behandeling 7 egter nie suksesvol om slag- en ekonomiese parameters te bevoordeel nie. Die resultate van die studie dui daarop dat dieët ‘n statistiese betekenisvolle rol in die meeste van die meetbare parameters by Dorper voerkraallammers het. Duidelike geslagsverskille is ook bespeur. Wye variasie in die data dui daarop dat verdere navorsing benodig word om individuele variasie te verminder asook om te verseker dat beide vroulike en manlike lammers ‘n positiewe opbrengs in die voerkraal lewer.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/124905
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