Effects of sunflower seed inclusion in finishing diets for steers on performance, carcass characteristics, muscle and adipose fatty acid composition and meat quality

The effectiveness of dietary sunflower seeds (SFS) in finishing diets composed of different components for beef cattle on increasing conjugated linoleic acid (CLA) isomers in beef was evaluated in a completely randomized design experiment with non-implanted, crossbred steers. Steers were individually fed six finishing diets (n = 12 per diet), to determine the effects of SFS inclusion, at 15% of diet dry matter (DM), on production performance, carcass characteristics, fatty acid (FA) profile of subcutaneous fat from the brisket and fat from the pars costalis diaphragmatis (PCD) muscle, and meat quality. On a DM basis, the control diet (1) contained 84% rolled barley and 15% barley silage, in diet 2 the barley silage was replaced with SFS, in diets 3, 4 and 5 the silage was linearly replaced from 15 to 7.5 to 0% with chopped alfalfa hay, and they all contained 15% SFS. Diets 5 and 6 were identical in composition, but the hay and SFS were included as a pellet. The higher fat and weight percent of linoleic acid (66% of total FA) of SFS supplemented diets over the control diet (51%), resulted in increased fat, energy and linoleic acid intake. Body weights at the initiation (434.2 ± 5.1kg) and end (596.2 ± 7.8 kg) of the trial were similar for steers fed all treatment diets. Dietary inclusion of SFS reduced dry matter intake (DMI) (P = 0.005) and ADG (P = 0.02) of steers to 8.9 and 1.0 kg d-1 compared with steers fed the control diet (10.2 and 1.2 kg d-1, respectively), but the feed conversion efficiency was unaffected. Back fat depth of steers fed SFS-containing diets was reduced (P = 0.02) to 13.8 from 17.0 mm for steers fed diet 1. Dietary supplementation with SFS increased weight percent both CLA isomers (CLA cis-9, trans-11 and CLA trans-10, cis-12) in fat from the PCD muscle (0.43 versus 0.22%; P = 0.001) and brisket fat (0.74 versus 0.44%; P = 0.0004), with the increase being greatest in steers fed the silage-free diets. Increase in weight percent of vaccenic acid was highest in tissues of steers fed hay along with SFS (11.7%) or barley and SFS (11.8%) relative to those fed the control diet (2.12%). Meat from steers fed the treatment diets was observed to have a higher (P = 0.02) juiciness scores, while initial tenderness (P = 0.1) and overall tenderness (P = 0.08) tended to be higher compared with beef from control steers. The steaks from the SFS-fed steers appeared to have a darker colour relative to steaks from control steers on day-7 (P < 0.0001). Feeding SFS in finishing diets of steers had little influence on meat discoloration, retail acceptance and Thio-barbituric acid reactive substances. Supplementation of finishing diets for steers with SFS increased content of CLA isomers and vaccenic acid in tissues, without affecting feed conversion efficiency or meat quality, especially when incorporated into silage-free diets.