Abstract
The objective of this investigation was to compare the productivity results, carcass composition and meat quality of pigs reared indoors (average ambient temperature 19.4°C) or outdoors (average ambient temperature 16.0°C) during the summer–autumn periods. A total of 56 Lithuanian White (LW)×Swedish Yorkshire (SY)×English Large White (ELW) crossbred pigs were selected out of 14 litters and allotted into two analogous by origin, gender, weight and condition score groups of 26 animals each. The indoor group pigs were raised in pens of 18.5 m2 area. The outdoor group pigs were raised outdoors in enclosures of 850 m2 area. The productivity of pigs was determined by individual weighing. The carcass measurements (carcass weight and length, dressing percentage, backfat thickness and loin lean area) were determined and recalculated for 100 kg weight. The samples of the longissimus muscle were analysed for physicochemical indicators of meat. The study indicated that in the growing period and during the whole experiment, the outdoor group pigs gained higher average daily weight, respectively, by 26.8 (P=0.003) and 12.7% (P=0.013) than the pigs in the indoor group. The carcass traits were not different between the groups, but in all cases the outdoor group showed lower fat thickness. Rearing environment did not significantly influence the physicochemical indicators of meat and backfat, but the meat from the pigs raised outdoors had slightly higher (0.76%, P=0.088) crude protein levels.
1. Introduction
The intensive raising of pigs is the result of the increasing demand for pig meat. However, the keeping of animals in pig houses all year along with the increase in the rate of stocking leads to the development of various health problems and lower production quality (Beattie et al. Citation2000; Miao et al. Citation2004). Moreover, pig raising in cramped pens increases their aggressiveness and stress susceptibility (Beattie et al. Citation2000) and restricts the biological and etiological demands of animals (Hötzel et al. Citation2004). Feed intake, growth intensity and meat quality are also influenced by the environment of the animal growth (Edmonds et al. Citation1998; Hyun et al. Citation1998; Maw et al. Citation2001).
Environmental enrichment with the use of substrates and great space allowance can significantly improve the welfare and increase the performance of pigs (Gonyou and Stricklin Citation1998; Morgan et al. Citation1998; Beattie et al. Citation2000; Street and Gonyou Citation2008). However, when keeping animals in barns, space is a resource that is limited in the interests of barn utilisation efficiency. As a result, there has recently has been a demand to develop pig production systems which will meet the requirements of animal health and welfare, but will not affect the intensity of production and pork quality.
A noticeable change from conventional or indoor to alternative housing systems is that pigs are kept outdoors. Outdoor growing of pigs became a matter of greater interest in some countries, especially Europe and North America (Sather et al. Citation1997). The interest in the outdoor raising of pigs is also stimulated by the possibility to take the market niche for higher quality production including the ecological one (McGlone Citation2001). From an animal welfare viewpoint, outdoor housing of pigs is more favourable and perceived to be more animal-friendly and more environmentally friendly (Gentry and McGlone Citation2003; Watson et al. Citation2003). Outdoor pigs are offered a lot of space and environmental diversity, allowing for physical activity. (Lebret Citation2008). Outside animals have the possibility of showing natural behaviours (Barton Gade Citation2002). Plentiful space and fresh air can reduce infection pressure (Edwards Citation2005) and pigs reared outdoors enjoy better health (Václavková and Bečková Citation2008). Moreover, ingestion of herbage and soil by pigs at pasture can make a substantial contribution to the energy, amino acid, mineral and micronutrient requirements (Edwards Citation2003).
In mild climates, pigs housed outdoors may grow faster than pigs housed indoors during warm months (Gentry et al. Citation2002a). However, the results from the studies of various authors are contradictory. Sather et al. (Citation1997) and Hoffman et al. (Citation2003) indicated that outdoor-reared pigs had a slower growth rate than confinement-reared pigs. Stern et al. (Citation2003) reported that pigs reared outdoors grew at a similar or faster rate than indoors.
The research data from different studies show that the effects of an outdoor housing system on carcass and meat quality are ambiguous. Sather et al. (Citation1997) and Gentry et al. (Citation2004) have reported that an outdoor rearing environment had only a small effect on carcass lean percentage and backfat thickness. However, Galian et al. (Citation2008) indicated that the outdoor group of pigs showed higher dorsal fat thickness.
Pigs of different local breeds are considered to be most suitable for outdoor growing. However, pigs of local breeds also have inferior carcass qualities and are therefore pushed out by hybrid pigs of specialised breeds that are adapted to the intensive pig growing system and characterised by lean carcasses, high feed consumption efficiency and growth intensity (Kelly et al. Citation2007).
Lithuanian White is a pig breed characterised as comparatively hardy and well adapted to local conditions (Sveistys Citation1983). The use of Swedish Yorkshire and English Large White pigs in crossbreeding with Lithuanian Whites resulted in improved fattening and carcass traits and lower backfat thickness of Lithuanian White pigs (Sveistys Citation1983; Jukna et al. Citation2007). As outdoor pig raising is becoming more widespread, the question arises as what influence this type of pig rearing has on the performance of pigs with higher productivity and higher muscling score.
To address these issues, this present experiment was carried out to measure indoor and outdoor environmental conditions for Lithuanian White and Swedish Yorkshire and English Large White crossbred pigs and to demonstrate the effects that these conditions have on growth performance, carcass composition and meat quality.
2. Material and methods
A total of 52 crossbred pigs of Lithuanian White (LW)×Swedish Yorkshire (SY)×English Large White (ELW) breeds were used in the experiment. The pigs (27.69±0.73 kg live weight) were selected out of 14 litters and were allotted into groups of 26 animals each analogous by origin, gender, weight and condition.
The pigs were placed in one of two environments, either indoors or outdoors. The indoor group pigs were fattened in a pigsty in pens on straw littered solid concrete floors of 18.5 m2 area. The rate of stocking was 13 pigs per 18.5 m2 area pens.
The outdoor group pigs were raised outdoors in the enclosures of 850 m2 area. The stocking rate was also 13 pigs per enclosure. Every enclosure was fitted with three-wall shades with the area of 7.5 m2. The shades were built using twofold wire net, filled with straw bales. The roof of the shade was covered with a twofold layer of polypropylene that served as a shelter from heat and cold. The front of the shade was covered with a transparent plastic sheet.
The pens in the pigsty and shades in the enclosures were straw littered during the whole experimental period. The pens and enclosures were equipped with troughs for pig feeding and watering.
The enclosures were made of wood. Additionally, an electric fence was installed on the inner part of the enclosure.
The pigs in both groups were fed twice daily with slop from the troughs and given an identical growing and finishing diet. The growing period of the pigs lasted from 2.5 to 4.5 months of age, i.e. 61 days and the finishing period from 4.5 to 6 months of age, i.e. 45 days. The amount of feed given to the pigs had to be sufficient for them to see them through to the next feeding with no remains leftover. The chemical composition of the diets was analysed using standard methods (AOAC Citation1990) and is presented in . The amount of drinking water was not restricted. The pigs were placed in the pigsty and outdoors on 18 June. The experiment lasted for 106.1±1.8 days depending on final finishing weight and was completed at the beginning of October.
Table 1. Chemical composition and nutritive value of the diets (in kg dry matter).
During the entire experiment, air temperature and relative air humidity were determined every hour with the device Testostor 175.
The growth rate of the pigs was determined by individual weighing at the start and the end of the experiment and every month.
The carcass quality was determined at the end of the experiment when 16 pigs (eight analogous animals – four gilts and four castrates from each group) – were selected for controlled slaughter. The pig carcasses were evaluated according to the rules for performance testing of breeding pigs approved in 2003 (Veislinių kiaulių produktyvumo kontrolės, vertinimo, informacijos kaupimo ir teikimo taisyklės Citation2003). All of the carcass indicators were recalculated for 100 kg weight. The samples of the longissimus muscle (M. longissimus dorsi) were analysed in duplicate for dry matter – moisture, crude protein, crude ash and crude fat according to the standard AOAC methods (AOAC Citation1990). Tryptophan was analysed with p-dimethylaminobenzaldehyde by Miller (Citation1967), hydroxyproline by Stegemann and Stalder's method, meat pH after 24 h following slaughter by the potentiometric method, colour intensity by the method of Khornsi's modification (Misik Citation1978), water holding capacity by the method of Grau and Hamm (Citation1953) and meat cooking losses by the method of Schilling (Citation1966).
Processing of the data was performed using software Statistica (Data Analysis Software System, Version 7.0; StatSoft, Inc., Tulsa, OK, USA). The individual pig served as the experimental unit for all growth, carcass measurements and investigation of physicochemical indicators of meat. The statistical evaluation of the results was performed using descriptive statistics and Student's t-test for independent samples. In the figures, all of the data are displayed as mean ()±standard error (SE) of mean. The probability level of P ≤ 0.05 was considered to be statistically significant.
3. Results
The analysis of the environmental parameters indicated the following: Indoors, the average air temperature and relative air humidity in the first and the second half of the experiment equalled 21.4±0.3°C and 73.4±0.5%, 17.0±0.4°C and 76.9±0.5%, respectively. Outdoors, the results equalled 18.6±0.2°C and 78.9±0.7%; 13.1±0.4°C and 85.7±0.6%, respectively ().
Figure 1. Microclimatic and climatic indicators.
The average air temperature and relative air humidity during the entire experiment were as follows: 19.4±0.3°C and 75.0±0.4% for indoors, 16.0±0.3°C and 82.1±0.6% for outdoors, respectively. In general, there were no significant differences for the average highest air temperature both indoors and outdoors in the first (23.4±0.3°C and 23.7±0.4°C, respectively) and second (18.9±0.4°C and 17.7±0.4°C, respectively) half of the experiment and during the entire experiment (21.2±0.3 and 20.8±0.4°C, respectively). The average lowest air outdoor temperature was significantly lower than indoors. In the first half of the experiment, the lowest air temperature indoors and outdoors was 19.9±0.3°C and 13.3±0.2°C, respectively. In the second half, it was 15.0±0.4 and 9.1±0.4°C, respectively and during the entire period it was 17.5±0.3 and 11.3±0.3°C, respectively.
The average lowest relative air humidity indoors and outdoors did not differ significantly during the entire experiment. The average highest relative air humidity outdoors was much higher than indoors by 15.0% in the first half of the experiment, 13.6% in the second half of the experiment and by 14.3% during the whole experiment and accounted for 94.6±0.7, 97.2±0.3 and 95.9±0.4%, respectively.
The growth characteristics of the pigs from the indoor and outdoor raising systems are shown in . Although the starting weight of the pigs did not differ between the two groups, both at the end of the growing period and the end of the experiment, pigs raised outdoors weighed on average 7.42 kg (13.3%, P=0.036) and 7.46 kg (8.5%, P=0.037) more than pigs raised indoors. Outdoor pigs had a significantly higher (by 26.8%, P=0.003) average daily gain during the growing period and by 12.7% (P=0.013) higher during the entire experiment. In the final period, both groups of pigs gained similar weights daily.
Table 2. Growth rate of pigs.
The outdoor pigs were in better health. In this group one pig was treated by a veterinarian for sunburn, while in the indoor group three pigs were treated for pneumonia.
The values of the controlled slaughter data of indoor or outdoor raised pigs are presented in . Due to the fact that pigs raised outdoors gained weight much faster, they had higher weights at slaughter compared to those raised indoors. Outdoor raised pigs had a somewhat higher warm carcass weight than indoor raised animals. However, there were no significant differences for the recalculated 100 kg warm carcass weight between indoor and outdoor raised pigs.
Table 3. Carcass measurements.
The dressing percentage of the pigs raised indoors and outdoors was also similar. The raising system did not significantly affect backfat thickness, but in all cases the outdoor group showed lower fat thickness. The length of the carcasses between both groups were similar, but outdoor pigs showed slightly higher length. Moreover, no significant differences were found for the loin lean area of the pigs raised indoors and outdoors, but the loin lean area from the outdoor pigs was 10.9% higher.
A slightly lower (0.76%, P=0.196) content of moisture was found in the meat of outdoor raised pigs (). Also, the meat from the outdoor raised pigs had slightly higher crude protein levels (0.76%, P=0.088) than that of the indoor raised pigs.
Table 4. Physicochemical indicators of meat.
The intramuscular fat content in the meat of both the indoor and outdoor raised pigs was approximately equal. Minor differences between both raising systems were observed for the ash content. The differences for the biological value of meat protein according to the contents of tryptophan and oxyprolin in the meat of indoor and outdoor raised pigs were also insignificant. There were almost no differences for the pH-values of the meat from pigs raised indoors and outdoors. Moreover, there were no significant differences found for the colour intensity, cooking losses, or water-holding capacity between the pigs raised indoors and outdoors.
4. Discussion
The motives for free-range housing of pigs include the possibility to reduce the cost of production and take the market niche for higher quality production. However, the research on the effects of outdoor rearing of pigs and the consequences for meat quality is controversial. Our investigation showed that outdoor reared pigs had 12.7% higher average daily gain than those reared indoors and this difference was statistically significant. This agrees with the results reported by Gentry, McGlone, Miller, et al. (Citation2002), Gentry et al. (Citation2004) who found that pigs born and reared outdoors had a higher average daily gain and at the end of the finishing period were heavier than those reared indoors. Also, Stern et al. (Citation2003) pointed out that daily weight gains were higher for pigs outdoors than indoors during Year one, but were similar for Year two. Several studies (Kelly et al. Citation2007; Rudine et al. Citation2007) showed that outdoor and indoor pigs had similar daily gains. However, Lebret et al. (Citation2002) reported that pigs reared outdoors on courtyards with free access to a shed had a similar growth rate during the winter season, but a decreased growth rate during the summer. However, the average outdoor temperatures in this experiment during winter and summer periods were approximately 18.3 and 26.0°C, respectively. On the contrary, some authors indicated that outdoor or free-range reared pigs had lower average daily gain than the pigs housed conventionally (Enfält et al. Citation1997; Sather et al. Citation1997; Hoffman et al. Citation2003; Strudsholm and Hermansen Citation2005).
The results from our study support the idea that better pig growth in the free-range group could be influenced by several factors. The increased possibilities for physical activity, i.e. freedom to move in large outdoor areas, fresh air, variation of ambient temperature could cause the increase of voluntary feed consumption and, as a result, the daily gain. Equally, the possibility to root and ingest the soil could enrich the ration of pigs with minerals and micronutrients and lead to improved metabolic processes.
In our investigation, outdoor raised pigs had significantly higher (26.8%, P=0.003) daily gains only during the growing period. In the finishing period, the pigs from both groups had similar growth rates. Lahrman et al. (Citation2004) and Lebret et al. (Citation2006) found that pigs in outdoor housing showed higher daily weight gain in growing and finishing periods. Also, these authors indicated that outdoor housing resulted in lower morbidity and mortality of pigs during all raising periods. Guy et al. (Citation2002) pointed out that outdoor pigs had less lung damage due to enzootic pneumonia compared to the indoor pigs. In their study, Miao et al. (Citation2004) referring to Thornton and Tubbs et al., indicated that pigs in outdoor units have better health than indoor herds, in particular fewer respiratory problems and a lower incidence of enteric disease. Millet et al. (Citation2005), referring to Muirhead and Alexander, pointed out that outdoor pigs often are exposed to sun. In our study we observed that outdoor pigs had problems with sunburn, however there were more problems in indoor group with pneumonia. These results agree with the findings of the above-mentioned authors and support the known fact that microclimate in the conventional rearing system is not always the most convenient for pigs.
The data in our study shows that outdoor raised pigs had somewhat higher warm carcass weight than indoor raised animals, but the dressing percentage between both groups was similar. This agrees with the results reported by Galian et al. (Citation2008) who also showed higher hot and cold carcass yield in pigs reared outdoors. The study of Gentry, McGlone, Miller, et al. (Citation2002) indicated that pigs reared outdoors from weaning to finishing had hot carcass weights similar to those of pigs reared indoors. Contrary to our findings in the research of Lebret et al. (Citation2002), hot carcass weight tended to be lower in pigs raised outdoors (P=0.07). They reported that body weight at slaughter was lower, but carcass dressing was higher compared with the control pigs reared indoors. Hoffman et al. (Citation2003) pointed out that there was a tendency for the conventionally housed pigs to have both higher warm (P=0.067) and cold (P=0.057) dressed weight, but neither warm nor cold dressing percentage differed significantly between the two housing systems. However, Stern et al. (Citation2003) and Hook Presto et al. (Citation2007) reported that the dressing percentage was higher for outdoor than for indoor pigs.
The literature survey indicates that housing systems may have an influence on carcass traits. In our study there were no significant differences between the outdoor and indoor pigs, but in all cases the pigs in the outdoor group showed lower backfat thickness. Several studies have suggested very similar results. Pugliese et al. (Citation2003) in the Nero Siciliano pigs reared outdoors found lower backfat thickness than in the pigs reared indoors. In the study of Hoffman et al. (Citation2003), free-range Landrace×Large White crossbred pigs had a lower P2 fat depth. Enfält et al. (Citation1997) and Sather et al. (Citation1997) reported a lower backfat thickness in lean pigs reared outdoors compared with those reared indoors. However, Hoffman et al. (Citation2003) indicated that free-range housed pigs had a significantly higher increase in subcutaneous fat. In the research of Lebret et al. (Citation2006), pigs reared alternatively with fluctuating ambient temperature and with free access to an outdoor area system had thicker backfat than pigs reared conventionally with controlled ambient temperature system. Olsson et al. (Citation2003) investigated the differences between organically reader outdoor pigs and those conventionally produced indoors and found that organically raised pigs showed thicker side fat than conventionally raised pigs. However, the pigs in their research were fed using a different feeding pattern. According to Galian et al. (Citation2008), pigs of the Chato Murciano breed showed slightly higher dorsal fat thickness in outdoor rearing environment.
The results from our study also showed no differences in carcass length of the pigs raised indoors and outdoors. These results agree with the findings of Gentry, McGlone, Miller, et al. (Citation2002) who suggested that the pig-rearing environment did not affect the carcass length. However, in the research of Millet et al. (Citation2004), pigs from the organic stable with free access to an outdoor area showed a shorter carcass length, especially within the organic feed groups. Gentry, McGlone, Miller, et al. (Citation2002) indicated that the pigs born and reared outdoors had a larger loin lean area than the pigs born and reared indoors. However, in the other study with indoor born and then outdoors on alfalfa pasture or indoors on concrete slats during the winter months finished pigs, the same authors found no differences in loin lean area measurements. This is in agreement with our findings when no significant differences were found for the loin lean area of pigs raised indoors and outdoors.
Some researchers have reported that the rearing system can affect the moisture contents of meat. In our study, no significant differences were found regarding the moisture content of the longissimus dorsi muscle between the two housing systems. Similarly, the content of moisture in the meat was unaffected under the outdoor housing system in comparison with the indoor system in the studies of Gentry, McGlone, Miller, et al. (Citation2002), Sather et al. (Citation1997) and Hoffman et al. (Citation2003). Gentry et al. (Citation2002b) also found no differences in the moisture content of the loin muscle from the pigs finished in a long pen with the increased space allowance, which was designed to increase exercise levels of the pigs or industry recommended space allowance. However, findings of Cava et al. (Citation2000) and Carrapiso et al. (Citation2007) showed higher moisture content in the meat in outdoor or free-range reared pigs.
In our study, no significant differences were detected regarding the percentage of protein between the two raising systems, but there was a tendency (P=0.088) for the meat from outdoor pigs to have higher protein content. This is in agreement with the study of Gentry, McGlone, Miller, et al. (Citation2002) and Hoffman et al. (Citation2003) who detected no differences in the protein content between the conventional and outdoor rearing systems. However, Nilzen et al. (Citation2001) pointed out that the meat from free-range housed pigs had a lower percentage of crude protein if compared with indoor-housed pigs. On the contrary, Enfält et al. (Citation1997) indicated that outdoor reared pigs had increased protein content in comparison with indoor reared ones.
Fernandez et al. (Citation1999) suggested that the acceptability of pork may be improved by increasing intramuscular fat levels but this effect disappeared for intramuscular fat levels higher than 3.5%. The correlations between bacon flavour and juiciness suggest a link between intramuscular fat and meat flavour (Maw et al. Citation2001). In our study, no differences were found between the two groups for the amount of intramuscular fat. Our findings agree with the study of Lebret et al. (Citation2002), who did not find any effect on intramuscular fat level between outdoor and indoor reared pigs. However, some authors indicated results to the contrary, i.e. meat from outdoor or free-range reared pigs had higher (Lebret et al. Citation2006) or lower (Enfält et al. Citation1997; Sather et al. Citation1997; Hoffman et al. Citation2003) amounts of intramuscular fat in comparison with indoor reared pigs.
In addition, our investigation did not show any significant differences in the percentage of ash between both raising systems. This is also supported by the study of Pugliese et al. (Citation2004). However, Galian et al. (Citation2008) found higher ash content in the meat of outdoor raised pigs.
According to our study, no significant differences in pH content were detected within the two groups. This is in line with findings of Sather et al. (Citation1997), Lebret et al. (Citation2002), Hoffman et al. (Citation2003), Gentry et al. (Citation2004) and Galian et al. (Citation2008) who indicated that a free-range and outdoor or indoor rearing environment had no effect on the ultimate pH. However, Klont et al. (Citation2001) noted that pigs reared in an enriched environment had a significantly higher pH at 24 h post-mortem than pigs kept under barren housing conditions. Contrary, Enfält et al. (Citation1997) and Stern et al. (Citation2003) indicated a significantly lower ultimate pH in outdoor-reared pigs than in conventional ones.
Outdoor environments can be an advantage for pork colour. When pigs were both born and finished outdoors, the pork was more red than the pork from pigs born indoors and reared indoors (Gentry et al. Citation2004). Hoffman et al. (Citation2003) and Micklich et al. (Citation2002) also showed improved results in meat colour. However, Pugliese et al. (Citation2004) pointed out that outdoor pigs produced lighter and more yellow meat, probably due to their higher intramuscular fat content. However, in our study no significant differences in the meat colour intensity of pigs raised indoors or outdoors were found. Moreover, we did not find any differences in the cooking losses and water holding capacity of meat. Our results agree with those of Jonsäll et al. (Citation2001), Gentry et al. (Citation2002b) and Gentry, McGlone, Miller, et al. (Citation2002). However, Beattie et al. (Citation2000) found greater cooking losses and Barton Gade and Blaabjerg (Citation1989) indicated reduced water-holding capacity in the meat of outdoor reared pigs.
In summary, we can conclude that the outdoor rearing environment did not influence meat composition. Although, we observed certain tendencies of improvement in some indicators, these differences were insignificant. This supports the suggestion that an outdoor environment did not substantially affect the quality of meat and indicates that other factors such as nutrition and genetics have more influence.
5. Conclusions
From the present investigation it can be concluded that outdoor-housed pigs had a higher growth rate than indoor-housed pigs. Carcass traits were not different between the groups, but in all cases, the outdoor group showed lower fat thickness. Rearing environment did not significantly influence the physicochemical indicators of meat and backfat.
Acknowledgements
The authors are grateful to the staff of the Skemiai agricultural enterprise for the help in pursuance of the research.
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