The beta-adrenergic receptors (beta-AR) are present on the surface of almost every type of mammalian cell. These receptors are stimulated physiologically by the neurotransmitter, norepinephrine and the adrenal medullary hormone, epinephrine. There are three subtypes of beta-AR, namely, beta1-AR, beta2-AR, and beta3-AR; the pharmacological and physiological responses of an individual cell result from the particular mixture of the three beta-AR subtypes present on that cell. Species-specific structure (amino acid sequence) also causes modification of the function of a given beta-AR subtype. Knowledge of the beta-AR subtypes present in various cell types, coupled with knowledge of receptor structure (sequence), will allow an understanding of the complexity of physiological function regulated by beta-AR. Oral administration of some beta-AR agonists increases muscle and decreases fat accretion in cattle, pigs, poultry, and sheep. The large number of physiological functions controlled by beta-AR suggests that the mechanism(s) for the observed changes in carcass composition may be extremely complex. Any proposed mechanism must begin with the possibility of direct effects of the agonist on skeletal muscle and adipocyte beta-AR. However, many other mechanisms, such as modification of blood flow, release of hormones, or central nervous system control of feed intake may contribute to the overall effects observed with a given beta-AR agonist in a given species. Furthermore, the pharmacodynamic properties of a particular agonist are complex and expected to vary among species as well as within the same species at different ages or when fed different diets.

Overview of the effects of beta-adrenergic receptor agonists on animal growth including mechanisms of action

The impact of using 2 beta-adrenergic agonists in feedlot cattle fed finishing diets was evaluated using 54 steers (45 crossbred Charolais and 9 Brangus) initially weighing 424 +/- 26.6 kg in a randomized complete block design with 3 treatments and 6 blocks (i.e., 18 pens with 3 steers per pen). Response variables were feedlot performance, carcass characteristics, and meat quality. Treatments were 1) control (no supplement added); 2) zilpaterol hydrochloride (ZH; 60 mg.steer(-1).d(-1)); and 3) ractopamine hydrochloride (RH; 300 mg.steer(-1).d(-1)). The beta-agonists were added to the diets during the final 33 d of the experiment. The groups of steers fed ZH or RH improved (P < 0.01) ADG by 26 or 24%, respectively, compared with control steers. Steers supplemented with RH consumed less (P = 0.03) DM (8.37 kg) than control steers (8.51 kg), whereas intake was similar (P = 0.37) for ZH and control steers. Addition of either beta-agonist to the diet considerably improved (P < 0.01) the G:F (ZH, 0.253 and RH, 0.248 vs. control, 0.185). Hot carcass weight and carcass yield were enhanced (P < 0.05) with both beta-agonists. The LM area was increased (P = 0.026) by ZH (75.2 cm(2)), but that of RH (72.2 cm(2)) was similar (P = 0.132) to the control steers (66.8 cm(2)). Meat from the ZH- (P = 0.0007) and RH- (P = 0.0267) supplemented steers had greater shear force values than control steers (ZH = 5.11; RH = 4.83; control = 4.39 kg/cm(2)). Variables related to meat color indicated that both beta-agonists led to a similar redness of the LM area related to the control group. In general, feedlot performance was greatly enhanced by beta-adrenergic agonists, and meat tenderness from treated animals was classified as intermediate. Furthermore, meat color was not altered by beta-agonist supplementation.

Effects of two β-adrenergic agonists on finishing performance, carcass characteristics, and meat quality of feedlot steers,

Effects of dietary factors and other metabolic modifiers on quality and nutritional value of meat

Swine growth models have the potential to evaluate alternative management decisions and optimize production systems. However, the lack of economical, yet accurate methods to obtain the growth parameters required to characterize pig genotypes, and which are required by growth models, limits their widespread implementation. The four primary parameters required are 1) daily whole-body protein accretion potential, 2) partitioning of energy, intake over maintenance between protein and lipid accretion, 3) maintenance requirements for energy, and 4) daily feed intake. Estimation of daily protein accretion rates requires that serial estimates of composition and growth be fitted to flexible nonlinear functions. Serial dissection and chemical analysis are too expensive to be routinely conducted on an adequate number of pigs for precise daily protein accretion rates at different live weights. Three alternate methods include 1) serial slaughter and double sampling; 2) use of serial live measurements to estimate composition, i.e., serial ultrasonic measurements; and 3) use of generalized functions that estimate daily protein accretion as a function of mean daily fat-free lean gain over a specified weight interval. The energy partitioning between lipid and protein accretion can be expressed as two interchangeable measurements, either as the slope of protein accretion or the change in the lipid: protein gain ratio as a function of energy intake at each live weight. Both methods require serial estimates of composition and scale feeding of pigs to specified energy intake levels. Maintenance requirements for energy are better expressed as a function of protein mass than body weight. However, differences in body protein mass do not fully explain difference in maintenance requirements between various pig genotypes. Daily feed intakes at each live weight can be estimated by accurately collecting feed intake data at least three live weight ranges and fitting the data to nonlinear functions. An alternative method to estimate daily feed intake is to develop daily lipid and protein accretion curves. On the basis of their energetic costs of lipid and protein deposition and assumed maintenance requirements, daily energy intakes can be estimated. Genetic selection changes the underlying growth parameters. The selection criteria and testing environment direct the relative genetic change for each growth parameter. The different sexes may also be affected differently by selection. For this reason, each closed uniformly selected population must be evaluated for each parameter for each sex.

Characterization of growth parameters needed as inputs for pig growth models

http://ssu.ac.ir/cms/fileadmin/user_upload/Mtahghighat/tfood/ARTICLES/meat/Auditing_animal_welfare_at_slaughter_plants.pdf

Auditing animal welfare at slaughter plants.

Six trials involving 888 pigs (Study 1) and three trials involving 360 pigs (Study 2) were conducted at various geographical locations in the US and Canada to evaluate the effect of ractopamine hydrochloride on the performance and carcass characteristics of finishing swine All trials were conducted using a randomized complete block design Trial data were pooled within study for statistical analysis Pigs averaged approximately 645 kg (Study 1) and 659 kg (Study 2) initially and had ad libitum access to a 16% crude protein corn-soybean meal or barley-soybean meal diet Ractopamine was included in the diet at 0, 25, 5, 10, 20 or 30 ppm (Study 1), or at 0, 5, 10, 15 or 20 ppm (Study 2); diets were fed for an average of 45 d (Study 1) and 50 d (Study 2) to a final weight of about 1043 kg (Study 1) and 1066 kg (Study 2) Carcass dissection data were collected in three of the six trials in Study 1 (0, 5 and 20 ppm ractopamine) and in all three trials in Study 2 (0, 5, 10, 15 and 20 ppm ractopamine) All ractopamine levels improved (P less than 05) ADG and feed: gain (Studies 1 and 2) above those of control pigs Ractopamine levels of 10 to 30 ppm (Studies 1 and 2) improved (P less than 05) dressing percentage over controls Pigs fed ractopamine at 5 and 20 ppm (Study 1) and 10, 15 and 20 ppm (Study 2) had increased (P less than 05) dissected leanness compared with controls(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of various levels of ractopamine hydrochloride on the performance and carcass characteristics of finishing swine

At approximately 68 kg live weight, crossbred barrows and gilts (n = 144) were allocated to be fed to one of two weight end points (107 kg and 125 kg). Pigs from each weight group were treated with Ractopamine (RAC) (0, 10, or 20 ppm; n = 24/ treatment) for the last 40 kg of gain. Feed consump- tion and weight gain were measured. Pigs were slaughtered and carcass measurements made at 24 h postmortem. Carcasses were fabricated into wholesale, trimmed wholesale, and boneless wholesale cuts for cutting yields. Hams were separated into muscle, fat, and bone. The RAC improved growth characteristics and carcass characteristics. Pigs fed RAC had in- creased ( P < .01) average daily gain and improved ( P < .01) feed:gain ratio over controls in each weight group. Carcasses from pigs treated with RAC had larger ( P < .01) longissimus muscle area and reduced ( P < .01) fat at the 10th rib. Cuts from 125-kg pigs were generally heavier than those from 107-kg pigs. The RAC increased ( P < .05) the boneless cut weights of both weight groups. Percentage of dissected lean from the hams of RAC-treated pigs was ( P < .05) higher than that of controls. Few consistent differences were observed between the 10 and 20 ppm of RAC treatments. Results from this study indicate that RAC had positive effects on the growth charac- teristics, carcass characteristics, and carcass cutting yields of pigs representative of the broad spectrum of market weights.

Effect of ractopamine on growth performance, carcass composition, and cutting yields of pigs slaughtered at 107 and 125 kilograms

An experiment was conducted to determine the effect of ractopamine, energy intake, dietary fat level, and sex on performance and carcass composition in finishing pigs. Three hundred six barrows and gilts were used in a factorial arrangement of treatments replicated over three seasons. Treatments consisted of two ractopamine levels (0 vs 44.7 mg/d), two sexes (barrows and gilts), two levels of fat addition (0 vs 5% added fat), and four energy intake levels (8.3, 8.9, 9.5, and 10.1 Mcal of ME/d for barrows and 7.7, 8.3, 8.9, and 9.5 Mcal of ME/d for gilts). Diets were formulated to maintain an equal lysine (28.5 g/d) intake at each feeding level through cornstarch dilution of the basal (7.7 Mcal of ME/d) diets. Pigs were fed daily based on a standard feed intake curve and prior weekly body weights. At slaughter (104 kg), carcass measurements and TOBEC HA-1 scanner measurements were recorded. Dietary fat addition improved live weight and lean efficiency (grams of carcass lean gain/kilogram of feed, P < .05). Dietary fat addition did not affect growth rate or carcass composition. Increasing energy intake resulted in a linear increase in average daily gain for both barrows and gilts (P < .01). Dietary ractopamine influenced the response of lean tissue accretion, lean tissue accretion efficiency, and fat tissue accretion to energy intake. Pigs with no added ractopamine demonstrated increased lean tissue accretion and improved efficiency and decreased fat tissue accretion with increasing energy intake (up to 9.5 Mcal of ME intake for barrows and 8.9 Mcal of ME intake for gilts). In contrast, pigs with added ractopamine did not respond to increasing energy intake and demonstrated increased fat tissue accretion with increasing energy intake. The response to ractopamine for growth was greatest from d 6 to 22 on test or during the test gain period of 7 to 18 kg. After d 22, the response of ractopamine declined linearly. These results indicate that ractopamine increases growth rapidly at the onset of feeding until a plateau is reached, after which there is a linear decline in growth response.

The impact of ractopamine, energy intake, and dietary fat on finisher pig growth performance and carcass merit

One hundred eighty barrows were evaluated to determine the effects of ractopamine hydrochloride (RAC) on lean carcass yields and pork quality The pens were blocked by weight (six pens per block) with starting block weights of 690, 707, 738, 766, 784, and 843 kg Pens within a block were assigned randomly to one of three RAC treatments so each treatment in a block was replicated twice Treatments (as-fed basis) included control diet, 10 ppm of RAC added (R10), and 20 ppm of RAC added (R20) and ranged from 25 to 41 d depending on block Pigs were slaughtered by blocks when block average live weights were 109 kg Gain and feed efficiency were improved (P 005) Dressing percentage was higher (P 005) among treatments Carcass weights were heavier (P 005) among dietary treatments Trained sensory evaluation panel results for tenderness decreased in a low-dose plateau response fashion for nonenhanced chops (P = 0004) Tenderness of enhanced chops decreased linearly (P = 004) with increasing RAC concentrations No differences (P > 005) were found in juiciness or flavor of enhanced or nonenhanced chops Feeding RAC to late-finishing swine resulted in faster growing, more efficient animals with increased boneless subprimal yields, and it had little effect on pork juiciness and flavor

The effects of ractopamine hydrochloride on lean carcass yields and pork quality characteristics.

This study was designed to evaluate the visual and palatability characteristics of boneless cured hams and fresh loin chops from pigs fed diets containing 0, 5, 10 or 20 ppm of the phenethanolamine, ractopamine hydrochloride (RAC). Sixty pigs were blocked by starting weight and randomly assigned to pens (four pigs/pen) within each of three blocks. Treatments were then randomly assigned to pens (six pens of the 0–ppm level and three pens each for the 5, 10 and 20 ppm RAC levels). Animals were slaughtered by weight block after approximately 48 days on trial. Fresh pork hams and loin sections (10–14th rib) were removed from the right side of the carcasses for subsequent analysis. Boneless hams were manufactured using commercial curing procedures. RAC had no effect (P > 0.05) on visual or palatability attributes of ham slices or boneless loin chops. Moisture content of the longissimus muscle from RAC treatments was lower (P < 0.05) than controls; however, this difference was small. These results indicate that RAC had no affect on the visual or palatability characteristics of boneless cured and smoked hams or fresh boneless pork loin chops.

D. J. Jones

Papers

The effect of various levels of ractopamine hydrochloride on the performance and carcass characteristics of finishing swine

Effect of ractopamine on growth performance, carcass composition, and cutting yields of pigs slaughtered at 107 and 125 kilograms

The impact of ractopamine, energy intake, and dietary fat on finisher pig growth performance and carcass merit

The effects of ractopamine hydrochloride on lean carcass yields and pork quality characteristics.

Palatability and visual characteristics of hams and loin chops from swine treated with ractopamine hydrochloride