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ANIMAL PRODUCTION |
* USDA-ARS, Livestock Behavior Research Unit, Purdue University, West Lafayette, IN 47907
Department of Animal Sciences, Purdue University, West Lafayette, IN 47907
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Abstract |
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 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Key Words: behavior • husbandry • physiology • pig • salbutamol
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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), cimaterol (Moser et al., 1986), and ractopamine (Watkins et al., 1990). Consumers demand lean meat that is wholly safe, and, in some markets, there is also strong demand for a product that meets certain animal well-being criteria. Concerns about the potential side-effects of drug administration on the animals (Hill and Dalrymple, 1987) and of possible dangers of drug residues for consumers (Salleras et al., 1995) has meant that approval for use of β-agonists in commercial production has taken many years.
Ractopamine HCl was approved for use in pigs by the US Food and Drug Administration in 1999. It has been shown to improve ADG, G:F, carcass yield, and carcass lean content (Gu et al., 1991a,b), but it has a short-term benefit, with the greatest response during the first 14 d of administration (Williams et al., 1994; Schinckel et al., 2003). It is recommended for use over a 4-wk period before slaughter. However, ractopamine has been shown to make pigs harder to handle and have elevated circulating catecholamine concentrations and greater heart rates (Marchant-Forde et al., 2003). They also have an increased risk of becoming fatigued during handling (FDA, 2002).
There would therefore appear to be a need for a repartitioning agent that does not have any human or animal health concerns. Salbutamol is a widely prescribed human pharmaceutical, having an established safety record worldwide, and evidence suggests that it has a repartitioning effect (Oksbjerg et al., 1996; Hansen et al., 1997). However, in addition to demonstrating positive production benefits, it is also important that the negative animal well-being effects observed with other compounds are absent or greatly decreased. The objective of this study was to evaluate the effects of the pure, single-enantiomer R-salbutamol and a racemic mixture of R- and S-enantiomer salbutamol on finishing pig behavior and physiology.
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MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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guidelines, and the project was approved by the Purdue Animal Care and Use Committee. Animals, Housing, and Husbandry
A total of 96 gilts and 96 barrows were used, offspring of PIC 280 sires on Danbred Yorkshire x Landrace gilts. They arrived in a group of 400 animals at the Purdue Animal Sciences Research & Education Center at weaning age (average 15.3 d), having come from a commercial farm in northern Kentucky with a journey time of 5 h. On arrival at the Purdue University Swine Evaluation Unit, approximately 350 animals were ear-tagged with individual numbers and randomly assigned to 1 of 12 identical pens with covered lying area and outdoor concrete-floored runs (14.0 m x 2.5 m). They were maintained on a standard commercial grower diet with access ad libitum. Ten days before the beginning of the experiment, about 300 of the pigs were weighed and 192 pigs were selected on the basis of the proposed target BW at the beginning of the imposed dietary treatments (88.8 kg). Selected pigs were blocked by BW and sex into 2 rows of 16 adjacent pens separated by a central corridor in 1 wing of the Swine Evaluation Unit, with 8 pens coming on trial per week for 4 successive weeks. Each pen (4.1 m x 1.4 m) housed 6 pigs and had fully slatted floors (the rear 2/3 being concrete slats, the front 1/3 being plastic-coated expanded metal). A single partition-mounted drinker was situated toward the rear of the pen, and a single-space feeder was situated at the front of each pen. Both water and feed were available ad libitum. The room was maintained at a minimum temperature of 18.5°C and naturally ventilated above the minimum level with air going through a heat exchanger.
As the blocks of pigs reached the proposed target BW, 1 pen of gilts and 1 pen of barrows were randomly assigned within block to 1 of 4 dietary treatments, which were fed over the final 4 wk before slaughter (d 0 to 28):
The major constituents of the diets are shown in Table 1.
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Animal Data Collection
Behavior in Home Pen
Behavior of all pigs in all 32 pens (8 per treatment) was recorded using ceiling-mounted cameras (Panasonic WV-CD110AE, Matsushita Electric Industrial Co. Ltd., Osaka, Japan) attached to time-lapse video-recorders (Panasonic AG6720A, Matsushita Electric Industrial Co. Ltd.) over a 24-h period, once during the week before imposition of dietary treatments and also weekly during dietary treatment (wk 1, 2, and 4). The video data were analyzed using a scan-sampling technique, with behavior, location, and posture of each pig in a pen recorded every 10 min using the ethogram presented in Table 2. Data from each pig were then combined to give a behavioral time budget with each pen being an experimental unit. Video data were also analyzed to determine the amount of agonistic interactions using all-occurrences sampling.
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for methodology) set to record and store successive interbeat intervals. In each pen, pigs to be recorded were the heaviest and lightest pigs and a middle weight pig, based on BW at allocation. Once the last monitor of the pig had been fitted, all monitors were started, and the experimenter stood in a corner of the pen and allowed the pigs to interact with him, while recording 1-min scan samples of the behavior of all pigs in the pen using the ethogram described in Table 4. The interactions took the form of reaching out and stroking and scratching any of the pigs that approached. The test was carried out for 10 min from the time that the last monitor in the pen was started. At the end of this period, the experimenter removed the equipment and repeated the procedure in the other pens. After each set of 4 pens, HR data were downloaded from the receivers onto a personal computer. The data were displayed in graphical and numerical form using Polar Precision Performance Analysis Software (Version 3.02.007, Polar Electro Oy, Kempele, Finland) and were analyzed to determine mean HR every 1 min over the 10-min period, in beats per minute (bpm), with each pen as an experimental unit.
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For plasma catecholamine analysis, samples were acidified and deproteinized with 4 M perchloric acid, and a commercial alumina-based solid phase extraction kit (ESA Inc., Chelmsford, MA) was used to extract catecholamines from the plasma. After extraction and injection onto the reverse-phase column, norepinephrine and epinephrine were detected using HPLC with electrochemical detection. All assays were done in 2 runs. The interassay CV for norepinephrine and epinephrine were 11.5 and 20.2%, respectively.
Plasma cortisol was measured using a competitive binding RIA (GammaCoat, DiaSorin, Stillwater, MN). The concentration of cortisol was calculated from a reference curve that ranged from 0 ng/mL (99.6% binding) to 600 ng/mL (17.6% binding) and a correlation coefficient of 0.99. All cortisol assays were done in a single batch, and the intraassay CV was 3.2%.
Plasma lactate was measured using a nonradioactive colorimetric assay kit (State University of New York, Buffalo) based on the reduction of 2-p-iodophenyl-3-p-nitrophenyl-5-phenyl tetrazolium chloride in a NADH-coupled enzymatic reaction to formazan, which is water-soluble and exhibits an absorption maximum at 492 nm. Because the intensity of the red color formed was proportional to the lactate concentration, the assay, using a set of lactate standards, measured the concentration of lactate released to the culture medium or circulation in a semiquantitative manner. All lactate assays were done in a single batch, and the intraassay CV was 14.1%.
Blood urea nitrogen, glucose, CK, and ammonia were measured on an IDEXX VetTest Chemistry Analyzer (IDEXX Laboratories, Westbrook, ME). Samples for analysis of CK were diluted up to 1:6 in normal saline, as per instructions of the manufacturer, to fall within the accurate detection range of the machine.
Plasma insulin was measured using a solid-phase RIA kit (Coat-A-Count Insulin, Siemens Medical Solutions Diagnostics, Los Angeles, CA). The concentration of insulin was calculated from a reference curve. All insulin assays were done in a single batch, and the intraassay CV was 3.1%. Nonesterified fatty acids were measured using an in vitro enzymatic colorimetric kit for quantification of nonesterified fatty acids (NEFA C, Wako Diagnostics, Richmond, VA), using the microtiter procedure. All NEFA assays were done in 4 runs. The intraassay CV was 2.4%, and the interassay CV was 4.5%.
HR During Transport Heart rate was also measured during transportation to the campus slaughter facility. Transportation took place on 8 separate mornings, with 24 pigs being transported daily from 4 of the pens. Due to equipment constraints, the HR of only 8 pigs was recorded each day. Thus, a total of 64 pigs were recorded (2 pigs recorded from each of the 32 pens). On transport days, the 8 selected pigs (2 per treatment) were fitted with HR monitors, with the transmitter belt and receivers then entirely covered with Vetrap (3M, 3M Center, St. Paul, MN) to prevent the equipment being damaged by other pigs during transport. Once the monitors had been fitted, the 8 pigs with monitors were released into the central corridor, together with the other 4 pigs from the control treatment, because all control pigs had to go through the slaughter line before any were treated with an experimental drug. They were herded down the corridor onto a hydraulic trailer lowered to floor level, situated in the central handling room between the 2 wings of the Evaluation Center. Once the 12 pigs were on the trailer, it was raised and pulled 20 m outside to a flatbed truck. The pigs were then herded off the trailer onto the truck and transported to the slaughter facility, after stopping to pick up a single pig elsewhere on the farm. Once at the slaughter facility, pigs were off-loaded straight into a lairage room, and the HR equipment was removed. The HR data were downloaded as above and were analyzed to determine mean HR every 1 min over the loading, transport, and unloading periods, in bpm, with each pig as an experimental unit.
Statistical Analysis
The experiment was a repeated measure design with repeated measurements of animals (main units) over time (subunits). Handling behavior data, human presence test behavior data, human presence test HR, and transport HR data were analyzed using the repeated option of PROC GLM (SAS Inst. Inc., Cary, NC). Dietary drug treatment, time, sex, time x treatment, and sex x treatment interactions were included in the model. In terms of the blood parameters, data for wk 0 to 4 were analyzed together using a repeated ANOVA with wk 0 as a covariate. Postslaughter data were analyzed separately, because these data represented the difference in the 24-h or 48-h withdrawal. Data were transformed as appropriate when the assumption of normality was not fulfilled (Sokal and Rohlf, 1981). Data expressed as proportions (for example, proportions of observations) were transformed using arcsine-root transformation. Count data were transformed using logarithmic transformation.
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RESULTS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Behavior in the Home Pen
In terms of location, 4R pigs spent a lesser proportion of total time (P < 0.01) at the back of the pen than 2R pigs or 8RS pigs (Table 5). There were no effects of treatment on the proportion of time spent in the middle or front of the pen. In terms of postures, there were no treatment effects (P > 0.14) on proportion of time spent standing, lying sternally, or lying laterally, but there were treatment effects (P < 0.02) on the proportion of time spent sitting (Table 5) and the amount of time spent kneeling (Table 5), with 2R pigs spending less time in both postures than 4R and 8RS pigs.
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) than 4R pigs. Control pigs spent less time rooting than 4R and 8RS pigs (P < 0.001, Figure 2a), and 2R pigs spent less time drinking than 8RS pigs (P < 0.05, Figure 2b). The 2R pigs were seen belly nosing more often than 4R pigs (P < 0.01, Figure 1b), and tail-biting was observed more often than control and 8RS pigs (P < 0.05, Figure 2c). There were no treatment effects (P > 0.26) on either scan-sampled aggression (Figure 2d) or all-occurrences-sampled aggression or on positive social behavior.
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) and decreasing proportions of time in the middle (P < 0.001, Table 5) and back of the pen (P < 0.001, Table 5). In terms of postures, pigs spent decreasing proportions (P < 0.001, Table 5) of time standing and lying sternally and increasing proportions (P < 0.01, Table 5) of time sitting and lying laterally. In terms of specific behaviors, pigs engaged in increasing amounts of inactivity over time (P < 0.001, Figure 1c), with decreasing proportions (P < 0.001) of time spent rooting and eating. The proportion of time spent walking was greatest in wk 2 (Figure 1d), and pigs spent an increasing proportion (P < 0.01, Figure 2b) of time drinking. Female pigs spent more time standing (P = 0.001) and less time sitting (P < 0.05) than male pigs and tended to spend less time lying laterally (P < 0.10). Female pigs also spent more time (P < 0.001) walking and rooting than male pigs.
Behavior During Handling
Overall, no treatment effects were observed (P > 0.34) on the number of pigs exiting the home pen voluntarily (CTL = 2.5 ± 0.2; 2R = 2.2 ± 0.2; 4R = 2.1 ± 0.2; 8RS = 2.6 ± 0.2), the time taken to exit the home pen (CTL = 23.8 ± 1.7 s; 2R = 25.1 ± 1.1 s; 4R = 27.3 ± 1.2 s; 8RS = 23.5 ± 1.4 s), the time taken to get the pig onto the weigh scale (CTL = 9.5 ± 0.5 s; 2R = 10.0 ± 0.5 s; 4R = 9.3 ± 0.4 s; 8RS = 9.3 ± 0.5 s), and the total number of physical interactions needed to get the pig onto the weigh scale (CTL = 2.6 ± 0.2; 2R = 3.0 ± 0.3; 4R = 2.6 ± 0.2; 8RS = 2.9 ± 0.3). Similarly, there were no treatment effects observed (P > 0.19) on the time taken to get the pig off the weigh scale (CTL = 3.6 ± 0.1 s; 2R = 4.0 ± 0.1 s; 4R = 3.8 ± 0.1 s; 8RS = 3.9 ± 0.1 s), the total number of physical interactions needed to get the pig off the weigh scale (CTL = 1.4 ± 0.1; 2R = 1.4 ± 0.1; 4R = 2.6 ± 0.1; 8RS = 1.4 ± 0.1), or the time taken to get the pigs back into the home pen (CTL = 24.6 ± 1.9 s; 2R = 23.2 ± 1.2 s; 4R = 21.8 ± 1.3 s; 8RS = 25.4 ± 1.7 s). Within given weeks, there were very few differences between treatments and no consistency across weeks.
No sex effects were observed in any of the variables measured, but there were several time effects. First, there was a tendency (P < 0.10) for more pigs to leave the pen voluntarily as the experimental period progressed (Figure 3a), but this did not affect the total amount of time taken for all pigs to exit the home pen. The amount of time taken to get pigs onto the scale did not vary over the experimental period, but it took increasingly more physical interactions from the handler (P < 0.001) to get the pigs onto the scale (Figure 3b). Once weighed, pigs needed an increasing number of physical interactions from the handler (P < 0.001, Figure 3c), and it took increasingly more time (P = 0.01) to get all the pigs back into the home pen (Figure 3d).
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In the week before implementation of the experimental diets, no treatment differences were observed (P > 0.10) in either overall mean HR (CTL = 145.7 ± 3.1 bpm; 2R = 146.7 ± 3.4 bpm; 4R = 146.3 ± 4.0 bpm; 8RS = 145.0 ± 2.9 bpm) or in mean HR at any of the 1-min time periods (Figure 4a). By wk 1, however, control pigs had less HR (P < 0.01) than pigs in all 3 treatments (CTL = 141.8 ± 2.2 bpm; 2R = 149.5 ± 1.7 bpm; 4R = 151.3 ± 2.3 bpm; 8RS = 153.5 ± 2.3 bpm). All 1-min time periods were also different except for the first minute compared with 4R pigs (Figure 4b). Control treatment pigs also had less HR (P < 0.06) during wk 3 than pigs in all 3 treatments (CTL = 138.8 ± 1.9 bpm; 2R = 148.5 ± 2.8 bpm; 4R = 146.5 ± 2.8 bpm; 8RS = 152.5 ± 3.0 bpm). Heart rates during 1-min time periods from the first to the eighth minute were mostly less in control pigs compared with the other 3 treatments (Figure 4c), but in min 9 and 10, there were no differences between treatments (P > 0.10).
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Human Presence Test—Behavior
In terms of behavior, no differences were observed (P > 0.10) between treatments in any of the variables measured. Most importantly, there were no treatment differences (P > 0.73) in the proportion of time that pigs spent either in contact with the human (CTL = 0.15 ± 0.03; 2R = 0.15 ± 0.02; 4R = 0.17 ± 0.02; 8RS = 0.15 ± 0.02), with their head and shoulders positioned in the third of the pen nearest to the human (CTL = 0.17 ± 0.02; 2R = 0.15 ± 0.01; 4R = 0.15 ± 0.01; 8RS = 0.14 ± 0.01), or purposefully interacting with the human (CTL = 0.14 ± 0.02; 2R = 0.15 ± 0.02; 4R = 0.14 ± 0.02; 8RS = 0.14 ± 0.02). There were also no treatment differences (P = 0.67) in the amount of aggressive social behavior.
The only sex differences were in the postural categories, with gilts spending more time standing (0.84 ± 0.02 vs. 0.75 ± 0.03, P = 0.01) and barrows spending more time sitting (0.04 ± 0.01 vs. 0.02 ± 0.01, P = 0.01) and tending to spend more time (P < 0.09) lying sternally and lying laterally. Several behaviors changed over time. Overall, pigs spent more time (P < 0.01) in contact with the human (Figure 5a) and interacting with the human over time (Figure 5b). They also tended to spend more time with their head and shoulders in the third nearest the human (P = 0.06) and spent less time with their head and shoulders in the farthest part of the pen (P < 0.001, Figure 5c). Time spent alert (Figure 5d), time spent walking (Figure 5e), and time spent engaged in positive social interactions (Figure 5f) all decreased over time (P < 0.04).
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From the repeated measures analysis performed on wk 0, 2, and 4 blood samples, treatment differences were observed (P < 0.02) in concentrations of CK (Figure 6a), with CTL pigs having less CK concentrations than pigs on all 3 salbutamol treatments, and BUN (Figure 6b), with CTL pigs having greater BUN concentrations than pigs on all 3 salbutamol treatments. There were also tendencies (P < 0.08) for CTL pigs to have lesser insulin concentrations than pigs on the other 3 treatments (CTL = 1.79 ± 0.25 µIU/mL; 2R = 2.36 ± 0.24 µIU/mL; 4R = 2.64 ± 0.50 µIU/mL; 8RS = 2.43 ± 0.25 µIU/mL) and for 2R and 4R pigs to have greater ammonia concentrations than CTL and 8RS pigs (CTL = 17.6 ± 2.4 µmol/L; 2R = 25.0 ± 3.0 µmol/L; 4R = 22.2 ± 3.0 µmol/L; 8RS = 17.4 ± 2.4 µmol/L). There were no treatment differences (P > 0.29) in circulating epinephrine concentrations (CTL = 140 ± 30 pg/mL; 2R = 212 ± 58 pg/mL; 4R = 199 ± 50 pg/mL; 8RS = 160 ± 28 pg/mL), norepinephrine concentrations (CTL = 886 ± 154 pg/mL; 2R = 1,307 ± 259 pg/mL; 4R = 1,086 ± 159 pg/mL; 8RS = 1,130 ± 262 pg/mL), or lactate concentrations (CTL = 8.4 ± 1.0 mM/mL; 2R = 6.2 ± 0.5 mM/mL; 4R = 6.1 ± 0.6 mM/mL; 8RS = 10.0 ± 1.1 mM/mL). There were sex effects (P < 0.02) for CK and BUN with barrows having greater concentrations than gilts and treatment x sex interactions for insulin (Figure 6c) and cortisol (Figure 6d). The only significant time effect (P < 0.01) was with ammonia concentrations, which showed a peak during wk 2.
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HR During Transport
No treatment effects were observed (P > 0.14) on overall HR during loading, transport, or unloading. However, there was a treatment effect (P = 0.02) on the peak or maximum HR recorded over the whole journey process, with 2R pigs having less peak HR (212.5 ± 7.9 bpm) than CTL pigs (234.8 ± 3.6 bpm) or 8RS pigs (232.3 ± 3.1 bpm). Treatment effects were also observed (P < 0.05) at some 1-min time points during the transport phase of the journey. At 4, 5, and 6 min and again between 18 and 24 min, CTL pigs had greater HR than pigs on the 3 salbutamol treatments (Figure 7). They also had greater HR during the fifth minute of unloading (Figure 7).
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), decreased over transport (P < 0.001, Figure 7), and increased again over unloading (P < 0.001, Figure 7). Overall, there were no sex effects and no effects of withdrawal time (P > 0.10). |
DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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), as have other β-agonists such as clenbuterol (O’Donnell, 1993b), isoproterenol (O’Donnell, 1993b), and zinterol (O’Donnell, 1993c). In swine, the β-agonist ractopamine had the opposite effect and increased both activity and time spent alert while decreasing time spent lying laterally (Marchant-Forde et al., 2003). There was some evidence of increased belly nosing and tail-biting in the 2R-salbutamol treatment, but these results must be viewed with extreme caution, because these behaviors are very short in duration and very low in incidence and thus not best suited to being robustly detected by scan sampling. Also, the incidence of belly nosing was already greater in the 2R-salbutamol pigs before going onto the dietary treatment, and the incidence of tail-biting shows no consistent pattern. Although tail-biting was observed, it had no clinical implications and did not need intervention.
No overall treatment effects were noted on handling parameters at any time during the experimental period. Pigs on all treatments became increasingly willing to exit the home pen and did not take longer to get onto or off the weigh scale over time. This is in contrast to results observed by Marchant-Forde et al. (2003) in a study of ractopamine-fed pigs, who became less willing to leave the home pen voluntarily and who took approximately twice as long to weigh as pigs on a control diet. Ractopamine-fed pigs also took more physical interactions from the handlers to complete the weighing process (Marchant-Forde et al., 2003). In the current study, all pigs were subjected to more physical interactions over time, making them increasingly difficult to handle. However, there were clear differences in willingness between the 2 experiments, and the fact that pigs in the current experiment needed more interactions was probably more due to the fact that they had become habituated to the weighing process and to the handler. Although fearfulness has been demonstrated to negatively affect ease of handling (Hemsworth, 2003), lack of fear can also make animals harder to handle (Grandin, 1987; Marchant-Forde, 2002). Pigs that are comfortable around humans can exhibit a negative flight zone and consequently take longer to move (McGlone and Pond, 2003).
The human presence test was also essentially a measure of the fearfulness of pigs of humans. The behavior results support the hypothesis that the pigs became less fearful over time. Results clearly show that pigs in all treatments spent increasing amounts of time in contact with or directly interacting with the human and less time in the third of the pen farthest away from the human. Again, no effect of treatment was observed. Treatment did affect HR during this test, with salbutamol-treated pigs having HR values between 8 to 12 bpm greater than control pigs. These results are similar to those observed in ractopamine-fed pigs (Marchant-Forde et al., 2003), which had HR of 8 bpm greater than control pigs. Nebulized administration of levalbuterol and racemic salbutamol is known to induce tachycardia in humans (Lam and Chen, 2003), and because there were no treatment differences in activity to account for the HR changes, the conclusion would be that this increase is pharmacological in nature. It was originally thought that the effect on HR was as a result of direct stimulation of β1 cardiac receptors or a baroreceptor-mediated reflex due to vasodilation and leading to a release in norepinephrine (Simonsson et al., 1972). However, salbutamol has more recently been shown to affect HR by a direct action on cardiac β2 receptors (Insulander et al., 2004). In humans with asthma and chronic obstructive pulmonary disease, the cardiovascular effects of salbutamol have been implicated in an increased risk of spontaneous arrhythmias (Kallergis et al., 2005) and even sudden death (Salpeter et al., 2004). Many of these data are derived from studies ranging in dosing length from 3 mo to 1 yr. There are no comparable data from healthy subjects taking repeated doses over 4 or more weeks. The clinical or welfare implications of the increased HR noted in our study are therefore unknown.
No treatment effect was observed on catecholamine or cortisol concentrations. Orally administered salbutamol given over 2 wk had no effect on epinephrine concentrations in humans (Warren et al., 1983). Also, salbutamol fed at 3 mg/kg has been shown to result in increased ACTH concentrations in 50-kg pigs after acute stress in behavioral tests (Jensen et al., 1994). These results indicate that salbutamol does not affect sympathetic-adrenal-medullary or hypothalamic-pituitary-adrenal axes activity. In contrast, ractopamine given orally over 4 wk to swine resulted in increased plasma epinephrine and norepinephrine concentrations (Marchant-Forde et al., 2003). Salbutamol-treated pigs had greater concentrations of CK and lesser concentrations of BUN, indicating increased protein accretion results and consistent with those observed with ractopamine (See et al., 2004). There was no treatment effect on plasma lactate concentrations, which is in contrast to results published elsewhere, showing that administration of salbutamol increased plasma lactate concentrations (Oksbjerg et al., 1996), as did clenbuterol (Baldi et al., 1994). Elevated plasma lactate concentrations have been implicated elsewhere in the issue of downer pigs (Anderson et al., 2002), with data suggesting that the downer pig is in a state of metabolic acidosis. Plasma lactate concentrations are known to be elevated in response to aggressive handling (Anderson et al., 2002; Hamilton et al., 2004), and a previous study showed that ractopamine made pigs harder to handle (Marchant-Forde et al., 2003) and thus potentially more at risk of being subject to aggressive handling.
In contrast to the human presence test results in this study, control pigs had greater HR during the transport process. In a previous study, control pigs had less HR response to transport than ractopamine-fed pigs (Marchant-Forde et al., 2003). One major difference in methodology of studies that may influence this difference is that of withdrawal. In the current study, pigs were withdrawn from salbutamol either 24 or 48 h before transport. Ractopamine-fed pigs in Marchant-Forde et al. (2003) had no withdrawal period. Another issue to consider is the design of the transport section of the study, which was confounded to some extent by meat hygiene regulations. On the first truckload to the slaughter plant, we had to accommodate all control pigs that were being killed that day, because they had to be slaughtered first. This truck therefore contained 6 CTL pigs (2 with HR monitors), two 2R pigs (with monitors), two 4R pigs (with monitors), and two 8RS pigs (with monitors). Thus, each control pig traveled with 6 nonpenmates, whereas each salbutamol pig traveled with 10 nonpenmates. Subsequent to loading, a single pig from another experiment was loaded at between 3 and 5 min. When unfamiliar pigs are mixed, they engage in agonistic behavior, and this behavior can induce increased HR (Marchant et al., 1995). We should therefore expect that salbutamol-treated pigs were subjected to greater degrees of social stress, because they were mixed with many more unfamiliar animals. In this study, we saw the opposite; control pigs had greater HR. Also, when the single pig was mixed, this clearly induced a cardiac response in control pigs but not in the salbutamol-treated pigs. Further research is necessary to explain these results.
Overall, results from this study appear to demonstrate that R-salbutamol fed at 2 and 4 mg/kg and R-S-salbutamol fed at 8 mg/kg have few effects on behavior and physiology of finishing pigs, when fed over a 4-wk period. Although HR may be increased by salbutamol during testing in the home pen, HR response to transport, after 24 or 48 h of withdrawal, is actually decreased relative to control.
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Footnotes |
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2 The use of a trade, firm, or corporation in this publication is for the information and convenience of the reader. Such use does not constitute an official endorsement or approval by the USDA or ARS of any product or service to the exclusion of others that may be suitable.
4 Present address: School of Veterinary Medicine, Purdue University, West Lafayette, IN 47907.
3 Corresponding author: jeremy.marchant-forde{at}ars.usda.gov
Received for publication March 31, 2008. Accepted for publication May 22, 2008.
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): a) the mean + SE proportion of time spent alert, b) the mean + SE proportion of time spent belly nosing; and compared by sampling period (
): c) the mean + SE proportion of time spent inactive and d) the mean + SE proportion of time spent walking. a–cBars lacking a common letter differ (P < 0.05). CTL = control; 2R = 2 mg/kg of R-salbutamol; 4R= mg/kg of R-salbutamol; 8RS = 8 mg/kg of RS-salbutamol.
