Fatty Acid Composition of Different Fat Depots from Purebred and Crossbred Hair Sheep Lambs Gradually Removed from Soy Hull Supplementation before Harvest

Soy hull has been recognized as an economical source of feed and can provide a highly digestible fiber supplemental for pasture-raised ruminants. Soy hull-supplementation in grazing lambs has increased growth rate and altered meat composition. Yet its timed removal before harvest on the fatty acid profile of different fat depots in lambs has not been reported. Thirty-six, 6-mo old purebred hair (Barbados Blackbelly or BB, BW = 20.0 ± 1.9 kg; St. Croix or SC, BW = 20.4 ± 3.1 kg) and crossbred wool (Dorset, D) × hair (BB; BW = 24.8 ± 3.1 kg or SC; BW = 24.5 ± 4.0 kg) sheep lambs rotationally grazed predominantly stockpiled tall fescue (13.3 to 19.4% CP) and ryegrass (16.5% CP) pastures. Lambs were allocated to four supplementation treatments (no supplementation; and supplementation until 42, 21 and 0 d before harvest). Lambs grazed as a single group and supplement was provided at 2% BW daily at individual feeding stations. After 63 d of grazing, lambs were harvested, and intramuscular, subcutaneous and kidney fats were obtained from each carcass. Total lipids from each fat depot sample were extracted by the chloroform-methanol method. Extracted lipids were prepared for the fatty acid methyl esters (FAME) and then analyzed by a gas chromatography. All data were analyzed as a completely randomized design with breed type (pure- or cross-bred) and supplement duration as main effects. The fatty acid profiles of different fat depots from experimental lambs were significantly influenced by breed type and supplement duration. Compared with non-supplemented lambs, lambs removed from supplementation 0 d before harvest had higher (P < 0.05) concentrations of palmitic (C16:0, 17.4 vs 15.0%) and trans-hexadecenoic (C16:1n9t, 0.99 vs 0.73%), but a lower (P < 0.05) concentration of elaidic (C18:1n9t, 0.23 vs 0.28%) acids in intramuscular fat; a lower (P < 0.05) concentration of a-linolenic (C18:3n3, 0.76 vs 1.24%) acid in subcutaneous fat; and a lower (P < 0.05) concentration of C18:1n9t (0.28 vs 0.36%) in kidney fat. Furthermore, lambs removed from supplementation 42 or 21 d before harvest had a lower (P < 0.05) C18:1n9t (0.23 vs 0.28%) in intramuscular fat, but lambs removed from supplementation 42 d before harvest had a higher (P < 0.05) linoleic (C18:2n6, 4.44 vs 2.87%) acids in intramuscular fat, compared with non-supplemented lambs. The results indicate that discontinuing supplementation before lamb harvest differentially affects fatty acids in fat depots from grazing lambs.