Potential effect of cattle diets on the transmission of pathogenic Escherichia coli to humans.

Grain feeding seems to promote the growth and acid resistance of Escherichia coli in fattening beef cattle, and acid-resistant E. coli are more likely to survive the human gastric stomach. When cattle were fed hay for only five days, the number and acid resistance of E. coli decreased dramatically

Microbes Infect 2000 Jan;2(1):45-53

Manipulating meat quality and composition.

Meat quality describes the attractiveness of meat to consumers. The present paper focuses on two major aspects of meat quality, tenderness and flavour. Both aspects of quality can be influenced by nutrition, principally through its effects on the amount and type of fat in meat. In several countries, high levels of intramuscular fat (marbling fat), are deemed necessary for optimum tenderness, although poor relationships between fat content and tenderness have generally been found in European studies, where fat levels are often very low.

Muscle lipid may be a marker for red oxidative muscle fibres which are found at higher concentrations in tender muscles and carcasses. Nutritional treatment can be used to manipulate the fatty acid content of muscle to improve nutritional balance, i.e. increase the polyunsaturated (PUFA): saturated fatty acid value and reduce the n-6:n-3 PUFA value.

When 18:3 levels are raised in lamb and beef because of grass feeding, the intensity of the flavours increases in comparison with grain-fed animals which consume and deposit relatively more linoleic acid (18:2). In ruminants, very high levels of 18:2 produced by feeding protected oil supplements cause the cooked beef to be described as oily, bland or pork-like.

Proc Nutr Soc 1999 May;58(2):363-70

Effects of forage vs grain feeding on carcass characteristics, fatty acid composition, and beef quality in Limousin-cross steers when time on feed is controlled.

Steers were used to compare forage vs grain feeding on carcass composition and palatability attributes of beef when time on feed was controlled. Grain feeding generally increased (P < .01) carcass weight, grade fat, and intramuscular fat content when compared with forage feeding at similar times on feed. Palatability attributes of ribeye roasts and ground beef were generally unaffected (P > .10) by diet with the exception of slightly less beef flavor and more off-flavor in forage-fed vs grain-fed beef. Higher (P < .01) concentrations of linolenic acid and lower (P < .10) concentrations of oleic acid in forage-fed beef may be partially responsible for diet differences in flavor.

J Anim Sci 1998 Oct;76(10):2619-30

Fatty acid composition, including conjugated linoleic acid, of intramuscular fat from steers offered grazed grass, grass silage, or concentrate-based diets

The effects of grazed grass, grass silage, or concentrates on fatty acid composition and conjugated linoleic acid concentrations of fat of steers fed to achieve similar carcass growth rates were investigated. Fifty steers were divided into 10 blocks based on body weight and assigned at random from within blocks to one of five dietary treatments. The experimental rations offered daily for 85 days preceding slaughter were:

• 1) grass silage for ad libitum intake plus 4 kg of concentrate
• 2) 8 kg of concentrate plus 1 kg of hay
• 3) 6 kg of grazed grass DM plus 5 kg of concentrate
• 4) 12 kg of grazed grass DM plus 2.5 kg concentrate
• 5) 22 kg of grazed grass DM

The concentration of polyunsaturated fatty acids (PUFA) in fat was higher (P < .05) for steers offered ration 5 than for those given any other ration. Decreasing the proportion of concentrate in the diet, which effectively increased grass intake, caused a linear decrease in the concentration of saturated fatty acids (SFA) (P < .01) and in the n-6:n-3 PUFA ratio (P < .001) and a linear increase in the PUFA:SFA ratio (P < .01) and the conjugated linoleic acid concentration (P < .001). The data indicate that i.m. fatty acid composition of beef can be improved from a human health perspective by inclusion of grass in the diet.

J Anim Sci 2000 Nov;78(11):2849-55

Factors influencing fatty acids in meat and the role of antioxidants in improving meat quality.

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 (20-50 g/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 poultry where the linoleic, alpha-linolenic and long-chain polyunsaturated fatty acid content responds quickly to raised dietary concentrations. In ruminants the challenge is to increase the P:S ratio while 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. Inpoultry, 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.

Br J Nutr 1997 Jul;78 Suppl 1:S49-60

Fall-weaned calves grazed or were fed different forages during winter followed by 1) N-fertilized tall fescue (Festuca arundinacea Schreb.) grazed alone, 2) bluegrass (Poa pratensis L.)-white clover (Trifolium repens L.) sequence grazed with tall fescue-red clover (Trifolium pratense L.), or 3) bluegrass-white clover sequence grazed with alfalfa (Medicago sativa L.)-orchardgrass (Dactylis glomerata L.). Heifers were supplemented with grain at 1% of BW from April until slaughter in July. One-half of steers were supplemented with grain at 1% of BW from July until slaughter in October.

Remaining steers were fed no grain but were finished on corn silage supplemented with .9 kg of soybean meal per steer daily, from October until slaughter in late January. Including alfalfa-orchardgrass in systems during the finishing phase resulted in higher daily and total gains during the grazing period, and carcasses had more marbling and higher USDA quality grades at slaughter compared with carcasses of cattle on systems using fescue-red clover. Correlation of final weight with carcass characteristics was low (r < .5).

Performance and carcass characteristics were influenced as much or more by forage consumed during the previous wintering phase as by forage fed during the finishing phase. Wintering cattle on stockpiled fescue-alfalfa or alfalfa-orchardgrass hay generally resulted in higher BW at slaughter and more desirable carcass characteristics than systems using tall fescue alone or in combination with red clover. This was particularly notable in steers that grazed without grain until October and were finished on corn silage plus supplement. Final BW and carcass characteristics in all cattle were improved by full season grazing followed by feeding corn silage, compared with cattle finished with grain on pasture

J Anim Sci 1996 Mar;74(3):625-38