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| Intramuscular
vs. dissected body fat in grass fed streers |
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| P. T. GARCIA and J. J. CASAL Instituto de Tecnologia de Carnes, CICV,INTA. CC 77, 1708 Moron, Buenos Aires, Argentina. |
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Summary The intramuscular.fat percentages (MF%) were determined in Biceps brachii (BB), Semitendinosus (ST) , Longissimus dorsi (LD) and Psoas major (PM) muscles from 340 grass fed steers of different breed types, at slaughter weight, relating the MF% to total dissected carcass fats (TDF). The average MF% were 2.7 -/+ 0.98; 1.7 -/+ 0.66; 2.9 -/+ 1.4 and 4.1 -/+ 1.58 for BB, S, LD and PM respectively. The 69% of the ST muscles have less than 2% of MF and the 81% of LD muscles less than 4% of MF. There are differences in relative growth among depots. The MF in LD and PM muscles grow at faster rates (p<0.5), relatively to TDF than in S or BB muscles. Introduction The intramuscular (marbling) fat influences the eating quality of beef and also is a very important aspect of its consumption as a result of the relation between dietary lipids and the on.set of cardiovascular diseases ( LRCP, 1984). The relationship between marbling and beef meat quality has also commercial importance and needs to be considered in any beef meat production system. Several studies have found a lower intramuscular fat content in meat from grass fed steers compared with meat from grain fed animals (Marmer et al., 1984; Westerling & Hedrick, 1979). This fact could be favorable for grass beef meat production systems if the meat quality is adequate. The relationship between intramuscular fat content and total body fat in the bovine is not well known. This lack of information is due to difficulties in the determination of the amounts of intramuscular fat. A further understanding of lipid deposition patterns in the bovine is needed, so that improved food products can be developed. The purpose of this paper was to determine the intramuscular fat percentages of four muscles from 340 grass fed steers of different breed types at slaughter weights, relating the intramuscular fat content to dissected body fats. Materials and Methods Three hundred and forty A. Angus and crosses of A.A. with Charolais, Holando, Nellore, Criollo and Limousine steers, placed on full feed on a mixed pasture of rye grass and white clover, were considered. Since the animals were managed and fed in the same way, no differences due to diet were expected. At the end of the trial the steers were slaughtered at the Castelar abattoir of INTA, after 24 h with water only. The left side of each carcass was chilled at 1ƒC until the total dissection was performed. The total weight of dissected fat (TDF) in the half carcass was calculated as the sum of the weights of the different fat depots. Carcass sampling: Mm Biceps brachii(BB) and Semitendinosus (ST): The total muscles minced and aliquot samples -/+ 200 g kept from each at -20ƒC until the analyses were performed. Mm Longissimus dorsi (LD) and Psoas major (PM) slices of -/+ 150 g from the middle of the muscles were minced and kept at -20ƒC until the analysis were performed. Two aliquot samples of 10g each from the minced muscles were extracted to determine the total amount of chemical fat according to the official Method of the British Standards Institution, 1958. The data were processed statistically by the NWASTATPAK Program, Northwest Analytical, Inc Portland Oregon USA. The allometric equation proposed by Huxley (1932) was used in the form l n y = l n a + b l n x to estimate the growth coefficient (b) of the part (y) relative to the whole (x). In the present study the part (x) was TDF and MF weights or % TDF and the part (y) subcutaneous fat (SCF), intermuscular fat (IMF), kidney fat (KF) and intramuscular fat (MF). Heterogeneity of standard errors of the various growth coefficients was taken into account by use of the Behrens-Fisher test in comparisons of growth rates (Berenson et al., 1983). Results and Discussion Means, standard deviation, coefficients of variation (%) and minimum and maximum values for slaugther weight, age, left side weight, left side fat weight and per cent of carcass fat for the total steer population (n=340) are shown in Table 1. The left side fat weight ranged from 7.2 to 54.1 kg and because of this wide range it was possible to examine the allometric growth rates of the individual fat depots and the MF in the four muscles in relation to the growth of TDF and its percentage. Means, standard deviation, coefficients of variation (%) and minimum and maximum values for % of intramuscular fat in the Mm Biceps brachii, Semitendinosus, Longissimus dorsi and Psoas maior are presented in Table 2. The distribution of the four muscles according to the % MF are shown in Fig.1: 69% of M. Semitendinosus had less than 2% of MF and 81% of M. Lonnissimus dorsi less than 4% of MF. Average values for % MF according to % TDF are shown in Table 3. These values are lower than the values given recently by The National Research Council (1988) for several USA beef cuts and grades. Marmer et al (1984) has also demonstrated that tissues from grass fed steers are leaner than tissues from grain fed steers. Crouse et al (1984) found that carcasses from grass fed heifers possessed lower (p<0.05) marbling scores than carcasses from grain fed heifers at 0.96 cm 12th rib fat thickeness. Smith et al (1977), Westerling & Hedrick (1979) found similar effects of the dietary regimen in the amounts of marbling. The sample correlation coefficients between MF % in the four muscles studied and TDF % are shown in Table 4. The values were similar to those detected previously for the authors (Garcia et al., 1986). Prediction of MF % considering only TDF % is not accurate enough at least in grass pasture systems. Considerable economic significance is attached not only to the total amount of carcass fat, but also to the relative amounts of fat deposited in particular carcass depots. The growth coefficients (b) for MF content in the four muscles relative to TDF are given in Table 5. These results indicated differences in relative growth among depots. The MF in LD and PM muscles grew at faster rates (p< 0.05) then in ST and BB muscles. Conclusions There are significant differences in relative growth of intramuscular fat among the studied muscles. The intramuscular fat growth faster in Longissimus dorsi and Psoas major than in Biceps brachii or Semitendinosus muscles. Prediction of intramuscular fat considering only total dissected fat weight is not accurate enough in grazing steers. Table 1. Some characteristics of the steer population (n=340). Mean (x), standard deviation (SD), coefficient of variation (CV %) and minimum and maximum values (Min-max).
Table 2.Percentages of muscular fat (MF%) of Mm Biceps brachii (BB), Semitendinosus (ST), Longissimus dorsi (LD) and Psoas major (PM). Mean (x), standard deviation (SD), Coefficient of variation (CV%) and minimum and maximum values (min-max).
Table 3. Average values of MF% according to the TDF% in the four muscles.
a, b, c, d, Values in rows with different letters differ (p < 0.05). Table 4. Simple correlation coefficients between TDF % and MF % in the four muscles studied.
Table 5. Growth coefficients (b) for MF(g) in BB, ST, LD and PM muscles relative to TDF, SB, IM, K and TDF %.
Distribution of MF% in the Mm BB, ST, LD and PM (n = 340) 38 th ICoMST Clermont-Ferrand France 1992 pag.57-60 References Animal Product Options in the Marketplace. In "Designing Foods". National Research Council USA. 1988. BERENSON M.L., LEVINE D.M and GOLSTEIN M., 1983. Intermediate Statistical Methods and Applications. Prentice. Hall Inc., Englewood cliffs, New Jersey 0762. BRITISH STANDARDS INSTITUTION, 1958. British Standard 684, London. CROUSE J.D., CROSS H.R. and SEIDEMAN S.C., 1984. Effect of a grass or grain diet on the quality of three beef muscles. J. Anim. Sci. 58,619-625. GARCIA P.T., CASAL J. J. and PARODI J.J., 1986. Effect of breed-type on the relationships between intramuscular and total body fat in steers. Meat Sci. 17,283-291. Lipid Research Clinics Coronary Primary Prevention Trial Results (LRCP), 1984. J. A.Mer. med. Assoc. 251,351-364; 365-374. MARMER W.M., MAXWELL R.J. and WILLIAMS J.E., 1984. Effects of dietary regimen and tissue site on bovine fatty acid profiles. J. Anim. Sci. 59,109-121. SMITH G.M., CROUSE H.D., MANDIGO R.W. and NEER K.L., 1977. Influence of feeding regime and biological type on growth, composition and palatability of steers. J. Anim-.Sci. 45,236-241. WESTERLING D.B. and HEDRICK H.B., 1979. Fatty acid composition of bovine lipids as influenced by diet, sex and anatomical location and relationship to sensory characteristics. J.Anim. Sci. 48,1343-1348. |
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