Alternative Pork Production Systems: Overview of Facilities,

Performance Measures, and Meat Quality

Jessica G. Gentry¹ and John J. McGlone²

¹Middle Tennessee State University, Murfreesboro, TN, USA 37132

²Pork Industry Institute, Texas Tech University, Lubbock, TX, USA 79409-2141

http://www.pii.ttu.edu

Correspondence: jggentry@mtsu.edu or john.mcglone@ttu.edu

Paper presentated at the 3^rd International Meeting on Swine Production, Universidade

de Trás-os-Montes e Alto Douro, April 4-5, 2003, Vila Real, Portugal.

Introduction

Intensive outdoor pig production systems have been considered in recent years in some parts of the world. These alternatives to traditional slatted-floor indoor systems may become more common as environmental and/or animal welfare regulations increase. The swine industry in North America has changed dramatically over the past 10 years as swine farms were consolidated and the number of swine farms declined. Environmental concerns linked to swine production have increased in the United States and in other countries. In large swine-producing areas, producers have faced increased costs to meet environmental regulations relative to swine manure, waste and odor management (Beghin and Metcalfe, 1998). Increased costs for environmental compliance may limit expansion of confinement farms in the near future. Outdoor swine finishing systems have been used in European nations and on a smaller scale in the United States and other countries for several years. Sustainability goals, awareness of animal welfare issues, and interest in niche retail marketing opportunities for pork producers have contributed to the increased interest in alternative production systems for livestock species.

One reason for interest in outdoor pig production has been the low capital cost of outdoor systems, which varies from 40-70% of the cost for conventional indoor systems (Thornton, 1988). Outdoor pig production can achieve similar gross margins as indoor production systems but with lower capital investments (Edwards, 1995). Others have suggested that outdoor pigs have a calmer behavior and are less susceptible to stress in connection with transport and slaughter (Warriss et al., 1983; Barton-Gade and Blaabjerg, 1989).

Sustainable agriculture systems are essential to preserve, protect and improve the environment and the animal’s experiences. Sustainable swine production combines production techniques to enhance profits and improve environmental and socioeconomic conditions on the farm (Honeyman, 1996). Opportunities for niche marketing of sustainable operations have certainly increased the number of producers striving to market sustainable, natural, or organic products in the United States. Many consumers want to purchase food products from various systems, including organic, free-range, antibiotic-free or others. Research at Texas Tech University has focused on the production of Sustainable Pork^® as an animal, environmentally, and worker friendly product. Studies examining environmental effects on pork quality have yielded widely differing conclusions (Warriss et al., 1983; van der Wal et al., 1993; Enfält et al., 1997; Sather et al., 1997; Olsson et al., 2003). To date, the effects of diverse birth and rearing environments on pig growth and pork quality have not been completely dissected.

Outdoor Housing Systems

Outdoor housing on pasture or dirt pens accounts for less than 2% of the pigs finished in the United States while an additional 9% of the pigs are housed in an open building with outside access (NAHMS, 2001). These systems usually consist of a large paddock and shelter for the pigs. Climatic conditions and land availability are two limiting factors to consider when producing pigs outdoors. Several criteria that are often considered when planning an alternative swine housing system include space allowance, ground cover, group size, and feeding regime. Alternative systems typically avoid the use of liquid manure and mechanical ventilation. Other constraints to outdoor finishing facilities are soil damage, land availability, pollution potential, and the logistics of supplying daily feed and water requirements in all weather conditions (Edwards, 1999). One very important factor to consider with outdoor pig production is the correct choice of location that includes evaluation of soil type and climatic conditions (Edwards, 1995). Outdoor housing systems are perceived to be more animal friendly and more environmentally friendly. If managed correctly, the outdoor systems can accomplish this, but under poor management, outdoor pigs can have poorer performance and cause damage to the environment. Some environmental factors that must be monitored under outdoor finishing systems are nitrate leaching, soil compaction, removal of vegetation, and soil erosion (Edwards, 1999).

Deep-bedded finishing Systems

Hoop-style pig finishing houses have become increasingly popular in the United States. A hoop structure consists of 1.2-m-high wooden sidewalls fitted with steel tubular arches covered by an opaque UV-resistant polypropylene tarp. Most of the floor area inside of the hoop building is bedded with cornstalks or other crop residues. The remainder of the floor area is a concrete slab for feeders and waterers. Group size can vary considerably and usually ranges from 75 to over 250 head per building.

Other producers raise pigs in deep-bedded buildings, including converted poultry houses or empty buildings. Deep-bedded growing/finishing systems have been considered an alternative and compared with traditional slatted-flooring indoor systems. Converted poultry buildings can hold 500 to 2,000 finishing pigs and are considered an “all in-all out” system. Pigs in these buildings are raised on some type of bedding (corn stalks, wheat straw, fescue hulls, or other crop residue) and this system is similar to hoop buildings in some ways. Bedded hoop structures or converted poultry buildings may work as a wean-to-finish housing system if nursery pigs can efficiently grow throughout the various climatic changes within a production cycle.

The major difference between hoop-style finishing and the conventional finishing buildings with slatted floors are: the use of bedding, dry manure management, natural ventilation, larger group sizes, more environmental variation, and low initial investment. Some advantages may exist for the animal if finished on bedding. Pigs on bedding show less tail biting, have fewer foot pad lesions, have fewer leg problems, and tend to have fewer respiratory problems than pigs on slatted flooring (McGlone, 1999; Table 1). Research comparing growth and meat quality characteristics of pigs finished in hoops has been limited. Lay et al. (2000) determined that pigs finished in hoops performed fewer abnormal behaviors, had a greater rate of play behavior, and fewer leg injuries than pigs finished in a non-bedded confinement system. In a 2-y study comparing bedded hoop structures (corn stalks) versus confinement, Honeyman and Penner (2000) reported that pigs finished in hoops during the summer grew faster than pigs in confinement, but during the winter, growth rates were similar between the two finishing systems. Also, during the summer, barrows had 10.6% and gilts 11.1% more backfat than their counterparts finished indoors in confinement. When results from the 2-y study were combined, the trials showed that pigs finished in hoops ate more feed, grew faster, and required more feed per unit of live weight gain than confinement pigs (Honeyman et al., 2000). Pigs finished in hoops had a higher incidence of roundworm infestations than pigs finished in confinements. Pigs finished in bedded hoop structures may need different diets than those finished in confinement to optimize lean growth.

Researchers have determined that growing pigs prefer to lie on straw under cool temperatures but prefer bare floors at higher temperatures (Fraser, 1985). Therefore, the potential benefit of bedding for finisher pigs would be for environmental enrichment during cool weather. Fraser et al. (1991) determined that the presence of straw in a pen of finisher pigs ten weeks old reduced rooting and chewing of penmates. The straw functioned to provide a stimulus and outlet for rooting and chewing which resulted in a reduction of these behaviors directed at penmates (Fraser et al., 1991).

Texas Tech University researchers examined foot pad and toe lesions on pigs housed on bedding or concrete slats. Feet were scored as clear, mild or severe (greater than 25% of the area in a wound). Data suggests that pigs housed on bedding had more severe foot pad and toe lesions (31% vs 9%) than pigs housed on concrete slats however pigs housed on slats had more overall lesions (55% vs 32%) than pigs housed on bedding (Table 1, Gentry et al., 2002a). Lung lesions were also scored for the same group of pigs. Overall, the percentage of clear and lesioned lungs was similar in the two housing systems. However, the percentage of severe lung lesions was about twice as high among pigs in slatted floor facilities than those on bedding.

Table 1. Percentage of foot lesions and lung lesions on pigs housed on bedding or concrete slats. Adapted from Gentry et al., 2002a.

	Bedded	Slats
Feet
Clear	68%	45%
All lesions	32%	55%
Severe*	31%	9%
Lungs
Clear	68%	76%
All lesions	32%	24%
Severe	6%	13%

*% of lesioned pigs’ feet, for example 31% of the

32% lesions were severe for pigs on bedding.

Growth and Composition of Indoor and Outdoor Finished Pigs

A summary of experiments comparing the effects of environmental housing on pig growth and carcass measurements is included in Table 2. Conflicting findings have been reported on the comparisons of indoor and outdoor pig finishing systems. Some researchers have reported that outdoor finished pigs had lower average daily gain (ADG) than indoor finished pigs during the winter months (Enfält et al., 1997; Sather et al., 1997) but Olsson et al. (2003) reported that organically grown pigs (outdoors) had a higher ADG than pigs grown in a conventional (indoor) system. Enfält et al. (1997) found that outdoor reared pigs had leaner carcasses than indoor reared pigs during the winter months. Sather et al. (1997) found that outdoor-reared pigs had a lower average daily gain than confinement-reared pigs. Outdoor pigs also required 13.5% more feed during the winter months, however rearing environment had only a small effect on carcass lean percentage (Sather et al., 1997). On a carcass dissection basis, confinement-reared pigs were fatter than outdoor-reared pigs (Sather et al., 1997). Another study conducted by Van der Wal et al. (1993) compared free-range pigs with intensive reared pigs and found no significant differences between the two groups in growth or carcass measures.

Beattie et al. (2000) concluded that pigs from enriched environments (3.5 m²/pig, solid flooring with straw bedding) had higher levels of backfat (P < 0.05) and higher growth rates (P < 0.001) during the last stage of finishing (15 to 21 weeks), compared to pigs finished in a barren environment (0.76 m²/pig, concrete slats). Other researchers evaluating environmental enrichment of pigs have shown that earth-like material (peat or moss) may be an effective enriching agent (Beattie et al., 1998). In previous studies, environmental enrichment was only incorporated after weaning (Warris et al., 1983; Pearce and Paterson, 1993). Hessing et al. (1993) suggested some characteristics that can affect pig performance and meat quality such as stress responsiveness are established earlier in life. Others have found that environmental enrichment resulted in no improvement in productivity (Pearce and Paterson, 1993; Blackshaw et al., 1997). The nature of the enrichment and the length of exposure to the enrichment may explain the conflicting findings thus far.

The effects of diverse birth (outdoors on pasture with farrowing huts vs. indoors in crate) and rearing (outdoors on alfalfa pasture vs. indoors on slats) production systems on pig growth and meat quality (Gentry et al., 2002b) were evaluated at Texas Tech University. This experiment was conducted over all seasons and pigs were processed in July and March. Four outdoor pens were built on alfalfa pasture. Long pens (12 m wide by 105 m long) were designed so that the pigs were required to walk from one end of the pen to the other since feed and water was located at opposite ends of the pen (212 m²/pig). A hut (10.1 m²) was provided for shelter. The indoor pens were 2.1 m by 3.6 m and on concrete slatted floors (1.2 m²/pig). Barrows (n = 12 per treatment) were allocated to each of the environments. The treatments were as follows: indoor-born/ indoor-finished, indoor-born/outdoor-finished, outdoor-born/outdoor finished, and outdoor-born/indoor finished. Animals were processed at a commercial packing plant. Outdoor-born pigs showed growth advantages on all weigh dates (d 28, 56, 112, and 143) compared to the indoor-born pigs (Figure 1). Outdoor-born pigs had heavier hot carcass weights and measured a larger loineye area (P < 0.05; Gentry et al., 2002b).

Rearing environment had no effect on pig growth rates. For the group finished during the winter months (processed in March), outdoor-born pigs were heavier (P < 0.05) at d 28 and 112 but no differences were detected in final weight or ADG (Gentry et al., 2003). In both of the experiments, outdoor reared pigs had a higher (worse) feed:gain ratio than the indoor reared pigs. During the winter trial, the outdoor-reared pigs had a higher (P < 0.05) average daily feed intake (ADFI) than indoor-reared pigs. Growth characteristics for pigs finished outdoors or in an enriched environment vary among all studies. Differences in feed intake and feed:gain also were variable. Perhaps this is due to the climatic conditions, the genetic lines evaluated or other factors.

Figure 1. Growth traits of pigs born either indoors (sows in farrowing crates) or outdoors (sows on pasture). Significant difference (P < 0.05) on d 28, 56, 112, and 143; rearing environment did not have a significant effect on pig growth rates. Adapted from Gentry et al., 2002b.

Pork Quality Measures of Indoor and Outdoor Finished Pigs

Postmortem pH and water holding capacity may be reduced in outdoor pigs (Table 3 ; Warriss et al., Enfält et al., 1997). A comparison of the effects of environmental housing systems on pork color and sensory characteristics are included in Table 3. Loins from outdoor reared pigs had a lower ultimate pH, higher drip loss, and higher Warner-Bratzler shear force values (Enfält et al., 1997) than loins from indoor finished pigs during the winter months in Sweden. Meat from outdoor finished pigs also had more lactate and crude protein, higher glycolytic potential, less intramuscular fat, and less water (Enfält et al., 1997).

Several researchers have found no differences in pork eating quality measurements comparing pork from indoor and outdoor reared pigs (van der Wal, 1991; Barton-Gade and Blaabjerg, 1989). Beattie et al. (2000) reported that pigs from enriched environments produced pork with greater tenderness than pigs raised in barren environments. Jonsäll et al. (2001) reported that ham from outdoor reared pigs was less juicy and acidulous than ham from indoor reared pigs (P < 0.05) but no differences were found in tenderness, odor intensity, or meat taste between the indoor and outdoor reared groups. Maw et al. (2001) reported that pigs housed on straw bedding produced bacon with a stronger fried meat flavor than bacon from pigs housed on concrete or slats (P < 0.05). Bacon from straw-bedded pigs was darker in color than bacon from pigs raised either on contrete or slatted flooring (Maw et al., 2001). Other researchers have found no effect of physical activity on sensory qualities of cuts from the ham and loin (Petersen et al., 1997; van der Wal et al., 1993; Essén–Gustavsson et al., 1988), but the degrees of exercise and enrichment of the environments varied.

A summary of carcass measurements, color scores, and sensory characteristics from Texas Tech University research comparing loins of pigs raised in indoor and outdoor finishing systems is included in Table 4. Pigs finished outdoors during the warm months had more backfat at the last rib than pigs finished indoors. For the group processed in March, the outdoor- born pigs had more backfat at the 1st and last rib than the indoor-born group. Also, outdoor-reared pigs had more backfat at the last rib but less marbling on the loineye.

Outdoor born and finished pigs had lower L* and higher a* values than indoor born and finished pigs (P < 0.05). Minolta a* values were highest for the pigs born and finished outdoors, indicating a redder color of the loin muscle.

Chops from the outdoor-born pigs (processed in July) had more desirable sensory panel scores for flavor intensity (Table 4) and lower shear force values, indicating more tender meat. However, no differences were detected in sensory panel scores or shear force values of loins from pigs processed in March. Loins from both groups had acceptable shear force values that would be considered very tender by most consumers (Miller et al., 2001).

Additional studies were conducted comparing each of the following finishing systems: indoors on concrete slats, indoors in converted poultry buildings on deep bedding with curtain sides, outdoors on a dirt lot, and outdoors on alfalfa pasture. Results from these experiments showed that pigs finished in alternative systems have similar carcass and pork quality characteristics compared to pigs finished in a conventional indoor system. Outdoor-housed pigs grew faster than indoor-housed pigs during the warm months (Gentry et al., 2002a). Seasonal differences in growth patterns may exist with outdoor finished pigs. Outdoor-reared pigs had heavier carcass weights, less backfat at the last rib, larger loineye area, and higher loin marbling scores (P < 0.05, Gentry et al., 2002a). In addition to growth and pork quality advantages, loins from the outdoor-finished pigs had higher scores for initial juiciness (more desirable) and less off-flavor (P < 0.05) as evaluated by a trained sensory panel. Overall, outdoor or deep-bedded systems may increase growth rates of pigs if suitable land area and resources are available, but pork quality of loins will be similar for pigs finished in either conventional or alternative systems.

Few differences were detected in loin muscle quality (color or pH) among the experiments. Shear force values were higher (tougher) for outdoor finished pigs in three experiments but lower (more tender) in two experiments. Again, results in loin muscle quality between indoor and outdoor (or alternative) housing systems are variable. Many other factors could be confounding results such as environmental conditions, management, diet, genetics, or others. Swine producers should consider all of these factors when choosing a production system to best suit their environment.

Conclusions

Overall, results comparing indoor and outdoor pig finishing systems have been variable. Some reasons for this variation include differences in pig birth environment, seasonal effects, and quality of ground or bedding surfaces. Research from Texas Tech University indicates that outdoor born pigs have higher growth rates but more backfat. A possible advantage for outdoor rearing may be linked to increased a* values and decreased L* values of the loin muscle. Darker colored pork is more desirable for export markets because of the increase in water holding capacity. A careful economic analysis should be conducted to determine if increased backfat and feed:gain that is associated with outdoor finished pigs could be offset by higher market prices for meat products from pigs finished in an outdoor environment. Alternative nutrition research could lead to decreased backfat levels of outdoor finished pigs. If consumers are willing to pay more for products that are produced as “sustainable”, “natural”, or others, then these production systems could be very successful in the future.

There are some real differences in pork quality noted in the literature. However, differences in pork quality vary among the different environments that were investigated. Consumer perception is such that when they enter a retail environment they are willing to buy pork products with social assurances. In some cases, consumers may believe the alternative pork products will taste better. We can say quite clearly that alternative products do not taste worse than conventional products. Pork produced from pigs born and reared outdoors was equal to or better than pork from conventional systems under some circumstances in our experiences. Success of alternative production systems will depend on many factors and consumer “willingness to pay” for these products would certainly increase economic benefits for these production systems.

Acknowledgements

This work was supported by a grant from the USDA Fund for Rural America, Consolidated Nutrition, and the Texas Tech University College of Agricultural Sciences and Natural Resources. The authors wish to thank project collaborators: Mark Miller, John Blanton, Consolidated Nutrition, USDA-ARS, Excel, and Seaboard Farms. We also would like to thank Texas Tech University staff and graduate students for their help in data collection and technical assistance.

Table 2. Summary of growth effects of alternative systems for finisher pigs.

			Alternative vs. Conventional^a
Authors	Year	Systems	Live wt^b	ADG^c	FI^d	F:G^e	Backfat^f
Warriss et al. (UK)	1983	Enriched (outdoor paddock) vs concrete	NS	-	-	-	-18.0%
van der Wal et al. (Netherlands)	1993	Straw vs concrete	NS	-	-	-	NS
Sather et al. (Canada)	1997	Outdoor vs indoor- winter	NS	-15.9%	NS	-11.2%	NS
	1997	Outdoor vs indoor- summer	+8.9%	-16.4%	-12.8%	NS	NS
Enfalt et al. (Sweden)	1997	Outdoor vs indoor	-	-15.8%	-	-	-15%
Beattie et al. (UK)	2000	Enriched (straw and 2x more space) vs barren	+5.0%	+16.0%	+6.0%	-9.0%	+26.8%
Gentry et al. (Texas, USA) Olsson et al. (Sweden)	2002	Outdoor pasture vs slats, birth environment	+10.6%	+12.5%	-	-	NS
	2002 2003	Outdoor pasture vs slats, rearing environment Organic vs conventional	NS NS	NS +8.5%	NS -	+3.2% -	+28.5% +35.4%

^aA positive value indicates an increase for the alternative production system and a negative value indicates a decrease for the alternative production system compared to the indoor system. NS = effects not significantly different (P > 0.05).

^bLive Wt = live weight (kg) of pigs prior to slaughter.

^cADG = average daily gain (kg/day).

^dFI = average daily feed intake.

^eF:G = kg of feed per kg of gain.

^fBackfat = measured at the last rib on carcass.

Table 3. Summary of pork loin measurements of alternative systems for finisher pigs.

			Alternative vs. Conventional^a
Authors	Year	Systems	L*^b	pH	Shear force^c
Warriss et al. (UK)	1983	Non-intensive (outdoor) vs intensive	-10%	NS	-
van der Wal (Netherlands)	1991	Free range vs indoor	NS	NS	NS
van der Wal et al. (Netherlands)	1993	Straw vs. concrete	NS	NS	NS
Sather et al. (Canada)	1997	Outdoor vs. indoor-winter	NS	NS	NS
		Outdoor vs indoor-summer	-3.0%	NS	+18%
Enfalt et al. (Sweden)	1997	Outdoor vs indoor	+5.8%	-1%	+12%
Beattie et al. (UK)	2000	Enriched vs barren	-	-	-9%
Gentry et al. (Texas, USA) Olsson et al. (Sweden)	2002	Outdoor pasture vs. slats, birth environment	NS	NS	NS
	2003	Outdoor pasture vs. slats, rearing environment Organic vs conventional	-4.7% NS	NS -0.9%	-9.1% +12.1%

^aA positive value indicates an increase for the alternative production system and a negative value

indicates a decrease for the alternative production system compared to the indoor system.

^bA decrease in L* indicates a darker colored loin. L* values range from 1 to 100 with 1 = pure black and 100 = pure white.

^cA higher shear force value indicates tougher meat.

Table 4. Summary of environmental effects on pork carcass measurements, loin shear force, and sensory characteristics over seasons (Gentry et al., 2002b; Gentry et al., 2003).

Processing date	July				March
	Birth		Rearing		Birth		Rearing
Measure^c	Indoor	Outdoor	Indoor	Outdoor	Indoor	Outdoor	Indoor	Outdoor
No. of pigs	12	12	12	12	12	12