Feeding steers extruded flaxseed and hay in a total mixed ration or sequentially can have substantial effects on beef fat polyunsaturated fatty acids and biohydrogenation intermediates.

There has been growing interest in increasing the content of polyunsaturated fatty acid (PUFA; esp. α-linolenic acid, ALA) and their biohydrogenation intermediates (BHI) in beef, particularly trans 11–18:1 (VA, vaccenic acid) and cis 9, trans 11–18:2 (RA, rumenic acid) due to their potential positive health effects. However, high variability in PUFA and BHI have been found in beef between and within trials. The present trial was designed to determine if feeding steers extruded flaxseed (Linpro-R™; O&T Farms Ltd., SK, Canada) and hay (25% and 75%; DM basis) together as a total mixed ration (TMR), or sequentially (non-TMR) would result in different enrichments of PUFA and BHI in different beef adipose tissues. Forty-eight Continental crossbred steers (325 ± 16 kg SD) were stratified by weight to 6 pens of 8 steers, pens were randomized to either TMR or non-TMR and steers were fed ad libitum for 240 d. At slaughter, subcutaneous fat (SCF) and perineal fat (PRF) samples were collected, freeze dried and directly methylated with 0.5 M sodium methoxide, and analyzed by GC using a 100 m CPSil 88 capillary column. Data were analyzed as a one-way ANOVA using the PROC MIXED procedure of SAS with diet as the main factor and pen as the experimental unit. Treatment means were generated and separated using the LSMEANS and PDIFF options, respectively. Compared to TMR steers, non-TMR steers had greater proportions of PUFA, trans-18:1, conjugated linoleic acids, and conjugated linolenic acids in both SC (+9.7%, +9.8%, +43.4%, +63.7%) and PR (+14.1%, +10.5%, +52.9%, +75.6%). In SCF, the percentages of ALA, VA and RA were increased (P < 0.001) from 0.91%, 4.92% and 1.91% in TMR steers to 1.10%, 6.82% and 2.69% in non-TMR steers. In PRF, the percentages of ALA, VA and RA were increased (P < 0.001) from 0.89%, 7.29% and 0.72% in TMR steers to 1.06%, 10.32% and 1.13% in non-TMR steers. Our results suggest that the method of feeding PUFA sources (e.g., flaxseed) can profoundly affect the enrichment of PUFA and their BHI in beef fat. In addition, the enrichment of these fatty acids also depends on fat depot, with PRF having greater proportions of VA, while SCF being higher in RA, which is likely due to the greater delta-9 desaturation of VA to RA in SCF.