Submitted to: Professional Animal Scientist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 6, 2012
Publication Date: April 2, 2012
Citation: Noviandi, C.T., Ward, R.E., Zobell, D.R., Stott, R.D., Waldron, B.L., Peel, M., Eun, J.S. 2012. Fatty acid composition in adipose tissue of pasture and feedlot-finished beef steers. Prof Animal Sci. 28:184-193. Interpretive Summary: Angus crossbred steers were used to evaluate the effects of pasture vs. feedlot-finishing on fatty acid composition of fat directly under the skin. Treatments included grazing tall fescue without nitrogen fertilizer, grazing tall fescue with nitrogen fertilizer, and feeding a feedlot total mixed ration for 16 weeks. Total fat concentration on the pasture fed steers did not differ due to fertilization. Similar total fat concentration was observed between pasture and feedlot fed steers on week 12 and 16. Steers from the nitrogen fertilized pastures showed increased C18:3 n-3 linolenic acid and polyunsaturated fatty acids concentrations throughout the study and increased conjugated linoleic acids (CLA) during later weeks of the study. Furthermore, pasture-finished steers had higher concentrations of C18:0, cis-9, trans-11 CLA, and linolenic throughout compared to the feedlot fed steers. However, C18:1 cis-9 and C18:2 n-6 linoleic acid concentrations of pasture-finished steers were lower compared to feedlot steers throughout study. While no effect was detected in fatty acid families due to nitrogen fertilization of pastures, higher saturated fatty acids and lower mono-unsaturated fatty acid were observed in pasture-finished steers on weeks 4, 12, and 16 than feedlot steers. Grazing on TF pasture elicited positive fatty acid composition; however, when carcass quality grading standards are considered pasture-finished steers had less back fat, rib fat, and ribeye area than feedlot-finished steers.
Technical Abstract: Twenty-seven Angus crossbred steers were used to evaluate the effects of N fertilization on pasture- vs. feedlot-finishing beef steers on fatty acid (FA) composition in subcutaneous adipose tissue. A completely randomized design with repeated measures was used with steers arranged into 3 treatments: grazing on tall fescue (TF) without N fertilizer (TF-NF), grazing on TF with N fertilizer (TF+NF), and feeding TMR on feedlot (FLT). Three replicated pastures or group pens with 3 steers per replicate were assigned into each treatment. A total of 168 kg/ha N fertilizer was applied in 3 split applications at 56 kg/ha to the TF+NF. From May through September 2010 (total 16 wk), pasture-finished steers were grazed on replicated 0.47-ha paddocks, while steers on the FLT were fed a typical finishing diet containing 76% barley grain. Adipose tissue biopsies were obtained on wk 4, 12, and 16. Total fat concentration in the TF pastures did not differ due to N fertilization, and similar total fat concentration was also detected between TF pastures and the FLT on wk 12 and 16. Nitrogen fertilization increased C18:3 n-3 and PUFA concentrations in TF pastures on all sampling dates (P<0.01). Applying N fertilizer to TF increased C18:0 on wk 12 and 16 and cis-9, trans-11 CLA on wk 16 (P<0.02). Pasture-finished steers had higher concentrations of C18:0, cis-9, trans-11 CLA, and C18:3 n-3 throughout grazing compared to those on the FLT treatment (P<0.01). However, C18:1 cis-9 and C18:2 n-6 concentrations in adipose tissue of pasture-finishing steers were lower compared to FLT steers throughout study (P<0.02). While no effect was detected in FA families in adipose tissue of beef steers due to N fertilization on TF pasture, higher SFA and lower MUFA and n-6:n-3 ratio were observed in pasture-finished steers on wk 4, 12, and 16 compared to FLT steers (P<0.01). Grazing on TF pasture elicited positive FA composition in adipose tissue; however, carcass quality and grading standards should be considered as TF pasture-finished steers had less back fat, rib fat, and ribeye area compared to feedlot-finished steers (P<0.04).