Ractopamine hydrochloride improves growth performance and carcass composition in immunocastrated boars, intact boars, and gilts

Transcription

1 Ractopamine hydrochloride improves growth performance and carcass composition in immunocastrated boars, intact boars, and gilts C. Rikard-Bell, M. A. Curtis, R. J. van Barneveld, B. P. Mullan, A. C. Edwards, N. J. Gannon, D. J. Henman, P. E. Hughes and F. R. Dunshea J Anim Sci : doi: /jas originally published online Jul 31, 2009; The online version of this article, along with updated information and services, is located on the World Wide Web at:

2 Ractopamine hydrochloride improves growth performance and carcass composition in immunocastrated boars, intact boars, and gilts C. Rikard-Bell,* M. A. Curtis,* R. J. van Barneveld,* B. P. Mullan,* A. C. Edwards,*# N. J. Gannon,* D. J. Henman,* P. E. Hughes,*, ** and F. R. Dunshea*, 1 *Pork Cooperative Research Centre, Roseworthy, SA 5371, Australia; Elanco Animal Health, Macquarie Park, New South Wales 2113, Australia; Barneveld Nutrition, South Maclean, Queensland 4280, Australia; Western Australian Department of Agriculture, Bentley Delivery Centre, Western Australia 6983, Australia; #ACE Consulting, Cockatoo Valley, SA 5440, Australia; The University of Queensland, Gatton, Queensland 4345, Australia; QAF Meat industries, Corowa, New South Wales 2646, Australia; **South Australia Research and Development Institute, Roseworthy, SA 5371, Australia; and Melbourne School of Land and Environment, The University of Melbourne, Parkville, Victoria 3010, Australia ABSTRACT: The β-agonist ractopamine is a dietary ingredient that improves growth and increases the lean mass with little change in fat mass in gilts and barrows. Limited data in boars indicate that dietary ractopamine may increase lean tissue and decrease fat deposition, whereas there are no data for immunocastrated boars. The aims of this investigation were 1) to assess whether the growth performance of all sexes could be maintained over 31 d by using a step-up dietary ractopamine feeding program of 5 mg/kg of ractopamine for the first 14 d, then increasing the dose to 10 mg/kg for a further 17 d, and 2) to determine if dietary ractopamine would increase lean mass in all sexes and decrease fat mass in boars and immunocastrated boars. The study involved 286 pigs randomized and proportionally allocated by breed into 24 groups of 11 or 12 pigs at 17 wk of age, with equal groups of boars, immunocastrated boars, and gilts. Dietary ractopamine decreased (P = 0.005) ADFI during the first 2 wk, particularly in the intact and immunocastrated boars, with the reduction in ADFI being maintained in the immunocastrated boars after the increment in dietary ractopamine. Daily BW gain was not altered by dietary ractopamine during the first 2 wk, but was increased (P < 0.001) after the increment in dietary ractopamine. Dietary ractopamine decreased (P 0.033) feed conversion ratio in all sexes with the response being greater after the increase in dietary ractopamine. Carcass weight was increased (P < 0.001) by dietary ractopamine in all sexes, whereas back fat tended (P = 0.076) to be reduced in the immunocastrated boars. Dietary ractopamine increased (P = 0.018) lean tissue mass by 4.0, 4.8, and 6.5 kg in the intact boars, gilts, and immunocastrated boars, respectively. In the entire and immunocastrated boars, the increase in lean tissue was accompanied with a decrease (P = 0.004) in fat mass. There was little effect of dietary ractopamine on fat mass in gilts. However, carcass percent fat was decreased (P = 0.004) and percent lean increased (P = 0.006) in all sexes. Immunocastration caused a decrease in lean tissue mass and an increase in fat mass and an increase in ADFI in the last one-half of the study. Dietary ractopamine may decrease fat mass in intact and immunocastrated boars and offers an excellent means of maximizing the effects of immunocastration and minimizing the increase in fat mass sometimes observed in immunocastrated boars. Key words: boar, body composition, growth, immunocastration, ractopamine 2009 American Society of Animal Science. All rights reserved. J. Anim. Sci : doi: /jas INTRODUCTION 1 Corresponding author: fdunshea@unimelb.edu.au Received March 31, Accepted July 9, Dietary ractopamine supplementation increases the rate of lean deposition, whereas effects on fat deposition are equivocal (Mitchell et al., 1990, 1991; Dunshea et al., 1993a,b, 1998a). For example, there was no effect of 20 mg/kg of dietary ractopamine on the rate of fat deposition in gilts with a wide range of energy and protein intakes (Dunshea et al., 1993a,b, 1998a), whereas 10 mg/kg of increased lean deposition and decreased fat deposition in restrictively fed gilts, but not boars (Dunshea et al., 2009). The increase in protein deposi- 3536

3 Ractopamine and immunocastration increase growth of pigs 3537 tion appears to be most pronounced at increased ADFI; thus, dietary energy may limit the response to ractopamine (Dunshea et al., 1998a). The ADFI of commercially housed pigs is less than that which maximizes protein deposition in contemporary pigs (King et al., 2004; Dunshea, 2005). Also, responses to ractopamine are most pronounced in the first 2 wk and decline thereafter (Dunshea et al., 1993a; Sainz et al., 1993b; See et al., 2004) due to downregulation of β-receptors (Sainz et al., 1993a; Spurlock et al., 1994; Dunshea et al., 1998b; Mills, 2002). Responses to ractopamine may be maintained by increasing the inclusion rate during the latter stage of treatment (See et al., 2004; Poletto et al., 2009). A vaccine containing a modified form of GnRH in a low reactogenic adjuvant system has been developed to reduce the accumulation of boar taint compounds in boar carcasses (Dunshea et al., 2001; McCauley et al., 2003; Oliver et al., 2003). The decrease in testosterone seems to also have effects on sexual, aggressive, and feeding activity, which in turn may be associated with increases in ADFI, ADG (Cronin et al., 2003), and sometimes backfat (Dunshea et al., 2001). Thus, simultaneous use of immunocastration and a step-up ractopamine feeding regimen might reduce the increase in fatness observed after immunocastration and provide sufficient energy to ensure full expression the benefits of dietary ractopamine. The hypotheses to be tested in this study were that 1) immunocastration would increase ADFI around 2 wk after secondary vaccination and that 2) a simultaneous step-up in dietary ractopamine concentration would allow the additional energy intake to be deposited as lean tissue rather than fat. MATERIALS AND METHODS All procedures were approved by the Institutional Animal Ethics committee. This study involved 286 pigs (190 boars and 96 gilts) representing 3 breeds [Terminal Sire Line (n = 184), Myora Large White (n = 48), and Myora Landrace breeds (n = 54)] housed at the South Australian Pig and Poultry Production Institute, Roseworthy, Australia. Ninety-six boars were randomly selected and given a primary dose (2 ml) of an immunocastration vaccine (Improvac, Pfizer Animal Health, Parkville, Australia) at 11 wk of age. At 17 wk of age, the pigs were stratified by BW and backfat within each sex and breed group and allocated to pens within the finishing barn. Pigs were housed at 0.95 m 2 /pig in groups of 11 or 12 on partially slatted floors within a naturally ventilated barn divided into 4 rooms; each room contained 6 pens in 2 rows of 3. Pigs were provided with ad libitum access to a single spaced feeder and 2 nipple drinkers at all times. The boars designated to be immunocastrated received their secondary vaccination (2 ml) at this stage. Within each sex group, pigs were allocated Table 1. Composition of basal experimental diet (as fed) 1 Item g/kg Ingredient Barley Triticale Wheat middlings Peas Canola meal 98.3 Meatmeal 33.3 Bloodmeal (ring dried) 10.0 Tallow 5.0 Limestone 7.0 Rock phosphate 5.0 Salt 2.0 Lysine-HCl hydroxy-4-(methylthio) butanoic acid (Alimet) l-threonine Chromium picolinate Vitamin and mineral premix Composition DE, 3 MJ of DE/kg 13.2 CP Available lysine, 3 g/mj of DE 0.56 Total lysine To make diets containing 5 or 10 mg/kg of ractopamine (Elanco Animal Health, Indianapolis, IN), 0.25 or 0.50 kg of Paylean premix 20 were added to 1,000 kg of basal diet. 2 Provided the following nutrients per kilogram of air-dry diet (mg): retinol, 6.4; cholecalciferol, 0.10; α-tocopherol, 22; menadione, 0.60; riboflavin, 3.0; nicotinic acid, 16; pantothenic acid, 5.6; pyrodoxine, 1.1; biotin, 0.56; choline, 1,100; cyanocobalamin, 0.016; Fe, 90; Zn, 56; Mn, 22; Cu, 7; I, 0.22; Se, 0.10; Cr, Estimated from ingredients. 4 Chemically determined. to 1 of 2 dietary ractopamine (Elanco Animal Health, Maquarie Park, Australia) regimens: 0 mg/kg of ractopamine for 31 d or 5 mg/kg of ractopamine for 14 d followed by 10 mg/kg of ractopamine for 17 d. Each room contained 1 of each sex-dietary treatment combination. The treatment and control diet were formulated to contain 0.56 g of available lysine per MJ of DE and an energy level of 13.2 MJ/kg (Table 1); feed samples were analyzed for DM, fat, protein, fiber, ash, and AA concentrations (Rayner, 1985; Agro LabMéxico, Gomez Palacio, City, México). The measured ractopamine concentrations were 6.3 and 9.6 mg/kg of (as fed) for the 5 and 10 mg/kg of ractopamine diets, respectively. Pigs were weighed at 0, 14, and 31 d, and feed refusals were weighed at 14 and 31 d. Backfat at the P2 site (65 mm off the midline over the last rib) was determined with real-time ultrasound at 0 and 31 d. After 31 d, the pigs were transported to the abattoir and slaughtered 12 h after arrival. After slaughter, carcass P2 and carcass weight were taken for each individual pig. Before slaughter, the 5 median BW pigs from each pen (a total of 120 pigs) were selected and were individually identified with a slap tattoo. After 24 h, the carcasses of the selected pigs were split in half, placed in carcass bags, and sent chilled to the Department of Primary Industries, Werribee, Victoria, Australia,

4 3538 Rikard-Bell et al. Table 2. The effect of sex (S) and ractopamine (R) 1 on growth performance of finisher pigs Boar Gilt Immunocastrate 2 Probability Item 0 5/10 0 5/10 0 5/10 SED 3 S R S R BW, kg d < d d < ADFI, kg/d 0 to 14 d to 31 d < to 31 d < ADG, kg/d 0 to 14 d < to 31 d <0.001 < to 31 d < G:F 0 to 14 d to 31 d < to 31 d < Ractopamine (Elanco Animal Health, Indianapolis, IN) dose was 0 mg/kg for 31 d (0) or 5 mg/kg for 14 d followed by 10 mg/kg for 17 d (5/10). 2 Boars were immunocastrated by giving 2 doses of Improvac (Pfizer Animal Health, Parkville, Australia) at 13 (d 28) and 17 wk (d 0) of age. 3 SED for sex ractopamine effect. For main effects of sex and ractopamine, multiply by and 0.578, respectively. where they were scanned for regional body composition using dual energy x-ray absorptiometry (Suster et al., 2004) within 48 h of slaughter. All data were analyzed using ANOVA with the GEN- STAT program (VSN International Ltd., Hemel Hempstead, UK). For growth performance data, the pen was the experimental unit. Effects were accepted as being significant at P < 0.05, and trends were noted if P < 0.1. There was a small but significant difference in initial BW between the boars and immunocastrated boars at the start of the study. Because the immunocastration vaccine does not produce any physiological effects until after the second vaccination and differences in BW at the time of the secondary vaccination have not been observed before (Dunshea et al., 2001; Cronin et al., 2003; McCauley et al., 2003; Oliver et al., 2003), initial BW was used as a covariate for analyses of carcass weight. A contingency table was used to confirm that the various breeds were distributed evenly across treatments before the study commenced (χ 2 = 4.3 with 4 df, P = 0.37). RESULTS There was a small difference in initial BW between the sexes (72.0, 71.6, and 70.1 kg for boars, gilts, and immunocastrates, respectively, P < 0.001), but appropriate randomization ensured there was no difference between the dietary ractopamine groups (P = 0.93; Table 2). Over the first 14 d of the study, gilts had less (P < 0.001) ADG than boars or immunocastrates (1.18, 0.99, and 1.20 kg/d for boars, gilts, and immunocastrates, respectively), but there was no effect of ractopamine (P = 0.57). Over the ensuing 17 d, the immunocastrates had greater ADG than the boars, which in turn were greater (P < 0.001) than the gilts (1.09, 1.01, and 1.30 kg/d for boars, gilts, and immunocastrates, respectively) and pigs fed ractopamine had greater (P < 0.001) ADG than the controls (1.09 and 1.19 kg/d for control and ractopamine pigs). Over the entire study, the immunocastrates had greater (P < 0.001) ADG than the boars, which in turn were greater than the gilts (1.13, 1.00, and 1.25 kg/d for boars, gilts, and immunocastrates, respectively), and pigs fed ractopamine had greater (P < 0.001) ADG than the controls (1.10 and 1.16 kg/d for control and ractopamine pigs). Consequently, at the end of the study, the immunocastrates were heavier (P < 0.001) than the boars, which in turn were heavier than the gilts (107.1, 102.7, and kg for boars, gilts and immunocastrates, respectively), and pigs fed ractopamine were heavier (P < 0.001) than the controls (105.2 and kg for control and ractopamine pigs). Over the first 14 d of the study, there was no effect (P = 0.19) of sex on ADFI, whereas ADFI was decreased (P = 0.005) in pigs consuming ractopamine (2.96 and 2.81 kg/d for control and ractopamine pigs; Table 2). Over the ensuing 17 d, the immunocastrates had greater (P < 0.001) ADFI than the boars or the gilts (3.18, 3.06, and 4.06 kg/d for boars, gilts, and immunocastrates, respectively), although there was no effect of dietary ractopamine (P = 0.87). Over the entire study, the immunocastrates had greater (P < 0.001) ADFI than the boars, which in turn ate more than the gilts (3.05, 2.95, and 3.54 kg/d for boars, gilts, and immunocastrates, respectively), and pigs fed ractopamine tended to eat less (P < 0.076) than the controls (3.22 and 3.14 kg/d for control and ractopamine pigs). However, there was

5 Ractopamine and immunocastration increase growth of pigs 3539 Table 3. The effect of sex (S) and ractopamine (R) 1 on half carcass characteristics measured using dual energy x-ray absorptiometry Boar Gilt Immunocastrate 2 Probability Item 0 5/10 0 5/10 0 5/10 SED 3 S R S R Full carcass, 4 kg < P2 5 back fat, mm Ultrasound 0 d < Ultrasound 31 d < Ultrasound change < Hennessy < Half carcass, 7 kg Total < Lean < Fat Ash < Half carcass, % Lean Fat Ash Ractopamine (Elanco Animal Health, Indianapolis, IN) dose was 0 mg/kg for 31 d (0) or 5 mg/kg for 14 d followed by 10 mg/kg for 17 d (5/10). 2 Boars were immunocastrated by giving 2 doses of Improvac (Pfizer Animal Health, Parkville, Australia) at 13 (d 28) and 17 wk (d 0) of age. 3 SED for sex ractopamine effect. For main effects of sex and ractopamine, multiply by and 0.578, respectively. 4 Carcass weight with the head on was analyzed using initial BW as a covariate. 5 Sixty-five mm off the midline over the last rib. 6 Determined with the Hennessy probe (Hennessy Grading Systems Limited, Auckland, New Zealand) at the abattoir on the day of slaughter. 7 Determined on the head-off half carcass using dual energy x-ray absorptiometry. an interaction (P = 0.054), such that the decrease in response to dietary ractopamine was most pronounced in the immunocastrated boars (Table 2). Over the first 14 d of the study, the gilts had less (P < 0.001) G:F than the boars or the immunocastrates (0.409, 0.351, and for boars, gilts, and immunocastrates, respectively), whereas dietary ractopamine increased (P = 0.033) G:F (0.375 and for control and ractopamine pigs; Table 2). Over the ensuing 17 d, the G:F of the immunocastrates tended to be less (P = 0.054) than that of the boars (0.344, 0.331, and for boars, gilts, and immunocastrates, respectively), and G:F was increased (P < 0.001) by dietary ractopamine (0.317 and for control and ractopamine pigs). Over the entire study, boars had greater (P < 0.001) G:F than immunocastrates, which in turn was greater (P < 0.001) than gilts (0.372, 0.340, and for boars, gilts, and immunocastrates, respectively), and G:F was increased (P < 0.001) by dietary ractopamine (0.341 and for control and ractopamine pigs). Carcass weight was greater (P < 0.001) in the immunocastrates than the other sexes (80.3, 79.4, and 83.6 kg for boars, gilts, and immunocastrates, respectively) and was increased (P < 0.001) by dietary ractopamine (80.2 and 82.2 kg for control and ractopamine pigs; Table 3). Initial P2 was greater (P < 0.001) in the gilts (8.5, 10.0, and 8.4 mm for boars, gilts, and immunocastrates, respectively); at the end of the study, P2 was greatest (P < 0.001) in the immunocastrates as analyzed with ultrasound (11.4, 12.8, and 13.3 mm for boars, gilts, and immunocastrates, respectively) or Hennessy probe (Hennessy Grading Systems Limited, Auckland, New Zealand; 11.3, 12.1, and 12.8 mm for boars, gilts, and immunocastrates, respectively). The change in ultrasound P2 backfat during the study was greater (P < 0.001) in immunocastrates (2.8, 2.9, and 5.0 mm for boars, gilts, and immunocastrates, respectively) and tended to be reduced (P = 0.076) by ractopamine (3.8 and 3.3 mm for control and ractopamine pigs). However, this latter response appeared to be largely in the immunocastrates (Table 3). Half carcass weight was greater (P = 0.008) in immunocastrates than in gilts with boars being intermediate (36.2, 35.5, and 37.0 kg for boars, gilts, and immunocastrates, respectively) and was increased (P < 0.001) by dietary ractopamine (35.3 and 37.1 kg for control and ractopamine pigs; Table 3). Half carcass lean mass was greater (P < 0.01) in boars than in gilts with immunocastrates being intermediate (25.8, 23.5, and 24.9 kg for boars, gilts, and immunocastrates, respectively) and was increased (P < 0.001) by dietary ractopamine (23.5 and 26.0 kg for control and ractopamine pigs). Half carcass fat mass was less (P = 0.004) in boars than in gilts and immunocastrates (3.92, 6.29, and 5.98 kg for boars, gilts, and immunocastrates, respectively) and was decreased (P = 0.013) by dietary ractopamine (6.14 and 4.65 kg for control and ractopamine pigs). Half carcass ash mass was less (P = 0.003) in gilts than in boars and immunocastrates (6.18, 5.95, and 6.21 kg for boars, gilts, and immunocastrates, respectively) and was decreased (P < 0.001) by dietary ractopamine (5.97 and 6.25 kg for control and ractopamine pigs). Percent lean in the half carcass was greater in boars (P = 0.006) than gilts or immunocastrates (71.2, 66.1, and

6 3540 Rikard-Bell et al. Table 4. The effect of sex (S) and ractopamine (R) 1 on half carcass characteristics measured using dual energy x-ray absorptiometry Boar Gilt Immunocastrate 2 Probability Item 0 5/10 0 5/10 0 5/10 SED 3 S R S R Shoulder, 4 kg Total Lean Fat Ash Loin, 4 kg Total <0.001 < Lean < Fat Ash < Belly, 4 kg Total Lean Fat Ash Ham, 4 kg Total < Lean < Fat < Ash Ractopamine (Elanco Animal Health, Indianapolis, IN) dose was 0 mg/kg for 31 d (0) or 5 mg/kg for 14 d followed by 10 mg/kg for 17 d (5/10). 2 Boars were immunocastrated by giving 2 doses of Improvac (Pfizer Animal Health, Parkville, Australia) at 13 (d 28) and 17 wk (d 0) of age. 3 SED for sex ractopamine effect. For main effects of sex and ractopamine, multiply by and 0.578, respectively. 4 Determined on the head-off half carcass using dual energy x-ray absorptiometry as outlined by Suster et al. (2004). 67.3% for boars, gilts, and immunocastrates, respectively) and was increased (P = 0.006) by dietary ractopamine (66.3 and 70.0% for control and ractopamine pigs). Conversely, percent fat in the half carcass was less (P = 0.004) in boars than in gilts and immunocastrates (10.9, 17.7, and 16.4% for boars, gilts, and immunocastrates, respectively) and was decreased (P = 0.004) by dietary ractopamine (17.4 and 12.5% for control and ractopamine pigs). Percent ash in the half carcass was not different between the sexes (P = 0.33) and tended to be increased (P = 0.054) by dietary ractopamine. The effects of sex and ractopamine on the composition of the various primal cuts of the carcass were, in general, qualitatively similar to what was observed in the whole carcass (Table 4), with a few exceptions. For example, the total weight of the shoulder did not appear to be responsive to ractopamine, except in the gilts where ractopamine increased total shoulder weight, as evidenced by the interaction (P = 0.029) between sex and dietary ractopamine. Belly weight was also not affected (P = 0.12) by dietary ractopamine, although there were compositional changes. Thus, dietary ractopamine increased lean tissue and ash and decreased fat tissue in all of the primal cuts (Table 4) as it did in the half carcass. The primal cut most responsive to ractopamine was the loin, in which there were 10 and 22% increases (P < 0.001) in total and lean tissue and a 21% reduction (P = 0.02) in fat in response to dietary ractopamine (Table 4). DISCUSSION The major finding from the present study was that the effects of a step-up dietary ractopamine regimen and immunocastration on growth performance in finisher boars are additive or synergistic and that these technologies can be used in combination to improve growth performance and carcass composition. Thus, immunocastrated boars supplemented with dietary ractopamine grew 30 and 15% greater than control boars over the last 17 or entire 31 d of the study, respectively. These effects of combined ractopamine and immunocastration are qualitatively similar to the additive effects between porcine ST and immunocastration (McCauley et al., 2003; Oliver et al., 2003). Also, Dunshea et al. (2009) reported additive effects of dietary ractopamine and betaine in finisher pigs, particularly gilts. King et al. (2004) reported that lean tissue deposition increases linearly with increasing DE intake up to at least ad libitum intakes of 47 and 40 MJ of DE/d in improved finisher boars and gilts, respectively. Also, dietary ractopamine increased protein deposition in boars and gilts across a range of energy intakes up to 50 MJ of DE/d, with responses greatest at increased DE intakes (Dunshea et al., 1998a). However, ADFI of this magnitude are rarely encountered under commercial conditions where energy intakes more typically are around 34 MJ of DE/d (Dunshea 2005). Even in the present study, conducted in a research institute with an increased health status, the DE intakes of group-

7 Ractopamine and immunocastration increase growth of pigs 3541 housed intact boars and gilts were 40 MJ of DE/d. Immunocastration increases ADFI, particularly in the period beyond 2 wk after the secondary vaccination (Dunshea et al., 2001; McCauley et al., 2003; Oliver et al., 2003), and this was confirmed in the present study where ADFI was increased by 1 and 32% over the period from 0 to 14 d and 15 to 31 d after the secondary vaccination, respectively. The present study was conducted based on the premise that the additional energy consumed by immunocastrates could be used for carcass growth, particularly lean tissue when combined with a step-up dietary ractopamine program. Indeed, ADG, final BW, and carcass weight were all increased by the combined treatment in boars, although this was not necessarily all lean tissue growth. Treatment of pigs with β-agonists, particularly ractopamine, has generally resulted in dose-dependent increases in daily BW gain, feed conversion rate, and carcass lean content (see Dunshea, 1993; Dunshea et al., 2005; Rikard-Bell et al., 2007). Feed intake is typically unchanged (Adeola et al., 1990; Gu et al., 1991; Yen et al., 1991, Marchant-Forde et al., 2003; Armstrong et al., 2004; See et al., 2004; Weber et al., 2006) or decreased slightly (Adeola et al., 1990; Watkins et al., 1990; Mitchell et al., 1991; Brumm et al., 2004; Carr et al., 2005; Mimbs et al., 2005) during dietary ractopamine feeding. Many of the earlier studies were conducted with 20 mg/kg of ractopamine, the dose where carcass responses are maximized (Armstrong et al., 2004); however, in many pork markets, this dose may not present the best return on investment. The growth and tissue responses to ractopamine diminishes over time, being most pronounced over the first 2 wk and reducing over subsequent weeks (Dunshea et al., 1993a; Sainz et al., 1993b; See et al., 2004) due to downregulation of β-receptors (Sainz et al., 1993a; Spurlock et al., 1994; Dunshea et al., 1998b; Mills, 2002). It is quite possible that a controlled incremental approach with ractopamine may be one way of ensuring a more consistent and sustained response. In a study designed to test the efficacy of different patterns of ractopamine supplementation, See et al. (2004) compared the growth performance of pigs fed a control diet, a constant concentration of ractopamine (11.7 mg/kg) for 6 wk, a step-up program (5 mg/kg for 2 wk, 10 mg/kg for 2 wk, and 20 mg/kg for 2 wk), or a step-down program (20 mg/kg for 2 wk, 10 mg/kg for 2 wk, and 5 mg/kg for 2 wk). Growth rate over the 6 wk was improved to the same extent by all dietary ractopamine regimens (+7%), but the pattern of growth differed among treatments. Over the first 4 wk of treatment (the period over which ractopamine is typically fed), the step-up program resulted in similar improvements in ADG as the constant feeding regimen (+14 vs. +15%), but with a less average inclusion concentration (7.5 vs mg/kg). Interestingly, the growth performance of all the supplemental ractopamine groups was less than the controls over the period between 4 and 6 wk (See et al., 2004). Similarly, under commercial management conditions, Armstrong et al. (2004) compared 2 step-up feeding regimens in which dietary ractopamine was increased from 5 mg/kg of ractopamine in the initial 14 or 21 d to 10 mg/kg of ractopamine in the final 14 or 21 d with a regimen of 5 mg/kg of ractopamine over the entire 35-d period. Armstrong et al. (2004) reported that not only were ADG and G:F increased in pigs fed diets containing ractopamine, but these characteristics were further improved for pigs fed the step-up ractopamine dietary regimens. Armstrong et al. (2004) also indicated that the step-up regimens produced heavier and leaner carcasses compared with those pigs that had been on the constant ractopamine feeding regimen. The present study utilized a similar step-up program of 5 and 10 mg/kg such that the stepup was timed to occur when the dramatic increase in ADFI commenced in immunocastrated boars, around 14 d after the secondary vaccination, in an effort to negate the increase in fatness observed in immunocastrated boars. The step-up ractopamine program increased ADG, G:F, and carcass weight by 6, 9, and 2.7%, respectively, with responses being observed in all sexes. Importantly, the G:F response was sustained across the full 31-d period. Carcass lean tissue mass was increased by 11%, whereas fat content was reduced by 24%. Again, the effects occurred in all sexes, although the effects on fat mass were less pronounced in gilts. The effects on G:F and carcass lean tissue mass were as expected from previous studies with 20 mg/kg of ractopamine (Mitchell et al., 1991; Dunshea et al., 1993a,b, 1998a; Crome et al., 1996; Armstrong et al., 2004); however, effects on fat mass have been more equivocal. Ractopamine is a potent stimulator of adipose tissue fat mobilization but often does not decrease fat deposition in pigs because of a combination of rapid downregulation of adipocyte β-adrenergic receptors (Dunshea and King, 1995; Dunshea et al., 1998b), lack of effect on lipogenesis (Liu et al., 1994; Dunshea et al., 1998c), and a relative insensitivity of porcine adipocytes to β-agonists (Pethick et al., 2005). For example, Dunshea et al. (1993a) found that there was no effect of 20 mg/kg of ractopamine on fat deposition and backfat in gilts and barrows, although there was a trend toward a 31% reduction in fat deposition in boars. Also, those authors failed to observe any decrease in the rate of lipid deposition (i.e., g/d) in pigs fed across a wide range of energy and protein intakes (Dunshea et al., 1993a,b, 1998a). Mitchell et al. (1991) reported that dietary ractopamine decreased empty body fat deposition rates in a low select line (animals selected for growth when fed a low protein diet) of barrows when fed a low protein diet but not when fed a high protein diet. In contrast, the rate of fat deposition was not altered by dietary ractopamine supplementation in the high select line of pigs, regardless of the dietary protein content. In another study, dietary ractopamine decreased fat deposition in barrows that were fed ad libitum but not when fed restrictively (Mitchell et al., 1991). Conversely, fat deposition was

8 3542 reduced by feeding 10 mg/kg of dietary ractopamine in restrictively fed pigs, particularly gilts (Dunshea et al., 2009). Clearly, there are dietary, genotype, and environmental factors and interactions that can modulate the effect of ractopamine on fat deposition. The more consistent reduction in fat mass observed in the present study, particularly in intact and immunocastrated male pigs, may have been in part due to the step program, which may have counteracted the rapid downregulation of β-receptors that occurs in adipose tissue of pigs fed ractopamine (Sainz et al., 1993a; Dunshea and King, 1995; Dunshea et al., 1998b; Mills, 2002), although this remains to be demonstrated. In conclusion, these data demonstrate that of dietary ractopamine increases lean tissue deposition in all sexes and reduces fat tissue deposition, particularly in entire and immunocastrated boars. Immunocastration of boars increased ADFI and ADG, particularly beyond 2 wk after the secondary vaccination. Although much of the additional growth in immunocastrated boars was as fat tissue, this could be attenuated by supplemental dietary ractopamine. LITERATURE CITED Adeola, O., E. A. Darko, P. He, and L. G. Young Manipulation of porcine carcass composition by ractopamine. J. Anim. Sci. 68: Armstrong, T. A., D. J. Ivers, J. R. Wagner, D. B. Anderson, W. C. Weldon, and E. P. Berg The effect of dietary ractopamine concentration and duration of feeding on growth performance, carcass characteristics, and meat quality of finishing pigs. J. Anim. Sci. 82: Brumm, M. C., P. S. Miller, and R. C. Thaler Response of barrows to space allocation and ractopamine. J. Anim. Sci. 82: Carr, S. N., P. J. Rincker, J. Killefer, D. H. Baker, M. Ellis, and F. K. McKeith Effects of different cereal grains and ractopamine hydrochloride on performance, carcass characteristics, and fat quality in late-finishing pigs. J. Anim. Sci. 83: Crome, P. K., F. K. McKeith, T. R. Carr, D. J. Jones, D. H. Mowrey, and J. E. Cannon Effect of ractopamine on growth performance, carcass composition, and cutting yields of pigs slaughtered at 107 and 125 kilograms. J. Anim. Sci. 74: Cronin, G. M., F. R. Dunshea, K. L. Butler, I. McCauley, J. L. Barnett, and P. H. Hemsworth The effects of immuno- and surgical-castration on the behaviour and consequently growth of group-housed, male finisher pigs. Appl. Anim. Behav. Sci. 81: Dunshea, F. R Effect of metabolism modifiers on lipid metabolism in the pig. J. Anim. Sci. 71: Dunshea, F. R Sex and porcine somatotropin impact on variation in growth performance and back fat thickness. Aust. J. Exp. Agric. 45: Dunshea, F. R., D. J. Cadogan, and G. G. Partridge Dietary betaine and ractopamine combine to increase lean tissue deposition in finisher pigs, particularly gilts. Anim. Prod. Sci. 49: Dunshea, F. R., C. Colantoni, K. Howard, P. Jackson, K. A. Long, S. Lopaticki, E. A. Nugent, J. A. Simons, J. Walker, and D. P. Hennessy Vaccination of boars with a GnRH vaccine (Improvac ) eliminates boar taint and increases growth performance. J. Anim. Sci. 79: Rikard-Bell et al. Dunshea, F. R., D. N. D Souza, D. W. Pethick, G. S. Harper, and R. D. Warner Effects of dietary factors and other metabolic modifiers on quality and nutritional value of meat. Meat Sci. 71:8 38. Dunshea, F. R., and R. H. King Responses to homeostatic signals in ractopamine-treated pigs. Br. J. Nutr. 73: Dunshea, F. R., R. H. King, and R. G. Campbell. 1993a. Interrelationships between dietary protein and ractopamine on protein and lipid deposition in finishing gilts. J. Anim. Sci. 71: Dunshea, F. R., R. H. King, R. G. Campbell, R. D. Sainz, and Y. S. Kim. 1993b. Interrelationships between sex and ractopamine on protein and lipid deposition in rapidly growing pigs. J. Anim. Sci. 71: Dunshea, F. R., R. H. King, P. J. Eason, and R. G. Campbell. 1998a. Interrelationships between dietary ractopamine, energy intake, and sex in pigs. Aust. J. Agric. Res. 49: Dunshea, F. R., B. J. Leury, and R. H. King. 1998b. Lipolytic responses to catecholamines in ractopamine-treated pigs. Aust. J. Agric. Res. 49: Dunshea, F. R., B. J. Leury, A. J. Tilbrook, and R. H. King. 1998c. Ractopamine increases glucose turnover without affecting lipogenesis in the pig. Aust. J. Agric. Res. 49: Gu, Y., A. P. Schinckel, J. C. Forrest, C. H. Kuel, and L. E. Watkins Effects of ractopamine, genotype, and growth phase on finishing performance and carcass value in swine: I. Growth performance and carcass merit. J. Anim. Sci. 69: King, R. H., R. G. Campbell, R. J. Smits, W. C. Morley, K. Ronnfeldt, and F. R. Dunshea The influence of dietary energy intake on growth performance and protein deposition in pigs between 80 and 120 kg live weight. Aust. J. Agric. Res. 55: Liu, C. Y., A. L. Grant, K. H. Kim, S. Q. Ji, D. L. Hancock, D. B. Anderson, and S. E. Mills Limitations of ractopamine to affect adipose tissue metabolism in swine. J. Anim. Sci. 72: Marchant-Forde, J. N., D. C. Lay Jr., E. A. Pajor, B. T. Richert, and A. P. Schinckel The effects of ractopamine on the behavior and physiology of finishing pigs. J. Anim. Sci. 81: McCauley, I., M. Watt, D. Suster, D. J. Kerton, W. T. Oliver, R. J. Harrell, and F. R. Dunshea A GnRF vaccine (Improvac ) and porcine somatotropin (Reporcin ) have synergistic effects upon growth performance in both boars and gilts. Aust. J. Agric. Res. 54: Mills, S. E Implications of feedback regulation of beta-adrenergic signaling. J. Anim. Sci. 80 (E. Suppl. 1):E30 E35. Mimbs, K. J., T. D. Pringle, M. J. Azain, S. A. Meers, and T. A. Armstrong Effects of ractopamine on performance and composition of pigs phenotypically sorted into fat and lean groups. J. Anim. Sci. 83: Mitchell, A. D., M. B. Solomon, and N. C. Steele Response of low and high protein select lines of pigs to the feeding of the beta-adrenergic agonist ractopamine (phenethanolamine). J. Anim. Sci. 68: Mitchell, A. D., M. B. Solomon, and N. C. Steele Influence of level of dietary protein or energy on effects of ractopamine in finishing swine. J. Anim. Sci. 69: Oliver, W. T., I. McCauley, R. J. Harell, D. Suster, D. J. Kerton, and F. R. Dunshea A gonadotropin-releasing factor vaccine (Improvac) and porcine somatotropin have synergistic and additive effects on growth performance in group-housed boars and gilts. J. Anim. Sci. 81: Pethick, D. W., G. S. Harper, and F. R. Dunshea Fat metabolism and turnover. Pages in Quantitative Aspects of Ruminant Digestion and Metabolism. J. Dijkstra, J. M. Forbes, and J. France, ed. CAB Int., Oxford, UK. Poletto, R., M. H. Rostagno, B. T. Richert, and J. N. Marchant- Forde Effects of a step-up ractopamine feeding program, gender and social rank on growth performance, hoof

9 Ractopamine and immunocastration increase growth of pigs 3543 lesions and Enterobacteriaceae shedding in finishing pigs. J. Anim. Sci. 87: Rayner, C Protein hydrolysis of animal feeds for amino acid content. J. Agric. Food Chem. 33: Rikard-Bell, C., Cs. Szabo, R. J. van Barneveld, B. P. Mullan, A. C. Edwards, N. J. Gannon, D. J. Henman, R. J. Smits, W. Morley, and F. R. Dunshea Increasing ractopamine levels in finisher pig diets improves growth performances in light, medium and heavy gilts. Page 119 in Manipulating Pig Production XI. J. Paterson, ed. Australas. Pig Sci. Assoc., Werribee, Australia. Sainz, R. D., Y. S. Kim, F. R. Dunshea, and R. G. Campbell. 1993a. Effects of ractopamine in pig muscles: Histology, calpains and beta-adrenergic receptors. Aust. J. Agric. Res. 44: Sainz, R. D., Y. S. Kim, F. R. Dunshea, and R. G. Campbell. 1993b. Temporal changes in growth enhancement by ractopamine in pigs: Performance aspects. Aust. J. Agric. Res. 44: See, M. T., T. A. Armstrong, and W. C. Weldon Effect of a ractopamine feeding program on growth performance and carcass composition in finishing pigs. J. Anim. Sci. 82: Spurlock, M. E., J. C. Cusumano, S. Q. Ji, D. B. Anderson, C. K. Smith, D. L. Hancock, and S. E. Mills The effect of ractopamine on beta-adrenoceptor density and affinity in porcine adipose and skeletal-muscle tissue. J. Anim. Sci. 72: Suster, D., B. J. Leury, C. D. Hofmeyr, and F. R. Dunshea The accuracy of dual energy X-ray absorptiometry (DXA), weight and P2 back fat to predict half-carcass and primal-cut composition in pigs within and across research experiments. Aust. J. Agric. Res. 55: Watkins, L. E., D. J. Jones, D. H. Mowrey, D. B. Anderson, and E. L. Veenhuizen The effect of various levels of ractopamine hydrochloride on the performance and carcass characteristics of finishing swine. J. Anim. Sci. 68: Weber, T. E., B. T. Richert, M. A. Belury, Y. Gu, K. Enright, and A. P. Schinckel Evaluation of the effects of dietary fat, conjugated linoleic acid, and ractopamine on growth performance, pork quality, and fatty acid profiles in genetically lean gilts. J. Anim. Sci. 84: Yen, J. T., J. A. Nienaber, J. Klindt, and J. D. Crouse Effect of ractopamine on growth, carcass traits, and fasting heat production of U.S. contemporary crossbred and Chinese Meishan. J. Anim. Sci. 69:

10 References This article cites 37 articles, 23 of which you can access for free at: