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ANIMAL PRODUCTION |
The Ohio State University and The Ohio Agricultural Research and Development Center, Columbus 43210-1095
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Abstract |
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 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Key Words: body composition • genetic • growth • pig • tissue development
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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The chemical composition of pigs has changed largely through genetic selection, but differences can also be influenced by nutrition, sex, age, and BW (Wagner et al., 1999
; Fisher et al., 2003; Correa et al., 2006). Our previous results evaluating 2 genetic lines and sexes demonstrated that the major differences between lean and fat tissue developmental patterns diverged largely after 75 kg of BW (Wiseman et al., 2007).
Body composition would be expected to differ in pigs of different genetic backgrounds. The amounts of muscle and fat could also influence the development of other body tissues and organs, particularly those involved in nutrient metabolism, as suggested by Cliplef and McKay (1993).
The objective of this study was to determine the weights of different body tissues and organs in barrows and gilts of 2 genetic lines differing in lean and fat tissue development from 20 to 125 kg of BW. We examined compositional changes within the major muscle masses at various BW and whether this might affect overall body composition.
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MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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). The current experiment was a continuation of that study, where various body tissues and organs were collected at 25-kg of BW intervals from 20 to 125 kg, whereupon chemical composition of the major components was determined.
The experiment was conducted as a 2 (genetic line) x 2 (sex) x 5 (BW) factorial arrangement of treatments in 2 groups of pigs (n = 120 pigs total) in a completely randomize design. A low-lean genetic line had an estimated herd average of 275 g of fat-free lean/d, whereas the second genetic line was a high-lean with a herd average of 380 g of fat-free lean/d. Barrows and gilts were evaluated within each genetic line. The genetic makeup of the pigs, management procedures, method of allotment, diets fed to each genetic line and sex, and slaughtering conditions were previously presented (Wiseman et al., 2007).
Six pigs from each genetic line and sex were initially slaughtered at 20 kg of BW. The remaining pigs were randomly allotted to the remaining 4 BW-at-slaughter groups at the beginning of the test period. Upon reaching their designated BW, 6 pigs from each treatment group (3 of each sex) were slaughtered at approximately 25 kg of BW intervals to a final BW of 125 kg. Pigs were electrically stunned and killed by exsanguination. Carcasses were processed after the animal was scalded and dehaired. Internal organs were removed and weighed to the nearest gram. Digesta from the stomach and intestinal tract was removed by physical expression, and the stomach and intestinal tract were flushed with water and weighed empty. The head was removed from the hot carcass, weighed, and combined with the stomach, internal tissue, and organs and frozen (–20°C) for 48 h before being ground.
Carcasses with jowls and legs attached were split medially through the vertebrae, and the HCW was recorded, whereupon the carcass was placed in a chilled room (4°C). Approximately 24 h postmortem, the carcass halves were weighed and the right side was dissected into 3 components. The loin and ham muscle masses were removed from the carcass and kept separate, but each was trimmed of skin and external fat; the bones from the ham were removed and the residuals were added to the remaining carcass component. Both muscle masses were independently weighed, covered to prevent moisture loss, and placed in the chilled room. After an additional 24 h in the chilled room, the loin and ham muscles were ground through a 12-mm and then a 3-mm die using a grinder (Model 5412, Stimpson, Louisville, KY), whereupon a homogeneous mixture of each was subsampled, placed in plastic Petri dishes, sealed with tape to prevent moisture loss, frozen (–4°C), and stored for later analysis.
The internal tissues and head, and the remaining carcass component, were ground twice in an industrial grinder (Autio 801, Autio Co., Astoria, OR) through a 9-mm die and then through a 4-mm die, subsampled, stored in plastic Petri dishes, sealed with tape to prevent moisture loss, frozen (–4°C), and stored for later analysis.
Samples from each of the 4 body components were freeze-dried for the determination of moisture, whereupon fat was extracted with petroleum ether (AOAC, 2000). The dried fat-free sample was subsequently ground in a cyclotec 1093 mill (Tectator, Höganäs, Sweden) using a 1-µm screen, whereupon a homogenous sample was analyzed for N (Perkin Elmer, Model 2410, Series 2) and then converted to protein by multiplying N x 6.25. Ash was determined after burning a fat-free dried sample in a Muffle furnace using AOAC (2000) methods.
Because there were animal differences in BW at slaughter, the tissue and organ weights are expressed on a BW and on a percentage of empty BW basis. Empty BW is defined as the live BW minus the intestinal digesta. The individual pig was considered the experimental unit. Data collected were analyzed using the MIXED procedure (SAS Inst. Inc., Cary, NC) using the following statistical model: Yijkl = µ + Gi + Nj + Wk + GNij + GWij + NWjk + GNWijk + eijkl, where Yijkl = the dependent variable; µ = the overall mean; Gi = the fixed effect of the ith level of sex (i = 1,2); Nj = the fixed effect of the jth level of genetic line (j = 1,2); Wk = the fixed effect of the kth level of BW group (k = 1, 2, 3, 4, 5); GNij = the interaction of the ith sex with the jth genetic line; GWij = the interaction of the ith sex with the kth BW group; NWjk = the interaction of the jth genetic line with the kth BW group; GNWijk = the interaction of the ith sex, jth genetic line, and kth BW group; and eijkl = the error term 
N(0, 
2k). Regression analysis was conducted on each trait for each body component as BW increased. The slice option of the MIXED procedure of SAS was used to compare the interactions at each BW.
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RESULTS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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As expected, the main effects of BW of the 2 sexes and the 2 genetic lines increased from 20 to 125 kg of BW, as did the increasing weights of tissues and organs (Tables 1 and 2). Most tissue weights increased quadratically (P < 0.01) with BW. When tissue and organ weights were expressed as a percentage of empty BW, there was a quadratic decline (P < 0.01) for most tissue and organ weights as BW increased, except the head, which also declined but in a cubic manner (P < 0.01).
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). Weight of the liver (P < 0.01), intestinal tract (P < 0.01), and perirenal fat (P < 0.06) were greater for barrows than gilts. Liver weight was consistently heavier at each BW for barrows, but the effect was significant only (P < 0.05) at 20 and 45 kg of BW. Intestinal tract weights were also heavier in barrows at 45 (P < 0.05), 75 (P < 0.01), and 100 kg of BW (P < 0.05) compared with gilts. Perirenal fat was numerically greater in barrows from 75 to 100 kg of BW, but the response was not significant. When these tissue weights were expressed on a percentage empty BW basis, the liver and intestinal tract weights continued at a greater percentage in barrows than gilts, but only the main effect responses were significant (P < 0.01). There was a sex x BW interaction (P < 0.01) for loin and ham muscle weights. As BW increased, the weights of these 2 major muscle groups increased more rapidly in gilts than barrows, with the weight differences exacerbated as BW increased.
The effect of tissue and body component weights for the 2 genetic lines with increasing BW is presented in Table 2. Loin and ham muscle weights were greater (P < 0.01) in the high-lean genetic line, responses significant (P < 0.01) at BW > 45 kg. This resulted in an overall genetic line x BW interaction response (P < 0.01) from 20 to 125 kg of BW.
The liver (P < 0.01), heart (P < 0.01), and head (P < 0.03) weights were greater in the high-lean genetic line, whereas the perirenal fat content was greater (P < 0.06) in the low-lean genetic line. A genetic line x BW interaction (P < 0.01) response for perirenal fat occurred where the weight of perirenal fat increased more rapidly as BW increased in the low-lean than in the high-lean genetic line.
When the weights of the various body components and tissue and organ weights are expressed as a percentage of empty BW for the 2 genetic lines, there was an overall quadratic decline (P < 0.01) for internal tissue weights, with the head also declining but in a cubic (P < 0.01) manner. The liver (P < 0.03) and heart (P < 0.01) were at a greater percentage of empty BW in the high-lean genetic line, whereas the head (P < 0.02) was greater in the low-lean genetic line.
Body Component Composition
Each of the various body component weights and their chemical compositions for the 2 sexes and the 2 genetic lines are presented in Tables 3 and 4. The main effect of loin and ham muscle mass composition demonstrated that the quantity of water, protein, fat, and ash contents increased in each of these muscle groups in a linear manner (P < 0.01) as BW increased. For the remaining carcass component, which included the skin and fat trimmings from the loin and ham muscles and the bones from the ham, and for the internal tissues and head components, both demonstrated that the quantity of water, protein, fat, and ash each increased in a quadratic or cubic (P < 0.01) manner as BW increased.
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) demonstrated a greater quantity of water, protein, and ash (P < 0.01) in loin and ham muscle masses in gilts more so than in barrows. This resulted in a sex x BW interaction (P < 0.01) for each of these muscle weights as BW increased. There was an increasingly greater quantities of water, protein, and ash in gilts than barrows particularly at BW > 45 kg. There was also a sex x BW interaction (P < 0.01) with a greater amount of fat in the ham muscles of barrows than gilts. In the remaining carcass component as well as in the internal tissue and head component, the water, protein, and ash contents were generally similar for the 2 sexes, but fat was greater in the remaining carcass and internal tissue components in barrows (P < 0.01) than in gilts. This resulted in a sex x BW interaction response (P < 0.01) with differences in fat content increasing more in barrows at heavier BW.
The interaction effect of genetic line at the various BW presented in Table 4 demonstrated that the greater loin and ham muscle weights resulted in greater (P < 0.01) quantities of water, protein, and ash contents in the high-lean compared with the low-lean genetic line, each resulting in genetic line x BW interactions (P < 0.01). Although the fat content in these 2 muscle groups was greater in the low-lean genetic line, the difference was not significant. In the remaining carcass component the high-lean genetic line continued to have greater (P < 0.01) amounts of water and protein, but less fat (P < 0.01) than the low-lean genetic line, whereas the ash content was similar. In the internal tissue component there was a greater amount of water (P < 0.03) and a lower (P < 0.01) quantity of fat in the high-lean genetic line.
Overall body composition demonstrated a genetic line x BW interaction (P < 0.01) of water, protein, ash, and fat contents with the high-lean genetic line having greater quantities of water and protein as BW increased, whereas body fat was increasingly greater (P < 0.01) in the low-lean genetic line as BW increased.
Percentage Chemical Composition
As BW increased there was a small but a quadratic decline (P < 0.01) in the percentage of water in the loin and ham muscle mass, but the percentages of protein, ash, and fat increased (P < 0.01) in these 2 muscle groups for both sexes and genetic lines (Tables 5 and 6). In the remaining carcass component, a decline (P < 0.01) in the percentage water (P < 0.01), protein (P < 0.01), and ash (P < 0.05) occurred, whereas the percentage fat increased (P < 0.01). For the internal tissue and head component there was a decline in the percentage water (P < 0.01), a small percentage increase in ash (P < 0.01), a larger increase in percentage fat (P < 0.01), whereas protein content initially increased but then declined slightly in a cubic manner (P < 0.01).
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. The results demonstrated that water (P < 0.03) and protein (P < 0.01) in the LM differed only slightly but gilts had greater (P < 0.01) percentages of water, and protein as BW increased. The loin fat content was greater (P < 0.01) in barrows as BW increased. Ham muscle mass and the percentage of protein were slightly greater (P < 0.01) in gilts, but the percentages of fat (P < 0.01) and ash (P < 0.01) were greater in barrows. In the remaining carcass component there was a greater (P < 0.01) percentage of water, protein, and ash in gilts, but the fat content was greater (P < 0.01) in barrows. The internal tissue plus the head component had greater (P < 0.01) percentages of water and protein in gilts, but the percentages of fat and ash were greater in barrows (P < 0.01).
The interaction effect of the 2 genetic lines with BW on the percentage composition of body components is presented in Table 6. Although percentage composition of the various body components showed the same general trends as sex, the differences between genetic lines were greater than between sexes. Composition of the LM mass showed a greater percentage of water (P < 0.01) and protein (P < 0.01) in the high-lean vs. the low-lean genetic line. Although the percentage fat in the loin was numerically greater for the low-lean genetic line, the effect was not significant. Ham muscles demonstrated greater percentages of water (P < 0.01) and protein (P < 0.01) in the high-lean genetic line as BW increased, but the percentage fat was lower (P < 0.01). A genetic line x BW interaction occurred for the loin and ham muscles in the percentages of protein (P < 0.01) and fat (P < 0.01). The percentage differences increased more for protein but declined more for fat in the high-lean genetic line as BW increased. In the remaining carcass component the percentage water (P < 0.01), protein (P < 0.01), and fat (P < 0.01) were greater in the high-lean genetic line, whereas the percentage fat (P < 0.01) declined. The internal tissue and head had a greater percentage water (P < 0.01) and protein (P < 0.01) in the high-lean genetic line, whereas percentage fat was greater (P < 0.01) in the low-lean genetic line.
When total body components were combined for both genetic lines and sexes, the percentage body water (P < 0.01) and protein (P < 0.01) increased for the high-lean genetic line and gilts. Fat content increased (P < 0.01) in the low-lean genetic line and barrows, but the greatest increase occurred from 100 to 125 kg of BW.
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DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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At 125 kg of BW, the high-lean genetic line had 3.6 kg (18%) more muscle mass of trimmed loin and ham than a low-lean genetic line, whereas gilts had 1.40 kg (6.5%) more mass from these 2 muscle groups than barrows. In our experiment, the heart (P < 0.01) and liver (P < 0.01) weights when expressed on a BW or as a percentage of empty BW basis were greater in the high-lean genetic line pigs. This suggests that pigs with a greater rate of lean deposition not only metabolize more protein, but there was a corresponding increase in the weight of those tissues that were active in the metabolism and distribution of amino acids. Lean growth deposition has been previously reported to influence visceral organ tissue growth (Cliplef and McKay, 1993; Quiniou and Noblet, 1995; Bikker et al., 1996). Friesen et al. (1994) reported increased heart weights in a high-lean genetic line at 104 and 127 kg of BW, but they did not demonstrate any sex effects on liver weights. However, when we compared the liver and intestinal tract weights of barrows and gilts, these tissues were heavier (P < 0.01) in barrows than in gilts and yet the latter sex was leaner. The 3-way interaction of these 3 factors, however, was not significant. Although we could not collect feed intake data with these pigs, barrows generally consume more feed and thus would be expected to also digest and metabolize more nutrients on a total basis than gilts. Consequently, the resulting intestinal tract and liver weights not only are reflective of lean growth of the animal, but they also reflect the amount of energy consumed or feed intake of the animal. Pigs with a greater feed intake would be expected to metabolize more total nutrients from the greater feed intakes. The composition data support this by indicating that total body fat content in the low-lean vs. the high-lean genetic line was greater by 8.1 kg (28.3%) while barrows had 3.4 kg (11.0%) more fat than gilts. Thus our results suggest that pigs with a genetic capacity to produce more lean tissue will have heavier liver and heart weights, but pigs that have greater feed intakes will also have heavier intestinal tract and liver weights.
The chemical composition of the pig in previous work has been shown to vary considerably due to genetics, BW, and nutrition (Shields et al., 1983; Bark et al., 1992; Wagner et al., 1999). Although the chemical compositions of the trimmed loin and ham muscle mass differed somewhat by sex and genetic line, their compositions were relatively similar with the possible exception for the greater amounts of fat in the hams of barrows and the hams of the low-lean genetic line. When the total body composition was considered, our study demonstrated an increased water and protein content in the high-lean genetic line and also a lower body fat content at each BW interval from 20 to 125 kg. Most of the chemical composition differences occurring between sex and genetic line were exacerbated after 75 kg of BW, which is consistent with our lean growth estimates on the live animal using ultrasound equipment (Wiseman et al., 2007).
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Footnotes |
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2 Appreciation is expressed to K. Mays and L. Warnock for animal care and data collection.
3 Corresponding author: mahan.3{at}osu.edu
Received for publication June 27, 2006. Accepted for publication March 16, 2007.
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LITERATURE CITED |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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This article has been cited by other articles:
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  T. G. Wiseman, D. C. Mahan, and N. R. St-Pierre Mineral composition of two genetic lines of barrows and gilts from twenty to one hundred twenty-five kilograms of body weight J Anim Sci, July 1, 2009; 87(7): 2306 - 2314. [Abstract] [Full Text] [PDF]
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A. P. Schinckel, D. C. Mahan, T. G. Wiseman, and M. E. Einstein Growth of protein, moisture, lipid, and ash of two genetic lines of barrows and gilts from twenty to one hundred twenty-five kilograms of body weight J Anim Sci, February 1, 2008; 86(2): 460 - 471. [Abstract] [Full Text] [PDF]
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