The effects of feeding Cistus ladanifer (Cistus) and a blend of soybean and linseed oil (1 : 2 vol/vol) on fatty acid (FA) composition of lamb meat lipids and messenger RNA (mRNA) expression of desaturase enzymes was assessed. In total, 54 male lambs were randomly assigned to 18 pens and to nine diets, resulting from the combination of three inclusion levels of Cistus (50 v. 100 v. 200 g/kg of dry matter (DM)) and three inclusion levels of oil (0 v. 40 v. 80 g/kg of DM). The forage-to-concentrate ratio of the diets was 1 : 1. Longissimus muscle lipids were extracted, fractionated into neutral (NL) and polar lipid (PL) and FA methyl esters obtained and analyzed by GLC. The expression of genes encoding Δ5, Δ6 and Δ9 desaturases (fatty acid desaturase 1 (FADS1), fatty acid desaturase 2 (FADS2) and stearoyl CoA desaturase (SCD)) was determined. Intramuscular fat, NL and PL contents were not affected by oil or Cistus. Oil supplementation reduced (P<0.05) 16:0, c9-16:1, 17:0, c9-17:1 and c9-18:1 FA and increased (P<0.05) 18:2n-6, 18:3n-3 and the majority of biohydrogenation intermediates in NL. Cistus alone had few effects on FA of NL but interacted with oil (P<0.05) by increasing t10-18:1,t10,t12-18:2,t10,c12-18:2 and t7,c9-18:2. The t10-/t11-18:1 ratio increased with both Cistus and oil levels. The c9, t11-18:2 did not increase (P<0.05) with both oil and Cistus dietary inclusion. Oil reduced c9-16:1, 17:0, c9-17:1,c9-18:1, 20:4n-6, 22:4n-6 and 20:3n-9 proportions in PL, and increased 18:2n-6, 18:3n-3, 20:3n-3 and of most of the biohydrogenation intermediates. The Cistus had only minor effects on FA composition of PL. Cistus resulted in a reduction (P<0.05) of 20:5n-3 and 22:6n-3 in the meat PL. The expression level of SCD mRNA increased (P=0.015) with Cistus level, although a linear relationship with condensed tannins intake (P=0.11) could not be established. FADS1 mRNA expressed levels increased linearly (P=0.019) with condensed tannins intake. In summary, the inclusion of Cistus and oil in 1 : 1 forage-to-concentrate ratio diets resulted in a large increase in t10-18:1 and no increase in c9,t11-18:2 or n-3 long chain poor in polyunsaturated fatty acids in lamb meat.

On the basis of the isomer-specific effects of trans fatty acids (FA) on human health, and the detrimental effect of t10,c12-conjugated linoleic acid (CLA) on cows’ milk fat production, there is a need to identify factors that affect the shift from trans-11 to trans-10 pathway during ruminal biohydrogenation of FA. This experiment was conducted in vitro and aimed at separating the effects of the diet of the donor cows from those of the fermentative substrate, which is necessary to prevent this shift. A total of four dry Holstein dairy cows were used in a 4 × 4 Latin square design. They received 12 kg of dry matter per day of four diets based on maize silage during four successive periods: the control diet (22% starch, <3% fat); the high-starch diet, supplemented with wheat plus barley (35% starch, <3% crude fat); the sunflower oil diet, supplemented with 5% of sunflower oil (20% starch, 7.6% crude fat); and the high-starch plus oil diet (33% starch, 7.3% crude fat). Ruminal fluid of each donor cow was incubated for 5 h with four substrates having similar chemical composition to the diets, replacing sunflower oil by pure linoleic acid (LA). The efficiency of isomerisation of LA to CLA was the highest when rumen fluids from cows receiving dietary oil were incubated with added LA. The shift from trans-11 to trans-10 isomers was induced in vitro by high-starch diets and the addition of LA. Oil supplementation to the diet of the donor cows increased this shift. Conversely, the trans-10 isomer balance was always low when no LA was added to incubation cultures. These results showed that a large accumulation of trans-10 FA was only observed with an adapted microflora, as well as an addition of non-esterified LA to the incubation substrate.