# Fatty Acid Composition and Volatile Profile of _M. longissimus thoracic_ from Commercial Lambs
## 4 Discussion
### Nutritional Quality: Selected Fatty Acids, Ratios and Indexes  
Excessive intakes of n-6 PUFA together with high n-6:n-3 ratios are commonly found in modern Western diets and associated with pathogenesis of many diseases, including cardiovascular disease, cancer and inflammatory and autoimmune diseases [50]. A dietary n-6:n-3 ratio below 4.0 was reported to reduce total cardiovascular disease mortalities by up to 70% after two years [51]. All lamb production groups used in the current study resulted in a mean n-6:n-3 ratio below 1.5. These ratios are similar to forage-reared lambs from Uruguay reported by [PERSON] et al. [8] and lower than those found by [PERSON] et al. [52] where concentrate feeding was used. The n-6:n-3 ratio, in contrast to the PUFA-SFA ratio, is highly influenced by the fatty acid composition of the diet fed to the animal [30]. Meat from forage-reared lambs has a lower n-6:n-3 ratio than meat from concentrate-reared ones, as C18:3n-3 is the major fatty acid in plant lipids, while C18:2n-6 predominates in concentrate diets [8]. The PUFA-SFA ratios in meat from all production systems in the current study were in the range of 0.17-0.35, which are below the recommended value of \(\geq\)0.45 [53]. For human diets, a high SFA intake has been associated with an increase in plasma cholesterol and greater risk of coronary heart disease [54], but not all saturated fatty acids have the same cholesterol-raising potential [55]. Higher amounts of C18:0 in the diet do not elevate plasma low-density lipoprotein-cholesterol because it is poorly digested and can be easily desaturated to C18:1 _cis_-9 [56]. Thus, different fatty acid indexes/ratios have been proposed in addition to the n-6:n-3 and PUFA-SFA ratios to take into account the different impact of fatty acids in human health, such as atherogenic and thrombogenic indexes and h/H and nutritional ratios. Low values of the atherogenic and thrombogenic indexes and the nutritional ratio are recommended for a healthy diet [21], while higher hypocholesterolemomic relative to hypercholesterolemiaomic fatty acids are beneficial for human health [22]. The atherogenic index range observed in the current study was similar to those found by [PERSON] et al. [31], who measured it on lambs reared under extensive conditions and slaughtered at 64 days of age. In the current study, the greater atherogenic index and nutritional ratio and lower h/H ratio of meat from 4-month-oldmilk-fed lambs was due to the greater proportions of C14:0 and C16:0 fatty acids that are high in milk, as discussed in Section 4.1, whereas the greater thrombogenic index of Merino lambs was due to their lower proportion of PUFA. The thrombogenic index range observed in the current study was similar to previously reported values for lamb, which are slightly greater than pork but lower than milk and cheese [21]. The h/H ratios of 6- to 12-month-old lambs ranged between 1.8 and 2.0, which were similar to the range previously reported for pasture-raised lambs by [PERSON] et al. [22]. The health benefits obtained by human consumption of meat lipids have been associated with quantitative LC-n-3-PUFA values, mainly EPA and DHA [57]. In the current study, 100 g of fresh muscle of lamb could provide 28 to 44 mg EPA plus DHA, with the greatest concentration coming from the lambs slaughtered at weaning. Similar EPA plus DHA contents in meat from lambs grazed on pasture have been reported by other authors [9; 58]. The EPA plus DHA content and proportion in the current study, however, were greater than values reported for lambs fed a concentrate diet [59], or even when concentrate-fed lambs were supplemented with linseed [60]. Meat from almost all lambs used in the current study could be considered as a \"source\" of n-3 fatty acids (EPA plus DHA) by the Australia and New Zealand reference standard [10], but only the meat from lambs which were slaughtered at weaning met the Australia and New Zealand standard to be considered as a \"good source\" of n-3.