Effect of sodium bentonite and vegetable oil blend supplementation on growth, carcass quality and intramuscular fatty acid composition of lambs

The effect of dietary sodium bentonite and a blend of sunflower and linseed oils at 1:2 (v/v) on growth, carcass and meat quality and fatty acid (FA) composition of longissimus dorsi muscle of lambs was studied. Thirty-two Merino Branco lambs with initial live weights (LW) of 16.2 ± 2.93 kg were divided according to a completely randomized experimental design within a 2 × 2 factorial arrangement of treatments in order to evaluate effects of the vegetable oil blend supplementation (0 g/kg versus 60 g/kg DM) and sodium bentonite inclusion in diets (0 g/kg versus 20 g/kg DM). The basal diet consisted of pellets with 750 g dehydrated lucerne/kg DM and 250 g manioc/kg DM. The experimental period was 6 weeks. Bentonite affected neither daily LW gain, dry matter (DM) intake, nor carcass composition. However, bentonite decreased the a* meat colour parameter (redness; P=0.004). Oil supplementation affected neither daily LW gain, nor DM intake. However, it increased fat proportion in chump and shoulder cuts (P<0.001), as well as kidney and knob channel fat (P<0.001) while it decreased muscle proportion in the dissected cuts (P<0.001). Oil supplementation increased intramuscular fat (P<0.001) and most meat FA. Polyunsaturated FA (PUFA) increased 23% with oil supplementation (P=0.007), mostly by increasing proportions of n-3 PUFA and biohydrogenation derived PUFA. Oil supplementation decreased n-6 long chain PUFA (P<0.001). The proportion of n-3 long chain PUFA was not affected by oil supplementation, so the increase in n-3 PUFA from 1.99 g/100 g of total FA to 4.23 g/100 g of total FA (P<0.001) was mainly due to the increase of α-linolenic acid (P<0.001). However, when expressed in mg/100 g of meat, oil supplementation increased n-3 long chain PUFA concentration from 20 to 31 mg (P<0.001). All biohydrogenation intermediates (BI) increased with oil supplementation, except for cis-11 18:1 which decreased, and cis-13 18:1 and trans-8, cis-10 18:2 which were unchanged. Conjugated linoleic acid increased with oil supplementation from 0.50 to 1.72 g/100 g of total FA (P<0.001). Bentonite did not affect most meat FA, although effects occurred on some BI. Bentonite increased trans-11 18:1, but prevented the increase of trans-10 18:1 in meat from oil supplemented lambs (P<0.001). Trans-11, cis-15 18:2, cis-9, cis-15 18:2 and cis-9, trans-11, cis-15 18:3 increased with dietary bentonite inclusion.