TY - JOUR
AU - Boler, D. D.
AB - ABSTRACT Objectives were to evaluate the administration of an anti-gonadotropin releasing factor (GnRF) analog on suppression of estrus, consistency of feed intake, and growth performance in market gilts and to investigate the impact the physiological changes would have on carcass characteristics and fresh meat quality. Gonadotropin releasing factor stimulates the anterior pituitary to release luteinizing hormone that acts on the ovary to induce follicle development and indirectly initiates ovulation. Improvest (Zoetis, Kalamazoo, MI) contains an incomplete version of naturally occurring GnRF and causes the production of anti-GnRF antibodies that bind to the GnRF receptor and thus render GnRF inactive. This in turn suppresses estrus in female pigs. Gilts were initially separated into 10 blocks based on age and then within each block allotted to a pen (n = 114; 5 pigs/pen) based on BW. Gilts received the first dose at 12 wk of age and the second dose at 16 wk of age, were exposed to a boar daily from 20 to 26 wk of age, and were slaughtered at 26 wk of age (10 wk after second dose). Meat quality was analyzed on the 2 gilts closest to pen average ending live weight in 5 of the 10 blocks. Pen served as the experimental unit for all data analysis. During the 15-wk finishing period, ADG was 0.03 kg greater (P < 0.01) and G:F was 0.009 greater (P = 0.02) in gilts administered GnRF suppression (treated) compared with untreated gilts (control). The majority of improvements in growth performance were observed from 16 to 20 wk of age (4 wk after second dose), as ADG was 0.07 kg greater (P < 0.001) and G:F was 0.021 greater (P < 0.01) in treated gilts compared with control gilts. Ovarian weights were reduced (P < 0.0001) by 64.15% and gilts exhibiting puberty were reduced by 87.80% (P < 0.001) in treated gilts compared with control gilts. Back fat depth was 3.78 mm greater (P < 0.0001) and estimated lean was 1.31 percentage units less (P < 0.0001) in treated gilts compared with control gilts. With the exception of subjective color, there were no differences (P ≥ 0.12) in meat quality parameters between treated and control gilts. Subjective color was darker (P = 0.03) in treated gilts compared with control gilts. These data suggest market gilts treated with an anti-GnRF analog had suppressed estrus and episodical changes in ADFI, while they had improved feed efficiency, increased ADG, and increased back fat depth when compared with gilts without an anti-GnRF analog treatment. INTRODUCTION Historically, 3-way crossbred gilts (0.69 kg/d) grew 5.8% slower than contemporary barrows (0.73 kg/d) from weaning until 91 kg BW (Comstock et al., 1944). Today, gilts consume 11.3% less feed, grow 7.3% slower, and yield a 1.53 percentage unit leaner carcass than counterpart barrows (Boler et al., 2014; Puls et al., 2014). Management strategies to increase growth rate and increase feed intake while maintaining feed efficiency in market gilts would be desirable to pork producers in managing pig flow and marketing of barrows and gilts. Anti-gonadotropin releasing factor (GnRF) analog (Improvest; Zoetis, Kalamazoo, MI) is currently used for temporary immunological castration and reduction of boar taint in intact male pigs intended for slaughter. However, GnRF is a compound both male and female pigs produce naturally; therefore, the opportunity to use an anti-GnRF analog in market gilts exists. In females, GnRF stimulates the anterior pituitary to release luteinizing hormone that acts on the ovary to induce follicle development and indirectly initiates ovulation. Improvest contains an incomplete version of naturally occurring GnRF and causes the production of anti-GnRF antibodies to competitively bind to the receptor, thus suppressing estrus in female pigs. The estrous period accompanying puberty lasts between 4 and 5 d (Eliasson, 1989), and feed intake and growth are typically decreased during this time (Hinson et al., 2012). To date, there has been limited research analyzing the effectiveness of managing market gilts with an anti-GnRF analog to suppress estrus. Even so, gilts managed with an anti-GnRF immunological consumed 5.99% more feed and grew 5.55% faster than control gilts when slaughtered at 125 kg (Latorre et al., 2013). Therefore, the objective of this study was to determine the effects of GnRF suppression for the management of market gilts on growth performance, estrus activity, carcass characteristics, and fresh meat quality. MATERIALS AND METHODS Experimental procedures involving animals were approved by the North Carolina State University Institutional Animal Care and Use Committee. No approval was obtained from The Ohio State University Institutional Animal Care and Use Committee for this experiment because only fresh meat was used in that portion of the experiment. Live-Phase Experimental Design Five-hundred seventy crossbred gilts (62.1 ± 1.3 d of age; Landrace × Large White × Yorkshire sows mated with 3 crossbred boars composed of Duroc, Hampshire, Pietran, and Spot breeds) were allocated into 10 blocks over a 20-wk period. Blocks were based on farrowing group (age) at the date of allocation. Each block consisted of 3 to 8 replications, based on the number of available gilts, with 5 gilts per pen. Pens contained 4.09 m2 of useable animal space, so each pig was initially provided 0.82 m2 of floor space. Each pen had 2 nipple drinkers and a 2-hole feeder to provide ad libitum access to feed throughout the experiment. Two finisher barns were used and each finisher barn had a curtain-sided, under-slat ventilation system equipped with thermostatically controlled cooling/stirring fans and misters. At 9 wk of age, gilts were individually weighed, examined, and selected for inclusion of the study (Fig. 1). Within each age block, gilts were allocated by BW and provided a 3-wk acclimation period. At 12 wk of age half of the replicates in each block were randomly assigned to the GnRF suppression treatment group (treated) and administered 2 mL of an anti-GnRF immunological product (Improvest; each milliliter contains 0.2 mg GnRF analog–diphtheria toxoid conjugate, 150 mg of diethylaminoethyl-dextran hydrochloride, 1 mg chlorocresol, sodium hydroxide as needed to adjust pH, and water for injection; Zoetis, Kalamazoo, MI) while the remaining half were assigned to the untreated group (control). At 16 wk of age, gilts were weighed and treated gilts were administered a second 2-mL dose of the anti-GnRF immunological product (Improvest) and control gilts remained untreated. No placebo injection was administered to control gilts. At 20 wk of age, gilts were weighed and daily boar exposure began. Boar exposure consisted of allowing a mature boar (3 yr old and 340 kg) to move freely in the alley in front of 2 to 3 pens for 10 to 15 min. Daily boar exposure continued until gilts were 26 wk of age. Feed remaining in the feeders was weighed and recorded as feed not consumed on the same day gilts were weighed during wk 9, 12, 16, 20, and 23. Feed remaining in the feeders was weighed on the day after gilts were sent to slaughter. At 26 wk of age, gilts were transported to the processing facility at each of the scheduled slaughter dates and were humanely slaughtered using electrical immobilization and exsanguination. Ovarian weights, ovarian morphology, and HCW (which included weight of the head) were obtained at the slaughter facility. Figure 1. View largeDownload slide Timeline of study. Figure 1. View largeDownload slide Timeline of study. Carcass Characteristics Back fat depth and LM area were estimated using real-time ultrasonography at approximately 25 wk of age. Real-time ultrasonography (Aloka 500 V, 3.5 MHz; Corometrics Medical Systems, Inc. Wallingford, CT) was conducted 2 to 5 d before scheduled slaughter date depending on the schedule of the ultrasound technician. These measurements, along with HCW, were used to predict estimated lean weight with the following equation (Burson and Berg, 2001): estimated lean, kg = 5.7769 + (0.401 × HCW, lb) – (18.838 × 10th rib fat depth, in.) + (4.357 × 10th rib loin muscle area, sq. in.) + (1.006 × sex of pig; gilt coefficient = 2). This procedure likely underestimates estimated lean, because HCW of this study included weight of the head. Estimated percent lean was determined by dividing estimated lean by HCW. Estrus Activity Ovarian activity was evaluated using 3 different methods. First, paired ovarian weights were obtained at the slaughter facility. Second, each gilt was given a numerical score based on ovarian morphology according to the following scale: 0 = no visible follicles; 1 = only small follicles present (≤3.0 mm in diam.); 2 = medium follicles present (3.1–5.9 mm in diam.); 3 = large follicles present (≥6.0 mm in diam.); 4 = corpora lutea, corpora hemorrhagica, or corpora albicantia present (1 ovulation cycle); and 5 = corpora lutea or corpora hemorrhagica and corpora albicantia (2 ovulation cycles). Third, the percentage of pens within each treatment that had at least 1 gilt ovulating during the study and the percentage of all gilts within treatments that ovulated were determined. Meat Quality Gilts were loaded on trucks on the morning of slaughter and transported approximately 60 km. Gilts were provided a short rest (<2 h) on arriving before slaughter. Meat quality was assessed in 5 of the 10 blocks. The 2 pigs in each pen of a selected block with ending live weights closest to the pen mean weight were selected for meat quality evaluation. A total of 116 loin sections were shipped from the slaughter facility to the meat science laboratory at The Ohio State University. Sections were cut from the posterior section of the 10th rib, vacuum packaged, and shipped under refrigeration. Sections remained vacuum packaged and were stored in a refrigerated cooler (4°C) on arrival. Fresh meat quality was assessed at 7 d postmortem. Initially, sections were faced and allowed at least 15 min to bloom. The piece removed from face was used to determine proximate composition (percentage moisture and fat). The loin sample was trimmed of all subcutaneous fat and homogenized in a food processor. A 10-g sample was oven-dried at 100°C for at least 24 h to determine moisture percentage. The dried sample was washed multiple times in warm petroleum ether to remove fat using the modified procedure from Novakofski et al. (1989). The fresh cut surface was evaluated for subjective color (1 = pale pinkish gray to white, 2 = grayish pink, 3 = reddish pink, 4 = dark reddish pink, 5 = purplish red, and 6 = dark purplish red; NPPC, 1999), marbling (1 through 10 corresponding to intramuscular lipid content; NPPC, 1999), and firmness (1 = soft; cut surface distorts easily; 2 = firm; cut surface tends to hold shape; and 3 = very firm; cut surface were very smooth with no distortion of shape; NPPC, 1999) by trained Ohio State University personnel and recorded in whole numbers. The surface was evaluated for ultimate pH using a handheld Hanna HI 99163 pH meter (Hanna Instruments; Woonsocket, RI.) and was evaluated for objective CIE L*, a*, and b* with a Minolta CR-400 (Konica Minolta; Chiyoda, Tokyo, Japan) using a D65 light source and a 0° observer and an aperture size of 50 mm. The remaining section was then cut into 1 chop cut 1.25 cm thick and 1 chop cut 2.54 cm thick. Water holding capacity was evaluated using the drip-loss method where the 1.25 cm thick chop was suspended from a fish hook in a Whirl-pak bag (Nasco; Fort Atkinson, WI) for approximately 24 h at 4°C. Chops were weighed before and immediately after suspension for 24 h. Results were reported as a percent of weight loss. Chops designated for Warner-Bratzler shear force (2.54 cm thick) testing were vacuum packaged and immediately frozen until further evaluation. Twenty-four hours before analysis, chops were removed from the freezer and placed in a cooler at 4°C to thaw. Chops were trimmed of excess fat and cooked on a clamshell-type grill. Chops were cooked to a final internal temperature of 70°C. Internal temperature was monitored using copper-constantan thermocouples (Type T; Omega Engineering, Stanford, CT) connected to a digital scanning thermometer (model 92000-00; Barnant Co., Barington, IL). Next, chops were allowed to cool to 25°C and four 1.25-cm diam. cores were removed parallel to the orientation of the muscle fibers. Cores were sheared using a Texture Analyzer TA.HD Plus (Texture Technologies Corp., Scarsdale, NY/Stable Microsystems, Godalming, UK) with a blade speed of 3.3 mm/s and a load cell capacity of 50 kg. A single shear force was determined on each of the 4 cores. Shear force was reported as the average of the 4 cores. Cook loss was determined by weighing chops used for shear force immediately before and after cooking. Reported values are percent weight lost during cooking. Statistical Analysis Data were analyzed with the MIXED procedure in SAS (SAS Inst. Inc., Cary, NC) as a randomized complete block design with the fixed effect of treatment and the random effect of replication nested within block. Pen served as the experimental unit for all analysis, with the exception of gilts exhibiting puberty, which used pig as the experimental unit. Statistical differences were considered significant at P ≤ 0.05 and tendencies at 0.05 < P ≤ 0.10 using a 2-tailed test. RESULTS Growth Performance Results for growth performance are presented in Table 1. From 12 to 16 wk of age (time between first and second dose), ADG was not different (P = 0.52) between treated and control gilts. Average daily feed intake was 0.09 kg (3.80%) less (P = 0.04) in treated gilts. Feed efficiency (G:F) was not different (P = 0.19). From 16 to 20 wk of age (0–4 wk after second dose, before boar exposure), ADG was 0.07 kg (8.54%) greater (P < 0.001) in treated gilts. Average daily feed intake was not different (P = 0.28). Feed efficiency (G:F) was 0.021 (7.12%) greater (P < 0.01) in treated gilts. From 20 to 23 wk of age (4–7 wk after second dose and during boar exposure), ADG was 0.05 kg (6.02%) greater (P = 0.01) in treated gilts. Average daily feed intake was 0.12 kg (3.87%) greater (P = 0.01) in treated gilts. Feed efficiency (G:F) was not different (P = 0.16). From 23 to 26 wk of age (7–10 wk after second dose and during boar exposure), ADG was not different (P = 0.73). Average daily feed intake was not different (P = 0.89). Feed efficiency (G:F) was not different (P = 0.66). During the entire finishing period (12 to 26 wk of age), ADG was 0.03 kg (3.66%) greater (P < 0.01) in treated gilts. Average daily feed intake was not different (P = 0.67). Feed efficiency (G:F) was 0.009 (3.09%) greater (P = 0.02) in treated gilts. Overall, treated gilts grew faster and were more feed efficient throughout the finishing period than control gilts (Table 1). Table 1. Effect of immunological gonadotropin releasing factor suppression on growth performance of market gilts during a 15-wk finishing period   Management      Parameter  Control  Treated1  SEM  P-value  Pens, n  57  57      12–16 wk2      ADG, kg/d  0.82  0.82  0.02  0.52      ADFI, kg/d  2.37  2.28  0.03  0.04      G:F  0.350  0.361  0.008  0.19  16–20 wk3      ADG, kg/d  0.82  0.89  0.02  <0.001      ADFI, kg/d  2.82  2.87  0.06  0.28      G:F  0.295  0.316  0.010  <0.01  20–23 wk4      ADG, kg/d  0.83  0.88  0.03  0.01      ADFI, kg/d  3.10  3.22  0.06  0.01      G:F  0.271  0.279  0.012  0.16  23–26 wk5      ADG, kg/d  0.83  0.82  0.03  0.73      ADFI, kg/d  3.24  3.25  0.08  0.89      G:F  0.258  0.255  0.006  0.66  12–26 wk      ADG, kg/d  0.82  0.85  0.01  <0.01      ADFI, kg/d  2.82  2.83  0.03  0.67      G:F  0.291  0.300  0.003  0.02  16–26 wk6      ADG, kg/d  0.82  0.86  0.02  <0.01      ADFI, kg/d  3.02  3.08  0.04  0.11      G:F  0.272  0.281  0.004  0.03    Management      Parameter  Control  Treated1  SEM  P-value  Pens, n  57  57      12–16 wk2      ADG, kg/d  0.82  0.82  0.02  0.52      ADFI, kg/d  2.37  2.28  0.03  0.04      G:F  0.350  0.361  0.008  0.19  16–20 wk3      ADG, kg/d  0.82  0.89  0.02  <0.001      ADFI, kg/d  2.82  2.87  0.06  0.28      G:F  0.295  0.316  0.010  <0.01  20–23 wk4      ADG, kg/d  0.83  0.88  0.03  0.01      ADFI, kg/d  3.10  3.22  0.06  0.01      G:F  0.271  0.279  0.012  0.16  23–26 wk5      ADG, kg/d  0.83  0.82  0.03  0.73      ADFI, kg/d  3.24  3.25  0.08  0.89      G:F  0.258  0.255  0.006  0.66  12–26 wk      ADG, kg/d  0.82  0.85  0.01  <0.01      ADFI, kg/d  2.82  2.83  0.03  0.67      G:F  0.291  0.300  0.003  0.02  16–26 wk6      ADG, kg/d  0.82  0.86  0.02  <0.01      ADFI, kg/d  3.02  3.08  0.04  0.11      G:F  0.272  0.281  0.004  0.03  1Gilts received a 2-mL subcutaneous injection of Improvest (Zoetis, Kalamazoo, MI) at 12 and 16 wk of age (initial BW at 12 wk of age = 38.23 kg). Gilts were slaughtered at 10 wk after second dose. 2Twelve- to sixteen-week period was between first and second Improvest dose (16-wk BW = 61.76 kg). 3Sixteen- to twenty-week period was after second injection but before boar exposure (20-wk BW = 85.63 kg). 4Twenty- to twenty-three-week period was after initiation of boar exposure but likely before estrous period (23-wk BW = 102.20 kg). 5Twenty-three- to twenty-six-week period was after initiation to boar exposure and likely during estrous activity (26-wk BW = 118.51 kg). 6Sixteen- to twenty-six-week period was after second injection until slaughter. View Large Table 1. Effect of immunological gonadotropin releasing factor suppression on growth performance of market gilts during a 15-wk finishing period   Management      Parameter  Control  Treated1  SEM  P-value  Pens, n  57  57      12–16 wk2      ADG, kg/d  0.82  0.82  0.02  0.52      ADFI, kg/d  2.37  2.28  0.03  0.04      G:F  0.350  0.361  0.008  0.19  16–20 wk3      ADG, kg/d  0.82  0.89  0.02  <0.001      ADFI, kg/d  2.82  2.87  0.06  0.28      G:F  0.295  0.316  0.010  <0.01  20–23 wk4      ADG, kg/d  0.83  0.88  0.03  0.01      ADFI, kg/d  3.10  3.22  0.06  0.01      G:F  0.271  0.279  0.012  0.16  23–26 wk5      ADG, kg/d  0.83  0.82  0.03  0.73      ADFI, kg/d  3.24  3.25  0.08  0.89      G:F  0.258  0.255  0.006  0.66  12–26 wk      ADG, kg/d  0.82  0.85  0.01  <0.01      ADFI, kg/d  2.82  2.83  0.03  0.67      G:F  0.291  0.300  0.003  0.02  16–26 wk6      ADG, kg/d  0.82  0.86  0.02  <0.01      ADFI, kg/d  3.02  3.08  0.04  0.11      G:F  0.272  0.281  0.004  0.03    Management      Parameter  Control  Treated1  SEM  P-value  Pens, n  57  57      12–16 wk2      ADG, kg/d  0.82  0.82  0.02  0.52      ADFI, kg/d  2.37  2.28  0.03  0.04      G:F  0.350  0.361  0.008  0.19  16–20 wk3      ADG, kg/d  0.82  0.89  0.02  <0.001      ADFI, kg/d  2.82  2.87  0.06  0.28      G:F  0.295  0.316  0.010  <0.01  20–23 wk4      ADG, kg/d  0.83  0.88  0.03  0.01      ADFI, kg/d  3.10  3.22  0.06  0.01      G:F  0.271  0.279  0.012  0.16  23–26 wk5      ADG, kg/d  0.83  0.82  0.03  0.73      ADFI, kg/d  3.24  3.25  0.08  0.89      G:F  0.258  0.255  0.006  0.66  12–26 wk      ADG, kg/d  0.82  0.85  0.01  <0.01      ADFI, kg/d  2.82  2.83  0.03  0.67      G:F  0.291  0.300  0.003  0.02  16–26 wk6      ADG, kg/d  0.82  0.86  0.02  <0.01      ADFI, kg/d  3.02  3.08  0.04  0.11      G:F  0.272  0.281  0.004  0.03  1Gilts received a 2-mL subcutaneous injection of Improvest (Zoetis, Kalamazoo, MI) at 12 and 16 wk of age (initial BW at 12 wk of age = 38.23 kg). Gilts were slaughtered at 10 wk after second dose. 2Twelve- to sixteen-week period was between first and second Improvest dose (16-wk BW = 61.76 kg). 3Sixteen- to twenty-week period was after second injection but before boar exposure (20-wk BW = 85.63 kg). 4Twenty- to twenty-three-week period was after initiation of boar exposure but likely before estrous period (23-wk BW = 102.20 kg). 5Twenty-three- to twenty-six-week period was after initiation to boar exposure and likely during estrous activity (26-wk BW = 118.51 kg). 6Sixteen- to twenty-six-week period was after second injection until slaughter. View Large Carcass Characteristics Results for carcass characteristics are presented in Table 2. Tenth rib LM area was not different (P = 0.91) between treated and control gilts. Tenth rib back fat depth was 3.78 mm (17.38%) greater (P < 0.0001) in treated gilts. Hot carcass weight was not different (P = 0.16). Estimated weight of the lean (an equation including LM area, back fat depth, and HCW; Burson and Berg, 2001) was not different (P = 0.46). Yet estimated lean percentage was 1.31% units less (P < 0.0001) in treated gilts. Overall, these data suggest that when slaughtered at 10 wk after second dose, treated gilts had more fat and a reduction in estimated carcass lean percentage compared with control gilts; however, muscling and estimated lean weight were not different between treated and control gilts (Table 2). Table 2. Effect of immunological gonadotropin releasing factor suppression on carcass characteristics of market gilts   Management      Parameter  Control  Treated1  SEM  P-value  Pens, n  57  57      Initial live weight,2 kg  38.43  38.02  0.68  0.18  Final live weight,3 kg  117.39  119.63  1.18  0.05  HCW (including head weight), kg  96.19  97.62  1.00  0.16  Back fat depth,4 mm  21.75  25.53  0.05  <0.0001  LM area,4 cm2  45.13  45.20  0.64  0.91  Estimated lean,5 kg  48.46  48.11  0.44  0.46  Estimated lean,5 %  50.53  49.22  0.21  <0.0001    Management      Parameter  Control  Treated1  SEM  P-value  Pens, n  57  57      Initial live weight,2 kg  38.43  38.02  0.68  0.18  Final live weight,3 kg  117.39  119.63  1.18  0.05  HCW (including head weight), kg  96.19  97.62  1.00  0.16  Back fat depth,4 mm  21.75  25.53  0.05  <0.0001  LM area,4 cm2  45.13  45.20  0.64  0.91  Estimated lean,5 kg  48.46  48.11  0.44  0.46  Estimated lean,5 %  50.53  49.22  0.21  <0.0001  1Gilts received a 2-mL subcutaneous injection of Improvest (Zoetis, Kalamazoo, MI) at 12 and 16 wk of age. Gilts were slaughtered at 10 wk after second dose. 2Initial weight was taken at 12 wk of age. 3Final weight was taken at 26 wk of age. 4Real-time ultrasonography images were used to estimate LM area and back fat depth 2 to 5 d before slaughter. 5Estimated lean was calculated using a modified version of procedure 6 of the procedures for estimating pork carcass composition (Burson and Berg, 2001). View Large Table 2. Effect of immunological gonadotropin releasing factor suppression on carcass characteristics of market gilts   Management      Parameter  Control  Treated1  SEM  P-value  Pens, n  57  57      Initial live weight,2 kg  38.43  38.02  0.68  0.18  Final live weight,3 kg  117.39  119.63  1.18  0.05  HCW (including head weight), kg  96.19  97.62  1.00  0.16  Back fat depth,4 mm  21.75  25.53  0.05  <0.0001  LM area,4 cm2  45.13  45.20  0.64  0.91  Estimated lean,5 kg  48.46  48.11  0.44  0.46  Estimated lean,5 %  50.53  49.22  0.21  <0.0001    Management      Parameter  Control  Treated1  SEM  P-value  Pens, n  57  57      Initial live weight,2 kg  38.43  38.02  0.68  0.18  Final live weight,3 kg  117.39  119.63  1.18  0.05  HCW (including head weight), kg  96.19  97.62  1.00  0.16  Back fat depth,4 mm  21.75  25.53  0.05  <0.0001  LM area,4 cm2  45.13  45.20  0.64  0.91  Estimated lean,5 kg  48.46  48.11  0.44  0.46  Estimated lean,5 %  50.53  49.22  0.21  <0.0001  1Gilts received a 2-mL subcutaneous injection of Improvest (Zoetis, Kalamazoo, MI) at 12 and 16 wk of age. Gilts were slaughtered at 10 wk after second dose. 2Initial weight was taken at 12 wk of age. 3Final weight was taken at 26 wk of age. 4Real-time ultrasonography images were used to estimate LM area and back fat depth 2 to 5 d before slaughter. 5Estimated lean was calculated using a modified version of procedure 6 of the procedures for estimating pork carcass composition (Burson and Berg, 2001). View Large Estrus Activity Results for estrus activity are presented in Table 3. Ovarian weights were 6.80 g (64.15%) lighter (P < 0.0001) in treated gilts compared with control gilts. Ovarian activity scores were 1.80 (75.00%) less (P < 0.0001) in treated gilts. Pens with at least 1 pubertal gilt were 28.10% units less (P < 0.001) in treated gilts. Gilts exhibiting puberty were reduced (P < 0.001) by 18.00% units in treated gilts. Overall, administering the anti-GnRF analog (Improvest) was an effective method for suppressing estrus in market gilts; however, it did not completely eliminate signs of puberty in market gilts. Possible explanations could be that when slaughtered at 10 wk after second dose (the maximum marketing window for male pigs), the GnRF analog immunity was beginning to diminish and dropped below suppressive antibody levels potentially allowing puberty to develop after antibody titers have degraded to a level lower than the level necessary to elicit an immune response. Table 3. Effect of immunological gonadotropin releasing factor suppression on estrus activity   Management      Parameter  Control  Treated1  SEM  P-value  Pens, n  57  57      Ovarian weight, g  10.60  3.80  0.40  <0.0001  Ovarian activity score2  2.40  0.60  0.10  <0.0001  Pens with a pubertal gilt, %  40.40  12.30  6.60  <0.001  Gilts exhibiting puberty, %  20.50  2.50  0.03  <0.001    Management      Parameter  Control  Treated1  SEM  P-value  Pens, n  57  57      Ovarian weight, g  10.60  3.80  0.40  <0.0001  Ovarian activity score2  2.40  0.60  0.10  <0.0001  Pens with a pubertal gilt, %  40.40  12.30  6.60  <0.001  Gilts exhibiting puberty, %  20.50  2.50  0.03  <0.001  1Gilts received a 2-mL subcutaneous injection of Improvest (Zoetis, Kalamazoo, MI) at 12 and 16 wk of age. Gilts were slaughtered at 10 wk after second dose. 2Numerical scoring system of 0 = no visible follicles; 1 = only small follicles present (≤3.0 mm in diam.); 2 = medium follicles present (3.1–5.9 mm in diam.); 3 = large follicles present (≥6.0 mm in diam.); 4 = corpora lutea, corpora hemorrhagica, or corpora albicantia present (1 ovulation cycle); and 5 = corpora lutea or corpora hemorrhagica and corpora albicantia present (2 ovulation cycles). View Large Table 3. Effect of immunological gonadotropin releasing factor suppression on estrus activity   Management      Parameter  Control  Treated1  SEM  P-value  Pens, n  57  57      Ovarian weight, g  10.60  3.80  0.40  <0.0001  Ovarian activity score2  2.40  0.60  0.10  <0.0001  Pens with a pubertal gilt, %  40.40  12.30  6.60  <0.001  Gilts exhibiting puberty, %  20.50  2.50  0.03  <0.001    Management      Parameter  Control  Treated1  SEM  P-value  Pens, n  57  57      Ovarian weight, g  10.60  3.80  0.40  <0.0001  Ovarian activity score2  2.40  0.60  0.10  <0.0001  Pens with a pubertal gilt, %  40.40  12.30  6.60  <0.001  Gilts exhibiting puberty, %  20.50  2.50  0.03  <0.001  1Gilts received a 2-mL subcutaneous injection of Improvest (Zoetis, Kalamazoo, MI) at 12 and 16 wk of age. Gilts were slaughtered at 10 wk after second dose. 2Numerical scoring system of 0 = no visible follicles; 1 = only small follicles present (≤3.0 mm in diam.); 2 = medium follicles present (3.1–5.9 mm in diam.); 3 = large follicles present (≥6.0 mm in diam.); 4 = corpora lutea, corpora hemorrhagica, or corpora albicantia present (1 ovulation cycle); and 5 = corpora lutea or corpora hemorrhagica and corpora albicantia present (2 ovulation cycles). View Large Meat Quality Results for meat quality are presented in Table 4. Subjective color evaluation scores were darker (P = 0.03) in treated gilts compared with control gilts. At the same time, objective color scores (L*, a*, and b*) were not different (P ≥ 0.50) between treated and control gilts. All other meat quality traits evaluated (including marbling, firmness, pH, drip loss, cook loss, shear force, percentage moisture, or percentage fat) were not different (P ≥ 0.12). Overall, meat quality parameters were not different between gilts administered the anti-GnRF analog (Improvest) and control gilts (Table 4). Table 4. Effect of immunological gonadotropin releasing factor suppression on fresh meat quality of market gilts   Management      Parameter  Control  Treated1  SEM  P-value  Pens, n  26  32      Subjective evaluations2      Color  2.24  2.53  0.10  0.03      Marbling  2.06  2.19  0.13  0.41      Firmness  2.19  2.19  0.08  0.99  Objective color scores      L*  55.40  55.75  0.38  0.50      a*  18.94  19.01  0.17  0.78      b*  7.53  7.59  0.15  0.76  pH  5.52  5.52  0.03  0.72  Drip loss, %  1.26  1.17  0.09  0.30  Cook loss, %  18.51  18.49  0.58  0.98  Shear force, kg  2.59  2.54  0.06  0.51  Proximate composition      Moisture, %  72.68  72.39  0.13  0.12      Fat, %  2.45  2.69  0.13  0.17    Management      Parameter  Control  Treated1  SEM  P-value  Pens, n  26  32      Subjective evaluations2      Color  2.24  2.53  0.10  0.03      Marbling  2.06  2.19  0.13  0.41      Firmness  2.19  2.19  0.08  0.99  Objective color scores      L*  55.40  55.75  0.38  0.50      a*  18.94  19.01  0.17  0.78      b*  7.53  7.59  0.15  0.76  pH  5.52  5.52  0.03  0.72  Drip loss, %  1.26  1.17  0.09  0.30  Cook loss, %  18.51  18.49  0.58  0.98  Shear force, kg  2.59  2.54  0.06  0.51  Proximate composition      Moisture, %  72.68  72.39  0.13  0.12      Fat, %  2.45  2.69  0.13  0.17  1Gilts received a 2-mL subcutaneous injection of Improvest (Zoetis, Kalamazoo, MI) at 12 and 16 wk of age. Gilts were slaughtered at 10 wk after second dose. 2Values assessed using National Pork Producers Council (NPCC, 1999) standards and recorded in whole numbers. View Large Table 4. Effect of immunological gonadotropin releasing factor suppression on fresh meat quality of market gilts   Management      Parameter  Control  Treated1  SEM  P-value  Pens, n  26  32      Subjective evaluations2      Color  2.24  2.53  0.10  0.03      Marbling  2.06  2.19  0.13  0.41      Firmness  2.19  2.19  0.08  0.99  Objective color scores      L*  55.40  55.75  0.38  0.50      a*  18.94  19.01  0.17  0.78      b*  7.53  7.59  0.15  0.76  pH  5.52  5.52  0.03  0.72  Drip loss, %  1.26  1.17  0.09  0.30  Cook loss, %  18.51  18.49  0.58  0.98  Shear force, kg  2.59  2.54  0.06  0.51  Proximate composition      Moisture, %  72.68  72.39  0.13  0.12      Fat, %  2.45  2.69  0.13  0.17    Management      Parameter  Control  Treated1  SEM  P-value  Pens, n  26  32      Subjective evaluations2      Color  2.24  2.53  0.10  0.03      Marbling  2.06  2.19  0.13  0.41      Firmness  2.19  2.19  0.08  0.99  Objective color scores      L*  55.40  55.75  0.38  0.50      a*  18.94  19.01  0.17  0.78      b*  7.53  7.59  0.15  0.76  pH  5.52  5.52  0.03  0.72  Drip loss, %  1.26  1.17  0.09  0.30  Cook loss, %  18.51  18.49  0.58  0.98  Shear force, kg  2.59  2.54  0.06  0.51  Proximate composition      Moisture, %  72.68  72.39  0.13  0.12      Fat, %  2.45  2.69  0.13  0.17  1Gilts received a 2-mL subcutaneous injection of Improvest (Zoetis, Kalamazoo, MI) at 12 and 16 wk of age. Gilts were slaughtered at 10 wk after second dose. 2Values assessed using National Pork Producers Council (NPCC, 1999) standards and recorded in whole numbers. View Large DISCUSSION The improved growth performance (Dunshea et al., 2001; Fàbrega et al., 2010) and carcass cutability (Boler et al., 2012) associated with male pigs immunologically castrated with an anti-GnRF analog in comparison to physically castrated barrows has been well documented. Dunshea et al. (2013) reported, via meta-analysis, that ADG was greater (0.16 kg) and back fat depth was less (2.64 mm) in immunologically castrated males when compared with physically castrated barrows. Immunologically castrated barrows had greater ADFI (0.43 kg), which resulted in greater ADG (0.12 kg), and an improved feed conversion ratio when compared with entire males, although back fat depth was also increased (1.53 mm; Dunshea et al., 2013). Therefore, immunologically castrated barrows have advantages in growth rate when compared to physically castrated barrows and entire males and have less back fat depth than physically castrated barrows but have more back fat depth than entire males. The management of gilts with an anti-GnRF analog has been considerably less well documented. Puberty of gilts occurs before marketing (less than 180 d) but is very dependent on genetics and management factors (including nutrition, exposure to boars, and growing season; Evans and O'Doherty, 2001). These data suggest gilts managed with an anti-GnRF analog had increased growth rates and improved feed efficiency compared with control gilts. Albeit, when slaughtered at 10 wk after second dose, gilts managed with an anti-GnRF analog had greater back fat thickness and reduced estimated lean percentage compared with control gilts. These findings were comparable with other available data. Among the limited available information, Latorre et al. (2013) reported gilts slaughtered at approximately 125 kg BW (67 kg of BW gain after second dose) managed with an anti-GnRF analog had greater ADG (0.99 vs. 0.94 kg) than control gilts but also had greater ADFI (2.83 vs. 2.67 kg) than control gilts; therefore, feed conversion was not different between treated and control gilts. Differences in response between the 2 studies was likely due to the present study ending at a fixed time and Latorre et al. (2013) ending at a fixed weight (125 kg). Even so, treated gilts in the current study grew 5% faster and were over 3% more feed efficient than control gilts without affecting feed intake during the finishing phase from the second injection through slaughter. Gómez-Fernández et al. (2013) reported treated gilts (slaughtered 14 wk after second dose, at approximately 170 kg) had greater ADG (0.84 vs. 0.80 kg), ADFI (3.48 vs. 3.21 kg), and reduced feed conversion (Feed:Gain; 4.16 vs 4.04) compared with control gilts. Furthermore, Gómez-Fernández et al. (2013) reported ending live weight and HCW tended to be greater in treated gilts compared with control gilts. Although Gómez-Fernández et al. (2013) did not report 10th rib LM area and back fat thickness, they did report that trimmed shoulder, loin, and trimmed ham were lower yielding in treated gilts compared with control gilts. Finally, in a study where gilts were slaughtered at 4 wk after the second dose, treated gilts grew 18% faster than control gilts but also consumed 18% more feed (Oliver et al., 2003). Therefore, feed efficiency was not different between treated and control gilts. The management of market gilts with an anti-GnRF analog is a novel concept to increase ADG and ADFI and in turn increase carcass weight with more desirable levels of carcass fat and marbling without exaggerated detrimental impacts on feed efficiency. In this study, treated gilts had slightly greater back fat and reduced estimated lean percentage and numerically increased fat content (0.24%, or approximately a 10% increase) in the LM when gilts were slaughtered 10 wk after the second dose. Market gilts tend to have leaner carcasses in comparison to physically castrated barrow counterparts (Ekstrom, 1991). From a U.S. pork packer perspective, gilts are consistently leaner and have more carcass muscle resulting in greater carcass cutability (Boler et al., 2014). However, a greater proportion of gilts can have carcasses that are considered excessively lean for the U.S. packing industry standards and have loin muscles with less marbling or fat content than counterpart barrows (Boler et al., 2014). Additionally, lean gilt carcasses can yield bellies that are excessively lean and thinner than bellies considered ideal to process under commercial conditions to optimize belly value (Kyle et al., 2014). Further research is warranted to better understand appropriate age and timing of slaughter after second dose to optimize lean growth, carcass fat deposition, carcass characteristics, and determine carcass cutability. LITERATURE CITED Boler D. D. Killefer J. Meeuwse D. M. King V. L. McKeith F. K. Dilger A. C. 2012. Effects of slaughter time post second injection on carcass cutting yield and bacon characteristics of immunologically castrated male pigs. J. Anim. Sci.  90: 334– 344. Google Scholar CrossRef Search ADS PubMed  Boler D. D. Puls C. L. Clark D. L. Ellis M. Schroeder A. L. Matzat P. D. Killefer J. McKeith F. K. Dilger A. C. 2014. Effects of immunological castration (Improvest) on changes in dressing percentage and carcass characteristics of finishing pigs. J. Anim. Sci.  92: 359– 368. Google Scholar CrossRef Search ADS PubMed  Burson D. Berg E. 2001. Procedures for estimating pork carcass composition. In: Pork quality facts.  National Pork Producers Council, National Pork Board, Des Moines, IA. p. 1– 3. Comstock R. E. Winters L. M. Cummings J. N. 1944. The effect of sex on the development of the pig III. Differences in growth rate between gilts and barrows by lines of breeding. J. Anim. Sci.  3: 120– 128. Google Scholar CrossRef Search ADS   Dunshea F. R. Allison J. R. D. Bertram M. Boler D. D. Brossard L. Campbell R. Crane J. P. Hennessy D. P. Huber L. de Lange C. Ferguson N. Matzat P. McKeith F. Moraes P. J. U. Mullan B. P. Noblet J. Quiniou N. Tokach M. 2013. The effect of immunization against GnRF on nutrient requirements of male pigs: A review. Animal  7: 1769– 1778. Google Scholar CrossRef Search ADS PubMed  Dunshea F. R. Colantoni C. Howard K. McCauley I. Jackson P. Long K. A. Lopaticki S. Nugent E. A. Simons J. A. Walker J. Hennessy D. P. 2001. Vaccination of boars with a GnRH vaccine (Improvac) eliminates boar taint and increases growth performance. J. Anim. Sci.  79: 2524– 2535. Google Scholar CrossRef Search ADS PubMed  Ekstrom K. E 1991. Genetic and sex considerations in swine nutrition. In: Miller E. R. Ullrey D. E. Lewis A. J. editors, Swine nutrition.  Buttenvorth-Heinemann, Stoneham, MA. p. 415– 424. Google Scholar CrossRef Search ADS   Eliasson L 1989. A study on puberty and oestrus in gilts. Zentralbl. Veterinarmed. A  36: 46– 54. Google Scholar CrossRef Search ADS PubMed  Evans A. C. O. O'Doherty J. V. 2001. Endocrine changes and management factors affecting puberty in gilts. Livest. Prod. Sci.  68: 1– 12. Google Scholar CrossRef Search ADS   Fàbrega E. Velarde A. Cros J. Gispert M. Suarez P. Tibau J. Soler J. 2010. Effect of vaccination against gonadotrophin-releasing hormone, using Improvac®, on growth performance, body composition, behaviour and acute phase proteins. Livest. Sci.  132: 53– 59. Google Scholar CrossRef Search ADS   Gómez-Fernández J. Horcajada S. Tomás C. Gómez-Izquierdo E. de Mercado E. 2013. The effect of immunocastration and surgically castration on growth performance and carcass quality in fattening period of Iberian female pigs. ITEA  109: 33– 48. Hinson R. B. Galloway H. O. Boler D. D. Ritter M. J. McKeith F. K. Carr S. N. 2012. Effects of feeding ractopamine (Paylean) on growth and carcass traits in finishing pigs marketed at equal harvest weights. Prof. Anim. Sci.  28: 657– 663. Kyle J. M. Bohrer B. M. Schroeder A. L. Matulis R. J. Boler D. D. 2014. Effects of immunological castration (Improvest®) on further processed belly characteristics and commercial bacon slicing yields of finishing pigs. J. Anim. Sci.  92: 3988– 3996. Google Scholar CrossRef Search ADS PubMed  Latorre M. A. Daza A. Olivares A. López-Bote C. J. 2013. The effect of immunocastration on growth performance and meat quality of heavy gilts. J. Anim. Sci.  91 ( E-Suppl. 2): 372– 373 ( Abstr.). National Pork Producers Council (NPPC) 1999. Official color and marbling standards. National Pork Producers Council, Des Moines, IA. Novakofski J. Park S. Bechtel P. J. McKeith F. K. 1989. Composition of cooked pork chops – Effects of removing subcutaneous fat before cooking. J. Food Sci.  54: 15– 17. Google Scholar CrossRef Search ADS   Oliver W. T. McCauley I. Harrell R. J. Suster D. Kerton D. J. Dunshea F. R. 2003. 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: 1959– 1966. Google Scholar CrossRef Search ADS PubMed  Puls C. L. Rojo A. Ellis M. Boler D. D. McKeith F. K. Killefer J. Gaines A. M. Matzat P. D. Schroeder A. L. 2014. Growth performance of immunologically castrated (with Improvest) barrows (either with or without feeding of ractopamine) compared to gilt, physically-castrated barrow, and intact male pigs. J. Anim. Sci.  92: 2289– 2295. Google Scholar CrossRef Search ADS PubMed  American Society of Animal Science
TI - Effect of gonadotropin releasing factor suppression with an immunological on growth performance, estrus activity, carcass characteristics, and meat quality of market gilts
JF - Journal of Animal Science
DO - 10.2527/jas.2014-7756
DA - 2014-10-01
UR - https://www.deepdyve.com/lp/oxford-university-press/effect-of-gonadotropin-releasing-factor-suppression-with-an-mmv6helzqe
SP - 4719
EP - 4724
VL - 92
IS - 10
DP - DeepDyve
ER -