Effects of narasin (Skycis) on live performance and carcass traits of finishing pigs sold in a three-phase marketing system

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1 Published October 9, 2015 Effects of narasin (Skycis) on live performance and carcass traits of finishing pigs sold in a three-phase marketing system E. K. Arkfeld,* S. N. Carr, P. J. Rincker, S. L. Gruber, G. L. Allee, A. C. Dilger,* and D. D. Boler* 1 *Department of Animal Sciences, University of Illinois, Urbana-Champaign 61801; Elanco Animal Health, A Division of Eli Lilly and Company, Greenfield, IN, 46140; and Porktech, LLC, Columbia, MO ABSTRACT: The objective was to evaluate the effect of feeding narasin (Skycis; Elanco Animal Health, Greenfield, IN) on growth performance and carcass characteristics of finishing pigs sold in a 3-phase marketing system. Pigs (n = 1,232) were housed in 56 single-sex pens (22 pigs/pen) divided into 2 even blocks based on initiation of treatment. Each treatment sex combination was replicated 14 times. Pigs were fed either 0 mg/kg narasin (control) or 15 mg/ kg narasin for up to 85 d of finishing (initiated at an average of kg BW). In each pen, 18% (4 pigs per pen) of pigs were sold in the first marketing group (Day 64 of dietary treatment), 50% (11 of the original 22) were sold in the second marketing group (Day 78), and 32% (the remaining 7 pigs) were sold in the third marketing group (Day 85). Data were analyzed as a randomized complete block design with pen as the experimental unit. The model included the fixed effects of diet, sex, and their interaction. Block and replicate nested within block were random variables. Carcass data from pigs in marketing group 3 of block 2 was not collected due to inclement weather. Narasin had no effect on growth performance traits (P 0.15) in phases 1 (Days 1 28) or 2 (Days 29 56), regardless of sex. Barrows fed narasin had a 2.0% greater overall (Day 0 85) ADG than barrows fed the control diet (P < 0.01), but ADG of gilts was not different due to diet (P = 0.69). Regardless of sex, narasin improved (P = 0.03) feed efficiency (G:F) by 1.3% throughout the 85-d feeding period. There were no effects (P 0.21) of narasin on carcass composition in marketing groups 1 and 2. Narasin-fed barrows in marketing group 3 had 0.9 percentage units lower (P < 0.01) estimated carcass lean compared with barrows fed control diets (51.0 vs. 52.0%); no difference existed in gilts (P = 0.21). This is likely due to narasin-fed barrows of marketing group 3 tending (P = 0.06) to have 7.7% greater fat depth than control barrows of marketing group 3. Pooled effects (across all 3 marketing groups) of feeding narasin tended (P = 0.08) to reduce loin depth by 1.1% (60.00 vs mm), but there were no effects on fat depth (P = 0.24) or estimated carcass lean (P = 0.11). Overall, narasin can be used during the last 85 d of feeding to increase feed efficiency of barrows and gilts with minimal impact on carcass composition. Key words: carcass, growth, marketing group, narasin, pig, Skycis 2015 American Society of Animal Science. All rights reserved. J. Anim. Sci : doi: /jas Introduction Ionophores are used in the beef industry to alter ruminal bacteria by modifying the movement of ions across biological membranes (Schelling, 1984). Similarly, ionophores function in swine by acting on gram-positive bacteria of the small intestine, which allows for improved protein utilization (Dierick et al., 1 Corresponding author: dboler2@illinois.edu Received May 15, Accepted August 18, ). Narasin, a polyether ionophore, is approved for use in swine to increase rate of weight gain when fed at to 30.0 mg/kg for at least 4 wk in the United States (FDA, 2012). Polyether ionophores have a hydrophilic interior and hydrophobic exterior; this allows the ionophore to attach to the cell membranes of gram-positive bacteria. The ionophore allows for the transport of Na +, K +, and H + across the cell membrane, leading to an increase in of [H + ] inside the bacterial cell (Russell, 1987). This inverts the ph gradient across the bacterial cell membrane, making the interior of the cell more acidic than the external environment,

2 Effects of narasin on performance of pigs 5029 impacting microbial cell homeostasis (Russell, 1987). This results in a reduction of the proportion of grampositive bacteria. Even though pigs are monogastric, the large intestine produces VFA that provide a source of energy (Argenzio and Stevens, 1984) that increases apparent nitrogen digestibility (Wuethrich et al., 1998) and ultimately improves growth performance. In a commercial setting, feeding 15 mg/kg narasin increased ADG by 1.5%, G:F by 1.8%, and HCW by 1.1% compared feeding 0 mg/kg narasin (Arentson et al., 2014). Inherent variation occurs in the BW of finishing pigs within a barn. Therefore, many producers market pigs in multiple groups to minimize the variation in BW, HCW, and carcass lean. Less is known about the effect of ionophores on swine performance and carcass characteristics in a split marketing system. Therefore, the objective was to evaluate feeding 15 mg/kg narasin for up to 85 d on growth performance and carcass composition of pigs sold in a 3-phase marketing system. Materials and Methods Experimental procedures for this experiment followed the guidelines stated in the Guide for Care and Use of Agricultural Animals in Agricultural Research and Teaching (FASS, 2010), with the exception of space allocation before the first marketing group to mimic current industry practices. A total of 1,232 pigs (barrows and gilts; PIC 337 sire PIC C22 dam; Pig Improvement Company, Hendersonville, TN) were allocated to single sex pens in a 2 2 factorial arrangement of treatments in a randomized complete block design experiment. A total of 56 single-sex pens were used and each pen initially housed 22 pigs. Pens were divided into 2 blocks, with block defined as initiation of treatment. The experiment had 2 dietary treatments; a diet formulated on a standard ileal digestible AA basis to meet NRC (2012) recommendations contained either 0 (control) or 15 mg/kg narasin (Skycis is a registered trademark of Eli Lilly and Company, Elanco Animal Health, Greenfield, IN) and was fed for 85 d (Table 1). Each treatment sex combination was replicated 14 times. Pigs were housed in a curtain-sided, naturally ventilated total confinement system with fully slatted concrete floors. Pen size was m 2, which resulted in 0.64 m 2 of floor space per pig. Gonyou et al. (2006) reported that at a k-value (k-value = area [m 2 ]/ BW0.667 [kg]) of or higher, the growth of a pig is no longer limited by space. The k-value at treatment initiation was (Table 2). Each pen had a single cup waterer and a 4-hole single-sided box feeder that provided a total of 122 cm of linear feeder space (5.55 cm/pig). Pigs were provided ad libitum access to feed and water for the duration of the 85-d feeding trial. Treatment diets were initiated when the population reached a mean BW of kg for block 1 and kg for block 2 and were continued until slaughter (up to 85 d). Pen BW were recorded 2 wk before initiation, at treatment initiation (0 d), and at d 28, 56, 64, 78, and 85 (termination) of the feeding trial (Fig. 1). Pen weights were recorded on both blocks. All pigs were evaluated by the investigators and considered sound and healthy before enrollment into the trial. Marketing Strategy Pigs used in the experiment were sold over 3 different marketing groups (Fig. 1; Table 2). In each pen, 18% (4 pigs per pen) of pigs were sold in the first marketing group (Day 64 of dietary treatment), 50% (11 of the original 22) were sold in the second marketing group (Day 78), and 32% (the remaining 7 pigs) were sold in the third marketing group (Day 85). First Marketing Period. The heaviest pigs in each pen (1 to 4, depending on the number of pigs remaining per pen; adjustments were made to account for morbidity and mortality loss) were marketed after 64 d on the feeding trial. Individual pigs were weighed in block 1, and the heaviest 1 to 4 pigs from each of the 28 pens were selected for marketing based on these individual weights. The heaviest 1 to 4 pigs from each of the 28 pens in block 2 were selected for slaughter based on visual appraisal per the production sites normal marketing procedure. Pigs selected for slaughter were tattooed, loaded on a truck, and transported to slaughter. Weight for the remaining pigs in each pen was recorded as the initial weight of the second marketing period. Each pen contained 18 pigs (0.78 m 2 floor space; k-value = ; Table 2) after the first marketing period. Second Marketing Period. The 11 heaviest remaining pigs in a pen, regardless of rank at the end of marketing group 1, were marketed in the second group after 78 d on the trial. Individual pigs were weighed in block 1, and the heaviest 11 pigs from each of the 28 pens were selected for marketing. The heaviest 11 pigs from each of the 28 pens in block 2 were selected for slaughter based on visual appraisal per the production sites normal marketing procedure. Pigs selected for slaughter were tattooed, loaded on a truck, and transported to slaughter. Weight for the remaining pigs in each pen (individual weights in block 1 and pen weights in block 2) were recorded as the initial weight of the third marketing period. Each pen contained 7 pigs (2.02 m2 floor space; k-value = ; Table 2) after the second marketing period. Third Marketing Period. On day 85 of the trial, all remaining pigs (7 per pen) in the barn were marketed. Individual weights were collected on pigs from block 1 and pen weights were collected on pigs from block

3 5030 Arkfeld et al. Table 1. Dietary composition, as-fed basis Phase 1 Phase 2 Phase 3 Days Narasin, mg/kg Item Ingredient, % Corn SBM, 1 48% CWG Monocalcium phosphate Limestone Salt l-lysine Alimet l-threonine Vitamin premix Mineral premix Narasin NRC ME, 5 Mcal/kg CP, % Total lysine, % SID 6 Lysine Available phosphorus, % Calcium, % SID Met + Cys:Lys SID Thr:Lys SID Trp:Lys SID Ile:Lys SID Val:Lys SBM = soybean meal. 2 CWG = choice white grease. 3 l-met precursor 2-hydrox-4-(methylthio) butanic acid (HMTBA), as an 88% aqueous solution of HMTBA (Novus International Inc., St. Louis, MO). 4 Trade name Skycis. Skycis is a registered trademark of Eli Lilly and Company (Elanco Animal Health), Greenfield, IN. 5 NRC (2012). 6 SID = standardized ileal digestible. 2. All pigs were tattooed, loaded on a truck, and transported to slaughter. Slaughter Procedures and Carcass Characteristics Pigs designated for slaughter in each marketing group were transported approximately 150 km to a federally inspected slaughter facility. Pigs were immobilized using carbon dioxide and exsanguinated. Data collected at the time of slaughter included HCW, back fat depth, loin depth, and estimated carcass lean. Carcass measurements were collected using a Fat- O-Meater system (Fat-O-Meater measurements; SFK Technology Fat-O-Meater, Herlev, Denmark) at approximately the 10th rib. Carcass yield (dressing percentage) was calculated by dividing the HCW by ending live weight collected at the farm and multiplied by 100. Estimated carcass lean was calculated using a proprietary plant equation. Statistical Analysis Data were analyzed as a randomized complete block design with 2 treatments. Pen served as the experimental unit for all response parameters and the model included the fixed effects of sex, diet, and sex diet interaction. Block and replicate nested within block were considered random variables. Carcass data from marketing group 3, block 2, was not included in the data set as pigs were unable to make it to the plant on time due to inclement weather. Therefore, analysis for carcass traits in marketing phase 3 included only replicate as a random effect. Least squares means and SE were calculated using the mixed procedure of SAS (SAS Inst. Inc., Cary, NC). Mean separation was conducted using the PDIFF option. Statistical differences were considered significant at P 0.05 and were considered tendencies at P 0.10 using a 2-tailed test. Due to the design of this study, no statistical inferences

4 Effects of narasin on performance of pigs 5031 Table 2. Summary of housing conditions and marketing strategy of pigs fed either narasin or a control diet and sold in 3 marketing groups 1 Narasin, mg/kg Item 0 15 Pens of group weighed pigs, no Initial number of pigs per pen, no First marketing period Days on feed Feeder space per pig, cm Floor space per pig, m Beginning k-value Concluding k-value Approximate number of pigs sold/pen 4 4 Second marketing period Days on feed Feeder space per pig, cm Floor space per pig, m Beginning k-value Concluding k-value Approximate number of pigs sold/pen Third marketing period Days on feed Feeder space per pig, cm Floor space per pig, m Beginning k-value Concluding k-value Approximate number of pigs sold/pen k-value = area (m2)/bw0.667 (kg). At a k-value of , growth is no longer believed to be limited by space (Gonyou et al., 2006) can be made on differences among marketing groups. However, due to the nature of the marketing strategy of the U.S. swine industry, it is important to characterize general tendencies across marketing groups. Results and Discussion Growth Performance Incorporation of ionophores into finishing cattle diets for increased growth and performance has been extensively studied. In a ruminant animal, ionophores work to alter rumen function by modifying movement of ions across biological membranes of endogenous bacteria (Schelling, 1984). The method by which movement of ions across a biological membrane is modified is ionophore dependent and is usually a result of ionophore structure. Polyether ionophores have a hydrophilic interior and hydrophobic exterior; this allows the ionophore to attach to the cell membranes of gram-positive bacteria. This results in a reduction of the proportion of gram-positive bacteria. In the rumen, this results in an increase in propionic acid and a decrease in acetic and butyric acids (Richardson et al., 1976). Although pigs are monogastric, their large intestine produces VFA and may provide an important source of energy (Argenzio and Stevens, 1984), similar to a ruminant animal. Furthermore, swine respond similar to cattle when fed polyether ionophores. Wuethrich et al. (1998) reported that feeding narasin to swine resulted in increased relative concentrations of propionic acid in the large intestine. Feeding narasin also resulted in increased apparent nitrogen digestibility (Wuethrich et al., 1998). Overall Performance. The results in the current experiment show a 2.0% increase in overall ADG (0 85 d) of barrows fed narasin compared with barrows fed the control diet (P < 0.01; Table 3). No difference (P = 0.69) in overall ADG (0 85 d) was observed in gilts (P = 0.69; Table 3). These results differ from previous research in a commercial setting that suggested feeding 15 mg/ kg narasin resulted in 1.5% greater ADG compared with a control diet (0 mg/kg narasin), regardless of sex (Arentson et al., 2014). Although a response in overall ADG was not observed in gilts fed narasin, pigs fed narasin had 1.3% increased G:F (P = 0.03), regardless of sex. Growth performance (ADG, ADFI, Feed:Gain, and G:F) was not affected (P 0.15) by dietary narasin inclusion during phase 1 or 2 of the feeding trial. Marketing Group Performance. In the first marketing group, barrows fed narasin had a greater ADFI than gilts fed narasin (P < 0.01) whereas there was no difference due to sex of pigs in the control diet (P = 0.96). No effects (P 0.11) of diet were observed for growth characteristics in marketing groups 2 and 3. Although no parallels can be drawn between the treated diet of the current study and other studies that have incorporated a 3-phase marketing system, comparisons between control pigs can be made. The current study, similar to studies by Christianson et al. (2014) and Gerlemann et al. (2014), marketed pigs of the first marketing group 1 wk after initiation of the third dietary phase (finishing phase) and marketed the second group 2 wk after the first marketing group. However, unlike the aforementioned studies, the current work marketed the final group of pigs 1 wk after the second cut whereas Christianson et al. (2014) and Gerlemann et al. (2014) marketed the final group of pigs 2 wk after the second marketing group. Despite a marketing strategy with similar intervals, there were differences in growth characteristics among the studies. Carcass Characteristics Overall pooled effects of all marketing groups suggested little impact on carcass composition due to diet (Table 4). A tendency did exist for carcasses from pigs fed the narasin diet to have a 1.1% reduction in loin depth when compared with pigs fed the control diet (P = 0.08). However, all other pooled carcass compo-

5 5032 Arkfeld et al. Figure 1. Timeline of experiment. Study length was 85 d and consisted of 3 dietary phases with 3 marketing groups within the third dietary phase. sition traits were not impacted by diet (P 0.11). No significant diet or diet sex interactions (P 0.08) were observed for carcass characteristics in marketing groups 1 and 2. In marketing group 3, a diet sex interaction existed (P = 0.04) for estimated carcass lean; barrows fed narasin had decreased estimated carcass lean compared with barrows fed the control diet (P < 0.01). This is likely due to the tendency (P = 0.06) for narasin-fed barrows to have 7.7% greater fat depth than control barrows of marketing group 3 (data not presented in tabular form). However, pooled across marketing groups, there was no effect of feeding narasin on fat depth of both barrows and gilts (P = 0.24). Sex Effects. Overall, barrows tended to have 2.18 kg heavier HCW (P = 0.08), 0.50 percentage units less carcass yield (P < 0.01), 1.73 percentage units less estimated carcass lean (P < ), 2.4% less loin depth (P = 0.05), and 19.1% greater fat depth (P < ) than gilts. This agrees with previous research where gilts were leaner at the 10th rib but had greater loin depth and estimated carcass lean measures than barrows (Boler et al., 2014). Floor Space Due to the design of this study, no statistical inferences can be made on differences among marketing groups. However, pigs from the second marketing period have numerically greater ADG than those from the first marketing period (Table 3). It is interesting to speculate that this might be attributed to allotted floor space per pig. In the current study, removal of the heaviest 18% of pigs in the first marketing group (n = 4 pigs per pen) resulted in an 4.7% increase in ADG, 5.1% increase in G:F, and 4.2% decrease in ADFI in the period between the removal of the first and second marketing groups, regardless of dietary treatment. However, although removal of the second marketing group (n = 11 pigs per pen) resulted in a 159.0% increase in floor space, ADG was decreased by 14.3%, ADFI was increased by 17.0%, and G:F was decreased by 25.8% in the period between the removal of the second and third marketing groups, regardless of dietary treatment. Previous research has suggested that when floor space is increased by 30% (by removing the heaviest 5 pigs in the pen), a 5.4% improvement occurred in ADG (Gerlemann et al., 2013), and an 18.8% increase in floor space (by removing the heaviest 4 pigs from the pen) improved ADG by nearly 20% (Gerlemann et al., 2014). Furthermore, Christianson et al. (2014) reported a 15.9% improvement in ADG and 7.8% improvement in G:F by removing 26% of the pigs from each pen. The aforementioned measures do not account for the size of the pig in the allotted pen space; therefore, it is important to gain an understanding of what factor the size of the animal plays in these growth changes due to marketing group. Gonyou et al. (2006) reported that at a k-value (k-value = area [m 2 ]/ BW0.667 [kg]) of or less, pigs experienced reductions in growth due to space limitation. Although, initially, the k-value in the current study (0.0483; Table 2) is less than this level, at the time of removal of the first marketing group from the barn, k-value had been reduced to , which may have limited maximum growth potential of the pigs in the pen. By removing the heaviest pigs from the pen (approximately 4 per pen), it allowed for an increase in k-value to and a numerical increase in ADG was observed. Similar results were reported by Christianson et al. (2014), where growth potential was potentially limited before removal of the first marketing group (k-value = 0.026) but after removal of the heaviest 25.7% of the pigs, the k-value was returned to a level that allowed for maximum growth potential (k-value = 0.033). It

6 Effects of narasin on performance of pigs 5033 Table 3. Effects of narasin on growth characteristics of barrows and gilts when sold in 3 marketing groups Diet Sex Diet sex Barrow Gilt Level of narasin 1 0 mg/kg 15 mg/kg 0 mg/kg 15 mg/kg P-values SEM Pen, no. 2 Overall pooled effects 3 Day 56 live weight, kg ab a b b Day 64 live weight, kg < Day 78 live weight, kg ab a bc c < Day 85 live weight, kg Concluding live weight, kg < ADG (Day 0 85), kg 0.99 b 1.01 a 0.97 c 0.96 c < ADFI (Day 0 85), kg < F:G 4 (Day 0 85) 3.01 a 2.94 b 2.84 c 2.83 c < G:F (Day 0 85) < Phase 1 (Day 0 28) Beginning live weight (Day 0), kg Day 28 live weight, kg ADG (Day 0 28), kg ADFI (Day 0 28), kg < F:G (Day 0 28) 2.62 a 2.56 b 2.43 c 2.44 c < G:F (Day 0 28) < Phase 2 (Day 29 56) Day 29 live weight, kg Day 56 live weight, kg ab a b b ADG (Day 29 56), kg ADFI (Day 29 56), kg < F:G (Day 29 56) 3.07 a 3.01 a 2.85 b 2.87 b < G:F (Day 29 56) b b a a < Phase 3 First marketing period (Day 64) Concluding live weight (Day 64), kg < ADG (Day 57 64), kg < ADFI (Day 57 64), kg 3.28 ab 3.39 a 3.29 ab 3.15 b F:G (Day 57 64) G:F (Day 57 64) a ab b ab Second marketing period (Day 78) Concluding live weight (Day 78), kg a a b b < ADG (Day 65 78), kg < ADFI (Day 65 78), kg < F:G (Day 65 78) G:F (Day 65 78) Third marketing period (Day 85) Concluding live weight (Day 85), kg ADG (Day 79 85), kg ADFI (Day 79 85), kg < F:G (Day 79 85) G:F (Day 79 85) a c Means with differing superscripts differ by P Trade name Skycis. Skycis is a registered trademark of Eli Lilly and Company (Elanco Animal Health), Greenfield, IN. 2 Pens originally housed 22 pigs per pen. 3 Overall mean include data from treatment initiation (Day 0) through study termination (Day 85). 4 F:G = Feed:Gain.

7 5034 Arkfeld et al. Table 4. Effects of narasin on carcass characteristics of barrows and gilts sold in a 3-phase marketing system Narasin, 1 mg/kg Sex 0 15 Barrow Gilt P-values Pen, no. Pen, no. Diet Trait SEM SEM Diet Sex sex Pooled effects HCW, kg Carcass yield, % < Loin depth, mm Fat depth, mm < Estimated carcass lean, % < First marketing period HCW, kg Carcass yield, % < Loin depth, mm < Fat depth, mm < Estimated carcass lean, % < Second marketing period HCW, kg < Carcass yield, % < Loin depth, mm < Fat depth, mm < Estimated carcass lean, % < Third marketing period HCW, kg Carcass yield, % Loin depth, mm Fat depth, mm < Estimated carcass lean, % <0.01 < Trade name Skycis. Skycis is a registered trademark of Eli Lilly and Company (Elanco Animal Health), Greenfield, IN. has also been suggested that removal of pigs results in increased growth rate as a consequence of increased feed intake and improved feed utilization (DeDecker et al., 2005). Although space was adequate in marketing group 3 (Table 2) and ADFI was numerically the greatest of any marketing group, pigs from marketing group 3 had the numerically poorest ADG and greatest ADFI, resulting in the poorest G:F. Similar to results of Christianson et al. (2014) and Gerlemann et al. (2013), it is hypothesized in the current study that added space could not compensate for poorer animal efficiency inherent in pigs in marketing group 3. Implications Feeding narasin for up to 85 d had little impact on growth performance within marketing group but did increase overall ADG in barrows by 2.0%. Regardless of sex, narasin improved feed efficiency by 1.3% over the 85-d feeding period. Although differences were observed within marketing groups, overall pooled results suggest feeding narasin did not change carcass characteristics of finishing pigs. Therefore, narasin at 15 mg/kg inclusion in a swine diet can be used for the improvement in ADG of barrows and improvement in feed efficiency of both sexes while having little impact on carcass composition. Literature Cited Arentson, R. A., J. J. Chewning, S. N. Carr, M. C. Brumm, and E. G. McMillan Effect of Skysis and Stafac on growth and carcass performance of finishing pigs A meta analysis. In: Abstracts from ASAS Midwestern Section and ADSA Midwest Branch Conference Proceedings, March 17 19, 2014, Des Moines, IA. J. Anim. Sci. 92(Suppl. 2): Argenzio, R. A., and C. E. Stevens The large bowel A supplementary rumen? Proc. Nutr. Soc. 43: doi: / PNS Boler, D. D., C. L. Puls, D. L. Clark, M. Ellis, A. L. Schroeder, P. D. Matzat, J. Killefer, F. K. McKeith, and A. C. Dilger Effects of immunological castration (Improvest) on changes in dressing percentage and carcass characteristics of finishing pigs. J. Anim. Sci. 92: doi: /jas

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