Abstracts of Original Communications
Proceedings of the Nutrition Society
Grasses and legumes are important to the livestock industry in developing more sustainable and environmentally friendly production systems. Grass is rich in α-linolenic acid and α-tocopherol, which enhances the content of n-3 polyunsaturated fatty acids (PUFA) in beef muscle and has important benefits for colour and shelf life in comparison with feeding grain-rich diets (Wood et al. 1999). The effect of legumes such as white and red clover on meat quality attributes such as fatty acid (FA)
... sition is not well established. The objective of this study was to determine the effects of forage type (grass or grass plus white or red clover) on the FA composition of beef from two breeds, the Welsh Black and Hereford. Forty-eight pure-bred Welsh Black and Hereford steers, average live weight 230 kg, were allocated to each of three forage systems, resulting in eight animals per breed per treatment. Animals grazed a grass sward, a grass/white clover sward or a grass/red clover sward from May to October in the first year and from May in the second year and received silage prepared from the same forage during the intervening winter. Across the study the proportions of grass : clover were approximately 60:40 on a dry matter basis. Animals were slaughtered in the second summer period to achieve a similar level of carcass finish (fat class 4L) across all treatments. Lipids were extracted from longissimus dorsi muscle and fatty acids were analysed by GC. Forage Breed Grass Grass/red clover Grass/white clover SED P Welsh Black Hereford SED P (mg per 100 g muscle) Total intramuscular lipid contents were similar across diets and breeds and averaged 3012 mg/100 g muscle. Muscle contents of trans C18:1 and conjugated linoleic acid (cis-9, trans-11 CLA) did not differ significantly between diet or breed with overall means (mg/100 g muscle) of 85.6 and 16.8, respectively. Similarly the saturated FA, C14:0, C16:0 and C18:0 were not different. Muscle content of C18:2n-6 and C18:3n-3 were increased by 0.35 and 0.21 and 0.14 and 0.17 on inclusion of red and white clover in the diet, respectively, in comparison to grass alone. This contributed towards beneficially higher ratios of polyunsaturated : saturated fatty acids (P:S) on the legumes compared with grass. In contrast, the n-6 : n-3 ratio was lower on grass than on legumes, although on all treatments the ratio (mean 1.39) was less than the recommended target of <2. It is recognised that feeding legumes results in higher dry matter intakes and this, along with reduced feed retention time in the rumen, helps to increase the flow of dietary C18:2n-6 and C18:3n-3 to the small intestine, and consequently higher contents of these fatty acids in beef muscle. The higher amounts of PUFA are highly desirable in terms of human nutrition. Sum of 12:0, 14:0, 16:0 and 18:0; 2 sum of 16:1, 18:1 n-9, 18:1 n-7 and 20:1 One way ANOVA (One way ANOVA with covariates: tissue vitamin E and/or fatness levels did not change the results significantly). The relative concentrations of linoleic and α-linolenic acids in muscle and liver reflected the dietary ratios, with more linoleic in C lambs and more α-linolenic in CG lambs. Thus the 18:2 n-6:18:3 n-3 ratio in muscle and liver of C lambs was above the maximum of 4.0 recommended for the complete human diet compared with the acceptable lower values in the CG lambs. Dietary effects on the valuable EPA and DHA PUFA were less than for linolenic acid and greater in liver than muscle. Lambs fed diet C had better P:S ratios compared with those on the CG diet but they remained below the recommended 0.4. Trans 18:1 was higher in the C fed lambs. Liver contained greater quantities of the n-3 PUFA and a 100 g serving from the CG lambs would meet the daily recommended intake. Adding some silage to the diet of concentrate fed lambs produces "healthier" meat.