How does the duration of finishing on lucerne pasture affect the fatty acid and vitamin E content of lamb muscle?

It is widely recognized that grazing leads to improved fatty acid profile (FA) and antioxidant concentrations in ruminant meat lipids compared to grain-feeding. However, the extent of this improvement as a function of pasture-finishing duration remains under-documented. Here we investigated the effects of duration of pre-slaughter lucerne grazing on the lipid content, FA composition and vitamin E level of lamb muscle. Romane lambs were grazed on lucerne for varying durations before slaughter (0, 21, 42 or 63 days, with 20 lambs per treatment group). The FA profile and vitamin E content of the longissimus thoracis et lumborum muscle were measured in 10 representative lambs from each treatment group. Increasing the duration of pasture-finishing led to a linear increase in muscle concentrations of total polyunsaturated FA (PUFA) (P < 0.0001), mainly n-3 PUFA (P < 0.0001) such as 18:3 n-3, 20:5 n-3, 22:5 n-3 and 22:6 n-3 (P < 0.0001, P < 0.0001, P = 0.001, and P = 0.002, respectively), whereas n-6 PUFA concentrations remained unchanged, except CLA which increased with increasing duration of pasture-finishing (P = 0.001). These results led to a linear decrease in n-6 PUFA/n-3 PUFA ratio and 18:2 n-6/18:3 n-3 ratio with lucerne grazing duration (P < 0.0001 for both). Vitamin E content increased linearly with the duration of lucerne pasture-finishing (P < 0.0001). The improvement in muscle FA profile and vitamin E content thus increased with lucerne pasture-finishing duration, leading to better-nutritional-quality meat without increasing the risk of oxidation .