J. Anim. Sci. 2003. 81:1959-1966
© 2003 American Society of Animal Science
A gonadotropin-releasing factor vaccine (Improvac) and porcine somatotropin have synergistic and additive effects on growth performance in group-housed boars and gilts1,2
W. T. Oliver3,*,
I. McCauley
,
R. J. Harrell4,*,
D. Suster,
D. J. Kerton and
F. R. Dunshea
* Department of Animal Science, North Carolina State University, Raleigh, NC 27695 and
and
Natural Resources and Environment, Victorian Institute of Animal Science, Werribee, 3030, Australia
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Abstract
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Two hundred and twenty-four pigs (112 boars, 112 gilts) housed in pens of seven pigs per pen were used in a 2 x 2 x 2 factorial design, with the factors of vaccination with a gonadotropin-releasing factor (GnRF) vaccine (Improvac; 0 or 2 mL at 13 and 17 wk of age), porcine somatotropin (pST; 0 or 5 mg/d from 17 wk of age), and gender. Pigs were weighed and feed intake was measured from 17 wk of age until slaughter at 21 wk of age. Body composition was estimated by dual-energy X-ray absorptiometry in two focus pigs per pen at 17 and 21 wk of age. Testes and ovary weights at slaughter were decreased by Improvac treatment (P < 0.001), but were not altered by pST treatment (P > 0.44). Daily gain was lower for gilts than boars (1,128 vs. 1,299 g/d, P < 0.001) and was increased by pST (1,172 vs. 1,255 g/d, P = 0.003) and Improvac (1,150 vs. 1,276 g/d, P < 0.001) treatments. Feed intake (as-fed basis) was lower in gilts than in boars (2,774 vs. 3,033 g/d, P = 0.002), was decreased by pST (3,037 vs. 2,770 g/d, P = 0.002), and was increased by Improvac treatment (2,702 vs. 3,105 g/d, P < 0.001). As a result of the differences in feed intake and daily gain, feed conversion efficiency (gain:feed) was lower for gilts than for boars (0.403 vs. 0.427 P = 0.025), was improved by pST (0.385 vs. 0.452, P < 0.001), but was unchanged by Improvac treatment (0.423 vs. 0.410, P = 0.22). Carcass weight was lower in gilts than in boars (75.3 vs. 77.0 kg, P = 0.012), was unchanged by pST treatment (75.9 vs. 76.4 kg, P = 0.40), and was increased by Improvac treatment (75.1 vs. 77.2 kg, P = 0.003). Lean tissue deposition rate was lower in gilts than in boars (579 vs. 725 g/d, P < 0.001), was increased by pST (609 vs. 696 g/d, P < 0.001) and by Improvac treatment (623 vs. 682 g/d, P = 0.014). Fat deposition rate tended to be lower in gilts than in boars (214 vs. 247 g/d, P = 0.063), decreased by pST treatment (263 vs. 198 g/d, P < 0.001), and increased by Improvac treatment (197 vs. 264 g/d, P < 0.001). For pigs treated with both pST and Improvac, daily gain and lean tissue deposition rate was greater than for pigs that received either treatment alone, whereas fat deposition rate and feed intake did not differ from untreated control pigs. In conclusion, Improvac increased growth rate through increased lean and fat deposition, but concomitant use of Improvac and pST increased lean gain above either alone, while negating the increase in fat deposition in pigs treated with Improvac.
Key Words: Gonadotropin • Pigs • Somatotropin • Vaccination
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Introduction
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Boar taint results from the accumulation of chemical agents, primarily skatole and androstenone, in the adipose tissue of mature, intact male pigs (Bonneau, 1982
). To negate the undesirable accumulation of these substances, male pigs are routinely castrated in the United States, which requires labor and introduces stress and the risk of complications from the surgery to the pigs. More importantly, barrows consume more feed, grow at a slower rate, and will have proportionally more fat and less muscle compared to boars (Campbell et al., 1989). An alternative to castration in the traditional manner is immunocastration, which is based on immunizing the animals against a hormone that is critical for normal sexual development and maintenance. The efficacy of anti-GnRF (GnRF, gonadotropin-releasing factor) vaccines has been well established in bulls and heifers (Adams et al., 1993; Prendiville et al., 1995; Huxsoll et al., 1998), and an anti-GnRF vaccine (CSL Ltd., Parkville, Australia) has recently been shown to be effective in suppressing sexual characteristics in boars (Dunshea et al., 2001) and gilts (McCauley et al., 2002). Unexpectedly, a positive growth response was observed in boars and gilts vaccinated against GnRF, but it is unknown whether metabolic or behavioral changes elicit this response.
Porcine somatotropin (pST) has been utilized effectively to alter the partitioning of energy in feed away from fat and toward muscle growth. The administration of exogenous pST to growing pigs has been shown to increase ADG by up to 30%, increase muscle deposition rate by up to 50%, and decrease fat deposition rate by up to 30% (Etherton et al., 1986; Campbell et al., 1988; Dunshea et al., 2002), which prompted the development of an exogenous source of pST (Reporcin), which is approved for use in Australia. The current experiment was conducted to determine the effects of active immunization against gonadotropin-releasing factor combined with daily injections of pST on growth performance in group-housed boars and gilts.
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Materials and Methods
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All procedures were approved by the Victorian Institute of Animal Science (VIAS) Animal Ethics Committee. Two hundred twenty-four pigs (112 boars, 112 gilts; Large White x Landrace) were used in two replicates of a 2 x 2 x 2 factorial arrangement, with the factors being vaccination with Improvac, daily injection of pST, and gender. Pigs were selected for the experiment from the VIAS experimental herd at approximately 13 wk of age (8 wk preslaughter) and blocked by sex, weight, and week of birth. At this time, pigs were randomly assigned to treatments and pigs selected to receive the Improvac (CSL Ltd.) treatment were given their primary vaccination (2 mL/pig). Improvac is a vaccine against the animal’s own GnRF. The control of testes function is regulated by GnRF produced by the hypothalamus. Improvac is an analog of GnRF conjugated to a carrier protein in an aqueous adjuvant system. Its mode of action is immunological. The analog has no hormonal or chemical activity (Dunshea et al., 1991). Improvac stimulates the pig’s immune system to produce specific antibodies against GnRF. These antibodies inhibit natural GnRF activity, temporarily inhibiting testes function. Pigs remained in the VIAS herd for an additional 4 wk until approximately 17 wk of age (4 wk preslaughter), at which time pigs received the second Improvac vaccination (2 mL/pig) and all pigs were weighed and moved to the experimental facility (d = 0; initiation of study). Pigs were randomly assigned to one of 16 pens according to treatment and sex (seven pigs per pen; 3.7 m2 of dry area per pen), and daily injections of pST (5 mg/d Reporcin) were initiated on pigs selected to receive pST treatment. Pigs were allowed to consume a standard wheat/soybean meal diet ad libitum (Table 1). Pigs were weighed and feed disappearance was measured weekly from the initiation of the experiment (17 wk of age) and continued until pigs were 21 wk of age, at which time they were sent to the abattoir for slaughter.
The median two pigs from each pen were chosen as focus pigs to determine changes in body composition in response to the various treatment combinations. Body composition was measured by dual-energy X-ray absorptiometry (DXA) before the initiation of the experiment and then again before slaughter. Briefly, pigs were anesthetized by a ketamine/xylazine cocktail (10.0 and 1.0 mg/kg of BW, respectively) and were maintained under anesthesia with isoflurane while being scanned on the DXA. Regression equations were generated by Suster et al. (2000) on the same genotype and equipment as those used for predictions of body composition in the present study.
Pigs were fasted overnight before being slaughtered via CO2 stunning at a commercial abattoir. The testes and ovaries were collected, trimmed, and weighed. Ovary scores were given on the basis of maturity (1 = immature, no follicles; 2 = small follicles; 3 = mature, very large follicles; 4 = mature, ruptured follicles).
Treatment effects were assessed by ANOVA for a factorial design with the main effects being sex, Improvac vaccination, and pST treatment. The effect of sex was not examined for testes weight (boars only) or ovary weight and score (gilts only). The experimental unit for all measures was the pen of pigs, except for the body composition analyses, where the experimental unit was the average of the two focus pigs per pen. For some measures (carcass weight, final tissue masses), initial live weight was used as a covariate to account for the small, nonsignificant differences in weights at the start of the study. All analyses were performed using GENSTAT (Payne et al. 1993).
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Results
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Animal Performance
The initial stratification and randomization ensured that there was very little variation between average starting weights of treatment groups (within each sex group; Table 2). Surprisingly, there was no difference in live weight between boars and gilts at 17 wk of age (63.6 vs. 64.7 kg for gilts and boars, respectively, P = 0.70). Over the first 2 wk of the study, ADG was lower for gilts than for boars (1,158 vs. 1,319 g/d, P < 0.001), but was unchanged by pST (1,246 vs. 1,232 g/d, P = 0.71) and Improvac treatment (1,210 vs. 1,267 g/d, P = 0.16). Over the ensuing 2-wk period, ADG was lower for gilts than boars (1,098 vs. 1,278 g/d, P < 0.001) and was increased by pST (1,098 vs. 1,278 g/d, P < 0.001) and Improvac treatment (1,090 vs. 1,286 g/d, P < 0.001). Over the entire 28 d of the study, ADG was lower for gilts than for boars (1,128 vs. 1,299 g/d, P < 0.001) and was increased by pST (1,172 vs. 1,255 g/d, P = 0.003) and Improvac (1,150 vs. 1,276 g/d, P < 0.001) treatments. Pigs, particularly boars, that received both pST and Improvac gained at a faster rate than pigs that received pST or Improvac alone.
Over the first 2 wk of the study, ADFI was lower for gilts than for boars (2,634 vs. 2,791 g/d, P = 0.021), was decreased by pST treatment (2819 vs. 2606 g/d, P = 0.003), and was increased by Improvac treatment (2,626 vs. 2,799 g/d, P = 0.012; Table 2
). However, there was a three-way interaction (P = 0.012), such that Improvac treatment increased ADFI in all classes of pigs except for untreated control boars. Over the ensuing 2-wk period, ADFI was lower for gilts than boars (2,914 vs. 3,275 g/d, P = 0.007), was decreased by pST (3,254 vs. 2,934 g/d, P = 0.015), and was increased by Improvac treatment (2,778 vs. 3,410 g/d, P < 0.001). When averaged over the entire 28 d of the study, ADFI was lower in gilts than in boars (2,774 vs. 3,033 g/d, P = 0.002), was decreased by pST (3,037 vs. 2,770 g/d, P = 0.002), and was increased by Improvac treatment (2,702 vs. 3,105 g/d, P < 0.001). Pigs that received both pST and Improvac consumed feed at a similar rate as untreated control pigs.
Over the first 2 wk of the stud, feed conversion efficiency (FCE; gain:feed) was lower for gilts than for boars (0.437 vs. 0.472, P = 0.011) and was improved by pST treatment (0.439 vs. 0.469, P = 0.017), but was unchanged by Improvac treatment (0.457 vs. 0.450, P = 0.63; Table 2). Over the ensuing 2-wk period, FCE was not different between boars and gilts (0.370 vs. 0.389, P = 0.21), was improved by pST (0.337 vs. 0.435, P < 0.001), and was unchanged by Improvac treatment (0.385 vs. 0.373, P = 0.40). When averaged over the entire 28 d of the study, FCE was lower for gilts than for boars (0.403 vs. 0.427, P = 0.025), was improved by pST (0.385 vs. 0.452, P < 0.001), but remained unchanged by Improvac treatment (0.423 vs. 0.410, P = 0.22). However, there was an interaction (P = 0.075) between sex and pST treatment, such that FCE was lower in control gilts than in boars (0.366 vs. 0.403), but not different between pST-treated gilts and boars (0.448 vs. 0.457). Pigs that received both pST and Improvac had a similar FCE as pigs treated with pST, both of which were higher than untreated controls.
Carcass Characteristics
At the end of the study, at 21 wk of age, back fat depth at the P2 position was lower in gilts than in boars (13.6 vs. 15.2 mm, P = 0.007), was decreased by pST treatment (15.4 vs. 13.4 mm, P = 0.001), and tended to be increased by Improvac treatment (13.9 vs. 14.9 mm, P = 0.066; Table 2). There was also an interaction (P = 0.099) such that Improvac increased backfat depth in pigs not treated with pST (14.4 vs. 16.3 mm), but not in pigs treated with pST (13.4 vs. 13.5 mm). Carcass weight was lower in gilts than in boars (75.3 vs. 77.0 kg, P = 0.012), was unchanged by pST treatment (75.9 vs. 76.4 kg, P = 0.40), and was increased by Improvac treatment (75.1 vs. 77.2 kg, P = 0.003; Table 2). Pigs that received both pST and Improvac had carcass weights similar to pigs treated with Improvac, both of which were heavier than untreated controls. Dressing percentage was higher in gilts than in boars (78.5 vs. 76.6%, P = 0.006), but was relatively unchanged by pST (78.0 vs. 77.0%, P = 0.12) or Improvac treatment (78.0 vs. 77.1%, P = 0.18), or by pST and Improvac in combination (Table 2).
Body Composition and Tissue Accretion Rates
The allocation of the median two pigs as the focus pigs within each pen ensured that the focus pigs were essentially the same live weight as the entire pen of pigs they were chosen to represent (Table 3). In this respect, the average live weights were the same for the group and focus pigs (64.2 vs. 64.3 kg, respectively, P = 0.72) and were highly correlated (group live weight = 2.24 [SE 3.65] + 0.967 [SE 0.0566] focus live weight, R2 = .90, P < 0.001). Growth performance of the focus pigs was very similar to that of the groups of pigs they were chosen to represent, with treatment effects similar to those observed for the analyses of the entire groups. At the start of the study, when the pigs were 17 wk of age and weighed approximately 64 kg, gilts contained more total body fat than boars (13.1 vs. 11.2 kg, P < 0.001), although there was no difference in lean (41.7 vs. 42.0 kg, P = 0.56) or ash (1.51 vs. 1.47 kg, P = 0.24) mass. As a percentage of live weight, gilts initially had more fat (21.5 vs. 18.7%, P < 0.001) and less lean tissue (68.7 vs. 70.4%, P < 0.001) than boars, but a similar ash content (2.49 vs. 2.47%, P = 0.65). Over the course of the study, lean tissue deposition rate was lower in gilts than in boars (579 vs. 725 g/d, P < 0.001) and was increased by pST (609 vs. 696 g/d, P < 0.001) and by Improvac treatment (623 vs. 682 g/d, P = 0.014; Table 3). However, there was a significant interaction (P = 0.031) in that pST increased lean tissue deposition rate to a greater extent in gilts than in boars. However, when combined with Improvac, a greater response to pST was observed in boars compared with gilts, as indicated by a three-way interaction (P = 0.081). Pigs that received both pST and Improvac gained lean tissue at a faster rate than pigs that received pST or Improvac alone. This is particularly evident for boars, in that pST or Improvac treatment alone had no effect, whereas treatment with both pST and Improvac increased lean deposition rate by 16%. Fat deposition rate tended to be lower in gilts than in boars (214 vs. 247 g/d, P = 0.063), decreased by pST treatment (263 vs. 198 g/d, P < 0.001), and increased by Improvac treatment (197 vs. 264 g/d, P < 0.001). Pigs that received both pST and Improvac gained fat tissue at a rate similar to untreated controls. Ash deposition rate was lower in gilts than in boars (21.6 vs. 26.9 g/d, P = 0.024), but was not altered by pST (23.7 vs. 24.9 g/d, P < 0.60) or Improvac treatment (23.7 vs. 24.8 g/d, P = 0.61). Largely as a result of the differing rates of tissue deposition during the experiment, gilts had less lean tissue (57.9 vs. 62.4 kg, P < 0.001) but similar fat (19.2 vs. 18.2 kg, P = 0.22) and ash (2.13 vs. 2.22 kg, P = 0.23) in their body at slaughter compared with boars. Porcine somatotropin treatment increased the lean tissue (58.9 vs. 61.4 kg, P = 0.002), decreased the fat (19.7 vs. 17.7 kg, P = 0.018), but had no effect on the ash (2.17 vs. 2.17 kg, P = 0.99) mass in the body at slaughter. Improvac had no significant effect on lean tissue (59.8 vs. 60.5 kg, P = 0.40) or ash (2.16 vs. 2.18 kg, P = 0.83), but increased fat (17.8 vs. 19.6 kg, P = 0.025) mass in the body at slaughter.
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Table 3. Effect of sex, porcine somatotropin (pST) and Improvac on growth performance and tissue deposition of focus finisher pigsabc
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Sexual Characteristics
Testes weight at slaughter was decreased by Improvac treatment (354 vs. 181 g, P < 0.001), but was not altered by pST treatment (256 vs. 279 g, P = 0.44; Table 4). Ovary weight at slaughter was decreased by Improvac treatment (6.99 vs. 2.99 g, P < 0.001), but was not altered by pST treatment (4.77 vs. 5.21 g, P = 0.52). Ovary maturity score was decreased by Improvac treatment (2.4 vs. 1.3, P < 0.001), but not altered by pST treatment (1.9 vs. 1.8, P = 0.63).
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Table 4. Effect of sex, porcine somatotropin (pST) and Improvac on testes and ovary weights and ovarian maturity in finisher pigsabc
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Discussion
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The overwhelming finding from the present study was that the effects of sex, pST, and Improvac on growth performance are additive or synergistic in group-housed finisher boars and gilts and that these technologies can be used in combination to dramatically improve growth performance and carcass composition. Thus, boars treated with both Improvac and pST had daily gains that were 43 and 64% greater than those of untreated control gilts over the entire 4 or last 2 wk of the treatment period, respectively. Importantly, the effects of the combined treatment with pST and Improvac were demonstrated in gilts as well as in boars. These data are qualitatively similar to those observed in individually housed gilts and boars treated with both pST and Improvac (McCauley et al., 2002).
Porcine somatotropin treatment improved growth performance in both sexes, although responses were more apparent in the gilts. The improvements in performance of gilts treated with pST alone were quite remarkable, with 17 and 29% increases in daily gain and lean tissue deposition and 19 and 22% improvements in FCE and fat deposition, respectively. Whereas pST treatment did not markedly improve ADG (+3%) or lean tissue deposition (-4%), it did increase FCE (+13%) and reduce fat deposition (-27%) in boars. Others have also reported that pST treatment reduced or negated the sex differences normally observed over the finishing phase (Campbell et al., 1989; Dunshea et al., 2002; McCauley et al., 2002). Thus, whereas benefits of pST are greatest in gilts, even boars with high lean growth potential still respond positively to pST, at least with respect to feed efficiency and body composition.
Improvac treatment did not appear to have a major effect on growth performance for the first 2 wk after the second vaccination, although feed intake was increased. However, over the second 2-wk period, pigs treated with Improvac had a higher ADG and ADFI. Over the entire 4-wk treatment period, Improvac alone increased feed intake and daily gain by 18%, without altering FCE, compared with untreated control gilts. Similarly, Improvac increased feed intake and daily gain by 13 and 9%, respectively, compared with untreated control boars, without any effect on FCE (-4%). In another study with group-housed boars, Improvac increased daily gain by 10 and 30% and feed intake by 15 and 21% without changing FCE during the last 4 wk in boars slaughtered at 23 and 26 wk, respectively (Dunshea et al., 2001). As with the present study, most of the performance responses were observed in the third and fourth weeks after vaccination. In individually housed gilts, Improvac increased daily gain and feed intake by 10 and 11%, respectively, without changing FCE (McCauley et al., 2002). In contrast, Improvac had no effect on feed intake or daily gain in individually housed boars (McCauley et al., 2002). Improvac has been shown to reduce sociosexual behavior to levels normally observed in surgical castrates (Cronin et al., 2001). The failure to observe a growth response due to Improvac treatment in the study by McCauley et al. (2002) may be due to the limited sexual and aggressive behavior of individually housed boars. Similarly, McCauley et al. (2000) found that Improvac increased daily gain more in group-housed (18%) vs. individually housed (11%) boars. Therefore, there is now a body of evidence that vaccination against GnRF improves growth performance in group-housed boars and gilts at least in part through reducing sexual and aggressive behaviors.
Housing conditions and the quality of the environment impacts animal performance and the response to metabolic modifiers (NRC, 1994). Group-housed boars have lower growth rates and ADFI than individually housed boars, presumably due to socioaggressive behaviors (Black et al., 2001). In the present study, group-housed boars that received pST treatment alone did not exhibit increased lean tissue deposition. However, in individually housed boars, pST increased lean tissue deposition by 16% (McCauley et al., 2002), presumably because of high feed intakes that resulted from the lack of adverse behaviors in group-housed animals. In situations of feed restriction, such as group-housed boars exhibiting sexual and aggressive behaviors, the further reduction in feed intake associated with pST may limit energy intake available for lean tissue deposition. Similar to pST, Improvac alone did not stimulate lean tissue deposition in the current study even though feed intake was increased, and thus the additional energy was deposited as fat. However, in the boars treated with both pST and Improvac, the additional energy was used for the anabolic effects of pST on lean tissue deposition. Improvac treatment seemed to ameliorate the feed restriction associated with group-housed boars by removing the adverse effects of sexual and aggressive behavior, thus allowing lean tissue deposition to increase. Improvac and pST had qualitatively similar effects in gilts, although the lower rate of lean tissue deposition in the untreated control gilts allowed increases in lean tissue deposition to be expressed in response to both technologies. In a companion study conducted with individually-housed pigs, the additional energy consumed by pigs that received both Improvac and pST compared with pST alone was used for fat rather than lean tissue deposition (McCauley et al., 2002). However, the present study demonstrates that the combined treatments can be beneficial in stimulating lean tissue deposition under circumstances where energy intake is limiting lean tissue deposition such as in group-housed animals, especially boars. These effects may be even more pronounced when pigs are maintained at a high stocking density, under hot conditions, or in genotypes exhibiting a low intrinsic propensity for fat deposition and feed consumption.
Improvac was initially developed to reduce the boar taint compounds skatole and androstenone in pork from boars to levels well below the detection threshold for consumers (Dunshea et al., 2001). In the present study, these compounds were not measured, but the effects on testes and ovary weights and ovary scores at slaughter demonstrate the efficacy of the vaccine to suppress sexual development. Testes and ovary weights were reduced approximately 57 and 58%, respectively, by treatment with Improvac. In addition, ovaries were approximately 50% less mature in Improvac treated gilts than those from control gilts. Dunshea et al. (2001) also observed decreased testes weight with a concomitant decrease in the odor-causing compounds androstenone and skatole. Although not measured, we expect similar observations to have occurred in the present study. Therefore, the administration of Improvac had the desired effects on arresting sexual development in both boars and gilts in the current study. Similar to McCauley et al. (2002), administration of pST had no effect on testes weight, ovary weight, or ovary score in the current study.
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Implications
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The results of the current experiment confirm earlier results that Improvac can arrest and reverse sexual development in boars. In addition, Improvac is efficacious in inhibiting sexual development in gilts. Furthermore, the concomitant use of Improvac and porcine somatotropin resulted in increased growth performance and lean tissue accretion above control levels and above pigs treated with Improvac or porcine somatotropin alone, particularly in group-housed boars. The use of Improvac delays sexual maturity, thereby reducing the occurrence of boar taint. When used alone or with porcine somatotropin, Improvac improves growth performance in group-housed boars and gilts.
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Footnotes
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1 We acknowledge CSL Ltd. (Parkville, Australia) and Alpharma Co. (Toorak, Australia) for providing the Improvac and Reporcin, respectively. 
2 Presented in part at the joint meeting of the ASAS, ADSA, AMSA, and PSA, Indianapolis, IN, July 24 to 28, 2001.
3 Current address: USDA/ARS Children’s Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, 1100 Bates St., Houston, TX 77030.
4 Correspondence: Box 7621 (phone: 919-513-1117; fax: 919-515-7780; E-mail: bob_harrell{at}ncsu.edu).
Received for publication May 6, 2002.
Accepted for publication February 27, 2003.
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Literature Cited
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Adams, T. E., C. A. Daley, B. M. Adams, and H. Sakurai. 1993. Testis function and feedlot performance of bulls actively immunized against gonadotropin-releasing hormone: effect of implants containing progesterone and estradiol benzoate. J. Anim. Sci. 71:811–817.[Abstract]
Black, J. L., L. R. Giles, P. C. Wynn, A. G. Knowles, C. A. Kerr, M. R. Jones, A. D. Strom, N. L. Gallagher, and G. J. Eamens. 2001. A review-Factors limiting the performance of growing pigs in commercial environments. Pages 9–36 in Manipulating Pig Production VIII. P. D. Cranwell, ed. Australas. Pig Sci. Assoc., Werribee, Australia.
Bonneau, M. 1982. Compounds responsible for boar taint, with special emphasis on androstenone: a review. Livest. Prod. Sci. 13:169–178.
Campbell, R. G., N. C. Steele, T. J. Caperna, J. P. McMurtry, M. B. Solomon, and A. D. Mitchell. 1988. Interrelationships between energy intake and endogenous porcine growth hormone administration on the performance, body composition and protein and energy metabolism of growing pigs weighing 25 to 55 kilograms live weight.J. Anim. Sci. 66:1643–1655.
Campbell, R. G., N. C. Steele, T. J. Caperna, J. P. McMurtry, M. B. Solomon, and A. D. Mitchell. 1989. Interrelationships between sex and exogenous growth hormone administration on performance, body composition and protein and fat accretion of growing pigs. J. Anim. Sci. 67:177–186.
Cronin, G. M., F. R. Dunshea, P. H. Hemsworth, J. L. Barnett, I. McCauley, K. L. Butler, and R. J. Smits. 2001. The behavior of group-housed, male finisher pigs. Page 49 in Manipulating Pig Production VIII. P. D. Cranwell, ed. Australas. Pig Sci. Assoc., Werribee, Australia.
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. 2001. Vaccination of entire boars with Improvac eliminates boar taint and increases growth performance. J. Anim. Sci. 79:2524–2535.[Abstract/Free Full Text]
Dunshea, F. R., M. L. Cox, M. R. Borg, M. L. Sillence, and D. R. Harris. 2002. Porcine somatotropin (pST) administered using a commercial delivery system improves growth performance of rapidly-growing, group-housed finisher pigs. Aust. J. Agric. Res. 53:287–293.
Etherton, T. D., J. P. Wiggins, C. S. Chung, C. M. Evock, J. F. Rebhun, and P. E. Walton. 1986. Stimulation of pig growth performance by porcine growth hormone and growth hormone-releasing factor. J. Anim. Sci. 63:1389–1399.
Huxsoll, C. C., E. O. Price, and T. E. Adams. 1998. Testis function, carcass traits, and aggressive behavior of beef bulls actively immunized against gonadotropin-releasing hormone. J. Anim. Sci. 76:1760–1766.[Abstract/Free Full Text]
McCauley, I., G. M. Cronin, J. L. Barnett, K. L. Butler, D. P. Hennessy, R. G. Campbell, B. Luxford, R. J. Smits, A. J. Tillbrook, and F. R. Dunshea. 2000. An immunocastration vaccine (Improvac) increases growth in individually and group-housed boars. J. Anim. Sci. 78(Suppl. 1):138.
McCauley, I., M. Watt, D. Suster, D. J. Kerton, W. T. Oliver, R. J. Harrell, and F. R. Dunshea. 2003. An immunocastration vaccine (Improvac) and porcine somatotropin (Reporcin) have synergistic effects upon growth performance in both boars and gilts. Aust. J. Agric. Res. 54:11–20.
NRC. 1994. Metabolic Modifiers: Effects on the Nutrient Requirements of Food-Producing Animals. Natl. Acad. Press, Washington, DC.
Payne, R. W., P. W. Lane, and Genstat 5 Committee. 1993. Genstat 5 Reference Manual. Oxford Science Publications, Oxford, U.K.
Prendiville, D. J., W. J. Enright, M. A. Crowe, L. Vaughan, and J. F. Roche. 1995. Immunization of prepubertal beef heifers against gonadotropin-releasing hormone: immune, estrus, ovarian, and growth responses. J. Anim. Sci. 73:3030–3037.[Abstract]
Suster, D., B. J. Leury, J. D. Wark, D. J. Kerton, E. Ostrowska, and F. R. Dunshea. 2000. Dual energy X-ray absorptiometry accurately predicts whole body and carcass composition in pigs. J. Anim. Sci. 78(Suppl. 1):145. (Abstr.)[Abstract/Free Full Text]
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Abstract
Introduction
