Final Report February 11, 2017 I. Project Title: Do old floor space allowances apply to modern finishing pigs marketed at 300 lb? Principle Investigator: Institution: Lee Johnston University of Minnesota Co-Principle Investigators: Dale Rozeboom, Michigan State Univ. Bob Goodband, Kansas State Univ. Steve Moeller, Ohio State Univ. Marcia Shannon, Univ. of Missouri Sarah Schieck, Univ. of Minnesota Extension II. Abstract: Current floor space allowances were determined in research studies conducted 10 to 20 years ago using pigs that were marketed at a body weight of no more than 250 pounds. Currently, pork producers are regularly marketing pigs that weigh over 280 pounds and often weigh 300 pounds. Given this precipitous increase in market weight, an obvious question is: Do the old floor space allowances still apply for modern production scenarios? To answer this question, we conducted two experiments. Study 1 was conducted at 5 research stations throughout the upper Midwest region. In this study, we evaluated the growth performance and welfare of pigs weighing between 60 and 300 pounds that were provided 7.6, 8.6, 9.6, 10.6 or 11.6 ft 2 /pig of floor space. Neither daily weight gain (range = 2.12 to 2.19 pounds), daily feed intake (range = 5.85 to 6.04 pounds) nor gain:feed (range 0.352 to 0.365) were influenced by the floor space allowances studied. Similarly, salivary cortisol concentrations (a measure of chronic stress in pigs) and lesion scores were not affected by floor space allowances. Based on previous prediction equations of Gonyou et al. (2006), we predicted pigs would not feel the negative effects of crowding until pigs reached 210 pounds body weight. So, about 62% of the total weight gain in Study 1 was under conditions that were not crowded. This period of early growth in un-crowded conditions likely masked any negative effects of crowding that might have been present at the end of the growing-finishing period. Therefore, we conducted Study 2 at four research stations that focused on growth performance of pigs weighing about 300 pounds. Pigs weighing about 293 pounds were assigned to pens that provided 7.6, 8.6, 9.6, 10.6, or 11.6 ft 2 /pig of floor space. After a 2- week growth period the study was terminated. Increasing floor space significantly increased average daily gain (1.89, 2.09, 2.09, 2.43, and 2.34 lb/d) and average daily feed intake (6.68, 7.19, 7.10, 7.70, and 7.17 lb/d) in a linear manner as floor space allowance increased. Results of Study 2 suggest that the optimal floor space allowance for pigs weighing about 300 pounds is 10.6 ft 2 /pig. Based on the results of the two experiments conducted in this project, it appears that the equation of Gonyou et al. (2006) used to predict floor space allowances for growing-finishing pigs based on their body weight is still valid for pigs marketed at about 300 pounds. Under commercial conditions when pens are topped, there will likely be
little if any depression of pig performance or welfare when using the Gonyou equation to determine floor space allowance. III. Introduction: During the 1990 s and early 2000 s, the North Central Regional research committee on Swine Confinement Management (NCR-89) and others conducted several studies to evaluate the impacts of various floor space allowances for growing-finishing pigs. These studies focused on pig performance, pig welfare, and economics of floor space allowance for pigs marketed at about 250 pounds live weight or less. Using data generated in these studies, researchers developed a mathematical equation to predict floor space requirements for optimal pig performance based on body weight of pigs. This equation determined that a market pig weighing about 250 pounds needed 8.5 ft 2 of floor space. Theoretically, this approach to determining floor space requirements should apply to a wide range of body weights but the equation was based on experiments that studied pigs to a final market weight of about 250 pounds. The utility of this equation for pigs weighing 300 pounds and heavier has not been determined. Currently, pigs are marketed at much greater body weights than were studied in earlier experiments on floor space. According to USDA, average slaughter weight for market hogs was 283 pounds in 2015. Anecdotal reports from various industry sources indicate that many groups of pigs are marketed at an average weight of 300 pounds which means that some pigs in the group weighed closer to 320 pounds or more at marketing. So, an obvious question posed by pork producers and industry professionals is: Do the floor space allowances provided when pigs are marketed at 250 pounds still apply in current marketing scenarios involving pigs weighing 300 pounds? This was the core question addressed in this research project. This question is a complex one and very important on several fronts. Economics is a very important driver of most decisions in a pork production system and floor space allowance is no exception. Once pigs begin to sense crowded conditions, individual growth performance typically declines with declining floor space allowance. However, within practical limits, the total output from a given amount of floor space measured as pounds of pork produced and the net revenue generated from that space increases as pigs are increasingly crowded. Therefore, this phenomenon drives producers to crowd pigs in barns with high capital costs so that fixed costs are spread over greater output (pig weight). However, economics is not the only factor to consider in floor space allowance. Welfare of each individual pig needs to be considered in the floor space allocation decision. Decreasing floor space allowance can cause an increase in incidence of behavioral vices such as tail biting, frequency of lesions on pigs, and the chronic stress experienced by pigs. All these responses indicate some degree of compromised welfare for individual pigs. Certainly, welfare of individual pigs is an important characteristic of a pork production system that producers and barn staff monitor daily. Monitoring welfare of individual pigs has come into increased prominence with the adoption of pig production site assessments under the PQAPlus program and packer-instituted audits of pork production sites. So, selecting the correct floor space allowance for growingfinishing pigs is a balancing act among economic considerations, growth performance of pigs, and welfare of individual pigs in the barn. 2
IV. Project Objective: The overall objective of this project is to determine the proper floor space allowance for growing-finishing pigs that are marketed at 300 pounds live weight. Specific objective 1: In Study 1, we will determine the effects of floor space allowance on growth performance and welfare of pigs throughout the growing-finishing period when marketed at an average pen live weight of 300 pounds. Specific objective 2: In Study 2, we will determine the effects of floor space allowance on growth performance of pigs weighing 300 pounds. V. Procedures: In this project, we conducted two experiments. The first experiment (Study 1) was a growth performance experiment designed to determine the effects of floor space allowance on pigs from about 60 pounds bodyweight to marketing at an average pen weight of 300 pounds. The second experiment (Study 2) was designed to specifically study the effects of floor space allowance on growth performance of pigs weighing 300 pounds without any influences from earlier portions of the growing-finishing period. Study 1 was conducted at five cooperating stations (Table 1) under a common protocol. Due to problems with availability of pigs, Study 2 was conducted at four cooperating stations (Table 2) under a common protocol. Study 1: At about 60 pounds body weight, pigs were blocked by weight, assigned to pens, and pens were assigned randomly within weight block to floor space treatments. Floor space treatments were: 7.6, 8.6, 9.6, 10.6, and 11.6 ft 2 /pig. A variance of + 0.25 ft 2 /pig was permitted to accommodate differences in gating and flooring designs across stations. Floor space allowances did not include space occupied by the feeder. Floor space treatments were imposed from initiation of the study until average weight of pigs in the pen reached 300 pounds. Floor space treatments were achieved by adjusting pen size for a constant group size across all treatments. Group size varied across participating stations but was constant across treatments within a replicate at each station. Standard management protocols observed at each participating station were followed throughout this experiment. Pigs had ad libitum access to dry feed and water throughout the entire experiment. Feeding program (diet formulations, number of phases, phase breaks, etc.) were determined by each station and were standardized across floor space treatments with the stipulation that nutrient requirements described by NRC (2012) were satisfied. All stations used diets based on corn, soybean meal and in some cases DDGS. Ractopamine was not fed at any point in the experiment. There was no topping of pens before the pen average body weight reached 300 pounds. The experiment ended when the average body weight of pigs in a pen reached 300 pounds. If a pig died or was removed for welfare reasons, pen size was adjusted to maintain the appropriate floor space allowance. Pigs were weighed individually and feed disappearance measured on a pen basis every two weeks throughout the experiment. From these data, average daily gain (ADG), average daily feed intake (ADFI; pen basis) and gain to feed ratio (G:F; pen basis) were 3
calculated. Coefficient of variation for live weight within pens was calculated at the beginning and end of the experiment. By suspending cotton ropes in each pen, saliva samples were collected on 3 separate days throughout the trial: when pen weight averaged about 175 pounds, 2 weeks prior to harvest and the week of harvest. After pigs chewed on the ropes, saliva was harvested and frozen for subsequent analysis. Saliva samples were analyzed for cortisol concentration by Salimetrics (State College, PA). During periods of normal barn activities, animal care staff watched for signs of estrus at stations that included gilts in the study. Incidence of mortality and morbidity were recorded throughout the experiment. Incidence of lameness was recorded subjectively using the following scale: 1 = normal walking; 2 = slight lameness, may have an arched back; 3 = obviously limping, but able to keep up with penmates when the group is walking; 4 = not able to keep up with penmates due to lameness; and 5 = can barely walk. Lesion scores as defined by Li and Gonyou (2013) were recorded for all pigs during the last week of the study according to the following scale: 1 = no cut, swelling, or previous wounds have healed; 2 = minor cut, slight swelling, or presence of scabs; and 3 = major cut, remarkable swelling, or open wounds. Lesion scores were recorded only at Minnesota and Ohio. Each station provided data from at least two replications for each treatment (Kansas provided six replications of each treatment). Because data were not normally distributed, the Glimmix procedure of SAS was used to analyze performance data. The statistical models included the fixed effects of floor space treatments with station included as a random effect. Repeated measures analysis was used for analysis of growth performance and salivary cortisol data. Pen nested within station served as the experimental unit in all analyses. Study 2: Pigs weighing about 300 pounds were selected for this experiment and assigned randomly to pens. Group size was constant across treatments within station but was not the same as in Study 1. Except for the Ohio station, pigs used in Study 1 were not used in this experiment. All pigs were allowed 7 days to re-establish their social hierarchy in pens that provide 11.6 ft 2 /pig. At the end of the acclimation period, pen size was adjusted to the pre-assigned treatment that provided 7.6, 8.6, 9.6, 10.6, or 11.6 ft 2 of floor space per pig. Pigs were weighed individually at the start of the experiment and 14 days later at the end of the experiment. Feed disappearance was measured on a pen basis when the experiment was terminated. From these data, ADG, ADFI, and G:F were calculated. Mortality, morbidity, and incidence of lameness were recorded as described for Study 1. Four stations contributed data from two replicate pens for each floor space treatment. Similar to Study 1, the Glimmix procedure of SAS was used to analyze growth performance data. The statistical model included the fixed effect of floor space allowance and station as a random effect. Pen nested within station was considered the experimental unit. VI. Results and Discussion: This experiment was conducted under a standardized protocol at 4 or 5 university research centers. This cooperation allowed greater replication of experimental treatments than is possible at any single institution, and provided replications across a broader area 4
of the upper Midwest region of the country. This approach lends greater credibility to the results compared with conducting the experiment at only one location. As expected, there were differences in most response variables among stations; however, with few exceptions, there were no station by floor space treatment interactions. This lack of station by treatment interactions suggests that the effects of floor space are consistent across stations. Since the effects of floor space were the primary interest of this experiment, station effects are ignored in the presentation of results. Study 1: Initial weight of pigs was not different across floor space allowances; however, there was a linear increase in final body weight of pigs (Table 3). As floor space allowance increased, so did the final body weight of pigs. Initial and final coefficients of variation were not different across the floor space allowances studied in this experiment. Neither average daily weight gain, average daily feed intake, nor gain:feed over the entire experiment were significantly influenced by floor space treatments. There were no significant effects of floor space allowance during the 16 weeks before marketing on average daily gain, average daily feed intake or gain:feed (Figures 1, 2, and 3, respectively). Strictly from a growth performance perspective, these data suggest that growth of pigs was unaffected by floor space allowances ranging from 7.6 to 11.6 ft 2 /pig through marketing at about 300 pounds. However, pig welfare also needs to be considered. We collected saliva samples from pigs to determine the cortisol concentration of the saliva. Cortisol is considered a reliable indicator of chronic stress in pigs. We collected the first sample when pigs weighed about 175 pounds because pigs assigned to all treatments had sufficient floor space according to the equation of Gonyou et al. (2006). This sample served as an initial assessment of baseline salivary cortisol in the pigs. Subsequent samples were collected 2 weeks before the end of the experiment and in the final week of the experiment when pigs should have experienced varying levels of crowding and presumably different degrees of stress. As expected, there were no differences in initial salivary cortisol concentration across floor space treatments (Table 4). Similarly, there were no differences in salivary cortisol due to floor space allowances in the final two weeks of the experiment when pigs should have experienced the greatest differences in crowding among treatments. Also noteworthy, there did not appear to be a noticeable increase in salivary cortisol that one might expect as pigs become more crowded with increasing body weight. Gross measures of pig health did not seem to be affected by floor space allowance (Table 5). The incidence of pigs that were removed from the experiment for welfare reasons, dead pigs, pigs with skin lesions or lameness were not different across floor space treatments. Similarly, the number of days pigs required injectable therapy were not influenced by floor space allowance. Based on the growth performance and pig welfare data collected in Study 1, an optimal floor space recommendation is not apparent. It appears that pigs marketed at 300 pounds can adapt to floor space allowances ranging from 7.6 to 11.6 ft 2 /pig. The equation of Gonyou et al. (2006) estimates that 300-pound pigs require 9.6 ft 2 of floor space. So, this study provided two treatments below and two treatments above the predicted requirement. Our data seem fairly clear that pigs in this study did not respond to floor space allowances greater than the predicted need of 9.6 ft 2 with improved growth performance or welfare. Similarly, performance and welfare of pigs did not deteriorate 5
significantly as floor space allowances declined to 8.6 and 7.6 ft 2. The lack of detrimental effects of restricted floor space allowances might be explained by the extended period during which pigs were not crowded in this experiment. The most restrictive floor space allowance (7.6 ft 2 /pig) would be sufficient to accommodate a pig weighing 210 pounds according to Gonyou et al. (2006). Theoretically, no pig would have experienced crowding until they reached a body weight of 210 pounds. So, for the first 150 pounds of body weight gain pigs assigned to the 7.6 ft 2 treatment would not have been crowded. This represents 62% of the total gain (300 lb final wt. 60 lb beginning wt.) achieved by pigs in the study. The acceptable growth performance during this relatively long period with no crowding could have masked any negative effects of crowding on growth performance near the end of the study. We anticipated this phenomenon would occur which was the motivation to design and conduct Study 2. Study 2: The primary objective of this study was to focus on the floor space requirements of pigs weighing 300 pounds. Initial body weight of pigs was not different across floor space treatments but we observed a linear increase (P < 0.01) in final body weight at the end of the 2-week period with increasing floor space allowance (Table 6). Similarly, increasing floor space allowance elicited a linear increase (P < 0.01) in ADG and ADFI of pigs. We also observed a quadratic increase (P < 0.05) in ADFI with increasing floor space allowance with maximal feed intake occurring at 10.6 ft 2 /pig. Floor space treatments had no effect on efficiency of gain in this study. Results of Study 2 suggest that the optimal floor space allowance for pigs weighing just over 300 pounds (308 pounds overall average in Study 2) appears to be 10.6 ft 2 /pig. We are aware of only one report in which floor space allowance for pigs weighing up to 300 pounds was studied (Brumm and NCR-89, 1996). These authors concluded that optimal performance of barrows marketed at 300 pounds was achieved when pigs were provided 9.0 to 10.7 ft 2 of floor space. VII. Summary and Conclusions Results of Study 1 did not indicate a floor space allowance that clearly optimized pig growth performance. This outcome is probably due to the diluting effects of the early growth period when floor space allowances were not predicted to crowd pigs. Furthermore, measures of pig welfare evaluated in Study 1 (lesion scores, lameness, salivary cortisol, morbidity and mortality) similarly did not indicate one floor space allocation that optimized pig welfare. In Study 2, growth performance of pigs that averaged 308 pounds of body weight was maximized at 10.6 ft 2 /pig. Based on the results of the two experiments conducted in this project, it appears that the equation of Gonyou et al. (2006) used to predict floor space allowances for growing-finishing pigs based on their body weight is valid for pigs marketed at about 300 pounds. Under commercial conditions when pens are topped, there will likely be little if any depression of pig performance or welfare when using the Gonyou equation to determine floor space allowance. 6
VIII. Citations Brumm, M. C. and NCR-89 Committee on Management of Swine. 1996. Effect of space allowance on barrow performance to 136 kilograms body weight. J. Anim. Sci. 74:745-749. Gonyou, H. W., M. C. Brumm, E. Bush, J. Deen, S. A. Edwards, T. Fangman, J. J. McGlone, M. Meunier-Salaun, R. B. Morrison, H. Spoolder, P. L. Sundberg, and A. K. Johnson. 2006. Application of broken-line analysis to assess floor space requirements of nursery and grower-finisher pigs expressed on an allometric basis. J. Anim. Sci. 84:229-235. Li, Y. Z., and H. W. Gonyou. 2013. Comparison of management options for sows kept in pens with electronic feeding stations. Can. J. Anim. Sci. 93:445-452. NRC. 2012. Nutrient Requirements of Swine. 11 th rev. ed. Natl. Acad. Press, Washington, DC. Acknowledgement: The authors appreciate the efforts of Ms. Adrienne Hilbrands for her skillful work in data management and statistical analysis in the completion of this project. This project was supported financially by Pork Checkoff funds distributed through the Minnesota Pork Board. 7
Table 1. Participating stations (Study 1) Station No. of replicates No. of pigs/pen Starting date Duration of experiment, days Initial pig wt., lb Final pig wt., lb Kansas 6 6 or 7 7/20/15 90 84.6 297.7 Michigan 2 11 12/19/15 114 48.2 310.0 Minnesota 2 19 3/11/16 126 55.6 307.0 Missouri 2 10 11/20/15 125 and 126 52.8 318.8 and 2/5/16 Ohio 2 11 12/23/15 and 5/11/16 105 54.5 295.8 Table 2. Participating stations (Study 2) Station No. of replicates No. of pigs/pen Starting date Initial pig wt., lb Final pig wt., lb Kansas 2 6 or 7 11/27/16 271 303 Michigan 2 11 9/30/16 297 332 Minnesota 2 8 7/18/16 296 321 Ohio 2 4 or 5 4/13/16 and 8/31/16 310 and 309 339 and 340 8
Table 3. Effects of floor space allowance on pig performance over the entire growing-finishing period (Study 1) Floor space allowances (ft 2 /pig) Trait 7.6 8.6 9.6 10.6 11.6 SE Significance (P < ) 1 Body weight, lb: Beginning 58.9 59.1 59.0 59.3 59.5 0.88 NS 2 Final 303.0 301.5 309.3 306.5 309.0 2.46 Trt. (0.10); Lin. (0.04) Coefficient of variation, % Beginning 4.85 5.14 5.06 5.17 4.82 0.75 NS Final 7.46 6.45 7.19 7.74 7.91 0.58 NS Average daily gain, lb 2.14 2.12 2.19 2.16 2.19 0.02 Trt. (0.14); Lin. (0.06) Average daily 5.85 5.86 5.94 5.93 6.04 0.072 NS feed intake, lb Gain:feed 0.365 0.361 0.361 0.358 0.352 0.004 Trt. (0.13); Station x Trt (0.05); Lin. (0.05) 1 Trt. = Floor space treatment effects; Lin. = Linear effects of floor space treatments; Station effects (P < 0.001) for all traits measured. 2 NS = not significant, (P > 0.15).
Table 4. Effect of floor space allowance on salivary cortisol concentration (µg/dl) of pigs (Study 1) Floor space allowances (ft 2 /pig) Sampling time 7.6 8.6 9.6 10.6 11.6 SE Significance (P < ) 1 Initial 2 0.194 0.228 0.183 0.195 0.212 0.009 Trt. (NS) 2 wk before 0.211 0.241 0.255 0.215 0.211 0.011 Time (0.08) marketing 1 wk before marketing 0.216 0.165 0.211 0.169 0.203 0.009 Trt. x Time (NS) Station (0.01) 1 Trt. = Floor space treatment effects; NS = not significant (P > 0.15); Time = Effect of time of sampling; Station = Effect of station. 2 Sample collected when pigs assigned to 7.6 floor space allowance weighed about 175 lb. 10
Table 5. Effect of floor space allowance on pig mortality, morbidity, lesion scores, and incidence of lameness (Study 1) Floor space allowances (ft 2 /pig) Trait 7.6 8.6 9.6 10.6 11.6 No. of pigs 144 144 144 144 138 No. of pigs 3 4 3 2 2 removed No. dead pigs 6 2 0 1 4 No. of days pigs 31 22 21 16 39 treated 1 No. of pigs with 28 15 19 18 19 lesions 2 Average lesion 1.62 1.38 1.44 1.44 1.44 score 3 No. of pigs with lameness score > 1 4 5 3 5 3 3 1 Number of days pigs required injectable therapy due to ill health. 2 Number of pigs with at least one lesion observed at some time during the experiment. A single pig could be counted more than once if fresh lesions appeared. Only data from 30 pigs per treatment in Ohio and Minnesota are included. 3 Lesion scoring system was: 1 = no cut, swelling, or previous wounds have healed; 2 = minor cut (cut does not go through the skin), slight swelling (skin is red with inflammation), presence of scabs; 3 = major cut (cuts through the skin), remarkable swelling, or open wounds. Floor space treatment was not significant (P < 0.15; SE = 0.147) 4 Lameness data for last week before marketing. Lameness scoring system was: 1 = Normal walking; 2 = Slight lameness, may have an arched back; 3 = Obviously limping, but able to keep up with penmates when group is walking; 4 = Not able to keep up with penmates due to lameness; 5 = Can barely walk. 11
Table 6. Effects of floor space allowance on performance of pigs two weeks before marketing (Study 2) Floor space allowances (ft 2 /pig) Trait 7.6 8.6 9.6 10.6 11.6 SE Significance (P < ) 1 Body weight, lb: Beginning 294.5 292.1 293.5 292.8 293.2 1.56 NS 2 Final 321.0 321.3 322.9 326.9 326.0 1.41 Trt. (0.05) Lin. (0.01) Average daily 1.89 2.09 2.09 2.43 2.34 0.09 Trt. (0.01); gain, lb Average daily feed intake, lb Lin. (0.01) 6.68 7.19 7.10 7.70 7.17 0.13 Trt. (0.01); Station x Trt (0.05); Lin. (0.01); Quad. (0.05) Gain:feed 0.264 0.278 0.283 0.304 0.317 0.015 NS 1 Trt. = Floor space treatment effects; Lin. = Linear effects of floor space treatments; Quad. = Quadratic effects of floor space treatments; Station effects (P < 0.001) for all traits measured except Gain:feed. 2 NS = not significant, (P > 0.15). 12
Figure 1. Average daily gain of pigs provided different floor space allowances during the 16 weeks before marketing (Time effect, P < 0.01; Station effect, P < 0.01; SE = 0.84). Figure 2. Average daily feed intake of pigs provided different floor space allowances during the 16 weeks before marketing (Time effect, P < 0.01; Station effect, P < 0.01; SE = 0.16).
Figure 2. Gain:feed of pigs provided different floor space allowances during the 16 weeks before marketing (Time effect, P < 0.01; Station effect, P < 0.01; SE = 0.01). 14