Effects of intensive or pasture finishing in spring and linseed supplementation in autumn on the omega-3 content of lamb meat and its carcass distribution

Abstract

Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are the n-3 polyunsaturated fatty acids (n-3 PUFA) for which there is ample evidence of human health benefits, and these are also the fatty acids for which there are cut-off points for ‘source’ and ‘good source’ claims. Two consecutive experiments were conducted to determine the effect of finishing systems on the n-3 PUFA content of lamb meat in Western Australia. In experiment I, a 4-week feeding experiment was conducted using 48 Poll Dorset × Merino lambs. The lambs were divided into two lots of 24 (12 males and 12 females) and randomly assigned to either concentrate (C1) finishing on commercial lamb finishing pellets or pasture (P) finishing on kikuyu (Pennisetum clandestinum) pasture. In experiment II, 28 lambs were divided into two groups of 14 lambs (seven males and seven females) and assigned to finishing either on concentrate pellets (C2) or concentrate pellets plus linseed (C2-L). This second experiment was conducted indoors for 10 weeks. The initial liveweight (mean ± s.e.) of the lambs was 43 ± 0.6 and 32.5 ± 0.9 kg for experiments I and II, respectively. At the end of experiment II, three chops each were sampled from the leg, loin, forequarter and neck region of each carcass. The final liveweight (42 ± 0.8 v. 50 ± 1.2 kg), hot carcass weight (19 ± 0.5 v. 24 ± 0.7 kg) and GR depth (5.6 ± 0.6 v. 12.8 ± 0.6 mm) were lower (P < 0.05) for P than C1 lambs. In contrast, C2 and C2-L lambs had similar final liveweight (44 ± 0.7 v. 45 ± 0.9 kg), hot carcass weight (19 ± 0.3 v. 20 ± 0.5 kg) and GR depth (13 ± 1.3 v. 14 ± 1.2 mm). In experiment I, the total n-3 PUFA yields for C1 and P lambs in the M. longissimus lumborum were 67 ± 2.5 and 78 ± 3.2 mg per 100 g muscle, respectively. The EPA plus DHA yields were 17 and 21 mg per 100 g muscle, respectively. The sum of the long-chain (≥C20) n-3 PUFA EPA, docosapentaenoic acid and DHA for C1 and P lambs were 30 and 37 mg per 100 g, respectively. Sex had no effect on any of the n-3 fatty acids. In experiment II, the total n-3 PUFA yields for C2 lambs were 61, 54, 60 and 104 mg per 100 g for leg, loin, forequarter and neck chops, respectively. The respective values for C2-L lambs were 153, 138, 139 and 178 mg per 100 g muscle. The claimable EPA plus DHA yields for C2 lambs were 13, 10, 12 and 15 mg per 100 g of trimmed leg, loin, forequarter and neck chops, respectively. The respective values for C2-L lambs were around 2-fold higher at 27, 21, 25 and 23 mg per 100 g raw meat. All the samples from pasture-finished and linseed-supplemented groups met the 30 mg cut-off point for ‘source’ claim in Australia when the computation was based on 100 g cooked lamb serve (140 g raw). We conclude that pasture-finished lambs have more n-3 PUFA per serve than their counterparts finished indoors on commercial pellets. Further, supplementing indoor-finished lambs with linseed provided equivalent n-3 PUFA per serve to finishing lambs on pasture. Supplementation with an omega-3 source improved omega-3 per serve across the whole carcass irrespective of sex.