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ANIMAL NUTRITION |
Department of Animal Sciences, Louisiana State University Agricultural Center, Baton Rouge 70803
| Abstract |
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Key Words: Carcass Traits Chromium Propionate Pigs Pork Quality
| Introduction |
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The effects of Cr on pork quality have been studied to a lesser extent than the effect of Cr on growth performance and carcass traits. The recent research of Matthews et al. (2003)
and Shelton et al. (2003)
indicated that Cr propionate (CrProp) improved subjective marbling scores and some measurements of water-holding capacity in fresh and frozen chops. OQuinn et al. (1998)
reported that Cr picolinate decreased drip loss and marbling score. Furthermore, OQuinn et al. (1998)
reported subjective color scores were lower in gilts fed Cr nicotinate than in gilts fed Cr picolinate.
Research has indicated that Cr may partially alleviate some of the effects of shipping stress in feedlot calves (NRC, 1997
), but we are unaware of research evaluating the effect of Cr on shipping stress in pigs. However, if Cr alleviates some of the effects of shipping stress, it might also improve pork quality.
With the heightened awareness of pork quality in the swine industry and possible supplementation of Cr in swine diets, the effects of Cr on pork quality need to be more clearly defined. Thus, the purpose of this study was to evaluate the effects of Cr as CrProp on growth, carcass composition, shipping shrink, and pork quality of finishing gilts.
| Materials and Methods |
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General
Forty crossbred gilts were allotted to two dietary treatments in a randomized complete block design on the basis of BW. Each treatment consisted of four replicates of five pigs per replicate, with an initial mean BW of 73 kg. A two-phase-finisher program was used with diets formulated to provide 0.82 and 0.64% total lysine for the weight ranges of 73 to 80 kg and 80 to 115 kg, respectively. All other AA and nutrients met or exceeded NRC (1998)
requirements. Dietary treatments included the following: 1) a corn-soybean meal diet containing 15% wheat middlings (basal; Table 1
); or 2) basal diet + 200 ppb Cr as CrProp (KemTRACE chromium, Kemin Industries, Inc., Des Moines, IA). Treatment diets in meal form and water were provided for ad libitum consumption. Pigs were housed in a curtain-sided building with 1.5 m x 3.0 m pens and concrete slotted floors. Pigs and feeders were weighed every 2 wk for calculation of ADG, ADFI, and G:F. The experimental period lasted 54 d.
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At trial termination (BW = 115 kg), four pigs from each replicate pen were randomly selected for determination of shrink loss (from feed withdrawal and shipping), carcass traits, and pork quality. On the day before slaughter, selected pigs were weighed and had feed withdrawn. After 18 h of feed withdrawal, pigs were reweighed for determination of shrink due to feed withdrawal. Pigs were then transported for 2.66 h (209.2 km) in two 6.1 m x 2.0 m trailers. Treatments and replications were equally represented within each trailer. The average temperature was 18°C during transportation. After transport, the pigs were weighed again for determination of shrink due to shipping. Immediately after weighing, pigs were bled for determination of plasma cortisol, lactate, and glucose concentrations and then transported to the Louisiana State University Agricultural Center Meats Laboratory for slaughter. Slaughter practices included electrical stunning followed by exsanguination. During exsanguination, a blood sample and rectal temperature were collected. All carcass data (loin muscle area; 10th-rib, 1st-rib, last-rib, and last-lumbar vertebrae backfat thickness; carcass length; and muscle score) were collected on the left side of the carcass after a 44-h chill at 2°C. Loin muscle area, 10th-rib backfat thickness, average backfat thickness, and dressing percent were determined as previously described by Matthews et al. (1998)
. Fat-free lean, percent lean, and muscle score were determined using the equations and procedures outlined by the NPPC (2000)
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Forty-five-minute and 24-h pH were determined in the loin muscle between the 10th and 11th ribs and in the semimembranous muscle of the ham using a hand-held pH meter (model IQ150, IQ Scientific Instruments, Inc., San Diego, CA) fitted with a stainless steel probe (part No. PH07-SS, IQ Scientific Instruments, Inc.). After collection of all carcass data, two 2.54-cm chops were collected from the 11th and 12th ribs, and a loin section from the 4th to 10th ribs also was collected. The 12th-rib chop was used to determine fresh chop drip loss (48 h) using a suspension method described by Matthews et al. (2001a)
. Fresh chop cooking and total loss were then determined as described by Matthews et al. (2001c)
. The 11th-rib chop was used to determine frozen chop thaw, cooking, and total losses as previously described by Matthews et al. (2001c)
. Immediately after collection of the loin section, Commission Internationale de lÉclairage L*, a*, and b* values (determined using the CIELAB space with a D65 illuminant) were obtained from three orientations on the 10th-rib loin interface using a Minolta spectrophotometer (model CM-508d; Minolta Corp., Ramsey, NJ). Pork quality scores (color, marbling, firmness, and wetness) also were determined on the 10th-rib loin interface using the guidelines of the NPPC (2000)
. Two individuals independently scored the loins and the average was used. For determination of purge loss, the loin sections were deboned and fat was uniformly trimmed. After trimming, loin sections were weighed, placed in vacuum bags, and vacuum-sealed. The loin sections were refrigerated at 2°C for 21 d, and then removed from the vacuum bags, blotted free of any excess surface moisture, and weighed again to determine the amount of purge loss. Percent purge loss was calculated as follows: ([initial loin weight, g final loin weight, g]/initial loin weight, g) x100.
Plasma Analyses
After collection of blood, the samples were kept at 2°C for 3 to 8 h, and then centrifuged for 15 min at 1,500 x g at 4°C. Plasma was collected and frozen (20°C) until subsequent analysis for cortisol, glucose, and lactate concentrations. Plasma cortisol concentrations were determined with a RIA kit (cortisol 125I RIA kit, Costa Mesa, CA). The intraassay CV for cortisol determined with a porcine plasma pool was 6.0%. Glucose concentrations were determined using a spectro-photometric procedure (Sigma, 1990
). Plasma lactate concentrations were determined using an enzymatic-colorimetric procedure using a lactate reagent (No. 735-10, Sigma, St. Louis, MO) at 540 nm.
Statistical Analyses
Data were analyzed by ANOVA procedures (Steel and Torrie, 1980
) using the GLM procedure of SAS (SAS Inst., Inc., Cary, NC) as a randomized complete block design. The pen of pigs served as the experimental unit for all data. Effects were considered significant at P < 0.10.
| Results |
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| Discussion |
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Research assessing the effects of Cr on pork quality is more limited than research on growth and carcass composition, but it is equally variable. OQuinn et al. (1998)
reported that gilts fed Cr picolinate had higher subjective color scores than did gilts fed Cr nicotinate. Matthews et al. (2003)
reported that CrProp had no effect on color scores (subjective or objective), and our data are in agreement. Matthews et al. (2003)
also reported that 45-min and 24-h pH measurements were not affected by Cr. Our data are in partial agreement, in that 45-min pH was not affected by Cr, but 24-h pH was higher in pigs fed Cr. OQuinn et al. (1998)
reported that Cr picolinate decreased marbling scores, but Matthews et al. (2003)
reported that CrProp increased marbling scores. Boleman et al. (1995)
reported that Cr picolinate had no effect on marbling score, which agrees with our findings. Matthews et al. (2003)
reported that a combined firmness-wetness score tended to be improved in pigs fed CrProp, but our data indicated that individual firmness and wetness scores were not affected by CrProp. Furthermore, reports have indicated that Cr does not affect shear force (Page et al., 1992
; Matthews et al., 2003
), and our data are in agreement.
The earlier research assessing water-holding capacity indicated that Cr picolinate does not improve drip loss or cooking loss (Page et al., 1992
; Boleman et al., 1995
). However, some of the more recent data indicate that Cr picolinate may decrease drip loss (OQuinn et al., 1998
) and that CrProp may decrease thaw loss (Matthews et al., 2003
). Our data are in agreement with these findings, in that drip loss and purge loss of fresh pork were decreased by CrProp supplementation, but thaw loss was only numerically lower in pigs fed CrProp.
We are unaware of any research that has addressed the percent weight loss (shrink) due to fasting or shipping in pigs fed Cr. Rosebrough and Steele (1981)
studied the effects of Cr on feed withdrawal in turkey poults, but they did not analyze the weights after feed withdrawal or estimate percentage of weight loss differences because of possible gut fill influences at initiation of feed withdrawal. Our data indicate that the percent weight loss due to feed withdrawal and shipping were not affected by CrProp.
Plasma cortisol, glucose, and lactate concentrations after shipping and during exsanguination were not affected by CrProp supplementation. Matthews et al. (2003)
proposed that differences in pork quality in pigs fed Cr could possibly be attributed to either decreased stress or a change in glycolytic potential. The absence of a change in plasma cortisol concentrations seems to indicate that Cr does not affect the stress status of the pig; thus, a change in glycolytic potential would seem more likely. We did not assess glycolytic potential, but plasma glucose and lactate concentrations did not differ between pigs fed the control and diets containing CrProp. However, the glycolytic potential of the muscle tissue could still be affected despite the lack of differences in plasma glucose or lactate during exsanguination. Rosebrough and Steele (1981)
reported that liver glycogen levels and glycogen synthase activity were increased in turkey poults fed Cr, but they did not assess muscle glycogen levels in response to Cr. Research should be conducted to determine whether Cr affects glycolytic potential in muscles of pigs.
The results of our research indicate that CrProp does not affect growth performance or carcass composition, but that it may affect some aspects of pork quality. If it can be demonstrated that Cr consistently affects these quality measurements, these changes in pork quality could be beneficial to the pork industry.
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| Footnotes |
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2 The authors thank the Louisiana State Univ. Agric. Center Meats Laboratory for assistance with data collection. The authors also thank C. Airhart, R. Payne, J. Shelton, B. Watson, and S. Williams for assistance with data collection and sample analyses. ![]()
3 Current address: Premium Standard Farms, 22123 Highway 5, P.O. Box 99, Milan, MO 63556. ![]()
4 Current address: AFB Int., 937 Lone Star Dr., OFallon, MO 63366. ![]()
5 Correspondencee-mail: lsouthern{at}agctr.lsu.edu.
Received for publication September 3, 2004. Accepted for publication December 22, 2004.
| Literature Cited |
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