The reduction of starch in finishing diets supplemented with oil does not prevent the accumulation of trans-10 18:1 in lamb meat

The experiment was conducted to test the hypothesis that the replacement of cereal with low-starch feed ingredients in lambs' finishing diets supplemented with oils could prevent the accumulation of t-10-18: 1 in meat. Forty lambs were fed 1 of 4 diets supplemented with soybean oil (5.9%) and fish oil (1%) for 6 wk before slaughter. The control (CON) diet contained 43% barley, and in the other diets, barley was completely replaced by dehydrated citrus pulp (DCP), dehydrated sugar beet pulp (DBP), or soybean hulls (SH). Growth performance, feed intake, and carcass and meat quality traits were analyzed. At slaughter, LM samples were collected for gene expression evaluation, and 3 d after slaughter, LM and subcutaneous (s.c.) fat samples were collected for fatty acid analysis. None of the diets affected meat quality, but the DCP diet reduced ADG (P < 0.05) and the DCP and SH diets decreased the feed-to-gain ratio (P < 0.01). The DCP diet increased (P < 0.05) the risk of parakeratosis and the severity of the lesions. Moreover, the DBP treatment led to increased a* (redness) and b* (yellowness) in s. c. fat compared with the CON treatment (P < 0.05). The lipid content of LM did not differ (P > 0.05) with treatment and averaged 34.4 g/kg of meat. Diets had no effect (P > 0.05) on SFA, PUFA, and cis-MUFA sums and on the n-6: n-3 ratio in both LM and s. c. fat. A lower expression of fatty acid synthase (FASN) was found with the DCP treatment than with the other treatments (P < 0.001). All treatments showed a high accumulation of t-10-18: 1, averaging 91 mg/g fatty acid in LM and 147 mg/g fatty acid in s. c. fat. The concentration of t-11-18: 1 in the tissues was considerably lower than that of t-10-18: 1, and thus the t-10-18: 1: t-11-18: 1 ratio was above 3 with all treatments. Despite this, the SH diet clearly promoted a larger deposition of t-11-18: 1 and c-9, t-11-18: 2 in tissues compared with the other treatments. Stearoyl-CoA desaturase (SCD) gene expression and SCD activity index in LM were reduced with the SH diet compared with the CON and DCP diets. Overall, these results clearly showed, for the first time, that low-starch/high-NDF diets are not able to prevent the establishment of t-10 shifted rumen biohydrogenation pathways, evaluated by the deposition of biohydrogenation intermediates in lamb meat and fat.