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Enhancing the n-3 polyunsaturated fatty acid (PUFA) content of beef is important in view of the generally saturated nature of fatty acids in ruminant meats and the negative effect this can have on human health. This study examined the effects of different sources of dietary n-3 PUFA on the performance of steers and the fatty acid composition of m. longissimus thoracis muscle and associated subcutaneous adipose tissue. Animals were fed ad libitum on grass silage plus one of four concentrates (60:40 forage:concentrate on a DM basis) containing differing sources of lipid: Megalac (16:0), lightly bruised whole linseed (18:3n-3), fish oil (20:5n-3 and 22:6n-3) and a mixture of linseed and fish oil (1:1, on an oil basis). Diets were formulated so that total dietary oil intake was 6 %, approximately half of which was from the experimental test oil. Linseed feeding not only increased the levels of 18:3n-3 in muscle phospholipid from 9´5 to 19 mg/ 100 g muscle but also enhanced the synthesis of 20:5n-3, the level of which increased from 10 to 15 mg/100 g muscle. Linseed also increased the proportion of 18:3n-3 in muscle neutral lipid and in adipose tissue lipids by a factor of 1´64 and 1´75 respectively. Fish oil feeding doubled the proportion of 20:5n-3 and 22:6n-3 in muscle phospholipids. The proportion of 18:1 trans in muscle neutral lipid was higher on the n-3 PUFA diets than the control diet, 0´04 and 0´02 respectively. Despite the implied modification to rumen metabolism, lipid source did not affect feed intake, growth rate, cold carcass weight or carcass fatness, but carcass conformation score was higher on fish oil treatments P , 0´05X However, total muscle fatty acid content was not different between treatments and ranged from 3´5±4´3 % of tissue weight. The increase in n-3 PUFA in the meat produced by feeding linseed or fish oil lowered the n-6:n-3 ratio but had little effect on the P:S ratio.Beef: Fatty acids: Health

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Meat has been identified, often wrongly, as a food having a high fat content and an undesirable balance of fatty acids. In fact lean meat is very low in fat (20-50g/kg), pork and poultry have a favourable balance between polyunsaturated and saturated fatty acids (P : S) and grazing ruminants produce muscle with a desirable n-6:n-3 polyunsaturated fatty acid ratio. In all species, meat fatty acid composition can be changed via the diet, more easily in single-stomached pigs and poultry where the linoleic, a-linolenic and long-chain polyunsaturated fatty acid content responds quickly to raised dietary concentrations. Recent work in pigs has attempted to manipulate the n-6 :n-3 ratio by feeding higher levels of a-linolenic acid (e.g. in rapeseed) or its products eicosapentaenoic acid (20: 5) and docosahexaenoic acid (22 : 6) present in fish oils. In ruminants the challenge is to increase the P : S ratio whilst retaining values for n-6 : n-3 found in cattle and sheep fed on forage diets. The saturating effect of the rumen can be overcome by feeding polyunsaturated fatty acids which are protected either chemically, by processing, or naturally e.g. within the seed coat. Some protection occurs when grain-based or grass-based diets are fed normally, leading to relatively more n-6 or n-3 fatty acids respectively. These produce different flavours in cooked meat due to the different oxidative changes occurring during storage and cooking. In pigs and poultry, high n-3 fatty acid concentrations in meat are associated with fishy flavours whose development can be prevented with high dietary (supranutritional) levels of the antioxidant vitamin E. In ruminants, supranutritional vitamin E delays the oxidative change of oxymyoglobin to brown metmyoglobin and may also influence the characteristic flavours of beef and lamb. Meat: Fatty acids: AntioxidantsIn recent years awareness of the importance of diet in human health has increased. Many authorities have recommended that the contributions of fat and especially saturated fatty acids to dietary energy intake should be reduced. In the UK recent recommendations are 35 % of energy for fat and 10 % of energy for saturated fatty acids (Department of Health, 1994). Within these general guidelines more particular advice is to reduce the intake of short-and medium-chain saturated fatty acids and the intake of n-6 polyunsaturates relative to n-3 (Gibney, 1993). Although it is the dietary balance of fatty acids in the total diet which is physiologically important, attempts have been made with many individual foods to change them in line with the new dietary guidelines in order to make them more attractive to consumers. The present paper considers the options for meat, a food which has been criticized on the grounds of its fat and fatty acid content. FAT AND FATTY ACID COMPOSITION OF RED MEATSA recent study by Bristol University investigated the fat content and composition of steaks or chops from equivalent parts of the carcass (the loin) in beef, lamb and pork. The results (Table 1) showed t...