Stable carbon isotope composition of perirenal adipose tissue fatty acids from Engadine sheep grazing either mountain or lowland pasture.

To provide further insights into ruminant lipid digestion and metabolism, and into cis-9,trans-11 18:2 synthesis, 12 growing Engadine lambs grazing either mountain pasture (2,250 m above sea level; n = 6) or lowland pasture (400 m above sea level; n = 6) were studied. Both pastures consisted exclusively of C(3) plants. Before the experiment, all animals grazed a common pasture for 6 wk. Grasses and perirenal adipose tissues of the sheep were analyzed for fatty acids by gas chromatography. Stable C-isotope ratios (δ(13)C values in ‰ vs. the Vienna Pee Dee Belemnite standard) were determined in the composite samples by elemental analysis-isotope ratio mass spectrometry. The δ(13)C of the individual fatty acids were measured by gas chromatography-combustion-isotope ratio mass spectrometry. The δ(13)C value of the entire mountain pasture grass was -27.5‰ (SD 0.31), whereas that of the lowland pasture grass was -30.0‰ (SD 0.07). This difference was reflected in the perirenal adipose tissues of the corresponding sheep (P < 0.05), even though the δ(13)C values were less in the animals than in the grass. The δ(13)C values for cis-9 16:1 and cis-9 18:1 in perirenal fat differed between mountain and lowland lambs (P < 0.05). The 16:0 in the adipose tissue was enriched in (13)C by 5‰ compared with the dietary 16:0, likely as a result of partly endogenous synthesis. The δ(13)C values of cis-9,trans-11 18:2 (cis-9,trans-11 CLA) in the adipose tissue were smaller than those of its dietary precursors, cis-9,cis-12 18:2 and cis-9,cis-12,cis-15 18:3; conversely, the δ(13)C values of trans-11 18:1 were not, suggesting that large proportions of perirenal cis-9,trans-11 18:2 were of endogenous origin and discrimination against (13)C occurred during Δ(9)-desaturation. The same discrimination was indicated by the isotopic shift between 16:0 and cis-9 16:1 in the mountain grazing group. Furthermore, the δ(13)C values of cis-9,trans-11 18:2 were smaller relative to the precursor fatty acids in the mountain lambs compared with the lowland group. This result suggests a reduced extent of biohydrogenation in lambs grazing on mountain grass in comparison with those grazing on lowland grass. This was supported by the smaller cis-9,trans-11 18:2 concentrations in total fatty acids found in the adipose tissues of the lowland lambs (P < 0.001). The results of this study demonstrate that natural differences between δ(13)C values of swards from different pastures and the adipose tissue fatty acids could be used as tracers in studies of lipid metabolism in ruminants.

Modification of milk fatty acid composition by feeding forages and agro-industrial byproducts from dry areas to Awassi sheep.

The study tested the hypothesis that certain underused forages and agro-industrial byproducts available in dry areas may positively influence fatty acid (FA) composition and antioxidative properties of milk by their contents of residual oil or phenolic compounds or both. Sixty multiparous fat-tailed Awassi ewes were allocated to 6 groups in a completely randomized block design. During 50 d, the ewes were group-fed 2.5 kg of dry matter/d per ewe 1 of 6 isonitrogenous and isoenergetic diets (forage:concentrate, 0.3:0.7). The test feeds, comprising 30% of the diets, replaced either barley straw [lentil straw, olive leaves, and Atriplex (saltbush) leaves, rich in phenolic compounds or electrolytes] or conventional concentrate ingredients (olive cake and tomato pomace; ∼10% lipids) from the control diet. The diets containing olive cake and tomato pomace were rich in oleic acid (18:1 cis-9; 27% of total dietary FA) and linoleic acid (18:2 cis-9,cis-12; 37%), respectively. Profiles of FA were determined in individual milk samples drawn on d 0 and in wk 1, 3, 5 and 7. Data was analyzed by repeated measurement analysis. No consistent treatment effects on yield and gross nutrient composition of the milk were observed, although some differences occurred. Milk resulting from the Atriplex leaf diet expressed the highest antiradical activity, which was low with control and olive leaves. Feeding the tomato pomace and olive cake diets decreased the proportions of short- and medium-chain FA, whereas oleic acid clearly increased in proportion to total FA. Olive leaves most effectively increased rumenic acid (18:2 cis-9,trans-11) and α-linolenic acid (18:3 cis-9,cis-12,cis-15) in milk fat. This also resulted in the highest α-linolenic acid transfer rate from feed to milk and suggests that olive leaves affect ruminal biohydrogenation at several steps. Several alternative feeds exist with an added value, as they enhance FA with potential health benefits and the stability of the milk with higher antioxidative activity, even though responses to test feeds differed largely. It remains to be investigated whether combinations of these feeds would be complementary in these beneficial effects.