The effect of finishing diet neutral detergent fibre content on South African Mutton Merino lamb performance, meat fatty acid composition, tenderness and stability

Abstract

A trial was conducted studying the effect of reducing neutral detergent fibre (NDF) content in the diet of finishing South African Mutton Merino wether lambs on meat fatty acid (FA) composition, tenderness and stability. Fifty four-month-old lambs (29.14±1.66 kg; mean±SD) were assigned at random to the five dietary treatments with n = 10 lambs per treatment (n = 1 lamb per replicate), culminating into a randomised trial design. The lambs were housed individually in pens (1.404 m²) on elevated wooden slatted floors. Five dietary treatments similar in nitrogen content were formulated differing in respect to the NDF content thereof. Treatments were described as containing 379 (CON), 314 (NDF1), 251 (NDF2), 192 (NDF3) and 143 (NDF4) gram NDF/kg dry matter (DM), respectively. The production study was conducted over a period of 61 days. Means were analysed using the LSMEANS/DIFF with treatment as fixed effect, and post hoc using Tukey's HSD test. Regression analyses was conducted by PROC REG. All estimates were tested at the 5 % probability level. A reducing dietary NDF content linearly decreased the stearic and α-linolenic acid content of South African Mutton Merino muscle tissue, but linearly increased the palmitic, palmitoleic, vaccenic, linoleic acid, total omega-6 (n-6) and n-6:omega-3 (n-3) ratio, as well as ∆⁹ desaturase index of the same tissue. Subcutaneous lipid tissue was more extensively affected by dietary treatment and linearly increased (P < 0.0001) oleic, vaccenic, linoleic and arachidonic acid content, ∆⁹ desaturase index, as well as total mono-unsaturated fatty acid (MUFA), poly-unsaturated fatty acid (PUFA), unsaturated fatty acid (UFA), n-6, n-6:n-3 and PUFA:SFA ratios following decreased dietary NDF content. In contrast, adipose tissue lipid content, stearic acid and total saturated fatty acid (SFA) content, as well as atherogenicity index linearly decreased (P < 0.0001) following a decreased dietary NDF content. Treatment did not affect the conjugated linoleic acid (CLA: C18:2c9,t11) content of lamb muscle or adipose tissue. Reducing dietary NDF content linearly decreased lamb longissimus muscle tissue lightness (L*) of day-4 and day-8 storage samples, yellowness (b*) and hue angle of the fresh (day-0) and day-8 samples, as well as chroma of the day-8 sample. In contrast, the redness (a*) of the day-8 storage muscle tissue increased linearly following a decrease in dietary NDF content. Dietary treatment had no effect on longissimus muscle tenderness nor oxidative stability. The advantage of reducing the NDF contend of a finishing diet for South African Mutton Merino lambs seems to favourably affect the PUFA:SFA ratio of subcutaneous lipid tissue, but negatively affect the n-6:n-3 ratio of both lipid and muscle tissue, whereas the total n-3 content was left unaffected. A lipid source high in n-3 would be of benefit if added to a low-NDF finishing diet fed to South African Mutton Merino wethers to possibly increase its content within their meat.