J. Anim. Sci. 2005. 83:223-230
© 2005 American Society of Animal Science
Effects of different cereal grains and ractopamine hydrochloride on performance, carcass characteristics, and fat quality in late-finishing pigs
S. N. Carr,
P. J. Rincker,
J. Killefer,
D. H. Baker,
M. Ellis and
F. K. McKeith1
Department of Animal Sciences, University of Illinois, Urbana 61801
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Abstract
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Forty-eight barrows and forty-eight gilts (PIC 337 sires x PIC C22 dams) were evaluated to determine the effects of feeding ractopamine hydrochloride (RAC) and different cereal grains on the carcass and fat quality in late finishing pigs. The study was carried out using four replicates with 24 animals in each replicate (four pigs per pen, six pens per replicate, two replicates per slaughter date, 12 pens per slaughter date). Treatments for the experiment included corn, wheat, and barley (early finisher period); and corn, corn + RAC, wheat, wheat + RAC, barley, and barley + RAC for the late finisher period. Ractopamine was fed at the level of 10 mg/kg (as-fed basis) of feed. Pigs were allotted to early finisher period treatments at approximately 45 kg BW. Pigs were then given late finisher period treatments at approximately 80 kg BW and fed for 28 d. The dietary digestible lysine level for all diets was maintained at 2.7 g/Mcal of ME. Pigs fed the wheat and corn diets during the late finisher period had a greater (P <0.05) G:F than those fed the barley diets. Pigs fed diets with RAC had lower (P <0.05) leaf fat weights, 10th-rib fat, last-rib fat, and belly firmness and had improved (P <0.05) dressing percents and loin muscle areas compared with those not receiving RAC. Pigs fed the wheat diets had a greater (P <0.05) dressing percent than those receiving the barley diets, but pigs fed the barley diets had a higher (P <0.05) Minolta L* for fat color than pigs fed wheat. Pigs fed diets containing RAC produced pork that was less tender (P <0.05) compared with pigs that did not receive RAC. Linoleic acid percent values were higher (P <0.05) for pigs fed diets with RAC than in those that did not. Feeding RAC improved G:F and lowered feed intake of pigs during the late finisher period (P <0.05). Feeding diets equal in lysine (2.7 g/Mcal of ME) but varying in ME, whether based on corn, wheat, or barley with or without RAC, had little to no effect on carcass, meat, or fat quality attributes.
Key Words: Cereal Grain • Fat Quality • Ractopamine • Swine
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Introduction
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During the last decade, the importance of the firmness and color of fat has increased dramatically. It is an important factor in the organoleptic and economic value of pork (Irie, 1999
). Fat quality affects both further processing characteristics and the ability of pork products to meet export specifications. Problems that may arise with bacon from soft fat include slices sticking together, an oily appearance in the package, separation of fat from lean during slicing, and oxidative rancidity occurring at a rapid rate (NPPC, 1999). Soft fat is also a concern in sausage manufacturing, where the ability to visualize particle definition of lean and fat is an important property. Soft and highly unsaturated fats have a lower melting point compared with firmer and saturated fats. With the temperature increase associated with grinding, highly unsaturated fats can start to melt and form a fat coating on the product, which is visually unattractive. Soft and dark fat is the principle factor in downgrading and lowering the price of the product due to decreased quality of the processed product.
The higher levels of pigments and unsaturated fatty acids found in corn can contribute to the development of dark and soft fat depots. One possible remedy for the problem of soft, dark pork fat would be the addition of barley or wheat to diets in place of corn. Barley and wheat contain lower levels of carotenoids or xanthophylls, and these cereal grains are lower in C18:2 than corn (NRC, 1998).
McKeith et al. (1990) and Engeseth et al. (1992) conducted experiments to determine the fatty acid profiles of lipid depots from swine fed corn–soybean meal diets supplemented with ractopamine (RAC). Only minor effects were reported for changes in fatty acid profiles of s.c. fat samples from pigs treated with RAC. The principle objective of the research reported herein was to evaluate the effect of RAC and cereal grain (corn, barley, or wheat) on carcass and fat quality of pork.
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Materials and Methods
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This study was performed as a nested randomized complete block design with a 3 x 2 factorial arrangement of dietary treatments. Three cereal grains (corn, wheat, and barley) and two levels of RAC (0 and 10 mg/ kg of feed on an as-fed basis) were evaluated in late-finishing pigs. A total of 96 pigs averaging approximately 45 kg were separated into 16 blocks of six pigs each based on ancestry, gender, and BW. There were eight barrow blocks and eight gilt blocks. The four heaviest blocks within gender were assigned to Replicate 1, and the four lightest blocks were assigned to Replicate 2. From blocks within each of the four replicates, pigs were randomly assigned to one of six dietary treatments. Thus, there were two barrow pens and two gilt pens assigned to each dietary treatment, and each of the 24 pens contained four pigs of the same gender. The University of Illinois Laboratory Animal Care Committee approved all experimental procedures.
During the early finisher period of the trial (approximately 45 to 80 kg BW), one of three cereal diets was fed, such that there were eight pens of four pigs each receiving the corn-, wheat-, and barley-based diets. Diets were formulated to provide adequate to excess levels of both CP and lysine for high-lean, early-finishing gilts and high-lean, late-finishing gilts receiving RAC (NRC, 1998). Thus, diets were the same with the exception of RAC, for both the early (approximately 45 to 80 kg) and late (approximately 80 to 109 kg) finishing periods (Table 1). Because finishing gilts have higher CP and lysine requirements (percentage of diet) than finishing barrows (NRC, 1998), the diets provided some degree of excesses of both CP and lysine for the barrows. In all cases, however, the diets were formulated to contain exactly 2.7 g of true digestible lysine/Mcal of ME. This was done on the assumption that the pigs would eat to meet their ME needs and would therefore consume more of the lower ME barley diets than of the higher ME corn and wheat diets. Fatty acid profiles of the corn, wheat, and barley used in the diets are presented in Table 2.
The study was conducted in a finishing unit at the University of Illinois Swine Research Center, which consists of part solid and part slotted concrete floors. Pigs were grouped in pens of four with a floor space allowance of 1.17 m2/pig. Diets were provided ad libitum access to feed from a single-space feeder, and water was freely available from a nipple waterer in each pen. Diets for the early finisher period (Table 1
) were provided from the time of allotment (approximately 45 kg) until the pig weight was approximately 80 kg. At this time, early finisher period diets were removed from the feeders and late finisher period diets were initiated. The target endpoint was when RAC had been administered for a 28-d period. Pigs and feeders were weighed every 14 d during the late finisher period of the experiment.
After RAC had been fed for 28 d, the feeders were removed from the pens, after which the pigs were weighed and then transported to the University of Illinois Meat Science Laboratory for slaughter the following morning. At the laboratory, the pigs were kept overnight in two pens with a similar number of pigs for each treatment represented in each pen. Each pig had access to water but not access to feed. The pigs were slaughtered in a random order starting at approximately 0700 the morning after delivery.
Pigs were weighed just before immobilization. After immobilization, the pigs were exsanguinated, scalded, dehaired, decapitated, eviscerated, split, inspected, and placed immediately into a 4°C chill cooler. Approximate target time from stun to cooler was 45 min. Leaf fat and HCW were collected, and one side of each carcass was used to obtain 45-min pH of the LM with a SFK Star Probe (SFK Technologies, Cedar Rapids, IA) just before the carcass was placed in the cooler. After chilling for approximately 20 h, an ultimate postmortem pH measurement was taken of the longissimus on all carcasses using the same SFK star probe. One pig from each pen was selected randomly for more extensive longissimus pH measurements. These measurements were made at 3, 4.5, and 6 h postmortem, in addition to the 45-min and approximately 20-h pH measures. Additional carcass measures that were collected at approximately 20 h postmortem included typical carcass measures: first-rib, last-rib, and 10th-rib fat depths; 10th-rib longissimus area; subjective color and marbling scores (NPPC, 1999) of the longissimus; Japanese color score of the longissimus; subjective firmness (NPPC, 1991) of the longissimus; and objective longissimus color. Once the loin had been fabricated, a 1.3-cm chop was cut for drip loss measurement and the remaining portion was aged for 10 d in a 2°C cooler. After aging, 2.54-cm chops were cut for Warner-Bratzler shear force determination and cooking loss, trained sensory panel evaluation, and proximate analysis (moisture and fat).
Subcutaneous fat samples were obtained from the loin in the area of the 10th rib. The sample was approximately 10 cm x 10 cm. This sample was carefully removed from the muscle so that the three fat layers would be intact. Subjective Japanese fat color and objective color with a Minolta Chromameter CR-300 (Minolta Camera Co., Japan; illuminant D65 and 0( observer) were obtained on these 10 cm x 10 cm fat samples. Fat samples (four pigs per pen) were composited and completely homogenized using a food processor for a total of 24 samples from the experiment for fatty acid profile determination (Hara and Radin, 1978). Iodine values were calculated according the procedure of Gatlin et al. (2002). As individual pigs were fabricated, the belly was identified and fat firmness was determined using the belly firmness procedure (Waylan et al. 2002). The bellies were placed on tables and covered for 24 h after fabrication, allowing the temperature of all bellies to equilibrate. Belly firmness measurements were performed at approximately 48 h postmortem.
Statistical Analyses
The GLM procedure of SAS (SAS Inst., Inc., Cary, NC) was used to analyze the data, with the pen of four pigs being the experimental unit for both the live and carcass data. The model included the effects of dietary cereal grain source, ractopamine hydrochloride, gender, and all interactions. Desired comparisons (barley vs. corn and wheat; corn vs. wheat; 0 vs. 10 mg/kg RAC; barley vs. corn and wheat x RAC; corn vs. wheat x RAC) for the growth and feed efficiency traits, and (corn vs. wheat and barley; wheat vs. barley; 0 vs. 10 mg/kg RAC; corn vs. wheat and barley x RAC; wheat vs. barley x RAC) for the carcass traits were tested for selected single-df contrasts.
The statistical model employed gender (1 df) as a blocking factor, thereby sacrificing precision in measuring gender effects, such that enhanced precision would be present for measuring dietary treatment differences. There were few gender x treatment interactions; hence, data were pooled across barrows and gilts in the tables of results.
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Results and Discussion
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Growth performance data are shown for pigs from 45 to 80 kg (early finisher period) in Table 3. Data are separated into three time periods, which included d 0 to14, 14 to 35, and 0 to 35. Pigs fed the corn diets consumed more (P <0.05) feed than those fed the wheat diets. No differences (P >0.05), were observed in ADG and G:F among treatments. That G:F was not decreased (P >0.05) in pigs fed the barley diets is surprising, given the 11% lower ME concentration of this diet compared with the corn and wheat diets.
Growth data are shown in Table 4 for the late finisher period of the experiment. Data were separated into three time periods, which included RAC fed for d 0 to14, 14 to 28, and overall inclusion of RAC (d 0 to 28). No differences (P >0.05) among treatments were found in ADG for any of the time periods. Pigs fed RAC had numerically higher ADG for all three time periods than the controls. Feed intakes were lower (P <0.05) for pigs fed RAC compared with pigs that did not receive RAC. This finding agrees with the results of Stites et al. (1991), Uttaro et al. (1993), and Crome et al. (1996), but is contradictory to those of S. N. Carr, D. J. Ivers, D. B. Anderson, D. J. Jones, D. H. Mowrey, M. B. England, J. Killefer, P. J. Rincker, and F. K. McKeith (unpublished results). Pigs fed the barley diets consumed numerically more feed than did the pigs fed the corn- or wheat-based diets in all time periods but this difference did not reach statistical significance (P >0.05). The barley diets contained the lowest amount of calculated energy density among the three diets. Assuming that pigs will eat to meet their energy requirements, it is logical that the pigs fed barley diets would consume more feed. Ractopamine improved (P <0.05) G:F during all time periods, and pigs fed the corn and wheat diets were more (P <0.05) efficient than those fed the barley diets. The only trend (0.10 >P >0.05) occurred in the corn vs. wheat comparison, where there was a tendency for an interaction (P <0.09) with RAC. Thus, without supplemental RAC, G:F of pigs fed wheat diets was superior to that of pigs fed corn diets, but with supplemental RAC, G:F was similar in pigs fed both the corn- and wheat-based diets. Pigs fed all three cereal-based diets responded to RAC with an average improvement in G:F of 17.2%. The percentage improvement was 24.2, 10.9, and 17.2% for pigs fed the corn-, wheat-, and barley-based diets, respectively.
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Table 4. Performance by pigs fed diets based on different cereal grains with or without 10 mg/kg of ractopamine (RAC) during the late finisher period (80 to 109 kg)a
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Carcass measurements are presented in Table 5. Pigs fed diets containing RAC exhibited lower (P <0.05) leaf fat weights, 10th-rib fat, last-rib fat, and belly firmness measurements. A higher belly firmness measurement indicates a firmer, higher-quality belly. The decrease in leaf fat weight agrees with the findings of Prince et al. (1987), Watkins et al. (1990), and Crome et al. (1996). Carr et al. (unpublished results) reported no difference (P >0.05) in leaf fat weights, or 10th-rib fat, last-rib fat, and belly firmness measurements, but did report numerical decreases in these measurements. Dressing percents were higher (P <0.05) for pigs fed the RAC diets than for the controls. This is also consistent with the results reported by Williams et al. (1987), Watkins et al. (1990), Stites et al. (1991), and Crome et al. (1996). Loin muscle area was increased (P <0.05) for pigs fed RAC compared with the control, which agrees with the findings of Stites et al. (1991), Uttaro et al. (1993), Crome et al. (1996), and Carr et al. (unpublished results). The overall 12.6% increase in loin muscle area was consistent across diets based on corn, barley, or wheat.
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Table 5. Carcass characteristics of pigs fed diets based on different cereal grains with or without 10 mg/kg of ractopamine (RAC) during the late finisher period (80 to 109 kg)a
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Results from the carcass quality measurements are shown in Table 6. Pigs receiving RAC had lower Minolta a* and b* color values of the cut longissimus, indicating less red and yellow pork, respectively, compared with the pigs receiving no RAC. This result is also consistent with the findings of Carr et al. (unpublished results). No other differences (P >0.05) due to RAC were observed for any subjective quality measurements for both muscle and fat samples. Minolta L* objective fat measurements were higher (P <0.05) for pigs fed the barley diets than for pigs fed the wheat diets, indicating a whiter fat with barley. Minolta a* values for the fat samples were higher (P <0.05) for pigs fed the wheat diets compared with the pigs receiving the barley diets. In the corn vs. wheat and barley comparison, there was an interaction (P <0.05) with RAC for the Minolta a* values concerning fat color. The Minolta a* value for corn increased numerically with the addition of RAC, whereas the value for both wheat and barley decreased. No differences (P <0.05) were observed for water-holding capacity among any of the treatments. Carr et al. (unpublished results) also found no effect of RAC on drip loss.
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Table 6. Carcass quality characteristics of pigs fed diets based on different cereal grains with or without 10 mg/kg of ractopamine (RAC) during the late finisher period (80 to 109 kg)a
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Data on pH decline are presented in Table 7. No differences (P >0.05) among treatments were observed at any of the time points. Carr et al. (unpublished results) reported numerically higher pH values for pigs fed 10 mg/kg of RAC at 3, 8, and 24 h postmortem.
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Table 7. Postmortem decline in pH of pigs fed diets based on different cereal grains with or without 10 mg/kg of ractopamine (RAC) during the late finisher period (80 to 109 kg)a
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Sensory, shear, and chemical evaluation data are shown in Table 8. No differences (P >0.05) among treatments were found for pork flavor, juiciness, off flavor, or cooking loss. Carr et al. (unpublished results) also reported no differences (P >0.05) in juiciness, off flavor, or cooking loss resulting from RAC feeding. Pigs fed RAC had loin chops that exhibited higher (P <0.05) shear force values and lower (P <0.05) tenderness scores from a trained sensory panel. These data agree with the results of Carr et al. (unpublished results). This lower tenderness could be due to the fact that RAC is responsible for an increase in fiber diameter. Swatland (1984) showed that increased diameters in muscle fibers have been associated with decreased tenderness independent of connective tissue strength or age. No differences (P >0.05) among treatments were observed in any proximate analysis component of either loin or fat samples.
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Table 8. Sensory, shear and proximate analysis evaluation of pigs fed diets based on different cereal grains with or without 10 mg/kg of ractopamine (RAC) during the late finisher period (80 to 109 kg)a
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Fatty acid profile and calculated iodine values for fat samples are presented in Table 9. Pigs fed RAC had higher (P <0.05) linoleic acid percentages compared with pigs not given RAC. Engeseth et al. (1992) reported numerical increases in linoleic acid as well. Overall, differences among all treatments were minimal in fatty acid profile, which agrees with the results reported by McKeith et al. (1990), Perkins et al. (1992), and Engeseth et al. (1992). No differences (P >0.05) among treatments were observed in calculated iodine values. All iodine values were considered desirable, with no values being over 68 mg of iodine/100 mg of fat. Lea et al. (1970) considered any fat with an iodine value below 70 mg of iodine/100 mg of fat as high quality. Thus, all fat from this experiment would be classified as high quality. This is probably a result of the pigs receiving only 1% added fat (beef tallow) to the diet for dust reduction, as opposed to adding increased amounts of fat or oil (mostly unsaturated) for energy purposes, which would cause a decrease in fat quality as measured by a spike in iodine values.
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Table 9. Fatty acid profile and iodine value calculations diets based on different cereal grains with or without 10 mg/ kg of ractopamine (RAC) during the late finisher period (80 to 109 kg)
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In summary, feeding ractopamine at 10 mg/kg during the last 28 d of finishing can be expected to improve G:F, loin muscle area, and dressing percent but decrease s.c. fat depth. Pigs fed higher-energy corn and wheat diets were more efficient than those fed the lower-energy barley diets. Ractopamine improved feed efficiency and loin muscle area of pigs consuming all three cereal-based diets, but it had no effect on loin color or marbling. Cereal grain did not affect sensory, shear, or proximate analysis values, but pork from pigs fed ractopamine was less tender. Pigs fed barley had higher objective fat color scores than those fed wheat. Minimal treatment differences were observed for fatty acid profiles and iodine values, although pigs fed ractopamine had higher linoleic acid percentages than those receiving the control diets. Feeding corn, wheat, or barley, with or without ractopamine, had little to no effect on muscle or fat quality attributes.
1 Correspondence: 205 Meat Science Lab, 1503 S. Maryland (phone: 217-333-1684; fax: 217-244-5142; e-mail: mckeith{at}uiuc.edu).
Received for publication October 22, 2003.
Accepted for publication September 28, 2004.
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Abstract
Introduction
