Feeding Ractopamine Research Articles

Gene expression of beta-adrenergic receptors and myosin heavy chain isoforms induced by ractopamine feeding duration in pigs not carrying the ryanodine receptor mutation

To evaluate the effects of ractopamine hydrochloride (RAC) feeding duration on mRNA abundance of beta-adrenergic receptors (β-AR) and myosin heavy chain (MyHC) isoforms in the Longissimus dorsi (LD) muscle of pigs not carrying the ryanodine receptor type I (RyR1) mutation, 80 finishing barrows (initial body weight=69.4±7.87kg) were randomly assigned to 1 of 5 treatments with 8 replicate pens per treatment and 2 pigs per pen. Pigs were fed a corn–soybean meal-based diet with no added RAC (control) or with 10mg/kg RAC fed for 7, 14, 21, or 28d before slaughter. On d 28, hair root samples were collected for RyR1 genotyping and LD muscle samples were collected to measure β-AR (β1- and β2-subtypes) and MyHC isoforms (Iβ, IIa, IIx/d, and IIb) gene expression using the quantitative real-time PCR method. Six heterozygous negative pigs for the RyR1 mutation were detected, and therefore not considered for statistical analysis. Increasing RAC feeding duration did not affect the abundance of β1-AR mRNA, but resulted in a tendency (P=0.073) towards a linear decrease in β2-AR mRNA abundance. Even though MyHC Iβ mRNA abundance was linearly decreased (P=0.002) with increasing RAC feeding duration, both MyHC IIa and IIx/d gene expressions were not affected by the RAC treatment. There was a linear increase (P=0.029) in MyHC IIb mRNA abundance as RAC feeding duration was increased. In conclusion, RAC feeding alters gene expression of β2-AR and MyHC isoforms in the LD muscle of pigs not carrying the RyR1 mutation in a time-dependent manner.

Effect of constant dose and step-up ractopamine-feeding programs on live performance and carcass traits of finishing pigs in a 3-phase marketing system

<h2>ABSTRACT</h2> The objective of this research was to determine the performance, efficiency, and carcass traits of ractopamine (RAC)-fed pigs in a step-up feeding program or a continuous dose program using a 3-phase marketing strategy. Two thousand five hundred cross-bred pigs were used in a randomized complete block design with 72 pens. Each pen initially housed 35 pigs. Twenty-six percent of the total population of pigs was sold during the first marketing period (7 d after the beginning of RAC feeding), 31% during the second marketing period (21 d after the beginning of RAC feeding), and the remaining 43% during the third marketing period (35 d after the beginning of RAC feeding). Few differences (P>0.05) were observed in performance and carcass characteristics between the 2 RAC-feeding programs. There were no differences in starting BW (<mml:math><mml:mi>x</mml:mi><mml:mo>-</mml:mo></mml:math> =83.53kg; P=0.54) or beginning live weight (<mml:math><mml:mi>x</mml:mi><mml:mo>-</mml:mo></mml:math> =95.85kg; P=0.32) among any of the 3 treatments groups. Pigs fed RAC had 0.17kg/d (19.4%) greater (P<0.0001) ADG, and had 0.07 (18.6%) greater (P<0.0001) G:F than pigs not fed RAC throughout the 35-d feeding trial. Additionally, HCW were 3.81kg (4.27%) heavier (P<0.0001) and standardized fat-free lean was 1.83kg greater (4.04%; P<0.0001) in RAC-fed pigs than pigs not fed RAC. Both RAC-feeding strategies yielded similar improvements over control pigs when used in conjunction with a 3-phase marketing strategy.

Effects of ractopamine on growth performance and carcass characteristics of immunologically and physically castrated barrows and gilts.

The study was performed to evaluate the effect of feeding ractopamine (RAC) to physically castrated barrows (PC), immunologically castrated barrows (IC), and gilts (gilts) using a randomized complete block design with a 3 × 3 factorial arrangement of treatments: 1) sex (PC, IC, and gilts) and 2) RAC inclusion level (0, 5, and 7.5 mg/kg). The IC received 2 doses of gonadotropin releasing factor analog-diphtheria toxoid conjugate (Improvest; Zoetis, Kalamazoo, MI) at the start of the study (wk 16 of age; 69.6 ± 2.96 kg BW) and 4 wk later. The study used 180 pigs housed in groups of 4 (5 groups/sex × RAC subclass) and was performed over a fixed time of 61 d with RAC being fed for the final 26 d of study. Diets were formulated to meet requirements of intact males for the first 35 d and of intact males fed 7.5 mg/kg RAC for the remainder of the study. Pigs had ad libitum access to feed and water throughout the study period. At the end of the study, pigs were harvested at a commercial facility and HCW and last rib backfat thickness were measured. There were no treatment interactions (P > 0.05) for any variables. For the overall study period, IC had greater (P ≤ 0.05) overall ADG compared to PC, which grew faster (P ≤ 0.05) than gilts (1,246, 1,083, and 1,025 g/d for IC, PC, and gilts, respectively; SEM = 20.3); ADFI was lower (P ≤ 0.05) for gilts than IC and PC, which had similar ADFI (3.36, 3.37, and 2.87 kg/d, respectively; SEM = 0.051); and G:F was greater (P ≤ 0.05) for IC than gilts and greater for gilts than PC (0.371, 0.322, and 0.358 kg/kg, respectively; SEM = 0.0039). For the period from the second dose to the end of study, IC had greater (P ≤ 0.05) ADG (28.6%), ADFI (12.3%), and G:F (14.3%) than PC. Carcass yield was lower (P ≤ 0.05) for IC compared to PC and gilts (72.8, 75.0, and 74.6%, respectively; SEM = 0.25). Feeding RAC increased (P ≤ 0.05) ADG (15.7 and 14.5% for 5 and 7.5 mg/kg, respectively), G:F (17.1 and 16.4%, respectively), carcass weight (3.7 and 3.2 kg, respectively), and carcass yield (1.0 and 1.0 percentage unit, respectively) compared to the control. These results highlight sex differences in and effects of RAC on growth and carcass characteristics and suggest that the relative response to RAC is similar in IC and PC.

Effects of feeding ractopamine hydrochloride (Paylean) to physical and immunological castrates (Improvest) in a commercial setting on carcass cutting yields and loin quality.

Effects of feeding ractopamine (RAC; 5 mg/kg) to physically castrated (PC) and immunologically castrated (IC) pigs on carcass characteristics, cutting yields, and loin quality were evaluated using 285 carcasses. Male pigs were randomly assigned to sex treatments (PC and IC) at birth and fed the same nursery diets before allotment into 32 pens with 22 pigs per pen in a grow-finish barn. Pigs in the PC group were physically castrated at approximately 5 d of age, and pigs in the IC group were administered Improvest at 11 and 18 wk of age. Diet treatments (control or RAC) were initiated on study d 87. Pigs were marketed at 12 d (4.5 wk post-second Improvest dose), 19 d (5.5 wk post-second Improvest dose), and 33 d (7.5 wk post-second Improvest dose) following the start of final diet treatments. Three carcasses per pen were selected for evaluation of cutting yields and loin quality. Data were analyzed using PROC MIXED in SAS with fixed effects of sex, diet, market group, and their interaction; carcass (N = 285) was the experimental unit. Carcasses from RAC-fed pigs were heavier (P < 0.01) and had deeper (P = 0.02) loins than control-fed carcasses. Carcasses from IC pigs were similar (P = 0.22) in weight but had less (P < 0.01) fat and shallower (P = 0.02) loins when compared to PC carcasses. There were differences (P < 0.05) among market groups for carcass weights, fat depths, loin depths, and estimated carcass leanness. For cutting yields, RAC-fed carcasses had greater (P ≤ 0.03) bone-in lean and total carcass cutting yields than control-fed carcasses while there were no differences (P > 0.05) between RAC-fed and control-fed carcasses when evaluating LM color, marbling, firmness, pH, drip loss, and tenderness. Carcasses from IC pigs had greater (P < 0.05) boneless lean yields, bone-in lean yields, and total carcass cutting yields than PC carcasses. There were minimal differences (P < 0.05) in LM marbling, firmness, composition, and tenderness between PC and IC pigs. There was an interaction (P = 0.03) between sex and diet for LM composition. Control-fed PC loins had more (P < 0.01) lipid than all other treatment combinations. Market group had effects (P < 0.05) on carcass cutting yields, LM color, marbling and firmness scores, pH, purge loss, composition, and tenderness. The results from this study indicated RAC and immunological castration were additive in terms of improving carcass cutting yields while having minimal effects on pork quality.

Effects of feeding ractopamine hydrochloride (Paylean) to physical and immunological castrates (Improvest) in a commercial setting on growth performance and carcass characteristics.

Growth performance and carcass characteristics of physically castrated (PC) and immunologically castrated (IC) pigs fed ractopamine hydrochloride (RAC; 5 mg/kg) were evaluated in 64 pens of 22 pigs each. Male pigs were randomly assigned to castration method at birth. Pigs in the PC group were physically castrated at 5 d of age while IC pigs were administered Improvest at 11 and 18 wk of age. Pigs entered the grow-finish barn at approximately 9 wk of age (d 0). Dietary treatments (control or RAC) were initiated on d 87. Final treatment arrangement was a 2 × 2 factorial of castration method and diet. Data were analyzed using a mixed model with fixed effects of castration method, diet, market group, and all 2- and 3-way interactions. Pen was the experimental unit. From d 0 to 65, IC pigs had 11.2% greater (P < 0.01) G:F and 11.6% less (P < 0.01) ADFI than PC pigs, but ADG was increased 1.0% in PC pigs compared with IC pigs (P < 0.01). From d 65 to 87, IC pigs had 7.9% greater (P < 0.01) ADG and 12.1% greater (P < 0.01) G:F than PC pigs while having similar (P = 0.16) ADFI. At the initiation of diet (RAC) treatments, BW of all treatments were similar (P ≥ 0.32). From d 87 to 120 (RAC feeding period), IC pigs had 10.0% greater (P < 0.01) ADG and 10.5% greater (P < 0.01) ADFI than PC pigs while having similar (P = 0.64) G:F. Feeding RAC increased (P < 0.01) ADG by 16.9% and G:F by 17.9% while having no effect (P = 0.42) on ADFI from d 87 to 120. There were no significant interactions between castration method and diet on growth performance from d 87 to 120. For the entire study (d 0-120), IC pigs had 2.6% greater (P < 0.01) ADG, 4.6% less (P < 0.01) ADFI, and 7.3% greater (P < 0.01) G:F than PC pigs. Averaged over market groups, IC pigs were 2.5 kg heavier (P < 0.01) and had similar (P = 0.10) carcass weights and 1.8 percentage units less (P < 0.01) dressing yields than PC pigs. Additionally, IC pigs had 1.3 mm less (P < 0.01) fat and 1.7 mm less (P < 0.01) loin depth than PC pigs. Pigs fed RAC were 2.9 kg heavier (P < 0.01) and had 2.3 kg heavier (P < 0.01) carcasses and 2.2 mm deeper (P < 0.01) loins but similar (P = 0.21) dressing yields and tended (P < 0.10) to have 0.4 mm less fat than control-fed pigs when averaged over market groups. Group 3 pigs were the heaviest (P < 0.01) at slaughter and had the heaviest (P < 0.01) carcasses, greatest (P < 0.01) dressing yields, and the most (P < 0.01) carcass fat of all market groups. Overall, immunological castration and RAC were additive in terms of improving growth performance and carcass characteristics.

Effect of feeding ractopamine hydrochloride (Optaflexx) with or without supplemental zinc and chromium propionate on growth performance, carcass characteristics, and meat quality of finishing steers.

Objectives of this study were to determine the effects of feeding ractopamine hydrochloride (Optaflexx) with or without supplemental Zn propionate (KemTRACE Zn) and Cr propionate (KemTRACE Cr) to finishing steers on growth performance, carcass characteristics, and meat quality. Angus cross steers (n = 142; BW = 527 ± 14 kg) were blocked by BW into 4 blocks (6 pens/block, 5 to 6 steers/pen). Steers targeted at an average 12th rib back fat thickness of 1.3 cm via ultrasound, by block, were randomly assigned to 1 of 3 dietary supplements for the final 35 d of feeding before slaughter: 1) no supplementation, where analyzed Zn and Cr were 49.82 and 0.98 mg/kg (DM basis), respectively (CONT), 2) 300 mg ractopamine hydrochloride·steer(-1) · d(-1), where analyzed Zn and Cr were 49.38 and 0.96 mg/kg (DM basis), respectively (RAC), or 3) 300 mg ractopamine hydrochloride, 1.0 g of Zn supplied as Zn propionate (KemTRACE Zn), and 3 mg of Cr supplied as Cr propionate (KemTRACE Cr) steer(-1) · d(-1), where analyzed Zn and Cr were 159.73 and 1.25 mg/kg (DM basis), respectively (RAC+TM). All steers were fed the same basal diet of 20% corn silage, 20% dried distillers grains, 50% corn, and 10% mineral-vitamin supplement (DM basis). Data were analyzed as a randomized complete block design with a fixed effect of treatment and a random effect of block. Average daily gain and G:F were increased (P < 0.01) by 16% in steers fed RAC when compared with steers fed CONT. However, ADG and G:F were not different (P ≥ 0.61) between steers fed RAC and RAC+TM. Furthermore, HCW was increased (P = 0.04) by 1.87% (6.61 kg) in steers fed RAC when compared with steers fed CONT, whereas HCW was not different (P = 0.80) between steers fed RAC and RAC+TM. Back fat thickness and marbling were not different (P ≥ 0.14) between steers fed RAC and CONT or (P ≥ 0.34) between steers fed RAC and RAC+TM. Warner-Bratzler shear force tended to be greater (less tender; P = 0.06) in steers fed RAC when compared with steers fed CONT yet was not different (P = 0.34) between steers fed RAC and RAC+TM. However, meat quality, as measured by pH, objective color, and moisture composition, did not differ (P ≥ 0.55) between steers fed RAC and CONT. Although steers fed RAC had improved ADG, feed efficiency, and HCW in this study, feedlot growth performance and carcass characteristics were not further improved by additional supplemental Zn and Cr.

Growth performance of immunologically castrated (with Improvest) barrows (with or without ractopamine) compared to gilt, physically castrated barrow, and intact male pigs

The study used a randomized complete block design (blocking factor was date of start on test) with 5 treatments: 1) physically castrated barrows (PC), 2) intact males (IM), 3) gilts (G), 4) immunologically castrated barrows (IC), and 5) immunologically castrated barrows fed ractopamine at 5 mg/kg (IC+RAC). The study used 192 pigs and was performed from the 16 wk of age (67.2 ± 2.52 kg BW) to a pen mean BW of 132.5 ± 3.60 kg. For IC+RAC, ractopamine was fed for the final 23 d of the study. Pigs were housed in groups of 4 (10 groups for PC, IM, G, and IC and 8 groups for IC+RAC) in a finishing building at a floor space of 1.18 m(2)/pig. Diets were formulated to meet requirements of IM except that the diet for the IC+RAC fed during the ractopamine feeding period was formulated to meet requirements of pigs on that treatment. Pigs had ad libitum access to feed and water throughout the study period and were individually weighed at the start, wk 2 and 4, and subsequently every week until the end of study. For the overall study period, IC had greater (P ≤ 0.05) ADG than the other genders (1,150, 1,024, 1,064, and 954 g/d for IC, PC, IM, and G, respectively; SEM = 25.8) and required fewer days to reach slaughter weight than the other genders (58.1, 61.6, 61.6, and 66.5 d for IC, PC, IM, and G, respectively; SEM = 1.26). Overall ADFI was less (P ≤ 0.05) for IM and G than IC and PC, which were similar (P > 0.05) in this respect (3.11, 3.06, 2.68, and 2.75 kg/d for IC, PC, IM, and G, respectively; SEM = 0.061). Overall G:F was greater (P ≤ 0.05) for IM than the other genders; IC had greater overall G:F than PC and G, which were similar in this respect (0.371, 0.335, 0.397, and 0.347 kg/kg for IC, PC, IM, and G, respectively; SEM = 0.0068). Immunologically castrated barrows had greater (P ≤ 0.05) ADG (30.7%) and ADFI (22.5%) than PC from the second week following the second Improvest dose to the end of the study. During the ractopamine feeding period, IC+RAC had greater (P ≤ 0.05) ADG (11.6%) and G:F (17.3%) than IC. The results of this study confirmed previously observed gender differences and effects of ractopamine on growth performance and that IC grew faster and had greater feed efficiency than PC during the study period.

Effect of gender (gilt and surgically and immunocastrated male) and ractopamine hydrochloride supplementation on growth performance, carcass, and pork quality characteristics of finishing pigs under commercial conditions1

This study evaluated the effects of gender and feeding of ractopamine on growth performance, carcass, and meat quality characteristics of pigs reared under commercial conditions. The study was performed as a randomized complete block design (blocking factor date of start on test) with a 3 × 2 factorial arrangement of treatments: 1) gender [gilt vs. surgical castrate vs. intact males immunocastrated] and 2) ractopamine level (0 vs. 5 g/ton). The study was conducted out over a fixed duration (126 d) from 1 wk after weaning (28 d of age; 8.04 ± 1.31 kg BW) to 154 d of age (111.44 ± 4.67 kg BW) in 3 growth periods: nursery (d 0 to 35 of the study), growing (d 35 to 70), and finishing (d 70 to 126). Ractopamine was fed for the final 28 d of the study (d 98 to 126). Pigs were kept in groups of 10 or 11 in the nursery phase and then moved to the growing-finishing facility where they were kept in groups of 22 to the end of the study. At the end of the growth study, pigs were harvested and carcass and pork quality were evaluated, including consumer evaluation of eating quality. During the nursery, there was no effect of gender (P > 0.05) on G:F, but surgical castrates grew faster (P < 0.05) than intact males and gilts and had greater (P < 0.05) ADFI than intact males. There was no effect of gender (P > 0.05) on ADG in the growing period; however, immunocastrated males had lower ADFI than surgical castrates and greater G:F than surgical castrates and gilts. In finishing, immunocastrated males and surgical castrates had similar ADG but grew faster than gilts; G:F was greater for immunocastrated males than the other genders. Feeding 5 compared to 0 g/ton ractopamine increased ADG and G:F but had no effect (P > 0.05) on carcass yield or fresh meat quality. Carcass yield was lower but percentage lean cut yield was greater for immunocastrated males than for surgical castrates. Longissimus muscle drip loss was greater (P = 0.05) for immunocastrated males than surgical castrates. Gender had no effect (P > 0.05) on consumer panel evaluation. Feeding ractopamine had no effect on pork flavor and tenderness but improved juiciness scores. Odor scores were similar (P > 0.05) for surgical castrates and immunocastrated males that were fed ractopamine. Consumers gave lower liking scores for odor for immunocastrated males than surgical castrates that were not fed ractopamine. This study highlights the feed efficiency and lean cut yield advantage for immunocastrated males compared to surgical castrates and suggests a similar growth response to feeding ractopamine in these genders. Although immunocastrated males had a lower carcass yield and higher drip loss, panelists were not able to detect differences in pork juiciness, flavor, and tenderness when compared to surgical castrate pigs.

The effects of a step-up ractopamine feeding program on growth performance and low-sodium ham characteristics of purebred Berkshire pigs1

Objectives were to test the effect of a low-sodium curing solution on processing characteristics of hams from purebred Berkshire pigs that were fed a step-up ractopamine HCl (RAC) feeding program or a negative control diet. Sixty pairs (n=120) of hams were selected from two blocks of purebred Berkshire pigs (n=200) that were fed either a control diet or 7.4 mg of ractopamine/kg of diet for 14 d followed by 10.0 mg of ractopamine/kg of diet for the last 14 d before slaughter. Three-piece, section-formed hams were cured with a standard (1.98% NaCl; REG) curing solution or a low-sodium with KCl replacement (0.67% NaCl and 1.29% KCl; LOW) curing solution. Pigs fed RAC had 3.18% greater BW, 11.90% greater ADG, and 10.34% greater G:F compared with control pigs. No differences (P≥0.07) were detected for the effect of diet, curing solution, or the interaction between diet and curing solution for ham weights, pump uptake, or cook yield [(cooked weight/green weight) 100]. Break strength (an indication of protein interaction and bind strength; 5.97 vs. 6.99 kg) and protein fat-free values (24.58 vs. 25.98%) were less (P≤0.05) in hams cured with LOW curing solution compared with hams cured with REG curing solution. Lightness (L*) and yellowness (b*) values were greater (P≤0.03), while redness (a*) values were less (P<0.01) in hams cured with LOW curing solution compared with hams cured with REG curing solution. A trained sensory panel detected less (P=0.03) flavor intensity in hams cured with LOW curing solution compared with hams cured with REG curing solution. Yet, no differences (P≥0.55) were detected between hams cured with LOW or REG curing solution for saltiness. Overall acceptability of hams cured with LOW curing solution tended to be less (P=0.09) compared with hams cured with REG curing solution; however, the magnitude of this difference was 0.34 on a 1 to 9 scale. Hams cured with LOW curing solution made hams paler and contain less intense flavor compared with hams cured with REG curing solution, but this was a justifiable way to lower sodium content by 64% units (1.44 vs. 4.04% Na) without detrimental processing or sensory effects.

Effects of feeding ractopamine to immunologically castrated pigs on ham and belly processing characteristics

Effects of feeding ractopamine to immunologically castrated pigs on ham and belly processing characteristics

The effect of a low sodium curing solution on further processed hams from purebred berkshire pigs fed a step-up ractopamine feeding program

The effect of a low sodium curing solution on further processed hams from purebred berkshire pigs fed a step-up ractopamine feeding program

Effects of ractopamine administration and castration method on the response to preslaughter stress and carcass and meat quality in pigs of two Piétrain genotypes1

The objective of this study was to evaluate the effects of ractopamine supplementation, castration method, and their interaction on the behavioral and physiological response to preslaughter stress and carcass and meat quality of 2 Piétrain genotypes. A total of 1,488 male pigs (115 ± 5 kg BW) were distributed according to a 2 × 2 × 2 factorial arrangement of treatments. The first factor was ractopamine supplementation with 2 groups of pigs (376 and 380 pigs each) receiving 7.5 mg/kg of ractopamine (RAC) or not (NRAC) in their diet during the last 28 d of the finishing period. The second factor was castration method, with 744 surgical castrates (SC) and 744 immunized males (IM), and the third factor was the genotype with 2 crossbreeds containing 50% (genotype A, GA; n = 744) or 25% (genotype B, GB; n = 744) Piétrain genetics. Surgical castration took place at 2 d of age, whereas immunization against gonadotropin-releasing factor (GnRF) was performed through 2 subcutaneous injections of GnRF analog (Improvest, 2 mL) at 10 and 4 wk before slaughter. At loading more vocal stimulation was needed by the handler to drive GB pigs forward through the farm alley (P = 0.01) and RAC-fed GB pigs through the ramp (P = 0.02). Feeding RAC to IM increased the number of fights in lairage compared with SC (P = 0.03). Feeding RAC shortened fighting bouts compared with NRAC pigs (P = 0.05). The SC-GA pigs showed a greater gastrointestinal tract temperature during unloading (P = 0.05) and lairage time (P = 0.03). Blood creatine kinase (CK) concentrations were greater (P = 0.04) in SC compared with IM, and no difference was found in the concentrations of stress hormones in urine collected postmortem. Dressing yield was greater (P = 0.01) in RAC and SC-GB pigs. Carcasses from RAC pigs and IM were leaner than those from NRAC and SC pigs (P < 0.001 and P = 0.002, respectively). Feeding RAC to IM increased drip loss in the LM (P = 0.05). Warner-Bratzler shear force values were slightly greater in the LM from RAC-GB pigs and from IM compared with SC (P = 0.01 and P < 0.001, respectively) and in the semimembranosus muscle of RAC pigs (P = 0.006). In conclusion, immunization against GnRF more than the use of Piétrain genotypes appears to be a viable alternative to the use of ractopamine, as it seems to promote production of lean carcasses without compromising animal welfare and pork quality.

Time-response relationship of ractopamine feeding on growth performance, plasma urea nitrogen concentration, and carcass traits of finishing pigs1

Ractopamine hydrochloride (RAC) improves swine production efficiency by redirecting nutrients to favor muscle accretion rather than fat deposition. In the present study, the time-dependent effect of RAC feeding on performance, plasma urea N (PUN) concentrations, and carcass traits of finishing pigs were evaluated. In a 28-d growth study, 80 barrows (average initial BW = 69.4 ± 7.9 kg) were assigned to 1 of 5 treatments in a randomized complete block design with 8 replicate pens per treatment and 2 pigs per pen. The pigs were fed a corn-soybean meal-based diet with no added RAC (control) or 10 mg of RAC/kg fed for 7, 14, 21, or 28 d before slaughter. All diets were formulated to contain 0.88% standardized ileal digestible Lys (1.0% total Lys) and 3.23 Mcal of ME/kg. Individual pig BW and pen feed disappearance were recorded weekly to determine BW changes, ADG, ADFI, and G:F. Anterior vena cava blood samples were taken on d 28 for determination of PUN concentrations. After 28 d on trial, the pigs were slaughtered and carcass measurements made at 24 h postmortem. Overall, providing pigs with different RAC feeding durations did not affect the final BW and ADFI but resulted in a tendency (P = 0.09) for a linear increase in ADG and a linear improvement (P = 0.003) in G:F. No effect of RAC feeding was found for weekly ADFI. Weekly improvements (P < 0.05) in ADG and G:F were observed over the first 21 d of RAC feeding. However, the growth response declined (P < 0.05) in wk 4 of RAC treatment. The concentrations of PUN exhibited a quadratic decrease (P = 0.004) as the RAC feeding duration increased. Although RAC feeding did not affect any backfat measurements and carcass length, increasing the RAC feeding duration linearly increased HCW (P = 0.01), dressing percentage (P = 0.03), LM depth (P = 0.001), LM area (P < 0.001), muscle-to-fat ratio (P = 0.004), and predicted carcass lean percentage (P = 0.02). These results indicate that a greater growth rate was achieved within the first 21 d of RAC feeding whereas the magnitude of carcass response was directly dependent on the duration of RAC feeding.

Effects of feeding ractopamine (Paylean) on growth and carcass traits in finishing pigs marketed at equal slaughter weights

The objective of this study was to determine the effect of feeding ractopamine hydrochloride (RAC) in an equal weight marketing scenario. Barrows and gilts (n = 427) were assigned to 3 different RAC feeding programs before slaughter: control (0 mg/kg), 5 mg/kg for up to 35 d, or 5 mg/kg for 21 d followed by a step-up to 7.4 mg/kg for up to 14 d. Treatments including RAC were pooled and compared against control pigs using single df estimate statements. Coefficient of variation in beginning BW of RAC (7.16%) and control pigs (6.95%) did not (P = 0.68) differ; however, RAC-fed pigs had a lower (P < 0.01) market BW CV (3.91%) than controls (5.27%). Pigs fed RAC reached market weight 2.5 d earlier (P = 0.01) than control pigs (26.8 vs. 29.3 d). Ractopamine-fed pigs had a 21% greater (P < 0.01) ADG than control pigs, even though ADFI did not (P = 0.19) differ between RAC and control pigs. Pigs fed RAC produced 3% heavier HCW (P < 0.01), 3% greater loin depths (P = 0.05), and a 1 percentage unit greater dressing percent (P < 0.01) than control pigs. Sort loss per kilogram was less (P < 0.01) for RAC-fed than control-fed pigs, with 8 control pigs having HCW less than the sort loss threshold compared with only 2 RAC pigs. Ractopamine can be an important tool in reducing the variation in market weight and sort loss of finishing pigs.

Effect of corn dried distillers grains with solubles, conjugated linoleic acid, and ractopamine (paylean) on growth performance and fat characteristics of late finishing pigs

An experiment was performed to evaluate effects of dietary ractopamine, CLA, and corn distillers dried grains with solubles (DDGS) on growth and carcass and fat quality of finishing pigs. This study was conducted as a split-split plot arrangement in a generalized randomized block design. In total 1,102 crossbred barrows and gilts (initial BW = 100.4 kg, SD = 3.7 kg; pic 337 × c22) were randomly assigned to 1 of 8 dietary treatments that consisted of 2 diet sources [corn-soybean meal (corn-soy) and corn-soy + 20% DDGS], 2 levels of ractopamine (0 and 7.4 mg/kg), and 2 levels of CLA (0% and 0.6%). The pen was the experimental unit, with 6 replications per treatment for a total of 48 pens with 23 pigs per pen. Pigs had ad libitum access to water and feed during the 27-d experimental period. Ractopamine addition improved (p < 0.05) ADG and G:F over the control group. Furthermore, carcass weight, carcass yield, loin depth, and lean percentage were increased and back fat depth was decreased (p < 0.05) by feeding ractopamine. Feeding CLA resulted in improved (p < 0.05) ADG and G:F and increased lean percentage but reduced carcass yield (p < 0.05). The inclusion of DDGS did not affect ADG, adfi, or g:f but reduced (p < 0.05) carcass dressing percent. An increase (p < 0.05) in the concentration of pufa was observed with inclusion of DDGS, ractopamine, and CLA. Iodine value (iv) increased (p < 0.001) in both belly and jowl samples by feeding DDGS and ractopamine, whereas a decrease (p < 0.01) was observed when CLA was included in the diets. The fatty acid profiles of belly and jowl fat samples were affected (p < 0.05) by diet source × ractopamine, indicating that effects of dietary ractopamine depend on the fatty acid profile of the diet. These results indicate that feeding ractopamine and CLA could improve growth and carcass measures and that CLA was effective in diminishing some of the negative effects, especially on IV, caused by DDGS.

Impact of dietary energy level and ractopamine on growth performance, carcass characteristics, and meat quality of finishing pigs

A total of 54 finishing barrows (initial BW = 99.8 ± 5.1 kg; PIC C22 × 337) reared in individual pens were allotted to 1 of 6 dietary treatments in a 2 × 3 factorial arrangement of treatments with 2 levels of ractopamine (0 and 7.4 mg/kg) and 3 levels of dietary energy (high, 3,537; medium, 3,369; and low, 3,317 kcal of ME/kg) to determine the effects of dietary ractopamine and various energy levels on growth performance, carcass characteristics, and meat quality of finishing pigs. High-energy diets were corn-soybean-meal-based with 4% added fat; medium-energy diets were corn-soybean meal based with 0.5% added fat; and low-energy diets were corn-soybean meal based with 0.5% added fat and 15% wheat middlings. Diets within each ractopamine level were formulated to contain the same standardized ileal digestible Lys:ME (0 mg/kg, 1.82; and 7.4 mg/kg, 2.65 g/Mcal of ME). Individual pig BW and feed disappearance were recorded at the beginning and conclusion (d 21) of the study. On d 21, pigs were slaughtered for determination of carcass characteristics and meat quality. No ractopamine × energy level interactions (P > 0.10) were observed for any response criteria. Final BW (125.2 vs. 121.1 kg), ADG (1.2 vs. 1.0 kg/d), and G:F (0.31 vs. 0.40) were improved (P < 0.001) with feeding of ractopamine diets. Feeding of the low-energy diet reduced (P = 0.001) final BW and ADG compared with the high- and medium-energy diets. Gain:feed was reduced (P = 0.005) when the medium-energy diets were fed compared with the high-energy diets. Additionally, G:F was reduced (P = 0.002) when the low-energy diets were compared with the high- and medium-energy diets. Feeding ractopamine diets increased (P < 0.05) HCW (93.6 vs. 89.9 kg) and LM area (51.2 vs. 44.2 cm(2)). The LM pH decline was reduced (P ≤ 0.05) by feeding ractopamine diets. The feeding of low-energy diets reduced (P = 0.001) HCW when compared with the high- and medium-energy diets and reduced (P = 0.024) 10th-rib backfat when compared with the high- and medium-energy diet. These data indicate that feeding ractopamine diets improved growth performance and carcass characteristics, while having little or no detrimental effect on meat quality. Reductions in energy content of the diet by adding 15% wheat middlings resulted in impaired ADG, G:F, and 10th-rib backfat. There were no ractopamine × energy level interactions in this trial, which indicates that the improvements resulting from feeding ractopamine were present regardless of the dietary energy levels.

Fatty acid profiles and iodine value correlations between 4 carcass fat depots from pigs fed varied combinations of ractopamine and energy

A total of 54 finishing barrows (initial BW = 99.8 ± 5.1 kg; PIC C22 × 337) reared in individual pens were allotted to 1 of 6 dietary treatments in a 2 × 3 factorial arrangement of treatments with 2 levels of ractopamine (0 and 7.4 mg/kg) and 3 levels of dietary energy (high: 3,537, medium: 3,369, and low: 3,317 kcal/kg of ME) to determine the effects of feeding ractopamine and various dietary energy levels on the fatty acid profile of 4 carcass fat depots (jowl, belly, subcutaneous loin, and intramuscular) and the predictive relationships of calculated iodine value (IV) between these 4 fat depots. Carcasses were sampled for fat tissues at the anterior tip of the jowl, posterior to the sternum on the belly edge, three-quarters the distance around the LM (subcutaneous fat; SC), and within the LM (intramuscular fat; IMF). Feeding ractopamine diets reduced (P < 0.05) total SFA in SC and IMF and increased (P = 0.04) total MUFA in SC. Also, feeding ractopamine diets increased (P < 0.01) the IV of IMF. Total MUFA of belly fat was reduced (P < 0.05) when the low-energy diet was fed compared with the high-energy diet. Jowl fat total MUFA was reduced (P < 0.05) and total PUFA was increased (P < 0.05) when the medium-energy diet was fed compared with the high- and low-energy diets. Iodine values, independent of treatment, were 60.97, 64.51, 55.59, and 58.26 for belly, jowl, IMF, and SC fat depots, respectively. The IV correlations within fat depots were not consistent across dietary treatments because of the effect of treatments on carcass fatty acid characteristics. Feeding ractopamine diets shifted the fatty acid profile from SFA to MUFA in the SC depot. Feeding ractopamine diets did not change belly fat profiles, thus avoiding the potential negative effect of softening belly fat, which is detrimental to processing value. The IV of one fat depot may not be a good indication of IV of other fat depots because of weak correlation coefficients and the apparent influence of dietary treatment.

Effects of ractopamine and gender on protein turnover in skeletal muscle of implanted steers and heifers

Effects of the β-agonist, ractopamine-HCl (ractopamine), on skeletal muscle protein turnover were evaluated in 16 steers (512 kg) and 16 heifers (473 kg). Treatments were arranged in a 2 × 2 factorial design and included gender (steer vs. heifer) and ractopamine (0 or 200 mg/d). Steers were implanted with 120 mg trenbolone acetate and 24 mg estradiol-17β, heifers with 140 mg trenbolone acetate and 14 mg estradiol-17β. Cattle were fed a diet based on steam-flaked maize. Muscle biopsy samples were collected from m. longissimus and m. biceps femoris on day 0 (prior to ractopamine feeding) and after 14 and 28 d of ractopamine feeding. In vitro protein synthesis rates in m. longissimus tended to be greater for steers than for heifers, but no effect of gender was observed in m. biceps femoris. Gender did not affect in vitro protein degradation rates for either muscle. Ractopamine significantly decreased rates of in vitro protein degradation in m. longissimus, but rates in m. biceps femoris were not affected by ractopamine. Ractopamine did not affect in vitro protein synthesis rates. In general, there were no striking differences between steers and heifers in response to ractopamine, indicating that its effectiveness should be similar between genders. Keywords: Cattle, β-agonist, protein turnover, ractopamine

Effects of sequential implanting and ractopamine hydrochloride supplementation on carcass characteristics and longissimus muscle tenderness of calf-fed steers and heifers1

A 4 × 2 factorial arrangement of treatments (4 growth-enhancement treatments × 2 sex classes) was used to quantify effects of initial implanting (I-implant, d 0), terminal implanting (T-implant, d 63), and feeding ractopamine hydrochloride [RAC, 200 mg/(animal/d)] for the last 28 d on feed on carcass characteristics and LM shear force (WBSF) of calf-fed steers (n = 159) and heifers (n = 132). Growth-enhancement treatments included the following: TRT1, T-implant only; TRT2, I-implant and RAC; TRT3, I-implant and T-implant; TRT4, I-implant, T-implant, and RAC. Growth responses (BW and ADG) were measured in 3 segments of the finishing period: 1) d 0 to 63, 2) d 63 to 28 d before slaughter, and 3) final 28 d. Cattle were slaughtered after 152, 166, or 180 d of finishing; carcass data were collected after a 48-h chill; and LM WBSF was measured at 3, 7, 14, 21, and 28 d postmortem. A priori contrasts were constructed to test effects associated with use vs. exclusion of growth enhancement in each segment of the finishing period. The interaction between sex class and treatment was not significant (P > 0.05) for any trait tested, indicating that the 4 treatments elicited similar effects in both sexes. Initial implanting improved (P < 0.001) ADG from d 0 to 63 by 11.5%, terminal implanting improved (P < 0.001) ADG from d 63 to 28 d before slaughter by 15%, and supplementing twice-implanted cattle with RAC enhanced ADG during the final 28 d of finishing by 12%. Effects of I-implant, T-implant, and RAC resulted in LM area increases of 3 cm(2) (P = 0.015), 6 cm(2) (P < 0.001), and 3 cm(2) (P = 0.011), respectively, and HCW responses of 11 kg (P = 0.011), 16 kg (P = 0.001), and 6 kg (P = 0.195), respectively. Initial implanting resulted in a 20-point reduction (P = 0.097) in marbling, and T-implant reduced marbling by 25 points (P = 0.04), whereas marbling score was unaffected (P = 0.236) by RAC supplementation. Cattle that received only 1 implant (TRT1 and TRT2) produced carcasses with greater (P = 0.026) mean marbling scores and greater (P = 0.01) rates of conformity to beef carcass marketing specifications for HCW, quality grade, yield grade, and LM area than did cattle that were implanted twice (TRT3 and TRT4). Values for LM WBSF were not affected (P > 0.05) by initial or terminal implanting; however, RAC supplementation increased (P = 0.007) mean LM WBSF by 0.23 kg, which translated into a reduction (P = 0.007) in predicted consumer acceptance of LM steaks.

Gene expression of serotonin and dopamine receptors and monoamine oxidase-A in the brain of dominant and subordinate pubertal domestic pigs (Sus scrofa) fed a β-adrenoreceptor agonist

Aggression is a major source of social stress with negative effects on health and well-being, yet limited information is known about the molecular mechanisms mediating aggressive behavior in swine. Ractopamine (RAC) is a β-adrenoreceptor agonist that enhances growth but increases aggressive behaviors in female pigs. Thus, the effects of RAC, sex, and social rank on the mRNA abundance of genes encoding serotonin and dopamine receptors, and monoamine oxidase (MAO)-A in brains of sub-adult pigs were evaluated. Top dominant and bottom subordinate pigs (16/sex) in pens of 4 pigs were determined, and fed either the control or RAC diets. At day 31, their raphe nuclei (RN), amygdala (AMY), frontal cortex (FC), and hypothalamus (HYP) were dissected; relative mRNA abundance for 5-HT1B, 5-HT2A, 5-HT2B, and D1 receptors, and MAO-A was determined by Q-RT-PCR and data subjected to multivariate linear mixed model analysis and Tukey post-hoc test. Expression of 5-HT1B and MAO-A was suppressed in the AMY of female pigs; 5-HT2B expression was also suppressed in the RN, FC and HYP of females and RN of dominant pigs (P<0.05). Expression of 5-HT2A was more up-regulated in RN of females compared to males (P<0.05). Expression of D1 varied in RN and FC mostly as a function of RAC feeding and its interaction with sex and social rank (P<0.05). While RAC feeding is related to changes in expression of the D1 receptor mRNA, suppression in expression of serotonergic genes detected in the brain of pigs, especially in females independent of social rank, may be mediating the inter-individual offensive aggression.