Effect of sunflower seed supplementation on the fatty acid composition of muscle and adipose tissue of pasture-fed and feedlot finished beef

This study examined the effects of whole sunflower seed (WSS) supplementation on pasture and in finishing diets on the fatty acid profile of muscle [gastrocnemius (GN), longissimus thoracis (LT), intercostals (IQ] and adipose tissue [subcutaneous (SQ), intermuscular (IM)]. Ninety-six yearling steers averaging 410 kg were randomly allocated to three pasture (P) dietary treatments: (1) supplemented with WSS (P-WSS, n = 48); (2) supplemented with cracked barley grain (P-BAR, n = 24), and (3) not supplemented (P-CON, n = 24). Steers rotationally grazed meadow bromegrass-alfalfa pasture for 66 d. After 66 d on pasture, half the steers from each dietary treatment were trucked to a feedlot where they were adjusted to finishing diets. The remaining 48 steers continued with their dietary treatment on stockpiled pasture for an additional 47 d (SD = 11) until they were slaughtered directly off pasture. In the feedlot, half the steers from each pasture dietary treatment were fed either a control (83% rolled barley, 10% alfalfa hay, 5% barley silage, 1% molasses and 1% vitamin/mineral premix; F-CON) or a WSS supplemented diet (68% rolled barley, 15% WSS, 10% alfalfa hay, 5% barley silage, 1% molasses and 1%; F-WSS). Provision of WSS to steers grazing pasture for 113 d followed by direct slaughter increased cis-9, trans-11 CLA content in the muscles by 17.0 to 29.1% (GN, 0.570 vs. 0.467; LT, 0.515 vs. 0.399; IC, 0.531 vs. 0.454 mg 100 mg(-1) fat) and in adipose tissue by 32.0% in IM (0.636 vs. 0.482 mg 100 mg(-1) fat) and 40.3% in SQ (0.839 vs. 0.598 mg 100 mg(-1) fat) fat depots compared with control steer slaughtered directly off pasture. On pasture supplementation of WSS also increased C18:1 trans-11 content in muscle by 20.1 to 40.8% and in IM adipose tissue by 55.0%. The inclusion of WSS in finishing diets increased CLA cis-9 trans-11 content in muscle by 31.5 to 209.0% and in adipose tissue by 40.7% in the SQ fat and 25.6% in the IM fat. It also increased C18:1 trans-11 content in muscle by 80.0 to 207.3% and in adipose tissue by 181% in the IM fat and 224% in the SQ fat. Strong, positive relationships were observed between tissues in the concentration of CLA cis-9 trans-11, C18:1 trans-11 and C18:3 (R-2, 0.69-0.88; P< 0.0001). The results indicate that increasing the dietary polyunsaturated fatty acids in beef cattle diets increased the levels of CLA cis-9 trans-11 and C18:1 trans-11 in muscle and fat tissues.