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Phenotypic measurements and various indices of lean and fat tissue development in barrows and gilts of two genetic lines from twenty to one hundred twenty-five kilograms of body weight^1,2

The Ohio State University and The Ohio Agricultural Research and Development Center, Columbus 43210-1095

	Abstract

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
Two genetic lines with different lean gains were evaluated for various body measurements and indices of lean tissue in barrows and gilts from 20 to 125 kg of BW. One genetic line was identified as the low-lean line [280 g of fat-free lean (FFL)/d], and the second line was the high-lean line (375 FFL gained/d). The experiment was conducted as a completely randomized design using a 2 x 2 x 5 factorial arrangement of treatments in 6 replicates (n = 120 pigs). The 2 genetic lines and sexes were provided ad libitum access to cornsoybean mixtures that met or exceeded their required amino acid requirements for their respective lean gain potentials. Six pigs of each sex and genetic line were slaughtered initially and at 25-kg of BW intervals to 125 kg of BW. Pigs slaughtered were measured for height, width, and length using metal calipers. Backfat and LM area were measured using real-time ultrasound, with backfat depth also measured using A-mode ultrasound technology. Longissimus muscle area and back-fat thickness at the 10th rib were measured on the chilled carcass. Data was analyzed using the MIXED procedure of SAS, with the animal as the experimental unit. Shoulders (P < 0.05) and lumbars (P < 0.05) were wider in the low-lean genetic line and in barrows. Gilts and the high-lean genetic line had less backfat and greater LM areas than the low-lean genetic line. As BW increased, there was a greater increase in FFL tissue and lower backfat depths in the high-lean vs. the low-lean genetic line. This resulted in a greater divergence of measurement values as BW increased. Femur weight, length, and cortical wall thickness were greater in the high-lean genetic line, but the differences were not significant. The high-lean genetic line had a greater (P < 0.01) organic matrix content in the femur and less ash, resulting in a lower percentage of bone ash (P < 0.01). The results indicate that differences occurred phenotypically between pigs having more muscle (wider hams) or more fat (wider shoulder and lumbar). As BW increased, the high-lean pigs had an increase in lean tissue, particularly after 75 kg of BW, and less backfat and less bone mineralization, whereas the low-lean line pigs had increased backfat and greater bone mineralization. Real-time ultrasound measurements using various formulas to estimate lean tissue produced values close to those determined from carcass measurements at 100 and 125 kg of BW.

Key Words: body composition • carcass • growth • pig

	INTRODUCTION

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
Lean tissue development in grower-finisher pigs has been extensively investigated over the past 2 decades (Shields et al., 1983; Tess et al., 1986; Gu et al., 1992; Wagner et al., 1999). This has resulted in a selection process with pigs having faster growth rates and greater amounts of lean and lesser amounts of fat tissue. Consequently, pork products of a lower fat content are more acceptable to consumers today than a few decades ago. Pigs are also being marketed at heavier BW because of the greater amount of carcass lean and lesser fat tissue, but there is also a greater throughput of salable pork per unit of fixed investment. The genetic improvements and resulting financial incentives to produce pigs of greater lean content have resulted in an increasing proportion of lean pigs being marketed.

Technologies to quantify body composition in animals have been actively pursued over the last century (Shields et al., 1983; Forbes, 1999; Mitchell and Scholz, 2001). Formulas have been developed using various measurement criteria (NPB, 2000; Schinckel et al., 2006), and are useful because differences in body leanness still exist between and within breeds, sexes, and genetic lines (Gu et al., 1992; Fisher et al., 2003). Consequently, there is a need to continually review the tools in common use and the criteria used in lean gain formulas in commercial pig production. Methodology having high accuracy and using noninvasive techniques that can accurately assess the amount of lean tissue would be desirable to both packers and producers.

The current study evaluated live and slaughtered animal body measurements and ultrasound methods to assess lean and fat tissue development in pigs during their growth cycle until market BW. The study involved barrows and gilts of 2 distinctly different genetic lines at various BW. The objective of this experiment was to characterize the lean and fat changes that occur during body development of 2 genetic lines as a way to better understand proper feeding programs at the farm level and to evaluate methods of evaluating their lean growth.

	MATERIALS AND METHODS

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
The experimental use of animals and procedures followed were approved by the College Animal Care Committee. Two genetic lines of pigs having different lean contents at market BW were used to evaluate differences in body measurements and their respective lean development pattern from 20 to 125 kg of BW. One genetic line [(Yorkshire x Large White) x Hampshire sire)] was identified as the low-lean line, where herd records had indicated an estimated 280 g of fat-free lean (FFL) gained/d. The Yorkshire x Large White females were derived and maintained as divergent in pedigree based on the original country of origin (Large White, United Kingdom; and Yorkshire, United States), whereas the Hampshire sire represented commercially available sire lines obtained through a semen supplier. The second line [(Large White x Landrace) x Newsham sire)] was identified as a high-lean line, with a herd average of 375 g of FFL gained/d.

Two groups of gilts and barrows from the 2 genetic lines were obtained at weaning, transported and housed at a common site, and fed identical starter diets throughout the nursery period. At 20 kg of BW, the pigs were moved to a totally enclosed, confinement facility, with each sex and genetic line placed in separate pens and fed different cornsoybean mixtures. Because of differences in lean gain potential, and the negative effects of feeding diets that greatly exceed the pigs’ protein and amino acid needs, diets were formulated to only slightly exceed NRC (1998) amino acid requirements for their projected lean gain potential (Table 1). Pigs were allotted by sex and genetic line and placed in groups of 6 pigs per pen (4.3 x 1.5 m). Each group contained 3 replicates (n = 6 total). The pen had partially (40%) slotted, concrete floors, 1 stainless-steel 3-hole feeder, and 1 nipple waterer. Access to treatment diets and water was provided on an ad libitum basis throughout the experiment. Additional pigs were available within each group in adjacent pens, were fed the same treatment diets, and were used only in the event that a pig that was initially allocated had to be removed from the study.

Pigs available at each BW were scanned at approximately the 10th-rib location with real-time (RT) and A-mode ultrasound devices. Real-time measurements of backfat depth (perpendicular to the skin) and LM area were collected. Backfat was measured with A-mode ultrasound at the 10th rib, approximately 5-cm lateral to the dorsal midline (Lean-Meater, Renco Corporation, Minneapolis, MN). The RT scans were collected using an Aloka, 500V scanner, fitted with a 3.5-MHz, 12.5-cm-long probe (Aloka Products Company, Tokyo, Japan), at the same location as the the RT scans.

In addition, linear body measurements, using adjustable metal calipers, included the height at the shoulder, 10th rib, and tail head. The difference between the caliper tips was measured with a tape to the nearest mm. Body length was measured with a tape from the base of the ear to the tail head. The width of the loin was measured at 3 sites with metal calipers. In the live animal, the width of the cranial loin was measured behind the shoulder (approximately the fifth rib), the width of the caudal loin was measured at approximately the fourth lumbar, and the middle of the loin was measured at the midpoint between the cranial and caudal locations.

Pigs selected for slaughter were taken to The Ohio State University abattoir and slaughtered. Pigs were placed in scalding water, dehaired, and later eviscerated in the approved manner. Carcasses with forelegs attached were split medially, hot carcass weight was recorded, and the carcass halves were placed in a chilled room (4°C). Both halves of the chilled carcass, at approximately 24 h after slaughter, were weighed and the right side was cut between the 10th and 11th rib. The cut surfaces were allowed exposure to air for approximately 15 min to standardize the recording of color and reflectance (Minolta CR-300, Ramsey, NJ) values. Backfat depth, including skin, was measured three-quarters the length of the transverse section of the exposed LM, from the edge of the muscle to the lateral edge and perpendicular to the skin. Longissimus muscle area was determined using a standard plastic pork grid (AS-235, Iowa State University, Ames).

Data collected were analyzed using the MIXED procedure (SAS Inst. Inc., Cary, NC) according to the following model: Y_ijkl = µ + G_i + N_j + W_k + GN_ij + GW_ij + NW_jk + GNW_ijk + e_ijkl, where: Y_ijkl = the dependent variable; µ = the overall mean; G_i = the fixed effect of the ith sex group (i = 1,2); N_j = the fixed effect of the jth genetic line (j = 1,2); W_k = the fixed effect of the kth BW group (k = 1, 2, 3, 4, 5); GN_ij = the interaction term of the ith sex with the jth genetic line; GW_ij = the interaction term of the ith sex with the kth BW group; NW_jk = the interaction term of the jth genetic line with the kth BW group; GNW_ijk = the interaction term of the ith sex, jth genetic line, and kth BW group; and e_ijkl = error term N (0, ²_k).

Individual pigs were considered the experimental unit. The slice option of the MIXED procedure of SAS was used to compare genetic line and sex, interactions at each BW, and for the overall 20- to 125-kg of BW range.

	RESULTS

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
Because of the confounding influence of various factors with pigs being removed from their respective pens, performance responses were not considered valid and thus are not reported. However, with the various measurement differences that resulted between sex and genetic line at various BW, interactions are presented as least squares means in tabular form.

As expected, when BW increased, phenotypic measurements for barrows and gilts increased (P < 0.01; Table 2). There were no sex differences in height at the shoulder, 10th rib, and tail head across all BW. Barrows were generally wider at the shoulder and ham, particularly at heavier BW, but the sex x BW interactions were not significant. No differences in loin width were observed when comparing barrows and gilts at any BW with the exception that barrows had a greater width of the loin at the lumbar region (P < 0.05) at 125 kg of BW. Body length increased quadratically (P < 0.01) as BW increased but was similar for both sexes as were the number of rib pairs counted of all pigs slaughtered.

Backfat thickness increased as BW increased (P < 0.01) for both sexes. Barrows had greater backfat thicknesses than gilts at each BW with differences between sexes increasing as BW increased, resulting in a sex x BW interaction (P < 0.05). However, backfat thickness measured with RT technology was greater when compared with carcass measurements at each BW, with the differences being greater at lighter but similar at heavier BW. In comparison, A-mode ultrasound also demonstrated a greater backfat thickness for barrows as BW increased (P < 0.01) than gilts, particularly at the heavier BW, resulting in a BW x sex interaction (P < 0.05). The A-mode ultrasound measurements, however, were not as accurate as RT measurements when compared with carcass measurements.

Indices of loin quality, as measured by the Minolta colorimeter (CR-310, 50 mm orifice, calibrated against a white tile, D65 illuminant; Minolta Corporation) did not show any difference in reflectance or lightness between sexes. The b* value increased linearly (P < 0.01) as BW increased, reflecting a more yellowish color appearance in the loin tissue.

Calculated lean at 100 and 125 kg of BW using NPB (2000) formulas for RT and carcass measurements demonstrated an increase in lean tissue at these BW (P < 0.01). Lean tissue was greater with gilts (P < 0.01) when express either on a quantity (i.e., kg) or percentage of carcass basis (Table 2). Both RT and carcass estimates of lean content resulted in relatively similar values at 100 and 125 kg of BW.

The high-lean genetic line had a greater height at the 10th rib (P < 0.02) and tail head (P < 0.01) from 20 to 100 kg of BW, but was similar for both genetic lines at 125 kg of BW (Table 3).

Width of the shoulder and ham were greater in the high-lean genetic line pigs at lighter BW, significant (P < 0.05) only when measured at the shoulder at 45 kg of BW. Similar body widths at heavier BW may be attributable to different ratios of muscle and fat accretions that were concurrently occurring between genetic lines.

As expected, LM area and backfat thickness both increased (P < 0.01) as BW increased for the genetic lines. This was demonstrated by the RT and carcass measurements at each BW. Longissimus muscle area was greater (P < 0.01) in the high-lean genetic line over all BW. Differences between LM areas of high-lean and low-lean genetic lines increased from 45 to 125 kg of BW resulting in a genetic line x BW interaction (P < 0.05). Longissimus muscle areas were generally underestimated at lighter BW using RT technology when compared with carcass measurements, but from 75 to 125 kg of BW the estimates were generally similar for both techniques.

The high-lean genetic line had lower backfat thickness at each BW when compared with the low-lean genetic line. Backfat thickness differences between genetic lines increased as BW increased resulting in a genetic line x BW interaction (P < 0.01). Backfat thickness measurements on the carcass were generally less at each BW when compared with RT measurements. The A-mode ultrasound single transducer equipment demonstrated increased backfat thickness as BW increased (P < 0.05) for both genetic lines, but at heavier BW greater backfat depth differences occurred between A-mode to carcass measurements and RT measurements. Comparing carcass backfat measurements with RT and A-mode measurements, the RT measurements were in closer agreement to those collected from the carcass than those from the A-mode measurements. However, RT measurements, generally overestimated backfat thickness an average of 8% when compared with carcass measurement, whereas the A-mode measurement underestimated backfat thickness by approximately 25%. Real-time ultrasound measurements appeared to consistently overestimate carcass measurements at all BW, but values were closer to measured carcass values compared with A-mode measurements. The RT and A-mode technologies were only consistently able to estimate the carcass measurement between 20 to 40 kg of BW. Thereafter, from 40 to 125 kg of BW the magnitude of divergence between A-mode and carcass backfat measurements were exacerbated as BW increased. The main effect of backfat thickness measurements with increasing BW using the 3 technologies is presented in Figure 1.

View larger version (12K): [in this window] [in a new window]   Figure 1. Backfat thickness measurements in the chilled carcass, or using real-time (RT) technology or A-mode ultrasound single transducer (ST) technology in pigs from 20 to 125 kg of BW (SEM = 0.04; n = 120).

Longissimus muscle area as measured by RT ultrasound and from the carcass was greater (P < 0.01) in the high-lean than the low-lean genetic line at all BW. Both RT and chilled carcass measurements resulted in a genetic line x BW interaction (P < 0.01) for LM area with the differences between high-lean and low-lean lines increasing as BW increased. These results also demonstrated similar LM areas for the 2 genetic lines at 20 kg of BW, whereupon they diverged as BW increased from 45 to 125 kg of BW. The data thus demonstrated, as expected, a greater difference in LM growth during the latter part of the grower period.

There were minimal differences in femur measurements between the 2 sexes, but there were more distinct differences in bone organic matrix and ash contents between the 2 genetic lines. The main effects of sex and genetic line on femur bone measurements are presented in Table 4 with the genetic line x BW interactions reported in Table 5.

Femur bone weight and diameter, cortical wall thickness, total organic matrix and ash content each increased linearly (P < 0.01) as BW increased. However, there was no interaction between genetic line and BW for these variables. Bone length and the quantity of bone organic matrix increased more rapidly at lighter BW than at heavier BW for both genetic lines, resulting in an overall quadratic BW response (P < 0.01). In contrast, the amount of bone ash appeared to increase at a greater rate at heavier BW, particularly in the low-lean genetic line.

Bone organic matrix, comprised largely of proteinaceous material, was greater (P < 0.01) in the high-lean genetic line, whereas their bone ash content (P < 0.01) was lower. Percentage bone ash increased (P < 0.01) with BW for both genetic lines but values were consistently higher for the low-lean genetic line, paralleling one another as BW increased. The decline in percentage ash from 20 to 45 kg of BW is consistent with that reported earlier (Shields et al., 1983).

	DISCUSSION

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
Evaluating muscle and fat development in the live pig is a common practice and historically several body characteristics have been used to assess these measures. However, new technologies, namely ultrasonic technologies, have allowed more accurate quantification of live animal compositional differences. Ultrasonic methods have inherent flaws, the more notable being the sophistication of the ultrasonic device, the technical ability of the person using the equipment, and the ability of the operator to accurately interpret their observations. Accuracy of RT ultrasound when compared with carcass measurements appears to vary largely due to differences in operator skill (McLaren et al., 1991). The modern pig of a high-lean composition, was found to be generally longer, wider in the ham area, and has narrower shoulders than pigs of a low-lean genetic potential. These characteristics, along with less backfat thickness and LM area as determined by ultrasound equipment, are frequently used to estimate the relative amount of muscle and body fat. Differences in lean and fat accretion appear to become more pronounced after 75 kg of BW concurrent with corresponding differences in phenotypic characteristics.

Using carcass measurements or RT technology, the quantity of calculated FFL increased linearly (P < 0.01) as BW increased to 125 kg of BW. The 2 genetic lines demonstrated different lean deposition accretion rates that could be detected using ultrasound equipment. The difference in FFL between genetic lines diverged as BW increased, resulting in a genetic line x BW interaction (P < 0.01). In the current study the high-lean genetic line deposited FFL at a greater linear rate than the low-lean genetic line from 20 to 125 kg of BW.

Our results show that RT technology equipment may be a relatively good tool in measuring backfat thickness and LM area. Using formulas developed by the NPB (2000) for estimating lean and fat tissue, the high-lean genetic line pigs and the gilts demonstrated more FFL tissue (P < 0.01) and a higher percentage of lean tissue (P < 0.01) than barrows. Results generally were comparable to those measurements collected from the carcass after slaughter. Both technologies resulted in similar quantities of lean tissue at 100 or 125 kg of BW.

Over the past 30 yr, studies have reported correlations averaging 0.67 for LM area and 0.78 for backfat thickness when contrasted to BW (Mitchell and Scholz, 2001). Moeller and Christian (1998) evaluated 8 genetic lines at 4 BW periods, and compared RT technology to carcass measurements at market BW. Their study with RT equipment tended to overestimate LM area by about 0.3 cm² and backfat depth by 0.11 cm. Our study comparing RT technology to carcass measurements found that LM area differences were greater at lighter but similar at heavier BW. Backfat depths using RT methodology tended to overestimate backfat thickness by an averaged 0.14 cm across all BW. However, differences between RT and carcass measurements were closer for backfat thickness at 100 and 125 kg of BW. The differences at the lighter BW may partially be explained by improper fitting of transducer equipment to the animal’s topline. Our results also demonstrate that the A-mode single transducer ultrasound equipment underestimated backfat depth, particularly when greater than 45 kg of BW. Although the A-mode ultrasound technology did reflect increased backfat thickness as BW increased and thus can be a useful tool, it is clearly limited in its accuracy. The A-mode data show a linear increase in backfat depth with BW, but the slopes are not even near the same as those from the carcass. The mean differences increased greatly as BW increased, thus the A-mode technology is not an accurate predictor when backfat thickness increases beyond what appears to be 10 mm. The A-mode machines may not accurately detect the third layer of subcutaneous fat.

Our results using the 2 genetic lines were generally consistent with other studies (Tess et al., 1986; Gu et al., 1992). Longissimus muscle area development in the pig increased in a quadratic manner, responses consistent with the results of Shields et al. (1983) and Wagner et al. (1999).

Differences in body composition between genetic lines and sex have been previously reported (Goerl et al., 1995; White et al., 1995; Edwards et al., 2003). Gu et al. (1992) evaluated 5 genetic lines using a combination of Hampshire, Duroc, Yorkshire, Landrace, and synthetic lines and reported a difference of 8 cm² of LM area (30.32 to 38.39) and 0.68 cm of backfat depth (4.25 to 3.57) for pigs slaughtered at 127 kg of BW. Genetic lines with improved carcass and meat quality traits were also evaluated by Edwards et al. (2003). In their study, Duroc- and Pietrain-sired progeny slaughtered at 148 and 140 kg of BW, respectively. Duroc sired pigs had a LM area of 50.2 cm² and 10th rib backfat of 2.6 cm compared with 53.2 cm² and 2.3 cm for the Pietrain.

Our results clearly demonstrated a difference in the growth and development of bone tissue between the 2 genetic lines, whereas sex differences were minor. The high-lean genetic line deposited approximately 3.5% less minerals in the femur bone while the organic matrix was greater by 1.2% (Table 4). Bones having a higher mineral content is of particular importance during reproduction, where bone mineral reservoirs are used during periods of high productivity (Mahan and Fetter, 1982). When developing maternal gilt lines having high productivity traits, it is possible that the mineral content of the bones may have inadequate mineral reserves capable of meeting the high demands of production. Our data imply that high-lean genetic lines may not have adequately mineralized their skeletal tissue.

Our results imply that the maturity of bone tissue may differ between genetic lines and may be less physiologically mature at each BW in high-lean genetic lines. Nimmo et al. (1981) demonstrated that first parity gilts fed NRC levels of Ca and P during the grower and gestation periods had a greater percentage of animals with leg problems during their reproductive cycle and had to be removed from the study.

In conclusion our study indicated that technology selection (RT ultrasound, A-mode single transducer) will demonstrate differences in body composition in the growing pig. Real-time ultrasound technology was more accurate in measuring backfat thickness than the A-mode ultrasound equipment. Our results also indicate that RT measured the LM area accurately, particularly when pig BW are 75 kg of BW. Of those linear measurements collected on the live animal that appeared to more accurately reflect body composition, the width at the shoulder and lumbar region reflected increasing depositions of subcutaneous fat, whereas width of the ham at heavier BW better reflected muscle accretion.

	Footnotes

 
¹ Salaries and research support were provided by state and federal funds appropriated to The Ohio Agric. Res. and Dev. Center and The Ohio State University.

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.

	LITERATURE CITED

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 


Edwards, D. B., R. O. Bates, and W. N. Osburn. 2003. Evaluation of Duroc- vs. Pietran-sired pigs for carcass and meat quality measures. J. Anim. Sci. 81:1895–1899.

Fisher, A. V., D. M. Green, C. T. Whittemore, J. D. Wood, and C. P. Schofield. 2003. Growth of carcass components and its relation with confirmation in pigs of three genotypes. Meat Sci. 65:639–650.[CrossRef]

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Goerl, K. F., S. J. Eilert, R. W. Mandigo, H. Y. Chen, and P. S. Miller. 1995. Pork characteristics as affected by two populations of swine and six crude protein levels. J. Anim. Sci. 73:3621–3626.[Abstract]

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McLaren, D. G., J. Novakofski, D. F. Parrett, L. L. Lo, S. D. Singh, K. R. Neumann, and F. K. McKeith. 1991. A study of operator effects on ultrasonic measures of fat depth and longissimus muscle area in cattle, sheep and pigs. J. Anim. Sci. 69:54–66.[Abstract]

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Moeller, S. J., and L. L. Christian. 1998. Evaluation of the accuracy of real-time ultrasonic measurements of backfat and loin muscle area in swine using multiple statistical analysis procedures. J. Anim. Sci. 76:2503–2514.[Abstract/Free Full Text]

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NPB. 2000. Pork Composition & Quality Assessment Procedures. National Pork Board, Des Moines, IA.

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Schinckel, A. P., S. Pence, M. E. Einstein, R. Hinson, P. V. Preckel, J. S. Radcliff, and B. T. Richert. 2006. Evaluation of different mixed model nonlinear functions on pigs fed low-nutrient excretion diets. Prof. Anim. Sci. 22:401–412.

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This Article Abstract Full Text (PDF) All Versions of this Article: jas.2006-406v1 85/7/1816    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Wiseman, T. G. Articles by Kim, Y. Y. Search for Related Content PubMed PubMed Citation Articles by Wiseman, T. G. Articles by Kim, Y. Y.