Masters Degrees (Animal, Wildlife and Grassland Sciences)

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Browsing Masters Degrees (Animal, Wildlife and Grassland Sciences) by Author "Booyens, Käte Erna"

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    The effect of dietary lipid saturation and antioxidant sources on performance and meat quality of lambs
    (University of the Free State, 2014-05-27) Booyens, Käte Erna; Einkamerer, O. B.; Hugo, A.; Van Der Merwe, H. J.
    English: A study was conducted to investigate the influence of antioxidant source and fatty acid saturation in a standard finishing diet on apparent digestibility, production performance, fatty acid composition and oxidative stability of lamb. The four dietary treatments consisted of the same basal diet (187 g CP- and 355 g NDF/kg DM) differing in the lipid source (30 g/kg of either saturated beef tallow or unsaturated soyabean oil) and type of antioxidant included (125 g/ton of either a synthetic or natural antioxidant). Eighty-four S.A. Mutton Merino lambs (27.64 ± 1.72 kg) were randomly allocated to the four dietary treatments (n=21 lambs per treatment) and subdivided into seven replicates per treatment (n=3 lambs per replicate). After dietary adaptation of 8 days all lambs received the experimental diets for the remaining period (41 days). A digestibility study was conducted over a 12-day period (4-day adaptation to the faecal bags followed by an 8-day collection period). Seven lambs per treatment were randomly selected and slaughtered at completion of the production study. Physical carcass characteristics, muscle pH, muscle- and subcutaneous fatty acid composition, as well as meat oxidative- (malonaldehyde content) and colour stability was measured. The apparent NDF digestibility was reduced (P =0.0548) with the inclusion of unsaturated soyabean oil in the diet compared to saturated beef tallow. This was associated with a significant (P <0.05) lower digestible NDF and ME content in the experimental diet. No significant (P >0.05) differences in dry matter intake, daily gain and feed efficiency of lambs occurred. The addition of unsaturated soyabean oil significantly increased (P =0.0003) the efficiency of ME utilisation in the diet. Lipid saturation level in finishing diets for lambs did not influence (P >0.05) the physical carcass characteristics and meat pH of lambs. Saturated beef tallow increased (P <0.05) the monounsaturated palmitoleic- and oleic acid content of lamb subcutaneous and/or muscle tissue, whereas the more unsaturated soyabean oil increased (P <0.05) the polyunsaturated linoleic acid, α-linolenic acid and CLA content of both muscle fat and subcutaneous lipid tissue. Monounsaturated vaccenic acid was increased in lamb meat when unsaturated soyabean oil was included in combination with the natural antioxidant. The total PUFA, total n-6 fatty acid and PUFA:SFA ratio of lamb meat increased (P <0.05) with the inclusion of the more unsaturated soyabean oil in the diet. A higher (P <0.0001) n-6:n-3 ratio occurred in the intramuscular fat of lambs fed the unsaturated soyabean oil diet. Unsaturated soyabean oil negatively influenced (P <0.05) the oxidative stability of lamb meat on days 0 (fresh) and 90 (frozen), compared to saturated tallow. The inclusion of a synthetic compared to a natural antioxidant in the diet decreased (P =0.0672) the apparent digestibility of NDF, which was also associated with a significantly (P =0.0159) lower digestible NDF content of the experimental diet. The meat pH measured 45 minutes after slaughter was significantly (P =0.009) decreased when a synthetic antioxidant was added to the diet. Meat pH measured at 24 hours post slaughter was lower (P =0.0433) when a natural antioxidant was added to the diet. With the exception of the natural antioxidant that increased (P <0.05) the saturated palmitic- and monounsaturated palmitoleic acid content of subcutaneous and/or muscle fat, and decreased (P <0.05) the monounsaturated stearic acid content of intramuscular fat, dietary antioxidant type did not to effect (P >0.05) the fatty acid composition of lamb meat, neither the colour- nor oxidative stability. These results suggest that the fatty acid profile of lamb can be manipulated by the saturation level of the lipid source included in the diet. However, the replacement of saturated tallow with unsaturated soyabean oil did not result, from a human health point of view, in the desirable PUFA:SFA and n-6:n-3 ratios in muscle fat and subcutaneous lipid tissue. Therefore, the manipulation of the fatty acid content of finishing diets to achieve the desirable ratios within lamb meat, as well as the optimal inclusion level of a bioflavonoid antioxidant warrants further research.