Influence of duration of supplementation with ruminally protected linseed oil on the fatty acid composition of feedlot lambs

A feeding experiment was conducted to determine if the duration of supplementation of lambs with protected linseed oil (PLO) affected the apparent conversion of alpha linolenicacid (ALA) into the longer chain n-3 polyunsaturated fatty acids PUFA (n-3 PUFA): eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Forty-eight 4-month-old Merino lambs with mean initial live weights of 29.5 +/- 0.27kg were divided into four groups of 12 and randomly assigned to OPLO, 3PLO, 6PLO or 9PLO treatments corresponding to 0, 3, 6 and 9 weeks of PLO Supplementation, respectively. At slaughter, all groups had similar live weight (37-40kg), hot carcass weight (15-16kg) and ultimate pH (5.76-5.85). The intramuscular fat content was lower (P<0.01) in OPLO (2.26g) than the supplemented group (2.94-3.12g/100g muscle); there was no difference among supplemented groups. Increases in ALA and total n-3 PUFA content in the intramuscular fat of the Longissimus dorsi muscle were greatest in the first three weeks. PLO increased (P<0.05) the concentrations of ALA, docosapentaenoic acid (DPA) and DHA in L dorsi: changes in EPA were not significant. The total n-3 (rng/100 g muscle) content was higher in the supplemented group (P<0.01) than in OPLO; but did not differ among the supplemented groups. The treatment means were 46, 75, 91 and 94 rng/100 g for OPLO, 3PLO, 6PLO and 9PLO, respectively. The sum of EPA and DHA, which forms the criterion for health claim, was 17mg for OPLO, which was lower (P<0.05) than that for 3 PLO (21 mg), 6PLO (27 mg) and 9PLO (31 mg/100 g muscle). Only the 9PLO value met the 30 mg cutoff point for "source" claim under Australian guidelines. Consumer panel ratings were not different (P>0.05) between treatments. The PLO supplement was effective in significantly enriching lamb meat with n-3 PUFA in three weeks, but longer periods were required to increase the levels of the longer chain PUFAs that are required for "source claim" and product differentiation. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.