Masters Degrees (Animal, Wildlife and Grassland Sciences)

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Browsing Masters Degrees (Animal, Wildlife and Grassland Sciences) by Author "De Klerk, Inalene"

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    The effect of NDF content in finishing diets on performance and meat quality of lambs
    (University of the Free State, 2016-02) De Klerk, Inalene; Einkamerer, O. B.; Hugo, A.; Greyling, J. P. C.
    English: A study was conducted to investigate the effect of incrementally increasing NDF levels of finishing diets on apparent digestibility, production performance, FA composition, oxidative stability and tenderness of lamb. The five dietary treatments were formulated to contain a similar nutrient composition, differing only in respect to the NDF content as the primary parameter. The NDF content increased from low roughage (primarily lucerne hay as fibre source) inclusion to a high roughage inclusion rate representing a dose-response trial in the following order: 12.76% (T15), 17.69% (T30), 22.53% (T45), 27.48% (T60) and 32.40% (T75) NDF/kg DM, respectively. No rumen modifiers or buffers were added to the diet. Sixty (60) South African Mutton Merino wether lambs (29.3±1.8 kg) were randomly allocated to the five dietary treatments (n=12 lambs per treatment) and further subdivided into 12 animals per replicate (n=1 lamb per replicate). After dietary adaptation of 10 days all lambs received the experimental diets for the remaining period (51 days). Live weight and feed intake were recorded on a weekly basis. A digestibility study was conducted over a 12-day period (4-day adaptation to the faecal bags followed by an 8-day collection period) where seven lambs (mean 48.11±2.94 kg live weight; total of 35 lambs) were randomly allocated to each treatment (n=7 lambs/treatment). At the end of the production study all lambs were slaughtered. Physical carcass characteristics, muscle and subcutaneous FA composition, meat oxidation (malonaldehyde content), colour stability, as well as meat tenderness were measured. The data was subjected to analysis of variance (PROC ANOVA) of the SAS program, version 9.2 (SAS, 2008). Tukey’s honest significant difference (HSD) test was used to identify significant differences (P <0.05) between treatments. From the results of the present study it is apparent that an incremental increase in the NDF content of lamb finishing diets presented a significant decrease (P <0.05) in DM, OM, NSC, GE, CP and EE digestibilities, as well as ash solubility. In addition, the significant (P <0.05) decrease in digestible OM, NSC and EE dietary content were associated with diet digestibility and resulted in a significant decrease (P <.0001) in ME content following an increased NDF incremental inclusion. A high roughage inclusion in finishing diets for lambs (T75) resulted in a significant (P <0.05) reduction in MEI, ADG, FCR, and therefore cold carcass weight and dressing percentage. Increased dietary NDF content significantly (P <0.05) increased saturated stearic acid, and significantly (P <0.05) decreased monounsaturated oleic and vaccenic acid, polyunsaturated linoleic acid, as well as total PUFA, n-6, n-6:n-3 and PUFA:SFA ratios of both lamb meat and adipose tissue. Apart from the NDF content significantly (P <0.05) affecting the monounsaturated palmitoleic acid (decreased) and polyunsaturated CLA (C18:2c9t11;n-6) content of muscle tissue, as well as total SFA (increased) and MUFA (decreased) content of only adipose tissue, the effect of dietary treatment between lamb deposit sites seem to be similar. Neutral-detergent fibre content did significantly (P <0.05) affect meat colour stability stored for 7 days at 4oC. Neutral-detergent fibre content had no effect (P >0.05) on meat tenderness. These results suggest that the FA profile of lamb can be manipulated by altering the NDF content of the finishing diet. This however did not result, from a human health point of view, in the desirable PUFA:SFA and n-6:n-3 ratios in muscle and subcutaneous lipid tissue. It is proposed that, to increase the total UFA content and its desirable effect on the mentioned ratios of lamb meat, regression equations should be used to establish the optimum response at a given NDF inclusion. Further research attempting to manipulate specific FAs (single or total) or FA ratios of lamb meat via dietary means to meet consumers’ demands need further attention.