Materials and methods: In Experiment

Objective: To evaluate effects of racto-pamine HCl (RAC) dose and treatment period on growth performance and carcass composition in a commercial finishing environment. Materials and methods: In Experiment One, a total of 880 pigs (PIC L337 × C22; initially 106.5 ± 0.5 kg) were allotted to four treatments, including doses of 0, 5.0, 7.5, and 10.0 ppm of RAC for 21 days before slaughter. In Experiment Two, 1035 gilts (initially 103.2 ± 0.62 kg) were allotted to nine treatments. Treatments included doses of 5 or 10 ppm RAC for 7, 14, 21, or 28 days before slaughter and a control treatment without RAC. Results: In Experiment One, average daily gain (ADG), gain-to-feed ratio (G:F), and carcass yield increased (linear, P < .05) with increasing dose of RAC. The largest numeric differences were observed as RAC dose increased from 0 to 5 ppm. In Experiment Two, ADG and G:F were greater (P < .05) for pigs fed 5 ppm RAC for 14, 21, or 28 days and for pigs fed 10 ppm for all treatment periods than for control pigs. Carcass yield was greater in pigs fed 10 ppm RAC (P < .05) than in pigs fed 5 ppm RAC or in the controls. RAC dose (5 ppm versus 10 ppm) did not affect carcass lean measures (P > .16). Implications: Feeding RAC at 5 to 10 ppm for 14 to 28 days before slaughter increases ADG, G:F, and carcass yield of pigs reared in a commercial finishing environment. Résumé-Effets de la dose de ractopamine HCl et de la période de traitement sur les performances des porcs dans un site de finition commercial Objectif: Évaluer les effets du dosage et de la période de traitement avec de la ractopamine HCl (RAC) sur les performances de crois-sance et la composition de la carcasse dans un environnement de finition commercial.


Résumé -Effets de la dose de ractopamine HCl et de la période de traitement sur les performances des porcs dans un site de finition commercial
Objectif: Évaluer les effets du dosage et de la période de traitement avec de la ractopamine HCl (RAC) sur les performances de croissance et la composition de la carcasse dans un environnement de finition commercial.
Résultats: Au cours de l'Expérience 1, le gain moyen quotidien (ADG), le ratio O pportunities to enhance growth performance and carcass value are of primary interest to pork producers.Ractopamine hydrochloride (RAC) (Paylean; Elanco Animal Health, Greenfield, Indiana) is a B-adrenergic agonist commonly fed by producers in an effort to improve finishing growth rate, feed efficiency, carcass yield, carcass lean content, and producer profitability.The biological effects of feeding RAC on finishing growth performance and carcass composition have been well described. 1,2any of the controlled studies reported in the literature have been conducted with small groups of animals housed at eight or fewer pigs per pen.However, in small-pen university research settings, feed intake may be as much as 30% greater than that observed in commercial research environments (≥ 20 pigs per pen). 3,4Therefore, our objective was to quantify the effect of RAC dose (0 to 10 ppm) and treatment period (0 to 28 days before slaughter) on growth performance, carcass yield, and carcass lean percentage (as determined by fat and loin depth measurements at the 10 th rib) in a commercial finishing environment.Understanding the biological effects of RAC dose and treatment period in commercial finishing environments will help pork producers determine if treatment with RAC is suitable for their operations, and if so, how it may best be applied.

Experiment One
A total of 880 pigs (initially 106.5 ± 0.5 kg; PIC, L337 × C22, Hendersonville, Tennessee) were assigned to treatment 21 days before slaughter in a commercial research facility.The four dietary treatments included 0, 5.0, 7.5, and 10.0 ppm of RAC.This trial was conducted as a randomized complete block, with pens allotted to treatment on the basis of gender and average pig weight.There were 20 to 23 pigs per pen, with 20 pens of barrows and 20 pens of gilts.This provided 10 observations per treatment (five gilt and five barrow).Pens were 3.05 m × 5.49 m, with a four-hole self-feeder and one cup waterer.The finishing facility had totally slatted flooring and a deep pit, and operated on mechanical ventilation in winter and natural ventilation (double curtainsided) in summer.Diets were based on corn and soybean meal and formulated to exceed nutrient requirements for optimal growth performance. 5Diets were formulated at 0.70% 6 and 0.90% 7 total dietary lysine (as fed) for the controls and RAC treatments, respectively (Table 1 gain-nourriture (G:F) et le rendement de la carcasse augmentaient (linéaire, P < .05)avec des doses croissantes de RAC.Les plus grandes différences numériques étaient observées lorsque la dose de RAC a augmenté de 0 à 5 ppm.Lors de l'Expérience 2, comparativement aux témoins, l'ADG et le G:F étaient plus grands (P < .05)pour les porcs nourris avec 5 ppm de RAC pendant 14, 21, et 28 jours et pour les porcs nourris avec 10 ppm pour toutes les périodes de traitement.Les doses de RAC (5 ppm versus 10 ppm) n'ont pas affecté les mesures de viande maigre des carcasses (P > .16).
genetic lines in the same research barns demonstrated that the lysine level required to maximize average daily gain (ADG) and gain-to-feed ratio (G:F) was not greater than the level fed to control pigs in this experiment.The second reason for feeding a lower lysine level to the control pigs than to the pigs fed diets containing RAC was to more closely represent the manner in which RAC treatment would be implemented by swine producers.Because RAC increases the lysine requirement of the pig, recommendations are to increase the lysine level of the feed by 0.25% to 0.3% when RAC is added to the diet. 7g welfare standards were in accordance with published guidelines, 8 and the research protocol was approved by the Kansas State University Institutional Animal Care and Use Committee.Pig weights and feed disappearance were measured for each pen and used to calculate ADG, average daily feed intake (ADFI), and G:F.Pigs in each pen were weighed weekly.Pigs were tattooed with unique numbers to enable pen identification to be maintained through the packing plant (Swift Inc, Worthington, Minnesota).All pigs were slaughtered on the same day, and carcass weight and fat and loin depth at the 10 th rib were measured to calculate carcass yield and lean percentage, respectively.

Experiment Two
A total of 1035 gilts (initially 103.2 ± 0.62 kg; PIC, L337 × C22) were used to determine the effects of dosage of RAC and treatment period in a commercial research facility.The nine treatments included treatment with RAC at 5.0 or 10.0 ppm for 7, 14, 21, or 28 days before slaughter.Control pigs (no RAC treatment) were slaughtered on day 28 with all other pigs.A total of 45 pens (23 pigs per pen) were allotted to treatments in a randomized complete-block design (five observations per treatment).Pens were allotted to treatment and blocked by average pen weight.Diets were based on corn and soybean meal and formulated to 0.75% and 1.00% total dietary lysine (as fed) for the control and ractopamine diets, respectively.Again, our objective with diet formulation was to ensure that the diets were not limiting growth of either control 6 or RAC-fed pigs. 7iets used are presented in Table 1.Pigs in Experiment Two were otherwise managed and parameters were measured as described for Experiment One.

Statistical analysis
Analysis of variance was used to analyze growth and carcass performance data from each trial according to the PROC GLM procedures of SAS (SAS Institute Inc, Cary, North Carolina).Data were analyzed by using pair-wise orthogonal contrasts between the dietary treatments and the main effects of RAC dose (Experiments One and Two) and treatment period (Experiment Two).
In Experiment One, the statistical model included the fixed effects of RAC dose (0, 5.0, 7.5, and 10.0 ppm), gender, and block.Because there were no RAC dose-by-gender interactions (P > .05), the dose-by-gender interaction term was dropped from the model.Linear and quadratic contrasts were used to determine the effects of increasing amount of RAC in the diet.Coefficients for unevenly spaced treatments were derived using the PROC IML procedure of SAS.
In Experiment Two, the statistical model included the fixed effects of dietary treatment and block.In addition, data were analyzed as a 2 × 4 factorial, with the fixed effects of RAC dose (5.0 or 10.0 ppm) and treatment period (7, 14, 21, or 28 days).Linear and quadratic contrasts were made to determine the effect of increasing treatment period (0, 7, 14, 21, and 28 days).Backfat, loin depth, and lean percentage were adjusted using carcass weight as a covariate.
Pen was the experimental unit in all analyses.For all analyses, P < .05 was considered statistically significant.

Experiment Two
Average daily gain, G:F, and slaughter weight were greater, compared to those for controls, for pigs fed 5.0 ppm RAC for treatment periods of 14, 21, or 28 days, and for pigs fed 10.0 ppm RAC for all treatment periods (P < .05;Table 3).The 5.0-ppm 7-day treatment group was intermediate in ADG, G:F, and slaughter weight.In pigs fed 5.0 ppm RAC for 21 or 28 days and 10.0 ppm for 7, 14, 21, or 28 days, ADFI was greater than that in the controls (P < .05),with ADFI for the 5.0ppm 7-day and 14-day treatments being intermediate.Carcass weight was greater, compared to that in the controls, in pigs fed RAC at 5.0 ppm for 14, 21, or 28 days and in pigs fed RAC at 10.0 ppm for all treatment periods (P < .05).Carcass weight was intermediate in pigs fed RAC at 5.0 ppm for 7 days.

Discussion
In these studies, in pigs fed diets with RAC added at 5.0 to 10.0 ppm for 14 to 28 days before slaughter, ADG was 24% greater and G:F was 20% greater than in the controls, that received no RAC treatment.Although numeric increases in both ADG and G:F were observed with increasing RAC dose, the 5.0-ppm RAC treatment captured 80% of the increase in ADG and 72% of the increase in G:F of the 10-ppm RAC treatment when fed 14 to 28 days before slaughter.These findings are consistent with results of studies conducted by Watkins et al, 9 who observed that in pigs fed RAC at 5.0 ppm for 45 to 50 days before slaughter, this treatment captured 100% of the increase in ADG and 85% of the increase in G:F of pigs fed RAC at 10 ppm.Armstrong et al 10 also observed greater growth performance with increasing RAC dosage and treatment period.Our results are also consistent with the review and meta-analysis of Kelley et al 1 and Apple et al. 2 The greater ADG and G:F observed in the present studies conducted under commercial finishing conditions are directionally similar, but generally larger in magnitude, than the improvements reported in many of the previous studies reported in the literature.Increase in ADG from 7% to 21% and in G:F from 9% to 17% have been previously reported, [11][12][13] but treatment periods in these referenced studies were generally longer than those in the present studies.This likely contributes to the elevated rate of change in growth performance observed in the current studies.5][16] These authors [14][15][16] have reported a smaller relative rate of increase over controls the longer RAC is fed, and suggest that the maximal improvement in growth performance is achieved during the first 14 to 22 days of RAC feeding.
Experiment Two in the current study further supports these previous observations of a temporal growth response to RAC feeding, in that no ongoing increases in overall ADG or G:F were observed for pigs fed 5.0 or 10.0 ppm RAC beyond 14 days before slaughter.It has been hypothesized that this diminished growth-performance response to RAC with extended treatment period is due to a decrease in cellular responsiveness to RAC. 17 The elevated growth performance responses in the present studies may have also been influenced by the pigs being 30 to 40 kg heavier at the start of the study than pigs in the majority of the previously reported studies.In addition, the studies herein were conducted in a commercial finishing environment, which commonly limits feed intake and growth performance, compared with those of pigs fed in research facilities housing one to eight pigs per pen. 3,4][20] Consequently, the response to RAC in the present studies is impressive, especially considering that the treated pigs were in a phase of increasing lipid deposition relative to protein, and that they were reared in a commercial environment.
Carcass yield was approximately 0.5% greater in pigs that received the lowest dose of RAC than in controls.Carcass yield also seemed to increase with RAC dose, inasmuch as carcass yield was on average 0.5% greater in pigs fed RAC at 10 ppm than in pigs fed RAC at 5 ppm.The present studies suggest that carcass yield is affected more by RAC dose than by treatment period.These findings are consistent with a previously reported 0.5% to 2.0% improvement in carcass yield due to feeding RAC. 10,12atkins et al 9 observed that carcass yield

†
Yield was calculated using live-carcass pen weights attained at the slaughter plant.‡ Backfat, loin depth, and lean percentage were adjusted using carcass weight as a covariate.a,b,c,d Means in the same row with no common superscript differ (P < .05;ANOVA).increased with increasing RAC dose.The magnitude of increase in carcass yield in the current studies was low compared with those in some other reports. 16,21However, those reporting carcass yield greater by 2.0% in treated pigs were feeding at or near 20 ppm RAC for treatment periods longer than 28 days. 16,21 the current studies, carcass lean percentage was derived from fat depth and loin depth measurements at the 10 th rib.Feeding RAC did not result in consistently better back fat, loin depth, or lean percentage.Although numerically lower 10 th rib back fat was observed as RAC dosage and treatment period increased, our findings did not demonstrate consistently lower back fat in treated pigs than in the control group.Numerous researchers have consistently illustrated the beneficial effects of feeding RAC on reducing back fat and increasing loin depth (or longissimus muscle area), primal lean yield, and overall carcass lean. 13,22It has also been demonstrated that, in contrast to the temporal effects of feeding RAC on growth performance, the improvements in carcass lean increase with treatment period. 16,23In addition, Watkins et al 9 and Crome et al 11 have demonstrated increasing longissimus muscle area as the dose of RAC increased from 0 to 20 ppm.Schinckel et al 24 demonstrated that only 20% to 50% of the true differences in fat-free lean mass between control pigs and pigs fed RAC were predicted from standard back-fat and loin-depth measurements taken at slaughter, thus suggesting that standard measures of carcass lean (back fat and loin depth) actually underestimate the true effect of RAC on carcass lean content.A consistent effect of RAC on carcass composition in the current studies was not found, which may be due to the combination of the relatively short RAC treatment period (0 to 28 days) and low dosages (0 to 10.0 ppm) evaluated.

Implications
• Feeding 5.0 to 10.0 ppm RAC for 14 to 28 days before slaughter can be an effective strategy to improve finishing ADG, G:F, and carcass yield in a commercial finishing environment.• Improvements in carcass lean percentage, as calculated from back-fat and loin-depth measurements, may not be evident when RAC is fed for relatively short treatment periods (0 to 28 days) and at low dosages (0 to 10.0 ppm).
• These experiments suggest that most of the overall improvement in ADG and G:F is captured at the 5.0-ppm inclusion rate, and negligible improvements in overall growth performance, are observed by extending the RAC treatment period beyond 14 days before slaughter.

Table 1 :
Diet composition (as-fed basis) in two studies investigating effects of increasing doses of ractopamine HCl (RAC) and three different treatment periods on growth parameters in finisher pigs in a commercial swine facility*

Table 2 :
Effects on growth performance of ractopamine (RAC) dose in pigs treated for 21 days before slaughter (Experiment One)*

Table 3 :
Effects of ractopamine (RAC) dose and treatment period on pig performance (Experiment Two)* A total of 45 pens (23 pigs/pen, five pens/treatment) of gilts were fed 5.0 or 10.0 ppm RAC for 7, 14, 21, or 28 days before slaughter.Controls were not treated with RAC.No RAC dose × treatment period interactions were observed (P > .05). *