Plasma fatty acid changes in lambs grazing mixed annual fodder crops

Context The fatty acid profile of pasture-fed beef and lamb, in particular, omega-3 fatty acids, depends largely on the fatty acids available in grazed forages. Annual forage crops are used to provide high-quality fodder for livestock during typical autumn–winter feed-gaps in the south-east of Australia; however, their fatty acid content and the influence of these on the fatty acid profile of grazing lambs have not previously been examined. Aims To determine the fatty acid profile of mixtures of annual species fodder crops and the relationship with the omega-3 content of lamb plasma following grazing. Methods In total, 96 Dorset × Border Leicester × Merino lambs (44.3 ± 0.55 kg) were allocated to one of four treatment groups (n = 24/treatment), including a single-species brassica (canola, Br) or mixed species containing brassica and cereal (canola, turnip, radish, wheat, cereal rye, B + C), brassica and legume (canola, turnip, radish, vetch, arrowleaf clover, B + L), or brassica, cereal and legume (B + C + L). Changes in the fatty acid profile of forages and plasma was determined over a 5-week grazing period. Key results The n-6:n-3 ratio was higher in the Br control (0.386 ± 0.010) than in any other forage treatment (B + C = 0.351 ± 0.011, B + L = 0.345 ± 0.010, B + C + L = 0.354 ± 0.010). Plasma total n-3 was higher for lambs grazing the Br control than for those grazing any other forage, whereas the n-6:n-3 ratio was highest when lambs grazed B + C + L (1.41 ± 0.02), compared with any other forage treatment (Br = 1.31 ± 0.02, B + C = 1.18 ± 0.02, B + L = 1.28 ± 0.02). Conclusions The higher n-6:n-3 ratio in lambs grazing the B + C + L forage mix was not expected, given the fatty acid profile of the forage grazed; however, selective grazing of vetch or brassica roots could have influenced the results. The relationship between forage fatty acid profile and fatty acid intake with changes in meat fatty acids and other physiological outcomes should be examined. Implications The total omega-3 content of animal tissue may be increased by grazing canola; however, if a lower n-6:n-3 ratio is optimal in meat for human consumption, grazing forage mixtures containing cereals may be more beneficial.