The effects of high-concentrate diets and pasture on the concentration of conjugated linoleic acid in beef muscle and subcutaneous fat

In view of the evidence indicating several potential benefits of high intakes of conjugated linoleic acid (CLA) on human health, an experiment was conducted to examine the effects of the diet of beef cattle on the total CLA concentration in muscle and subcutaneous fat. High-concentrate [steers consumed 515 g concentrates and 485 g grass silage kg(-1) dry matter (DM) for 8 weeks followed by 887 g concentrates and 113 g grass silage kg(-1) DM for 14 weeks until slaughter] and high-forage (steers consumed 803 g grass silage and 197 g concentrates kg(-1) for 8 weeks followed by grass silage only for 10 weeks and then grazed perennial ryegrass-based pasture for 23 weeks until slaughter) treatments were imposed on 48 steers, which were crosses of continental beef breeds (initially 414 kg live weight) The concentrates were based on barley, extracted soyabean meal, molassed sugarbeet pulp and maize meal. The silages were of medium to low digestibility and contained 117-137 g crude protein kg(-1) DM and 83-158 g ammonia-N kg(-1) total N. The pasture was of high quality and contained 168 g crude protein, 234 g acid-detergent fibre and 222 g water-soluble carbohydrate kg(-1) DM. Samples of muscle were taken post slaughter from the m. semimembranosus, m. gluteobiceps, m. longissimus and m. deltoideous muscles, and subcutaneous fat was taken from over the m. longissimus . Concentrations of total CLA in the tissues were for the high-concentrate and high-forage treatments, respectively (mg 100 g(-1) fresh tissue), m. gluteobiceps 18 and 47 (s.e. 3.5); m. semimembranosus 9 and 20 (s.e. 1.6); m. longissimus 15 and 35 (s.e. 3.2), m. deltoideous 20 and 59 (s.e. 4.3); subcutaneous fat 584 and 1975 (s.e. 138.7). It is concluded that muscle and subcutaneous fat tissue from grass-fed cattle contained three times as much CLA as those from concentrate-fed cattle, and that the consumption of beef from grass-fed cattle should be effective in increasing the intake of CLA by humans.