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Compared development of intermuscular and subcutaneous fat in carcass and primal cuts of growing pigs from 30 to 140 kg body weight
Meat Science 81 (2009) 270–274
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Meat Science journal homepage: www.elsevier.com/locate/meatsci
Compared development of intermuscular and subcutaneous fat in carcass and primal cuts of growing pigs from 30 to 140 kg body weight M. Kouba *, M. Bonneau UMR1079, INRA-Agrocampus Rennes Systèmes d’Elevage Nutrition Animale et Humaine, F-35590 Saint Gilles, France
a r t i c l e
i n f o
Article history: Received 22 January 2008 Received in revised form 9 July 2008 Accepted 2 August 2008
Keywords: Pigs Lipids Subcutaneous fat Intermuscular fat Growth Development
a b s t r a c t A total of twenty two Large White X Landrace castrated males were slaughtered at 30, 70, 110 or 140 kg BW. Carcasses were weighed and cut into four primal cuts (belly, ham, loin, and shoulder). Each cut was weighed and dissected into bone, muscle, skin, and intermuscular and subcutaneous adipose tissues. Kidney fat was also taken and weighed. Kidney fat grew more rapidly than subcutaneous or intermuscular fat averaged over all four cuts. In the shoulder and loin, about one third of total adipose tissue was in the intermuscular fraction. In the belly, there was as much (in 30–110 kg BW pigs) or more (in 140 kg BW pigs) intermuscular than subcutaneous adipose tissue. In the ham, the intermuscular fraction of adipose tissue grew more slowly than the subcutaneous one, so that it represented less than one fourth of total ham adipose tissue in 140 kg BW pigs. Intermuscular adipose tissue exhibited a lower lipid content than subcutaneous adipose tissue, whatever the body weight, but the differences in lipid content between the adipose tissues decreased with increasing weight. These results show that the relative development of intermuscular and subcutaneous adipose tissues differs according to anatomical location. Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction Reduction of fat deposition has been a major goal in the continuing improvement of pork production for many years. Selection and breeding for meat-producing qualities in animals is based on the fact that as the animal grows up, the proportions of the body change, and that these changes involve changes in the composition of the animal, that is, in the proportions of muscle and fat, which are required for human food purposes (Hammond, 1947). The selection for leaner carcasses, based on the reduction of subcutaneous fat, has led to a decrease in total fat (Cliplef & McKay, 1993; Nguyen, MacPhee, & Wade 2004). Carcass fat is deposited in different anatomical locations as subcutaneous, visceral, intermuscular (between muscles) or intramuscular (within muscle) fat. These various deposits do not have the same importance for carcass and meat quality. Visceral and subcutaneous fats can be easily trimmed off the lean meat that is delivered to the consumers, whereas in most instances, intermuscular fat cannot be removed from some joints without mutilating them. Therefore, intermuscular fat content has a high impact on consumer acceptability of meat commodities containing several muscles, such as pork chops or ham slices. Although of major commercial importance, the partition of fat between depots and its distribution through the carcasses of meat animals have commanded little attention from research workers (Fisher, Green, Whittemore, Wood, & Schofield, * Corresponding author. Tel.: +33 0223485367; fax: +33 0223485900. E-mail address: [email protected] (M. Kouba). 0309-1740/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.meatsci.2008.08.001
2003; Kempster & Evans, 1979; Wood & Riley, 1982; Wood, Whelehan, Ellis, Smith, & Laird, 1983) in comparison with other aspects of growth and development. In particular, very few studies have been carried out on the development of intermuscular fat in pigs. There is a need for a better understanding of the relative development of intermuscular fat relative to other fat deposits, in the carcass and the different primal cuts (belly, ham, loin, and shoulder). The aim of the present study was to describe the development of subcutaneous, intermuscular and kidney fats in the carcass and in primal cuts of pigs from 30 to 140 kg live BW. 2. Material and methods 2.1. Animals, experimental design, and measurements Twenty two castrated male pigs Large White X Landrace from 20 sows from the INRA experimental herd were used in the study. The pigs were housed in individual pens in environmentally controlled buildings under normal husbandry conditions. The animals were reared in compliance with national regulations on the humane care and use of animals in research. Pigs were fed ad libitum a standard diet for commercial slaughter pigs. The diet was based on wheat, barley, maize and soybean meal and contained 17.7% of crude protein and 13.7 MJ of DE/kg. Fresh water was freely available. Animals were individually weighed each week, and before slaughter around 30 kg (n = 4), 70 kg (n = 4), 110 kg (n = 9), or 140 kg (n = 5). Corresponding ages, actual live weight and carcass weight (mean ± sem) were 78.8 ± 0.5, 127.3 ± 0.3, 165.8 ± 1.6 and
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206.6 ± 2.7 days, 29.6 ± 0.8, 71.4 ± 0.9, 108.3 ± 1.1 and 140.1 ± 1.1 kg live weight, 10.9 ± 0.3, 25.0 ± 0.3, 39.5 ± 0.4 and 52.6 ± 0.5 kg carcass weight (weight of the dissected half carcass). At slaughter, after approximately 16 h of fasting, (without feed but with water), the animals were electrically stunned and bled. Internal organs (heart, lungs, liver, spleen, digestive and reproductive tracts) were removed. After 24 h chilling at 4 °C, the head, feet, kidneys, kidney fat and tail were separated from the carcass. The left side of each carcass was weighed, and cut into four anatomically defined primal cuts (belly, ham, loin, and shoulder) according to Metayer and Daumas (1998). The cuts were weighed and each of them was subsequently physically dissected into six tissue fractions, skin, bone, muscle, subcutaneous fat, intermuscular fat, and miscellaneous (tendons, aponevroses, lymph nodes, glandular tissue, and possible remnants of nerves and blood vessels). Weights of the tissue fractions of each cut were recorded. Prior to tissue dissection, 30 g muscle samples and 20 g adipose tissue samples were taken from the individual cuts. The weight of samples was added to the weight of corresponding dissected tissues. A sample of kidney fat was also taken. 2.2. Analytical methods for the determination of tissue composition Samples of muscles were analyzed for dry matter and protein concentrations, according to Association of Official Analytical Chemists (AOAC) (2006). The lipids were extracted from muscle and adipose tissue samples, using the chloroform/methanol method procedure of Folch, Lees, and Stanley (1957). 2.3. Calculations and statistical analyses Analyses of variance and linear regressions were performed, using the GLM and REG procedures of SAS (SAS, 1999), respectively. Allometric analyses of the development of fat depots in the carcass (Table 1) were conducted by calculating the linear regressions of log transformed fat depot weights on log transformed carcass weight, muscle weight in the carcass or total fat weight in the carcass, using the following model developed by Huxley (1932)
log y ¼ b log x þ log a; where a is a constant and b is the allometric coefficient when b = 1, the rate of growth of fat depots is similar to the independent variable, whereas when b < 1 or when b > 1, the growth of fat deposits is, respectively, slower or faster than the growth of the independent variable. An analysis of variance was conducted with a model including the effects of fat depot, carcass weight (as co-variable) and the interaction between fat depot and carcass weight. The interaction was considered for testing the significance of differences in regressions slopes between fat depots. Allometric analyses of the devel-
Table 1 Allometric developmenta of subcutaneous, intermuscular, and kidney fat relative to carcass weight, muscle, and total fat in the carcass Allometry relative to item Carcass weight Muscle Total fat
Fat depot Subcutaneous
Intermuscular
Kidney
1.47y 1.62y 1.00y
1.42y 1.57y 0.96y
1.93z 2.13z 1.31z
Diff. btw fat depotsb *** *** ***
***, P < 0.001. y,z Within line, values not followed by the same superscript differ (P < 0.05). a Slope of the regressions of ln(fat depot weight) on ln(carcass weight), ln(muscle weight in the carcass), or ln(total fat weight in the carcass). b Significance of differences in regressions slopes between fat depots.
Table 2 Allometric developmenta of subcutaneous and intermuscular fat relative to cut weight, muscle and total fat in the four primal cuts Allometry relative to item Cut weight
Muscle weight in the cut
Total fat weight in the cut
Fat depot
Diff. btw fat depotsb
Cut
Subcutaneous
Intermuscular
Belly Shoulder Ham Loin Diff. btw cutsc
1.25y 1.48x 1.55x 1.48x **
1.34xy 1.49x 1.21y 1.37x *
NS NS ***
Belly Shoulder Ham Loin Diff. btw cutsc
1.43 1.63 1.65 1.65 NS
1.57x 1.65x 1.30y 1.54x *
NS NS **
Belly Shoulder Ham Loin Diff. btw cutsc
0.97 1.00 1.07 1.02
1.03x 1.00x 0.82y 0.94x **
NS NS *** *
NS
NS
x,y NS, P > 0.10; , P < 0.10; *, P < 0.05; **, P < 0.01; ***, P < 0.001. Within fat depot and item, values in the same row not followed by the same superscript differ (P < 0.05). a Slope of the regressions of ln(fat depot weight) on ln(cut weight), ln(muscle weight in the cut), or ln(total fat weight in the cut). b Significance of differences in regression slopes between fat depots, within cut. c Significance of differences in regression slopes between cuts, within fat depot.
opment of fat depots in the various primal cuts (Table 2) were conducted in a similar way. Analyses of variance were conducted within each fat depot with a model including the effects of cut, cut weight (as co-variable) and the interaction between cut and cut weight. The interaction was considered for testing the significance of differences in regressions slopes between cuts (Table 2). Similar analyses were conducted with muscle weight or total fat weight as co-variable. Changes with weight in the composition of muscle (Table 3) and adipose tissue (Table 4) samples were analysed by calculating allometric regressions of composition parameters on carcass weight. For each parameter, analyses of variance were performed with a model including the effect of sample, carcass weight (as co-variable) and the interaction between sample and carcass weight. The interaction was considered for testing the significance of differences in regression slopes between samples.
Table 3 Slopes of the regressions of log transformed muscle composition parameters on log transformed carcass weight Muscle samples
Dry matter contenta c
Signif. Belly_RA Shoulder_SS Ham_SM Ham_AD Loin_Ant_LD Loin_Ant_TR Loin_Mid_LD Loin_Mid_PS Diff. btw slopese
*** *** *** *** *** *** **
d
Lipid contenta
Slopes
Signif.
0.072 0.099 0.099 0.035 0.094 0.134 0.073 0.084
*** ** *** NS * *** ** *
c
Protein contentb d
Slopes
Signif.
0.390y 0.310y 0.646y 0.057z 0.305yz 0.576y 0.397y 0.292yz **
NS ** * NS *** NS NS
c
Slopesd -0.017x -0.014x -0.070yz 0.015w -0.012wx -0.107z -0.019xy 0.000wx ***
NS, P > 0.10; , P < 0.10; *, P < 0.05; **, P < 0.01; ***, P < 0.001. a % of fresh weight. b % of dry matter weight. c Significance of the regressions. d Slopes of the regressions. e Overall significance of differences in slopes between samples; w, x, y, z, slopes within column affected the same letter did not differ significantly at the 5% level.
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Table 4 Slopes of the regressions of log transformed adipose tissue lipid contents on log transformed carcass weight Adipose tissue samples
Lipid contenta Signif.b
Slopesc
Belly_IM Shoulder_IM Ham_IM Loin_Ant_IM Loin_Mid_IM Loin_Mid_SC Kidney fat Diff. btw slopesd
*** *** *** *** ** *** **
0.444x 0.196y 0.367x 0.406x 0.382x 0.124yz 0.093z ***
NS, P > 0.10; , P < 0.10; *, P < 0.05; **, P < 0.01; ***, P < 0.001. a % of fresh weight. b Significance of the regressions. c Slopes of the regressions. d Overall significance of differences in slopes between samples.; w, x, y, z, slopes within column affected the same letter did not differ significantly at the 5% level.
3. Results 3.1. Allometric development of subcutaneous, intermuscular and kidney fats The slopes of the allometric growth of subcutaneous and intermuscular fats in the carcass did not differ significantly (Table 1) and they were significantly lower than that of kidney fat (P 6 0.001). In the shoulder and belly, the slopes of the allometric growth of subcutaneous and intermuscular fats did not differ significantly, whatever the item relatively to which they were calculated (Table 2). In the loin, the slopes did not differ when calculated relatively to loin weight or muscle weight in the loin. The slope was however, significantly lower for intermuscular than for subcutaneous fat when calculated relatively to total fat in the loin (P = 0.04). In the ham, the slopes of the allometric growth of intermuscular fat were significantly lower than those of subcutaneous fat (P 6 0.005). The slope of the allometric growth of subcutaneous fat relative to primal cut weight was significantly lower in the belly than in the other three cuts (P < 0.025). However, they did not differ significantly between cuts, when calculated relatively to muscle or total fat weights in the cuts. The slopes of the allometric growth of intermuscular fat were significantly lower in the ham than in the other three cuts (P < 0.05). However, they did not differ significantly between ham and belly when calculated relatively to cut weight (P = 0.09). 3.2. Changes in the proportions of intermuscular and subcutaneous fats in carcass or primal cut weights during growth
times, from 14.4% to 26.8%. The belly is the only cut where proportions of intermuscular and subcutaneous fats are similar in the 30 kg live weight pigs and where the intermuscular fat proportion is higher than the subcutaneous fat one in 140 kg live weight pigs. 3.3. Weight-related changes in the composition of muscle and adipose tissue samples Dry matter content increased significantly with carcass weight in all muscle samples, with the exception of Ham_AD (P = 0.10) (Table 3). The slopes of the regressions of dry matter content on carcass weight did not differ significantly between samples. Lipid content increased significantly with carcass weight in all muscle samples, with the exception of Ham_AD (P = 0.49). The slopes of the increase in lipid content did not differ significantly between the 7 samples where the regression was significant. Protein content increased significantly with carcass weight in Ham_AD, decreased significantly in Ham_SM and Loin_Ant_TR, and did not change significantly with weight in the remaining 5 samples. Lipid content increased significantly with carcass weight in all adipose tissue samples (Table 4). The slopes of the increase in lipid content were significantly higher in Belly_IM, Loin-Ant_IM, Loin_Mid_IM and Ham_IM, than in Shoulder_IM, Loin_Mid_SC and kidney fat. It was also significantly higher in Shoulder_IM than in kidney fat. The higher slopes in intermuscular adipose tissue samples were associated with significantly lower lipid content at low carcass weight (P < 0.001; Fig. 1), so that lipid contents were similar in all adipose tissue samples at 140 kg live weight (P = 0.06) whereas there were significant differences between samples at lower weights (P < 0.001). 4. Discussion There is very little available published information on the compared development of the various adipose tissues in the different joints. Many experiments on growth and body composition of pigs have been carried out in serial slaughter trials in which pigs were slaughtered at defined body weights or ages (Kouba, Bonneau, &
Lipid content (% of fresh weight) 110
70
30
140
90 Loin_Mid_SC 80 Kidney 70 Shoulder_IM
The proportion of total fat in carcass weight increased from 16.1% at 30 kg to 33.6% at 140 kg live weight. A twofold increase was observed for the proportions of subcutaneous (from 10.2% to 20.5%) and intermuscular (from 5.4% to 10.6%) fats, whereas a four fold increase was measured for the proportion of kidney fat, (from 0.6% at 30 kg to 2.5% at 140 kg). The changes in the proportions of fats in the shoulder and loin were very similar to those observed in the carcass, a two fold increase being observed for both intermuscular and subcutaneous fats between 30 and 140 kg. In the ham the proportion of subcutaneous fat increased 2.2 times from 7.8% to 17.2% between 30 and 140 kg, whereas that of intermuscular fat augmented only 1.4 times from 3.6% to 5.1%. The reverse was observed in the belly where the proportion of subcutaneous fat increased only 1.4 times from 15.8% to 22.4%, whereas intermuscular fat augmented 1.9
60
50
40
Ham_IM
Belly_IM
Loin_Mid_IM
Loin_Ant_IM
30 10
20
30
40
50
Half carcass weight (kg) Fig. 1. Allometric regressions lines of the lipid content of the various adipose tissue samples on half carcass weight. The bold horizontal lines indicate the range of variation of individual half carcass weights at 30, 70, 110 and 140 kg live weight. All regressions were highly significant (P < 0.01).
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Noblet, 1999; Quiniou & Noblet, 1999; Wagner, Schinckel, Chen, Forrest, & Coe, 1999). In most studies, however, only overall fatness or overall lean content have been measured (Gu, Schinckel, & Martin, 1992; Schinckel, Preckel, & Einstein, 1996; Schinckel, Wagner, Forrest, & Einstein, 2001; Swantek, Marchello, Tilton, & Crenshaw, 1999). Kolstad (2001) considered total subcutaneous and intermuscular adipose tissues in the carcass, but not their distribution in individual joints. Earlier studies (Davies & Pryor, 1977; Kempster, 1980; Kempster & Evans, 1979) described the intermuscular fat growth in relation to the body weight. They found that the intermuscular fat growth was slower than the growth of subcutaneous adipose tissue and the kidney fat (with b = 0.972 against b = 1.007 and b = 1.077, respectively, for Davies and Pryor, and b = 0.87 against 1.01 and 1.24, respectively, for Kempster and Evans). However, in our present study, the growth of subcutaneous adipose tissue in relation to the carcass weight was similar to the growth of intermuscular fat (with b = 1.47, and 1.42, respectively), which is not in accordance with these earlier studies. As demonstrated by (Davies & Pryor, 1977; Kempster & Evans, 1979), in the present work, kidney fat exhibited the fastest growth (b = 1.93). In more recent studies dealing with tissue composition of a joint (Fisher et al., 2003; Mohrmann et al., 2006), the cutting and dissection patterns are very different from those used in the present experiment. The closest experiment to the present study was carried out by Fisher et al. (2003) in pigs from 35 to 115 kg live weight. They found similar allometric coefficients for intermuscular and subcutaneous adipose tissues in the shoulder whereas subcutaneous adipose tissue grew faster than intermuscular adipose tissue in the ham. These observations are in good agreement with the results of the present study. The proportion of the intermuscular fraction in total adipose tissue was higher in the belly and lower in the ham than in the other cuts. This is in keeping with the previous observations of (D’Souza et al., 2004; Franci, Pugliese, Bozzi, Acciaioli, & Parisi, 2001; Monziols, Bonneau, Davenel, & Kouba, 2005). The rates of development of intermuscular and subcutaneous adipose tissues were similar in the whole carcass. These tissues presented allometric coefficients of growth higher than 1, which meant that they grew faster than the increase in total body weight, as already demonstrated by Fortin, Wood, and Whelehan (1983). There were however, some dissimilarities according to anatomical location. In the ham, intermuscular fat grew less rapidly than subcutaneous fat, in accordance with the previous observations of Franci et al. (2001) and Fisher et al. (2003). The reverse was observed in the belly where intermuscular fat grew more rapidly than subcutaneous fat, as already shown by Fisher et al. (2003). As a consequence, the ratio of intermuscular to subcutaneous fat increased with weight in the belly, decreased in the ham and remained stable in the shoulder and loin. The high content of belly total fat, and among total fat, the high development of intermuscular fat may be detrimental to consumer acceptance of bellies from heavy pigs. Muscle protein and lipid contents differed between muscles, in accordance with previous studies (Minvielle et al., 2002; Sharma, Gandemer, & Goutefongea, 1987; Zullo, Barone, Colatruglio, Girolami, & Matassino, 2003). Increasing slaughter weight did not dramatically change muscle protein content. These results do not agree with previous studies (Candek-Potokar, Zlender, Lefaucheur, & Bonneau, 1998; Stant, Martin, Judge, & Harrington, 1968), who showed a weight related increase in muscle protein content in the pig. The observed increase with weight in intramuscular lipid content is consistent with previous observations (Candek-Potokar et al., 1998; Kouba, Enser, Whittington, Nute, & Wood, 2003; Mourot & Hermier, 2001). The lower lipid content in intermuscular than in subcutaneous adipose tissue in 30 to 110 kg BW pigs has been previously described by Clark, Wander, and Hu, (1992) in
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106 kg BW pigs and Monziols, Bonneau, Davenel, and Kouba (2007) in 115 kg BW pigs. The fact that the differences in lipid contents between intermuscular and subcutaneous fats decrease with increasing weight is however, to our knowledge, a new finding. This observation suggests that intermuscular fat is maturing (accumulating lipids) later than subcutaneous fat.
5. Conclusion Detailed information about the composition of carcass cuts is an essential prerequisite for efficient marketing of pork. Our study indicates that fat deposition in the belly, particularly its intermuscular fraction that cannot be easily trimmed off, increases dramatically with weight comparatively to what is observed in the shoulder, loin and ham. Therefore, the trend to increasing carcass weights to maximise production efficiencies, may lead to problems for the valorisation of the belly which could be considered as excessively fat by the consumer. The present study shows that the lipid content is lower in intermuscular than in subcutaneous adipose tissue, whatever the body weight, but the differences in lipid content between the adipose tissues decrease with increasing body weight. So, a better understanding of the intermuscular adipose tissue deposition pattern is necessary, to set up any management strategies to decrease intermuscular fat proportion in the pig, and especially in the belly.
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Meat Science journal homepage: www.elsevier.com/locate/meatsci
Compared development of intermuscular and subcutaneous fat in carcass and primal cuts of growing pigs from 30 to 140 kg body weight M. Kouba *, M. Bonneau UMR1079, INRA-Agrocampus Rennes Systèmes d’Elevage Nutrition Animale et Humaine, F-35590 Saint Gilles, France
a r t i c l e
i n f o
Article history: Received 22 January 2008 Received in revised form 9 July 2008 Accepted 2 August 2008
Keywords: Pigs Lipids Subcutaneous fat Intermuscular fat Growth Development
a b s t r a c t A total of twenty two Large White X Landrace castrated males were slaughtered at 30, 70, 110 or 140 kg BW. Carcasses were weighed and cut into four primal cuts (belly, ham, loin, and shoulder). Each cut was weighed and dissected into bone, muscle, skin, and intermuscular and subcutaneous adipose tissues. Kidney fat was also taken and weighed. Kidney fat grew more rapidly than subcutaneous or intermuscular fat averaged over all four cuts. In the shoulder and loin, about one third of total adipose tissue was in the intermuscular fraction. In the belly, there was as much (in 30–110 kg BW pigs) or more (in 140 kg BW pigs) intermuscular than subcutaneous adipose tissue. In the ham, the intermuscular fraction of adipose tissue grew more slowly than the subcutaneous one, so that it represented less than one fourth of total ham adipose tissue in 140 kg BW pigs. Intermuscular adipose tissue exhibited a lower lipid content than subcutaneous adipose tissue, whatever the body weight, but the differences in lipid content between the adipose tissues decreased with increasing weight. These results show that the relative development of intermuscular and subcutaneous adipose tissues differs according to anatomical location. Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction Reduction of fat deposition has been a major goal in the continuing improvement of pork production for many years. Selection and breeding for meat-producing qualities in animals is based on the fact that as the animal grows up, the proportions of the body change, and that these changes involve changes in the composition of the animal, that is, in the proportions of muscle and fat, which are required for human food purposes (Hammond, 1947). The selection for leaner carcasses, based on the reduction of subcutaneous fat, has led to a decrease in total fat (Cliplef & McKay, 1993; Nguyen, MacPhee, & Wade 2004). Carcass fat is deposited in different anatomical locations as subcutaneous, visceral, intermuscular (between muscles) or intramuscular (within muscle) fat. These various deposits do not have the same importance for carcass and meat quality. Visceral and subcutaneous fats can be easily trimmed off the lean meat that is delivered to the consumers, whereas in most instances, intermuscular fat cannot be removed from some joints without mutilating them. Therefore, intermuscular fat content has a high impact on consumer acceptability of meat commodities containing several muscles, such as pork chops or ham slices. Although of major commercial importance, the partition of fat between depots and its distribution through the carcasses of meat animals have commanded little attention from research workers (Fisher, Green, Whittemore, Wood, & Schofield, * Corresponding author. Tel.: +33 0223485367; fax: +33 0223485900. E-mail address: [email protected] (M. Kouba). 0309-1740/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.meatsci.2008.08.001
2003; Kempster & Evans, 1979; Wood & Riley, 1982; Wood, Whelehan, Ellis, Smith, & Laird, 1983) in comparison with other aspects of growth and development. In particular, very few studies have been carried out on the development of intermuscular fat in pigs. There is a need for a better understanding of the relative development of intermuscular fat relative to other fat deposits, in the carcass and the different primal cuts (belly, ham, loin, and shoulder). The aim of the present study was to describe the development of subcutaneous, intermuscular and kidney fats in the carcass and in primal cuts of pigs from 30 to 140 kg live BW. 2. Material and methods 2.1. Animals, experimental design, and measurements Twenty two castrated male pigs Large White X Landrace from 20 sows from the INRA experimental herd were used in the study. The pigs were housed in individual pens in environmentally controlled buildings under normal husbandry conditions. The animals were reared in compliance with national regulations on the humane care and use of animals in research. Pigs were fed ad libitum a standard diet for commercial slaughter pigs. The diet was based on wheat, barley, maize and soybean meal and contained 17.7% of crude protein and 13.7 MJ of DE/kg. Fresh water was freely available. Animals were individually weighed each week, and before slaughter around 30 kg (n = 4), 70 kg (n = 4), 110 kg (n = 9), or 140 kg (n = 5). Corresponding ages, actual live weight and carcass weight (mean ± sem) were 78.8 ± 0.5, 127.3 ± 0.3, 165.8 ± 1.6 and
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206.6 ± 2.7 days, 29.6 ± 0.8, 71.4 ± 0.9, 108.3 ± 1.1 and 140.1 ± 1.1 kg live weight, 10.9 ± 0.3, 25.0 ± 0.3, 39.5 ± 0.4 and 52.6 ± 0.5 kg carcass weight (weight of the dissected half carcass). At slaughter, after approximately 16 h of fasting, (without feed but with water), the animals were electrically stunned and bled. Internal organs (heart, lungs, liver, spleen, digestive and reproductive tracts) were removed. After 24 h chilling at 4 °C, the head, feet, kidneys, kidney fat and tail were separated from the carcass. The left side of each carcass was weighed, and cut into four anatomically defined primal cuts (belly, ham, loin, and shoulder) according to Metayer and Daumas (1998). The cuts were weighed and each of them was subsequently physically dissected into six tissue fractions, skin, bone, muscle, subcutaneous fat, intermuscular fat, and miscellaneous (tendons, aponevroses, lymph nodes, glandular tissue, and possible remnants of nerves and blood vessels). Weights of the tissue fractions of each cut were recorded. Prior to tissue dissection, 30 g muscle samples and 20 g adipose tissue samples were taken from the individual cuts. The weight of samples was added to the weight of corresponding dissected tissues. A sample of kidney fat was also taken. 2.2. Analytical methods for the determination of tissue composition Samples of muscles were analyzed for dry matter and protein concentrations, according to Association of Official Analytical Chemists (AOAC) (2006). The lipids were extracted from muscle and adipose tissue samples, using the chloroform/methanol method procedure of Folch, Lees, and Stanley (1957). 2.3. Calculations and statistical analyses Analyses of variance and linear regressions were performed, using the GLM and REG procedures of SAS (SAS, 1999), respectively. Allometric analyses of the development of fat depots in the carcass (Table 1) were conducted by calculating the linear regressions of log transformed fat depot weights on log transformed carcass weight, muscle weight in the carcass or total fat weight in the carcass, using the following model developed by Huxley (1932)
log y ¼ b log x þ log a; where a is a constant and b is the allometric coefficient when b = 1, the rate of growth of fat depots is similar to the independent variable, whereas when b < 1 or when b > 1, the growth of fat deposits is, respectively, slower or faster than the growth of the independent variable. An analysis of variance was conducted with a model including the effects of fat depot, carcass weight (as co-variable) and the interaction between fat depot and carcass weight. The interaction was considered for testing the significance of differences in regressions slopes between fat depots. Allometric analyses of the devel-
Table 1 Allometric developmenta of subcutaneous, intermuscular, and kidney fat relative to carcass weight, muscle, and total fat in the carcass Allometry relative to item Carcass weight Muscle Total fat
Fat depot Subcutaneous
Intermuscular
Kidney
1.47y 1.62y 1.00y
1.42y 1.57y 0.96y
1.93z 2.13z 1.31z
Diff. btw fat depotsb *** *** ***
***, P < 0.001. y,z Within line, values not followed by the same superscript differ (P < 0.05). a Slope of the regressions of ln(fat depot weight) on ln(carcass weight), ln(muscle weight in the carcass), or ln(total fat weight in the carcass). b Significance of differences in regressions slopes between fat depots.
Table 2 Allometric developmenta of subcutaneous and intermuscular fat relative to cut weight, muscle and total fat in the four primal cuts Allometry relative to item Cut weight
Muscle weight in the cut
Total fat weight in the cut
Fat depot
Diff. btw fat depotsb
Cut
Subcutaneous
Intermuscular
Belly Shoulder Ham Loin Diff. btw cutsc
1.25y 1.48x 1.55x 1.48x **
1.34xy 1.49x 1.21y 1.37x *
NS NS ***
Belly Shoulder Ham Loin Diff. btw cutsc
1.43 1.63 1.65 1.65 NS
1.57x 1.65x 1.30y 1.54x *
NS NS **
Belly Shoulder Ham Loin Diff. btw cutsc
0.97 1.00 1.07 1.02
1.03x 1.00x 0.82y 0.94x **
NS NS *** *
NS
NS
x,y NS, P > 0.10; , P < 0.10; *, P < 0.05; **, P < 0.01; ***, P < 0.001. Within fat depot and item, values in the same row not followed by the same superscript differ (P < 0.05). a Slope of the regressions of ln(fat depot weight) on ln(cut weight), ln(muscle weight in the cut), or ln(total fat weight in the cut). b Significance of differences in regression slopes between fat depots, within cut. c Significance of differences in regression slopes between cuts, within fat depot.
opment of fat depots in the various primal cuts (Table 2) were conducted in a similar way. Analyses of variance were conducted within each fat depot with a model including the effects of cut, cut weight (as co-variable) and the interaction between cut and cut weight. The interaction was considered for testing the significance of differences in regressions slopes between cuts (Table 2). Similar analyses were conducted with muscle weight or total fat weight as co-variable. Changes with weight in the composition of muscle (Table 3) and adipose tissue (Table 4) samples were analysed by calculating allometric regressions of composition parameters on carcass weight. For each parameter, analyses of variance were performed with a model including the effect of sample, carcass weight (as co-variable) and the interaction between sample and carcass weight. The interaction was considered for testing the significance of differences in regression slopes between samples.
Table 3 Slopes of the regressions of log transformed muscle composition parameters on log transformed carcass weight Muscle samples
Dry matter contenta c
Signif. Belly_RA Shoulder_SS Ham_SM Ham_AD Loin_Ant_LD Loin_Ant_TR Loin_Mid_LD Loin_Mid_PS Diff. btw slopese
*** *** *** *** *** *** **
d
Lipid contenta
Slopes
Signif.
0.072 0.099 0.099 0.035 0.094 0.134 0.073 0.084
*** ** *** NS * *** ** *
c
Protein contentb d
Slopes
Signif.
0.390y 0.310y 0.646y 0.057z 0.305yz 0.576y 0.397y 0.292yz **
NS ** * NS *** NS NS
c
Slopesd -0.017x -0.014x -0.070yz 0.015w -0.012wx -0.107z -0.019xy 0.000wx ***
NS, P > 0.10; , P < 0.10; *, P < 0.05; **, P < 0.01; ***, P < 0.001. a % of fresh weight. b % of dry matter weight. c Significance of the regressions. d Slopes of the regressions. e Overall significance of differences in slopes between samples; w, x, y, z, slopes within column affected the same letter did not differ significantly at the 5% level.
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Table 4 Slopes of the regressions of log transformed adipose tissue lipid contents on log transformed carcass weight Adipose tissue samples
Lipid contenta Signif.b
Slopesc
Belly_IM Shoulder_IM Ham_IM Loin_Ant_IM Loin_Mid_IM Loin_Mid_SC Kidney fat Diff. btw slopesd
*** *** *** *** ** *** **
0.444x 0.196y 0.367x 0.406x 0.382x 0.124yz 0.093z ***
NS, P > 0.10; , P < 0.10; *, P < 0.05; **, P < 0.01; ***, P < 0.001. a % of fresh weight. b Significance of the regressions. c Slopes of the regressions. d Overall significance of differences in slopes between samples.; w, x, y, z, slopes within column affected the same letter did not differ significantly at the 5% level.
3. Results 3.1. Allometric development of subcutaneous, intermuscular and kidney fats The slopes of the allometric growth of subcutaneous and intermuscular fats in the carcass did not differ significantly (Table 1) and they were significantly lower than that of kidney fat (P 6 0.001). In the shoulder and belly, the slopes of the allometric growth of subcutaneous and intermuscular fats did not differ significantly, whatever the item relatively to which they were calculated (Table 2). In the loin, the slopes did not differ when calculated relatively to loin weight or muscle weight in the loin. The slope was however, significantly lower for intermuscular than for subcutaneous fat when calculated relatively to total fat in the loin (P = 0.04). In the ham, the slopes of the allometric growth of intermuscular fat were significantly lower than those of subcutaneous fat (P 6 0.005). The slope of the allometric growth of subcutaneous fat relative to primal cut weight was significantly lower in the belly than in the other three cuts (P < 0.025). However, they did not differ significantly between cuts, when calculated relatively to muscle or total fat weights in the cuts. The slopes of the allometric growth of intermuscular fat were significantly lower in the ham than in the other three cuts (P < 0.05). However, they did not differ significantly between ham and belly when calculated relatively to cut weight (P = 0.09). 3.2. Changes in the proportions of intermuscular and subcutaneous fats in carcass or primal cut weights during growth
times, from 14.4% to 26.8%. The belly is the only cut where proportions of intermuscular and subcutaneous fats are similar in the 30 kg live weight pigs and where the intermuscular fat proportion is higher than the subcutaneous fat one in 140 kg live weight pigs. 3.3. Weight-related changes in the composition of muscle and adipose tissue samples Dry matter content increased significantly with carcass weight in all muscle samples, with the exception of Ham_AD (P = 0.10) (Table 3). The slopes of the regressions of dry matter content on carcass weight did not differ significantly between samples. Lipid content increased significantly with carcass weight in all muscle samples, with the exception of Ham_AD (P = 0.49). The slopes of the increase in lipid content did not differ significantly between the 7 samples where the regression was significant. Protein content increased significantly with carcass weight in Ham_AD, decreased significantly in Ham_SM and Loin_Ant_TR, and did not change significantly with weight in the remaining 5 samples. Lipid content increased significantly with carcass weight in all adipose tissue samples (Table 4). The slopes of the increase in lipid content were significantly higher in Belly_IM, Loin-Ant_IM, Loin_Mid_IM and Ham_IM, than in Shoulder_IM, Loin_Mid_SC and kidney fat. It was also significantly higher in Shoulder_IM than in kidney fat. The higher slopes in intermuscular adipose tissue samples were associated with significantly lower lipid content at low carcass weight (P < 0.001; Fig. 1), so that lipid contents were similar in all adipose tissue samples at 140 kg live weight (P = 0.06) whereas there were significant differences between samples at lower weights (P < 0.001). 4. Discussion There is very little available published information on the compared development of the various adipose tissues in the different joints. Many experiments on growth and body composition of pigs have been carried out in serial slaughter trials in which pigs were slaughtered at defined body weights or ages (Kouba, Bonneau, &
Lipid content (% of fresh weight) 110
70
30
140
90 Loin_Mid_SC 80 Kidney 70 Shoulder_IM
The proportion of total fat in carcass weight increased from 16.1% at 30 kg to 33.6% at 140 kg live weight. A twofold increase was observed for the proportions of subcutaneous (from 10.2% to 20.5%) and intermuscular (from 5.4% to 10.6%) fats, whereas a four fold increase was measured for the proportion of kidney fat, (from 0.6% at 30 kg to 2.5% at 140 kg). The changes in the proportions of fats in the shoulder and loin were very similar to those observed in the carcass, a two fold increase being observed for both intermuscular and subcutaneous fats between 30 and 140 kg. In the ham the proportion of subcutaneous fat increased 2.2 times from 7.8% to 17.2% between 30 and 140 kg, whereas that of intermuscular fat augmented only 1.4 times from 3.6% to 5.1%. The reverse was observed in the belly where the proportion of subcutaneous fat increased only 1.4 times from 15.8% to 22.4%, whereas intermuscular fat augmented 1.9
60
50
40
Ham_IM
Belly_IM
Loin_Mid_IM
Loin_Ant_IM
30 10
20
30
40
50
Half carcass weight (kg) Fig. 1. Allometric regressions lines of the lipid content of the various adipose tissue samples on half carcass weight. The bold horizontal lines indicate the range of variation of individual half carcass weights at 30, 70, 110 and 140 kg live weight. All regressions were highly significant (P < 0.01).
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Noblet, 1999; Quiniou & Noblet, 1999; Wagner, Schinckel, Chen, Forrest, & Coe, 1999). In most studies, however, only overall fatness or overall lean content have been measured (Gu, Schinckel, & Martin, 1992; Schinckel, Preckel, & Einstein, 1996; Schinckel, Wagner, Forrest, & Einstein, 2001; Swantek, Marchello, Tilton, & Crenshaw, 1999). Kolstad (2001) considered total subcutaneous and intermuscular adipose tissues in the carcass, but not their distribution in individual joints. Earlier studies (Davies & Pryor, 1977; Kempster, 1980; Kempster & Evans, 1979) described the intermuscular fat growth in relation to the body weight. They found that the intermuscular fat growth was slower than the growth of subcutaneous adipose tissue and the kidney fat (with b = 0.972 against b = 1.007 and b = 1.077, respectively, for Davies and Pryor, and b = 0.87 against 1.01 and 1.24, respectively, for Kempster and Evans). However, in our present study, the growth of subcutaneous adipose tissue in relation to the carcass weight was similar to the growth of intermuscular fat (with b = 1.47, and 1.42, respectively), which is not in accordance with these earlier studies. As demonstrated by (Davies & Pryor, 1977; Kempster & Evans, 1979), in the present work, kidney fat exhibited the fastest growth (b = 1.93). In more recent studies dealing with tissue composition of a joint (Fisher et al., 2003; Mohrmann et al., 2006), the cutting and dissection patterns are very different from those used in the present experiment. The closest experiment to the present study was carried out by Fisher et al. (2003) in pigs from 35 to 115 kg live weight. They found similar allometric coefficients for intermuscular and subcutaneous adipose tissues in the shoulder whereas subcutaneous adipose tissue grew faster than intermuscular adipose tissue in the ham. These observations are in good agreement with the results of the present study. The proportion of the intermuscular fraction in total adipose tissue was higher in the belly and lower in the ham than in the other cuts. This is in keeping with the previous observations of (D’Souza et al., 2004; Franci, Pugliese, Bozzi, Acciaioli, & Parisi, 2001; Monziols, Bonneau, Davenel, & Kouba, 2005). The rates of development of intermuscular and subcutaneous adipose tissues were similar in the whole carcass. These tissues presented allometric coefficients of growth higher than 1, which meant that they grew faster than the increase in total body weight, as already demonstrated by Fortin, Wood, and Whelehan (1983). There were however, some dissimilarities according to anatomical location. In the ham, intermuscular fat grew less rapidly than subcutaneous fat, in accordance with the previous observations of Franci et al. (2001) and Fisher et al. (2003). The reverse was observed in the belly where intermuscular fat grew more rapidly than subcutaneous fat, as already shown by Fisher et al. (2003). As a consequence, the ratio of intermuscular to subcutaneous fat increased with weight in the belly, decreased in the ham and remained stable in the shoulder and loin. The high content of belly total fat, and among total fat, the high development of intermuscular fat may be detrimental to consumer acceptance of bellies from heavy pigs. Muscle protein and lipid contents differed between muscles, in accordance with previous studies (Minvielle et al., 2002; Sharma, Gandemer, & Goutefongea, 1987; Zullo, Barone, Colatruglio, Girolami, & Matassino, 2003). Increasing slaughter weight did not dramatically change muscle protein content. These results do not agree with previous studies (Candek-Potokar, Zlender, Lefaucheur, & Bonneau, 1998; Stant, Martin, Judge, & Harrington, 1968), who showed a weight related increase in muscle protein content in the pig. The observed increase with weight in intramuscular lipid content is consistent with previous observations (Candek-Potokar et al., 1998; Kouba, Enser, Whittington, Nute, & Wood, 2003; Mourot & Hermier, 2001). The lower lipid content in intermuscular than in subcutaneous adipose tissue in 30 to 110 kg BW pigs has been previously described by Clark, Wander, and Hu, (1992) in
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106 kg BW pigs and Monziols, Bonneau, Davenel, and Kouba (2007) in 115 kg BW pigs. The fact that the differences in lipid contents between intermuscular and subcutaneous fats decrease with increasing weight is however, to our knowledge, a new finding. This observation suggests that intermuscular fat is maturing (accumulating lipids) later than subcutaneous fat.
5. Conclusion Detailed information about the composition of carcass cuts is an essential prerequisite for efficient marketing of pork. Our study indicates that fat deposition in the belly, particularly its intermuscular fraction that cannot be easily trimmed off, increases dramatically with weight comparatively to what is observed in the shoulder, loin and ham. Therefore, the trend to increasing carcass weights to maximise production efficiencies, may lead to problems for the valorisation of the belly which could be considered as excessively fat by the consumer. The present study shows that the lipid content is lower in intermuscular than in subcutaneous adipose tissue, whatever the body weight, but the differences in lipid content between the adipose tissues decrease with increasing body weight. So, a better understanding of the intermuscular adipose tissue deposition pattern is necessary, to set up any management strategies to decrease intermuscular fat proportion in the pig, and especially in the belly.
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