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Management systems that enhance carcass yield can increase the efficiency and competitiveness of beef producers, but meat quality should not be negatively affected. Continental or British crossbred steers were finished to either 12 to 13 or 18 to 20 months of age and were either untreated or treated with hormonal implants, ractopamine hydrochloride, or both. Slaughtering steers at 18 to 20 month of age, using British-Continental crossbreeding, and implanting steers reduced meat tenderness but meat yield was greater than that of 12 to 13 month old steers, British-British crossbred steers, and non-implanted steers. Decreased meat tenderness was associated with increased myofibre diameter and reduced collagen solubility. Slaughtering at 18 to 20 months of age, hormonal implants, and ractopamine hydrochloride reduced meat water-holding capacity. Muscle weight appeared to be the best indicator of shear force and it may cumulatively represent complex changes related to age and growth that occur in muscle. / Animal Science

Master of Science / Department of Animal Sciences and Industry / John M. Gonzalez / Pigs fed ractopamine-HCl (RAC) are more prone to fatigue and exhaustion when improperly handled. Wireless electromyography (EMG) can be used to directly measure median power frequency (MdPF) and root mean square (RMS) as indicators of action potential conduction velocity and muscle fiber recruitment, respectively. The objectives of this study were to determine the effect of RAC on exhaustion, EMG measures, and muscle fiber type characteristics when barrows were subjected to increased levels of activity. Thirty-four barrows were assigned to one of two treatments: a commercial finishing diet containing 0 mg/kg (CON) RAC or a diet formulated to meet the requirements of finishing barrows fed 10 mg/kg RAC (RAC+) for 35 d. After 32 d of feeding, barrows were walked around a circular track at 0.79 m/s until subjective exhausted was reached. Time, distance, and speed were measured. Wireless surface EMG sensors were affixed to the Deltoideus (DT), Triceps brachii lateral head (TLH), Tensor fasciae latae (TFL), and Semitendinosus (ST) muscles. After harvest, samples of each muscle were collected for fiber type, succinate dehydrogenase, and capillary density analysis. Speed was not different (P = 0.82) between treatments, but RAC+ barrows reached subjective exhaustion quicker and covered less distance than CON barrows (P < 0.01). The end-point MdPF was not affected by the RAC diet. The RAC diet did not change end-point RMS values in the DT or TLH; however, the RAC+ barrows tended to have decreased ST and increased TFL end-point RMS values (P < 0.07). The percentage of type I fibers tended to be greater (P = 0.07) in RAC+ barrows, but the RAC diet tended to increase (P = 0.07) size of type I fibers and increase (P = 0.03) the size of type IIA fibers. Succinate dehydrogenase was not different between treatments. The RAC+ barrows had more (P = 0.03) capillaries per fiber than CON barrows. A diet containing RAC contributes to increased onset of subjective exhaustion, possibly due to rapid loss of active muscle fibers and chronic loss of oxidative muscle fibers with no change in muscle metabolism.

These experiments were conducted to determine if ractopamine hydrochloride (RAC) could improve nutrient utilization and decrease water use in hog operations. The growth experiment utilized a comparative slaughter technique that consisted of 120 barrows (95 ± 3 kg BW) including 12 assigned to an initial slaughter group; the remaining pigs were slaughtered at 108- or 120-kg. Growth performance and nutrient retention were determined. The 15 d metabolism experiment consisted of 54 pigs (95 ± 3 kg BW). Growth performance, feed, and water intake and urine and fecal output were measured. The metabolism experiment used 9 dietary treatments arranged as a 3 x 3 factorial: 3 levels of RAC (0, 5 and 10 ppm) and 3 standardized ileal digestible lysine: digestible energy (DE) ratios (1.75, 2.25 and 2.75 g/Mcal DE). The growth study was designed as a 3 x 3 x 2 factorial to include slaughter weight as an additional factor.<p> In the growth experiment, RAC had no effect ADG, ADFI, or G:F (P > 0.10). With increased Lys levels G:F improved (P < 0.05), but not ADG or ADFI (P > 0.10). Protein deposition rates numerically increased (P = 0.11), water deposition rates tended to increase (P < 0.10), whereas lipid deposition tended to decrease with RAC inclusion (P < 0.10). In the metabolism experiment, with greater levels of RAC and Lys the pigs had improved ADG (P < 0.05) and G:F (P < 0.001). Water intake (P < 0.05.) and urine output (P < 0.05) decreased with greater RAC inclusions. Lys inclusion did not alter water balance (P > 0.10). Urinary N excretion (P < 0.05), total N excretion (P < 0.05), and the urine N:fecal N ratio (P < 0.001) decreased with addition of dietary RAC; however fecal N (P < 0.05) increased with dietary RAC inclusion. Retention of N improved with addition of RAC to the diet (P < 0.05). With greater dietary Lys inclusion fecal N was reduced (P < 0.001). The pigs fed the 2.25 g/Mcal Lys tended to have the lowest urinary N and total N excretion and highest N retention (P < 0.10) and greatest urinary N:fecal N ratio (P < 0.05). A RAC x Lys interaction was observed for N digestibility, excretion, and retention and fecal and urinary N (P < 0.05). By improving N and water utilization in finishing pigs, RAC containing diets supplemented with sufficient Lys can reduce the environmental footprint of pork production.

These experiments were conducted to determine if ractopamine hydrochloride (RAC) could improve nutrient utilization and decrease water use in hog operations. The growth experiment utilized a comparative slaughter technique that consisted of 120 barrows (95 ± 3 kg BW) including 12 assigned to an initial slaughter group; the remaining pigs were slaughtered at 108- or 120-kg. Growth performance and nutrient retention were determined. The 15 d metabolism experiment consisted of 54 pigs (95 ± 3 kg BW). Growth performance, feed, and water intake and urine and fecal output were measured. The metabolism experiment used 9 dietary treatments arranged as a 3 x 3 factorial: 3 levels of RAC (0, 5 and 10 ppm) and 3 standardized ileal digestible lysine: digestible energy (DE) ratios (1.75, 2.25 and 2.75 g/Mcal DE). The growth study was designed as a 3 x 3 x 2 factorial to include slaughter weight as an additional factor.<p> In the growth experiment, RAC had no effect ADG, ADFI, or G:F (P > 0.10). With increased Lys levels G:F improved (P < 0.05), but not ADG or ADFI (P > 0.10). Protein deposition rates numerically increased (P = 0.11), water deposition rates tended to increase (P < 0.10), whereas lipid deposition tended to decrease with RAC inclusion (P < 0.10). In the metabolism experiment, with greater levels of RAC and Lys the pigs had improved ADG (P < 0.05) and G:F (P < 0.001). Water intake (P < 0.05.) and urine output (P < 0.05) decreased with greater RAC inclusions. Lys inclusion did not alter water balance (P > 0.10). Urinary N excretion (P < 0.05), total N excretion (P < 0.05), and the urine N:fecal N ratio (P < 0.001) decreased with addition of dietary RAC; however fecal N (P < 0.05) increased with dietary RAC inclusion. Retention of N improved with addition of RAC to the diet (P < 0.05). With greater dietary Lys inclusion fecal N was reduced (P < 0.001). The pigs fed the 2.25 g/Mcal Lys tended to have the lowest urinary N and total N excretion and highest N retention (P < 0.10) and greatest urinary N:fecal N ratio (P < 0.05). A RAC x Lys interaction was observed for N digestibility, excretion, and retention and fecal and urinary N (P < 0.05). By improving N and water utilization in finishing pigs, RAC containing diets supplemented with sufficient Lys can reduce the environmental footprint of pork production.

The objective of this study was to monitor the effects on physical and reproductive parameters in mares supplemented with Ractopamine HCl (RAC), in an effort to provide some insight concerning the use of RAC in horse diets. Physical deviation was recorded via measurements of body weight (BW), muscle size, and fat deposition. Reproductive deviation was recorded via ultrasonographic measurement of follicular growth and ovulation, while hormonal analyses were conducted for leptin and luteinizing hormone (LH). Data analyses of physical measurements indicated an effect of RAC supplementation (P<.001) as treated horses had a greater increase in BW compared to the controls. Treatment horses increased gaskin circumference (P<.001) compared to horses on the control diet. Both groups showed an increase in rump fat with the treated horses gaining less (P<.05). A similar effect was revealed in body fat percentage (P<.01) with the treated horses gaining less when compared to the controls. No statistical differences were noted for changes in forearm circumference or rib fat. No change was derived for length of estrous or pre-ovulatory follicle size between groups. When analyzing the data from first to last cycle in the treatment group, length of estrous was significantly (P<.05) shortened over the 90-day study. Upon analysis of serum leptin concentrations, the control group had a significantly (P<.001) higher overall concentration as compared to the treated horses; however, no difference was noted for normalized data, though RAC supplementation may have caused the profile of leptin to become more erratic. Analysis of LH concentrations revealed a strong trend (P=0.0527) of RAC-supplemented horses having a lower mean concentration of LH throughout the 90-day study as compared to the controls. Means were also analyzed for day and treatment by day effects, suggesting possible trends (P=0.2944 and P=0.1591 respectively) of seasonality. Area Under the Curve (AUC) was calculated for individual horses and analyzed for treatment effects. Only a trend (P=0.1631) was noted for RAC-supplemented horses having a smaller AUC (80.10 ± 29.72) as compared to the controls (140.60 ± 27.50).

Doctor of Philosophy / Department of Animal Sciences and Industry / Evan C. Titgemeyer / Ractopamine is a repartitioning agent that can increase muscle growth and has led to our interest in determining the mechanisms involved in enhancing muscle growth. Therefore, three studies were conducted to determine the impact of ractopamine on growth in cattle. The first experiment evaluated the impact of increasing metabolizable protein supply to finishing heifers fed ractopamine. Three different diets were fed to increase the amount of metabolizable protein reaching the small intestine, and the diets contained urea, solvent soybean meal, or expeller soybean meal as the primary supplemental protein source. From this study it was determined that increasing metabolizable protein supply above that present in typical feedlot diets containing urea and steam-flaked corn is not necessary to improve responsiveness to ractopamine. The second experiment evaluated the effect of feeding ractopamine to growing Holstein steers implanted with trenbolone acetate/estradiol. Half of the steers were implanted 28 days prior to all steers receiving ractopamine for the final 28 days; this model represents an intense implant program. The mode of action of the ractopamine and of steroidal implants was different based on their different effects on serum insulin-like growth factor (IGF)-I and longissimus expression of IGF-I mRNA. Additionally, administering a combination of the two growth promotants, based on nitrogen retention, yields a less than additive response using our model of growing Holstein steers. The third study was conducted to evaluate the differential response to ractopamine of implanted, finishing steers and heifers. Treatments were steer vs. heifer and 0 vs. 200 mg/d ractopamine fed for the final 28 days. This study attempted to address some questions generated from the previous study, which were how serum and local tissue production of IGF-I are affected by ractopamine. Ractopamine had different effects on serum IGF-I between steers and heifers and numerically increased IGF-I mRNA abundance in longissimus and biceps femoris muscles. Additionally, ractopamine impacted protein turnover differently in different muscles and changed myosin heavy chain IIA expression. The effect of ractopamine on IGF-I warrants more research. These experiments aid in our understanding of the mode of action of ractopamine in cattle.

Ractopamine hydrochloride (RAC) has been used in the pig production industry for over 30 years. RAC is a beta-adrenergic agonist which is supplemented in the feed during the last 28 days prior to harvesting in finisher pigs to modify the pig's metabolism such that nutrients are redirected to favour muscle accretion rather than adipose deposition, and hence improve growth efficiencies, feed utilisation and carcass revenues. The objective of this study was to investigate the effect of dietary ractopamine (Paylean®) supplementation at levels of 0, 5, and 10 mg.kg-1 (hereafter referred to as 0-RAC, 5-RAC, and 10-RAC respectively) on animal growth performance, efficiency and carcass characteristics including daily voluntary feed intake, feed efficiency, absolute daily growth rate (ADG) and daily live weight gain, and backfat thickness for the last 27 days in finishing gilts. In this 27-day study, a homogenous group of 71 grower gilts (LW = 43 ± 1 kg) were pre-selected at a source farm. The gilts were then housed in similar and equally sized group pens at the Hatfield experimental facility of the University of Pretoria and fed a standard maize-soya oilcake based grower ration formulated to contain 0.94% standardised ileal digestible Lys (1.05% total Lys) and 14.01 MJ ME kg-1 during the 28 day pre-adaptation phase. From these gilts, individuals were weighed and 58 gilts selected (average LW = 68.7 ± 4.3 kg), and placed into individual pens and the same diet for 7 days (adaptation phase), afterwhich they were assigned to 1 of 3 treatments in a completely randomized block design with 19, 19, and 20 replicate pens per treatment. The pigs were then fed a standard maize-soya oilcake finisher (treatment) diet containing either 0-RAC, 5-RAC or 10-RAC for 27 d before harvesting. All treatment diets were formulated to contain 1.02% standardised ileal digestible Lys (1.13% total Lys) and 13.96 MJ ME kg-1. Individual pig LW, P2 thickness and pen feed disappearance were recorded weekly to determine LW changes, ADG, ADFI, and G:F. After 27 d on trial, gilts were slaughtered and carcass measurements were recorded at 24 h post-mortem. Overall, RAC supplementation did not affect ADFI or P2 (P > 0.05) but did influence LW (P = 0.049) and overall G:F (P = 0.012) after d27. At d15-d21 and d22-27, only a tendency (P = 0.169, 0.104 respectively) for a linear decrease in G:F with RAC supplementation was found. RAC also affected HCY (P= 0.045) and CCY (P = 0.045) but not fat depth, meat depth or fat % (P > 0.05). These results indicate that RAC may have small but beneficial effects in modern pig production, but further research is required to optimize concentrations and duration of supplementation in modern lean pig genotypes. / Dissertation (MSc (Agric))--University of Pretoria, 2016. / Animal and Wildlife Sciences / MSc (Agric) / Unrestricted

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Doctor of Philosophy / Department of Animal Sciences and Industry / James S. Drouillard / Beta-adrenergic agonists, which are synthetic catecholamines, increase rate of gain, improve feed efficiency, and decrease carcass fat, when fed to cattle before slaughter. However, little attention has been given to the potential effects of beta-adrenergic agonists on the rumen ecosystem. Natural catecholamines, such as norepinephrine, epinephrine, and dopamine, have been observed to stimulate bacterial growth. The objectives of this research were to determine if ractopamine hydrochloride (RAC) a synthetic catecholamine has direct effects on growth and fermentation products of ruminal bacteria, and to determine the effects of protein source on ruminal fermentation and proteolysis when cattle are fed RAC. The effects of varying concentrations of RAC on ruminal fermentation were evaluated in vitro. Ractopamine hydrochloride had a quadratic effect on in vitro gas production (P < 0.05). Total VFA production was not changed with RAC (P > 0.50). Different concentrations of RAC were evaluated in vitro with different nitrogen sources to determine effects of nitrogen degradability on response to RAC. There was an interaction between RAC and nitrogen substrate (P < 0.01), with more degradable forms of nitrogen eliciting greater changes in in vitro dry matter disappearance (IVDMD) with RAC supplementation. Significant main effects also were detected for RAC, substrate, and hour (P < 0.001). In vitro analysis of proteolysis revealed that RAC lowered ammonia and amino acid concentrations (P < 0.001). In vivo ruminal ammonia concentrations also were lower when RAC was fed in combination with dry-rolled corn, but not when fed in conjunction with steam-flaked corn (grain processing × RAC, P < 0.01). Addition of RAC, steam-flaked corn, and distiller’s grains (DG) all resulted in lower ruminal ammonia concentrations (P < 0.01). Amino acid concentrations were decreased when RAC was added to diets with DG but were unchanged in diets without added DG (DG × RAC, P < 0.05). Results from these studies suggest that RAC affects fermentation by ruminal microflora. However, there were no differences in growth or fermentative end products of pure bacterial cultures with the addition of RAC (P > 0.10). Overall beta-adrenergic agonists alter ruminal fermentation, which could have important implications for diet formulation.