Effect of Growth Rate on Beef Fatty Acid Profile from Hereford Steers Finished Either on Pasture or in Feedlot

Different nutritional management during the rearing and finishing period can determine changes on beef fatty acid (FA) profile. Beef lipid composition was quantified in 224 male Hereford calves, weaned at 8 months of age with an average initial live weight (LW) of 170±17 kg. After weaning, 4 nutritional treatments were imposed to obtain different daily liveweight gains (LWGs, kg/day) during the first winter. Nutritional management groups were: high LWG in feedlot (HF); low LWG in feedlot (LF); high LWG in pasture (HP); low LWG in pasture (LP). Finishing phase began when each group reached a mean liveweight (LW) of 350±28 kg. During the finishing phase, one half of the HF, LF, HP and LP animals were finished on pasture and the other half in feedlot. The animals were slaughtered when each treatment attained a mean LW of 500 kg. Analysis of beef FA was performed by extraction, metilation from longissimus muscle and the FAs were quantified using a gas chromatography. The statistical model included the groups at growing phase (HF, LF, HP and LP) and the groups at finishing phase (feedlot or pasture), the interaction between growing and finishing phase as fixed effects and LW at the beginning of the finishing phase as covariable. Tukey test was applied to compare the means (P<0.05). There was interaction between the growing and finishing phase for miristic and conjugated linoleic acid (CLA cis 9, trans 11). Animals from HF finished on pasture presented the highest concentration of miristic (2.54%) when compared to the other treatments. LP and HP finished on pasture had more CLA cis 9, trans 11 on their beef composition (0.60% and 0.58%, respectively), while animals finished in feedlot presented the lowest concentrations (average of 0.28%). Finishing phase affected the FAs profile (P<0.05). Higher concentrations of palmitic, oleic, and linoleic acid on beef from animals finished in feedlot were observed than did those finished on pasture. However, the beef from animals finished on pasture presented high concentrations of stearic, docosapentaenoic DPA and docosaexaenoic DHA acid. Animals finished on pasture had higher concentrations of linolenic acid, arachidonic, and eicosapentaenoic acid compared to those finished in feedlot. Interestingly, LP presented higher concentrations of linolenic and eicosapentaenoic acid, regardless of the finishing phase. The same results were observed in LF group for arachidonic. In general, the LP and HP groups finished on pasture resulted in healthy beefs, with greatest CLA and omega 3 concentrations.