Development of a model to describe the compositional growth and dietary lysine requirements of pigs fed ractopamine

Ractopamine at the Center of Decades-Long Scientific and Legal Disputes: A Lesson on Benefits, Safety Issues, and Conflicts

Ractopamine (RAC) is a synthetic phenethanolamine, β–adrenergic agonist used as a feed additive to develop leanness and increase feed conversion efficiency in different farm animals. While RAC has been authorized as a feed additive for pigs and cattle in a limited number of countries, a great majority of jurisdictions, including the European Union (EU), China, Russia, and Taiwan, have banned its use on safety grounds. RAC has been under long scientific and political discussion as a controversial antibiotic as a feed additive. Here, we will present significant information on RAC regarding its application, detection methods, conflicts, and legal divisions that play a major role in controversial deadlock and why this issue warrants the attention of scientists, agriculturists, environmentalists, and health advocates. In this review, we highlight the potential toxicities of RAC on aquatic animals to emphasize scientific evidence and reports on the potentially harmful effects of RAC on the aquatic environment and human health.

Ractopamine-induced fiber type-specific gene expression in porcine skeletal muscles is independent of growth

Feeding ractopamine (RAC), a β-adrenergic agonist (BAA), to pigs increases type IIB muscle fiber type-specific protein and mRNA expression. However, increases in the abundance of these fast-twitch fiber types occur with other forms of muscle hypertrophy and thus BAA-induced changes in myosin heavy chain (MyHC) composition may simply be associated with increased muscle growth known to occur in response to BAA feeding. The objective of this study was to determine whether RAC feeding could change the MyHC gene expression in the absence of maximal muscle growth. Pigs were fed either an adequate diet that supported maximal muscle hypertrophy or a low nutrient diet that limited muscle growth. RAC was included in diets at 0 or 20 mg/kg for 1, 2, or 4 wk. Backfat depth was less (P < 0.05) in pigs fed the low nutrient diet compared with the adequate diet but was not affected by RAC. Loin eye area was greater (P < 0.05) in pigs fed an adequate diet plus RAC at 1 wk but did not differ among remaining pigs. At 2 and 4 wk, however, pigs fed the adequate diet had greater loin eye areas (P < 0.05) than pigs fed the low nutrient diet regardless of RAC feeding. Gene expression of the MyHC isoforms, I, IIA, IIX, and IIB, as well as glycogen synthase, citrate synthase, β 1-adrenergic receptor (AR), and β 2-AR were determined in longissimus dorsi (LD) and red (RST) and white (WST) portions of the semitendinosus muscles. MyHC type I gene expression was not altered by RAC or diet. Feeding RAC decreased (P < 0.01) MyHC type IIA gene expression in all muscles, but to a greater extent in WST and LD. MyHC type IIX gene expression was lower (P < 0.05) in WST and LD muscles in response to RAC but was not altered in RST muscles. RAC increased (P < 0.05) MyHC type IIB gene expression in all muscles, but to a greater extent in RST. β 1-AR gene expression was unaffected by RAC or diet, whereas the expression of the β 2-AR gene was decreased (P < 0.001) by RAC. No significant RAC * diet interactions were observed in gene expression in this study, indicating that RAC altered MyHC and β 2-AR gene expression in porcine skeletal muscles independent of growth.

Effect of ractopamine and conjugated linoleic acid on performance of late finishing pigs

The dietary inclusion of feed additives to improve the carcass characteristics of the final product is of great importance for the pork production chain. The aim of our study was to evaluate the effects of the association of ractopamine (RAC) and conjugated linoleic acid (CLA) on the performance traits of finishing pigs during the last 26 days prior to slaughter. In total, 810 commercial hybrid barrows were used. Animals were distributed among treatments according to a randomised block design in a 3 × 3 factorial arrangement, with three RAC levels (0, 5 or 10 ppm) and three CLA levels (0, 0.3 or 0.6%). Pigs fed the diet with 5 ppm RAC had higher average daily feed intake (ADFI) (2.83 kg; P < 0.05) when compared with those fed 10 ppm RAC and the control diet (2.75 and 2.74 kg, respectively). Lower ADFI values (P < 0.01) were observed with the diets containing CLA compared with the control diet with no CLA (2.73 and 2.75 v. 2.85 kg/day, respectively). The average daily weight gain of pigs fed 5 and 10 ppm RAC was +148 and +173 g/dayhigher (P < 0.001), respectively, than those fed the control diet. Dietary RAC levels influenced (P < 0.001) feed conversion ratio (FCR), which was reduced as RAC levels increased, with the pigs fed 10, 5 and 0 ppm RAC presenting FCR values of 2.57, 2.71 and 3.05, respectively. FCR also improved (P < 0.05) with the inclusion of 0.6% CLA relative to the control diet (2.70 v. 2.84, respectively). There was a significant interaction between CLA × RAC levels (P < 0.01) for final BW, loin eye area (LEA) (P < 0.05) and backfat thickness (BT) (P < 0.05). The treatments containing 10 ppm RAC + 0.6% or 0.3% CLA increased LEA and reduced BT. In conclusion, the level of 10 ppm inclusion of RAC increased the overall performance parameters of pigs and therefore improved production efficiency. The combined use of RAC and CLA promoted a lower feed conversion ratio as well as better quantitative carcass traits, as demonstrated by the higher LEA and lower BT. The dietary inclusion of CLA at 0.3% improved feed efficiency, however, without affecting LEA or BT yields.

Effects of dietary hop (Humulus lupulus L.) β-acids on quality attributes, composition and oxidative stability of pork meat

BACKGROUND

The effects of dietary levels of hop β-acids on physical attributes, lipid oxidation and chemical composition of pork meat were evaluated. Thirty-two castrated male pigs obtained from a complete block design feeding experiment (6.23 ± 0.42 kg initial body weight (BW) to 20.45 ± 0.95 kg final BW) and fed diets supplemented with 0, 120, 240 or 360 mg kg^-1 hop β-acids during 35 days were slaughtered to sample longissimus dorsi muscle for meat analysis.

RESULTS

No effects (P > 0.05) of dietary hop β-acids were observed on meat physical attributes. Quadratic effects (P < 0.05) of hop β-acids were observed on lipid and protein contents and on thiobarbituric acid-reactive substance (TBARS) values of meatballs, whose equations allowed the estimation of dietary hop β-acid levels of 176, 169 and 181 mg kg^-1 to provide up to 16.20% lipid reduction, 1.95% protein accretion and 23.31% TBARS reduction respectively.

CONCLUSION

Dietary hop β-acids fed to pigs might reduce lipid, increase protein and reduce lipid oxidation without affecting physical attributes of the pork meat. © 2017 Society of Chemical Industry.

A multivariate approach to determine the factors affecting response level of growth, carcass, and meat quality traits in finishing pigs fed ractopamine

The effect of ractopamine (RAC) supplementation on growth, carcass, and meat quality traits of finishing pigs was studied using a meta-analytical approach. The database was composed of 57 studies published from 2004 to 2016. The dependent variables extracted for the meta-analysis included final BW, ADG, ADFI, feed:gain ratio, HCW, dressing percentage, carcass length, lean yield, back fat thickness, loin muscle area, loin depth, postmortem pH, meat brightness, redness, and yellowness. The studies were grouped by similarity in 3 clusters (C1, C2, and C3) by hierarchical clustering on principle components. The main differences observed between clusters were those of animal initial weight, which increased from C1 through C3. Linear mixed models were used to analyze the data, where studies were assumed as random effect, whereas the total amount of RAC in the diet, cluster, and sex category were considered fixed effects. The interactions between cluster and sex category (barrows, gilts, and mixed sex) and RAC level were also evaluated. Dietary RAC was effective in improving final weight ( < 0.0001), ADG ( < 0.0001), and feed:gain ratio ( < 0.0001) and had a positive effect on HCW ( < 0.0001), lean yield ( = 0.0081), loin muscle area ( = 0.0190), and loin depth ( < 0.0001). In addition, a relatively limited effect on pork quality was observed in the current study. The RAC supplementation was more effective, mainly when pigs started supplementation with higher initial weight, although different responses were observed according to sex category ( < 0.05). There is ample indication that growth and carcass traits could be improved by dietary RAC supplementation. Ractopamine supplementation did not influence the pork quality.

Effect of natural betaine and ractopamine HCl on whole-body and carcass growth in pigs housed under high ambient temperatures

Betaine is an osmolyte that helps to maintain water homeostasis and cell integrity, which is essential during heat stress. We hypothesized that supplemental betaine can improve growth during heat stress and may further improve the response to ractopamine. Two studies were conducted to determine: 1) the effects of betaine in combination with ractopamine; and 2) the optimum betaine level for late finishing pigs during heat stress. Heat stress was imposed by gradually increasing temperatures over 10 d to the target high temperature of 32°C. In Exp. 1, pigs ( = 1477, BW = 91.6 ± 3 kg) were assigned within BW blocks and sex to 1 of 4 diets arranged in a 2 × 2 factorial RCB design (68 pens; 20 to 23 pigs/pen). Treatments consisted of diets without or with ractopamine (5 mg/kg for 21 d followed by 8.8 mg/kg to market) and each were supplemented with either 0 or 0.2% of betaine. Betaine reduced ( ≤ 0.05) BW (123.1 vs. 124.3 kg), ADG (0.780 vs. 0.833 kg/d), and ADFI (2.800 vs. 2.918 kg/d), but did not impact carcass characteristics. Ractopamine increased ( < 0.01) BW (125.5 vs. 121.9 kg), ADG (0.833 vs. 0.769 kg/d), G:F (0.295 vs. 0.265), HCW (94.1 vs. 90.0 kg), carcass yield (74.8 vs. 73.8%), loin depth (63.6 vs. 60.0 mm), and predicted lean percentage (53.2 vs. 51.7%) and reduced ADFI (2.822 vs. 2.896 kg/d, = 0.033) and backfat depth ( < 0.001; 20.2 vs. 22.5 mm). In Exp. 2, pigs ( = 2193, BW = 95.5 ± 3.5 kg) were allocated within BW blocks and sex to 1 of 5 treatments in a RCB design (100 pens; 20 to 24 pigs/pen). Treatments consisted of diets with 0, 0.0625, 0.125, 0.1875% of betaine, and a positive control diet with ractopamine, but not betaine. Betaine tended to decrease carcass yield quadratically ( = 0.076; 74.1, 73.5, 73.8, and 73.9 for 0, 0.0625, 0.125, 0.1875% of betaine, respectively), but did not impact other responses. Ractopamine improved ( < 0.001) BW (121.6 vs. 118.5 kg), G:F (0.334 vs. 0.295), carcass yield (74.7 vs. 73.8%), loin depth (61.7 vs. 59.0 mm), and predicted lean percentage (53.2 vs. 52.6%), and reduced backfat (18.7 vs. 20.4 mm). Collectively, data indicate that under commercial conditions, betaine did not improve performance of pigs housed under high ambient temperatures, regardless of ractopamine inclusion. Ractopamine improved whole-body growth and especially carcass growth of pigs raised under high ambient temperatures. The ability of ractopamine to stimulate growth during heat stress makes it an important production technology.

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-HT₁(B), 5-HT₂(A), 5-HT₂(B), 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-HT₁(B) and MAO-A was suppressed in the AMY of female pigs; 5-HT₂(B) expression was also suppressed in the RN, FC and HYP of females and RN of dominant pigs (P < 0.05). Expression of 5-HT₂(A) 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.

Efeito da ractopamina e de métodos de formulação de ração sobre o desempenho e as características de carcaça de leitoas em terminação

Avaliou-se o efeito da ractopamina e de diferentes métodos de formulação de dietas sobre o desempenho e as características de carcaça de leitoas em terminação. Foram utilizadas 60 leitoas, híbridas comerciais, distribuídas em delineamento experimental de blocos ao acaso, em esquema fatorial 2x3, sendo dois níveis de ractopamina e três métodos de formulação de dietas. Houve interação de métodos de formulação versus ractopamina para ganho de peso diário, peso corporal, conversão alimentar e taxa de deposição de carne magra (TDCM) na avaliação de carcaça in vivo por ultrassom. A dieta formulada com alta proteína bruta proporcionou maior consumo de dieta (CRD), de lisina (CLD), ganho de peso diário (GPD) e peso corporal final. A suplementação de ractopamina não influenciou o CRD e o CLD, entretanto aumentou o GPD. O método de formulação da dieta não influenciou as características de carcaça aos 28 dias, enquanto a suplementação de ractopamina reduziu a espessura de toucinho, aumentou a profundidade de lombo e o rendimento de carne magra. A dieta formulada com alta proteína bruta proporcionou melhores resultados de desempenho e taxa de deposição de carne magra na carcaça de leitoas em terminação, suplementadas com ractopamina.

Partition of minerals in body components from a high- and low-lean genetic line of barrows and gilts from 20 to 125 kilograms of body weight

An experiment was conducted to determine if the macro- and micromineral contents of the ham and loin or the remaining body component differed by genetic line, sex, or BW. The experiment was a completely randomized design with a factorial arrangement (2 × 2 × 5) using barrows and gilts of 2 genetic lines at 5 BW intervals in 2 groups with 6 replicates (n = 120 pigs). Pigs were housed in groups of 5 per pen and removed when individual pigs reached their targeted BW. Twelve pigs (3 from each genetic line and sex) were killed at 23 kg of BW and at 25-kg intervals up to 125 kg of BW. After slaughter, loin and ham muscles were dissected and trimmed of fat, with the ham deboned. This muscle mass constituted the first body compartment. The trimming from these muscles, ham bones, the remaining body, internal tissues, skin, and head were combined and constituted the second body component. The data were analyzed by PROC MIXED using the animal as the experimental unit. Muscle weights and their protein contents differed (P < 0.01) between the high- and the low-lean pigs and barrows and gilts and also among 5 BW groups/intervals. Total macro- and micromineral contents in the loin and ham were greater (P < 0.01) in the high-lean genetic line and gilts and increased (P < 0.01) as BW increased. Genetic line × BW and sex × BW interactions (P < 0.01) occurred for the macrominerals and for Fe, Se, and Zn, with contents diverging, and were greater as BW increased in high-lean pigs and gilts. The weight and protein content of the remaining body component was greater (P < 0.01) in the high-lean genetic line but not for the 2 sexes. In this body component, macromineral contents were greater as BW increased (P < 0.01), as were the microminerals Fe, Se, and Zn (P < 0.01). When the minerals were expressed on a per kilogram of body component basis, the ham and loin mineral compositions were similar for both genetic lines and sexes, but Na and Cl declined (P < 0.01) as BW increased. Most microminerals showed a small increase with BW. In the remaining body component, Ca increased (P < 0.03) in the low-lean line, whereas K was greater (P < 0.01) in the high-lean genetic line. When expressed on a unit protein basis, the low-lean genetic line had more macrominerals in the loin and ham than the high-lean genetic line. These results indicate that high-lean genetic line pigs and gilts have greater total macro- and micromineral contents in the ham and loin than the low-lean pigs, thus indicating that their dietary mineral needs are greater during the latter part of the finisher period in heavier muscled pigs.

Partitioning of limiting protein and energy in the growing pig: description of the problem, possible rules and their qualitative evaluation

A core part of any animal growth model is how it predicts the partitioning of dietary protein and energy to protein and lipid retention for different genotypes at different degrees of maturity. Rules of partitioning need to be combined with protein and energy systems to make predictions. The animal needs describing in relation to its genotype, live weight and, possibly, body composition. Some existing partitioning rules will apply over rather narrow ranges of food composition, animal and environment. Ideally, a rule would apply over the whole of the possible experimental space (scope). The live weight range over which it will apply should at least extend beyond the 'slaughter weight range', and ideally would include the period from the start of feeding through to maturity. Solutions proposed in the literature to the partitioning problem are described in detail and criticised in relation to their scope, generality and economy of parameters. They all raise the issue, at least implicitly, of the factors that affect the net marginal efficiency of using absorbed dietary protein for protein retention. This is identified as the crucial problem to solve. A problem identified as important is whether the effects of animal and food composition variables are independent of each other or not. Of the rules in the literature, several could be rejected on qualitative grounds. Those rules that survived were taken forward for further critical and quantitative analysis in the companion paper.

Effects of dietary lysine and energy density on performance and carcass characteristics of finishing pigs fed ractopamine1

Two hundred sixteen crossbred barrows and gilts (84.3 kg BW) were used to test the effects of dietary energy density and lysine:energy ratio (Lys:ME) on the performance, carcass characteristics, and pork quality of finishing pigs fed 10 ppm ractopamine. Pigs were blocked by BW and gender, allotted to 36 pens (six pigs per pen), and pens were assigned randomly within blocks to dietary treatments (as-fed basis) arranged in a 2 x 3 factorial design, with two levels of energy (3.30 or 3.48 Mcal/kg) and three Lys:ME (1.7, 2.4, or 3.1 g lysine/Mcal) levels. Pigs were fed experimental diets for 28 d, and weights and feed disappearance were recorded weekly to calculate ADG, ADFI, and G:F. Upon completion of the feeding trial, pigs were slaughtered and carcass data were collected before fabrication. During carcass fabrication, hams were analyzed for lean composition using a ham electrical conductivity (TOBEC) unit, and loins were collected, vacuum-packaged, and boxed for pork quality data collection. Energy density had no (P > 0.22) effect on ADG or ADFI across the entire 28-d feeding trial; however, pigs fed 3.48 Mcal of ME were more (P < 0.02) efficient than pigs fed 3.30 Mcal of ME. In addition, ADG and G:F increased linearly (P < 0.01) as Lys:ME increased from 1.7 to 3.1 g/Mcal. Carcasses of pigs fed 3.48 Mcal of ME were fatter at the last lumbar vertebrae (P < 0.08) and 10th rib (P < 0.04), resulting in a lower (P < 0.03) predicted fat-free lean yield (FFLY). Conversely, 10th-rib fat thickness decreased linearly (P = 0.02), and LM depth (P < 0.01) and area (P < 0.01) increased linearly, with increasing Lys:ME. Moreover, FFLY (P < 0.01) and actual ham lean yield (P < 0.01) increased as Lys:ME increased in the diet. Dietary energy density had no (P > 0.19) effect on pork quality, and Lys:ME did not (P > 0.20) affect muscle pH, drip loss, color, and firmness scores. Marbling scores, as well as LM lipid content, decreased linearly (P < 0.01) as Lys:ME increased from 1.7 to 3.1 g/Mcal. There was a linear (P < 0.01) increase in shear force of cooked LM chops as Lys:ME increased in the finishing diet. Results indicate that 3.30 Mcal of ME/kg (as-fed basis) is sufficient for optimal performance and carcass leanness in pigs fed ractopamine. The Lys:ME for optimal performance and carcass composition seems higher than that currently used in the swine industry; however, feeding very high Lys:ME (> 3.0 g/Mcal, as-fed basis) to ractopamine-fed pigs may result in decreased marbling and cooked pork tenderness.