Feedlot performance, carcass composition and meat quality of free-range reared pigs

Transcription

1 Feedlot performance, carcass composition and meat quality of free-range reared pigs A. P. Sather, S. D. M. Jones, A. L. Schaefer, J. Colyn and W. M. Robertson Agriculture and Agri-food Canada, Research Centre, 6000 C & E Trail, Lacombe, Alberta, Canada T4L 1W1. Received 27 August 1996, accepted 31 January Sather, A. P., Jones, S. D. M., Schaefer, A. L., Colyn, J. and Robertson, W. M Feedlot performance, carcass composition and meat quality of free-range reared pigs. Can. J. Anim. Sci. 77: The effects of the housing system (confinement versus free-range) and season (summer versus winter) on growth performance, carcass composition and meat quality were determined from commercial pigs with known NN genotype at the halothane locus. Free-range-housed pigs reared from 25 to 105 kg required 16 ± 1.2 (SEM) more days to reach market weight compared with confinement-housed pigs. Housing did not affect feed requirements during the summer, but food consumption increased by 13.7% for free-range pigs during the winter. Confinement-reared pigs had a 0.75 ± 0.28 kg heavier commercial carcass weight than free-range-reared pigs. While there was no difference in carcass fat thickness, muscle depth was 2.4 ± 1.02 mm greater in free-range-reared pigs with increased predicted lean yield from 59.1 ± 0.24% to 59.8 ± 24%. Free-range-reared pigs had heavier butts, loins and hams, and lighter bellies, which increased their wholesale carcass value by 2.9%. Furthermore, they had greater dissected lean in the picnic (2.0%) butt (4.0%), loin (4.5%) and ham (2.0%) with no compromise to pork quality. If the wholesale price is adjusted for the increased lean content of each cut by an additive or multiplicative model, apparent value was further increased to 5.7 or 8.1%. While these results suggest a beneficial effect on carcass merit when rearing hogs in outdoor facilities, they further suggest potential benefits to carcass grading using developing technologies that recognize differences in carcass conformation. Key words: Animal ethics, Landrace, carcass value, housing systems Sather, A. P., Jones, S. D. M., Schaefer, A. L., Colyn, J. et Robertson, W. M Performances en parc d engraissement, composition de la carcasse et qualité de la viande chez les porcs élevés sur parcours. Can. J. Anim. Sci. 77: Nous avons étudié sur des porcs d exploitation commerciale possédant le génotype NN au locus de sensibilité à l halothane, les effets du système de logement, claustration ou parcours, et de la saison, été ou hiver, sur les performances de croissance, sur la composition de la carcasse et sur les qualités de la viande. Les sujets élevés en parcours à partir du poids de 25 à celui de 105 kg requéraient 16 ± 1,2 (ETM) plus de jours pour atteindre le poids de marché que les porcs élevés en claustration. Le mode de logement ne modifiait pas les besoins alimentaires durant l été, mais en hiver la consommation augmentait de 13,7 % chez les porcs de parcours. L élevage en claustration produisait des carcasses de 0,75 ± 0,28 kg plus lourdes que l élevage en parcours. S il n y avait pas de différence relativement à l épaisseur du gras dorsal, la profondeur du muscle était de 2,4 ± 1,02 mm supérieure chez les porcs de parcours, ce qui, du fait même, relevait le rendement en maigre prédit de 59,1 ± 0,24 % à 59,8 ± 0,24 %. Par ailleurs, le poids plus élevé des socs, des longes et des jambons et la moindre proportion de flancs accroissait de 2,9 % la valeur de carcasse au gros. En outre, les proportions respectives de maigre de dissection dans l épaule picnic, dans le soc, dans la longe et dans le jambon des sujets éleves en parcours étaient de 2,0, 4,0, 4,5 et 2,0 % plus fortes sans effets négatifs sur la qualité de la viande. Si on corrige le prix de gros en fonction de l accroissement de la teneur en maigre de chaque morceau, selon un modèle additif ou un modèle multiplicateur, la valeur apparente de la carcasse augmente plus encore, soit, respectivement, de 5,7 ou de 8,1 %. En plus de suggérer l effet positif de l élevage en parcours sur la qualité de la carcasse, nos observations laissent voir les avantages éventuels que représenterait pour le classement en carcasse la mise au point de techniques tenant compte des différences de conformation des carcasses. Mots clés: Éthique animale, Landrace, valeur de carcasse, système de logement In the past few years there has been commercial interest in animal products originating from animal systems that could be considered natural or traditional. The most extreme example of this trend has been the marketing of natural beef in North America, where beef cattle are fed and marketed under a set of specifications, such that the animals are not exposed to antibiotics, growth stimulants, and the feed is regularly checked for the presence of chemical residues. While natural beef has found only a small niche market, it demonstrates a perception that some consumers consider modern intensive animal production systems may not always be synonymous with product quality. Intensive animal production systems such as those practiced with pigs and poultry are being questioned by animal welfare groups, 225 as these the animals are bred, reared and fattened through to slaughter in total confinement. Free-range eggs have been a small part of the overall egg market in Europe and North America for a long time, as some consumers believe the free-range product is not only fresher but also of better nutritional value than its counterpart from intensive egg-laying operations. Relatively little has been reported on the effects of the rearing environment and its possible effects on pig carcass composition and meat quality. Warriss et al. (1983) reported that the rearing environment (confinement versus free- Abbreviations: DFD, dark, firm, dry; LT, longissimus thoracis; PSE, pale, soft, exudative; SM, semimembranosus

2 226 CANADIAN JOURNAL OF ANIMAL SCIENCE range) of pigs had no effect on indicators of stress (blood cortisol levels and adrenal gland ascorbic acid levels) but, based on casual observation, they suggested that free-range housed pigs behaved differently from confinement-reared pigs. These observations collectively indicated that these pigs were more easily startled and much more difficult to load into trucks than free-range-housed pigs. Barton-Gade and Blaabjerg (1989) found that free-range pigs also had a different behaviour compared to commercially reared pigs and considered them to be calmer and more easily handled in the abattoir although no actual behavioural measurements were recorded. Grandin (1989) considered that environmental enrichment (access to toys, outdoor rearing etc.) reduced excitability in hogs, which in turn allowed easier handling and less stress prior to slaughter. Housing pigs outdoors has been reported to result in less backfat and darker meat colour (Warriss et al. 1983) than in confinement reared pigs. However, Barton-Gade and Blaabjerg (1989) found that free-range pigs had lower ph measurements at 24 h post-slaughter and a tendency to produce higher levels of PSE meat than confinement-reared pigs. These authors reasoned free-range pigs had higher levels of muscle glycogen than pen-reared counterparts which directly resulted in lower ph readings. Van der Wal (1991) found no significant differences in carcass composition and meat quality in free-range compared with commercially reared pigs. Thus, conclusion over the effects of rearing environment on carcass composition are somewhat different depending largely on the nature of the study. The purpose of this study was first to determine if freerange housing of pigs in the northern climate was practical in terms of feed utilisation and growth rate, but of greater interest to determine what effects, if any, could be found on meat quality traits. Since resources did not permit the comparison of indoor and outdoor rearing of pigs at a systems level, documentation of the effects of the two rearing systems on carcass merit was considered to be the primary goal of the study. MATERIALS AND METHODS The animals used in this study were raised and slaughtered in accordance with the principles and guidelines set out by the Canadian Council on Animal Care (1993). Two trials (winter versus summer) were conducted to evaluate the effects of feeding pigs in indoor pens or outdoor lots. Only progeny from commercial F 1 Manor Hybrid (National Pig Development Corp., Canada) sows (Large White Landrace cross) backcrossed to Landrace boars with a known NN-genotype at the halothane locus as determined by a DNA probe (Fujii et al. 1991) were used. Trial 1 was conducted during the Winter period (January April), while Trial 2 was conducted during the summer months (June October). In Canada, as in other countries in the northern hemisphere, there are great seasonal extremes of climatic conditions (see Fig. 1) that may also impact on swine behaviour and muscle quality. Season is particularly difficult to define. To assist the reader to better understand western Canadian climatology, maximum and minimum daily temperatures during the winter and summer seasons as well as the morning indoor barn temperatures were recorded and are plotted in Fig. 1. The protocol (Table 1) called for groups of pigs, in each season, at approximately 25 kg liveweight to be allocated on a random basis to three indoor or three outdoor lots each containing 12 pigs (total number = 72 pigs per season), balanced by sex (Table 1). The pigs in the indoor pens ( m) were bedded with wood shavings over a concrete floor. The outdoor pigs were housed in pens ( m) over dirt with a cabin ( m) that had straw as bedding to provide for protection against extremes in temperature. The same procedure was repeated in both trials. All pigs were fed a grower/finisher diet designed to meet or exceed the requirements specified by the National Research Council. The diet had an average protein content of 15.5% and an energy content of kj. All pigs were weighed every 28 d and feed disappearance, because recording of feed wastage was not possible, was recorded weekly. Pigs were taken off test at approximately 105 kg and transferred to the research abattoir on the afternoon before the day of slaughter. There they were held overnight in lairage, without feed but with full access to water. In the morning, they were re-weighed (live plant weight), electrically stunned (head to back at 400 V and 1.7 A) for 3 4 s, stuck, scalded and dressed, following commercial procedures. The carcasses were shackled by alternate hind legs to reduce the possibility of side to side variations in meat quality. Warm split sides were weighed approximately min post-slaughter and initial ph (ph 45min ) was recorded in the centre of the LT between the 10th and 11th ribs and at a depth of 3 cm from the medial surface of the SM. The left carcass sides were probed for fatness and muscle depth between the 3rd and 4th last rib using a Hennessy Grading Probe. Kidney fat and liver weight was recorded on the slaughter floor. All carcasses were chilled at 1 C with an air velocity of 1 m s 1 for an average time of 24 h. Chilled carcasses were re-weighed to determine shrinkage losses. Left carcass sides were fabricated into the major primal cuts (shoulder, loin, ham and belly) and the four lean cuts (butt, picnic, loin and ham) were completely defatted and deboned. The weight of lean tissue in the four lean cuts was expressed as a proportion of the combined primal weights. The LT from the 3rd to the 13th ribs and the SM were removed and used for the evaluation of muscle quality. After removing the LT on the day following slaughter, a 25-mmthick chop was excised from the area of the 12th rib for the determination of drip loss, by measuring the amount of purge (drip loss) during a 48-h period at 2 C (Murray et al. 1989). At 48 h post-slaughter, a chop adjacent to the 11th rib was removed for the measurement of ph (ph 48h ), and the determination of meat texture and colour. This ph-value was considered to be the ultimate ph of the chop. Only the LT was assessed for subjective colour (5 point scale with 1 = extremely pale and 5 = extremely dark) and structure (5 point scale with 1 = extremely soft with dough-like appearance and 5 extremely firm) assessment on a fresh cut surface after allowing 20 min for the meat to bloom. A 25 mm

3 SATHER ET AL. FREE-RANGE REARED PIGS 227 Fig. 1. Daily indoor and outdoor temperatures during winter and summer test periods. Table 1. The effect of housing within season on live animal performance traits adjusted to an off-farm weight of 105 kg Season Contrast Summer Winter Main effect Housing Confinement Free-range Confinement Free-range Season Housing Summer Winter Trait Mean SE Mean SE Mean SE Mean SE P>F P>F P>t P>t Weight on test z Weight off test z Plant weight Age to market Average daily gain Feed conversion Daily food intake Total food consumption Number of pigs Number of pens z Unadjusted for off-farm weight. steak was obtained from both muscles for determination of objective muscle colour, after a 30 min bloom, and shear force. L *, a * and b * values (Commission Internationale de l Eclairage 1976) were then measured using a Minolta Chroma Colour Reflectance Meter II (Minolta Camera Corp., Meter Division, Ramsey, NJ), using duplicate readings. These values where used to calculate chroma (C * ) and hue angle by the following equations: 2 2 Chroma = ( a * + b * ) and Hue angle ( ) = tan 1 b * a * After grinding a portion of LT between the 6th and 10th ribs through a 5-mm grinding plate, protein solubility was determined according to the procedures outlined by Murray et al. (1989). Shear values were expressed as the average of three, 19 mm-cores obtained from a cooked chop, 72 h postslaughter, using the Instron Model 4301 Materials Testing System (Instron Canada Inc., Burlington, ON). Statistical analysis was performed using the general linear model procedure (GLM) from the SAS Institute, Inc. package (1989). The following model was used to determine the effect of housing, season and sex, adjusting for off-farm, plant or carcass weight: Y ijkl = µ + G i + S j + H k + GS ij + GH ik + SH jk + βw ijk + ε ijkl where: Y ijkl = trait from the lth pig within the kth housing system

4 228 CANADIAN JOURNAL OF ANIMAL SCIENCE Table 2. The effect of housing within season on carcass weight and grading traits adjusted to a plant weight of 100 kg Season Contrast Summer Winter Main effect Housing Confinement Free-range Confinement Free-range Season Housing Summer Winter Trait Mean SE Mean SE Mean SE Mean SE P>F P>F P>t P>t Commercial carcass weight (kg) Kidneys (kg) Kidney fat (kg) Liver (kg) Predicted lean yield (%) Fat thickness (mm) Muscle depth (mm) from the jth season and ith sex, µ = a common intercept, G i = sex (gilt, barrow), S j = season (winter, summer), H k = housing (confinement, free-range), W ijkl = weight covariate for those traits being expressed in kg (weight off farm, or weight at arrival at the abattoir, carcass weight), and ε ijkl = a random error of measurement term. Those traits expressed as a proportion of weight (e.g. with units of percent of g kg 1 ) and the meat quality traits were not adjusted for weight. All traits were expressed as a midsex value. Feed utilisation data was analyzed by a model similar to the one above, but using pen rather than animal as the experimental unit, without a weight covariate. The data were expressed on a single animal equivalent basis. χ 2 -values were calculated using the FREQ procedure (SAS Institute, Inc. 1989) to test for homogeneity of subclass frequencies of the subjective meat colour and structure scores. RESULTS AND DISCUSSION Feedlot Performance The live animal performance of the confinement and freerange reared pigs in the winter and summer months is shown in Table 1. Pigs grown in confinement pens grew 148 ± 7.0 g d 1 faster averaged over both seasons than those in outdoor lots (P = ). Thus, they attained market weight 16.1 ± 0.61 d earlier than the free-range pigs (P = ). In both the summer and the winter confinement housed pigs grew faster (P = ) than free-range reared pigs. In general, winter-reared pigs tended to grow faster (P = ) than summer pigs. Daily food consumption was lower (P = ) during the summer months, which could also contribute to the slower growth of summer-reared than winterreared pigs. However, total feed consumption was not affected by season (P = ). Daily food intake was higher for confinement-housed (P = ) pigs in either season when compared with free-range-reared fed pigs. During the summer, but not in the winter, free-range-reared pigs were more food efficient than confinement-housed pigs. The implications of rearing pigs in free-range lots compared with the more conventional confinement housing from 25 to 100 kg included a reduction in growth rate and an increase in slaughter age, with a modest increase in feed conversion and in total feed consumption during the winter months. Pigs are typically placed in conventional feeder facilities for approximately 16 wk. However, the feeder/finisher period required by the free-range-reared pigs was 15% greater. This would imply a proportionally greater land base and labour resources of free-range pigs than expected assuming they had a similar age to market as did the confinement housed pigs. Carcass Grading and Evaluation On a constant live plant-weight basis (i.e., 100 kg), confinement-housed pigs reared during the summer season had a 1.4 ± 0.39 kg heavier (P = ) commercial carcass than free-ranged-reared pigs. However, Warriss et al. (1983) found rearing environment had no significant effect on dressing proportion. During the winter season, there were no differences in carcass weight among confinement and freerange reared pigs (Table 2). Neither season nor housing environment affected liver weight. While there was an indication that free-range-reared pigs had larger kidneys (P = ) and less kidney fat (P = ), the effects were inconsistent across seasons. There was a trend, though it was not statistically significant, for free-range-reared pigs to have less fat thickness between the 3rd and 4th last rib. However, they had 2.4 ± 1.1 mm greater (P = ) muscle depth when compared with confinement-reared pigs. This difference increased (P = ) to 3.4 ± 1.4 mm during the summer months. Warriss et al. (1983) found that backfat thickness was reduced in a stressresistant genotype that was housed outside. Van der Wal (1991) reported that while free-range pigs had similar fat and muscle thickness to confinement-reared pigs when compared at the same carcass weight, estimated carcass lean percentage tended to be higher for free-range compared with confinement-reared pigs. This effect was also observed in the current study, where predicted lean yield was 0.37± 0.34% (P = ) in free-range-reared pigs. However, this effect was observed only in the summer months. In a subsequent study (Van der Wal et al. 1993), the confinementreared pigs tended to be leaner than the outdoor-fed pigs. Despite not finding consistent differences in linear measures that reflect differences in carcass composition in the

5 SATHER ET AL. FREE-RANGE REARED PIGS 229 Table 3. The effect of housing within season on the weight and separation of wholesale cuts into lean, fat and bone (adjusted to 85 kg) Season Contrast Summer Winter Main effect Housing Confinement Free-range Confinement Free-range Season Housing Summer Winter Separation Mean SE Mean SE Mean SE Mean SE P>F P>F P>t P>t Picnic (kg) Lean (g kg 1 ) Fat (g kg 1 ) Bone (g kg 1 ) Butt (kg) Lean (g kg 1 ) Fat (g kg 1 ) Bone (g kg 1 ) Loin (kg) Lean (g kg 1 ) Fat (g kg 1 ) Bone (g kg 1 ) Ham (kg) Lean (g kg 1 ) Fat (g kg 1 ) Bone (g kg 1 ) Belly (kg) present study, the carcass dissection results (Table 3) showed that free-range-reared pigs had a higher proportion of lean and a lower proportion of fat in the lean cuts and the primal cuts had different means weights. Free-range-reared pigs had heavier butts (P = ), loins (P = ) and hams (P = ) and lighter bellies (P = ). This trend was most pronounced for summer slaughtered pigs. These results collectively suggest that free-range-reared pigs produce carcasses with higher lean yield and greater lean content when compared with the more conventionally confinement-housed pigs. Meat Quality Attributes There were few consistent effects of housing system on the lean meat quality attributes of the LT muscle (Table 4). Initial ph of the free-range-reared pigs tended to be lower (P = ), indicating a potential for reduced lean meat quality. Barton-Gade and Blaabjerg (1989) also reported free-range pigs had lower ph measurements at 24 h postslaughter and an increased incidence of PSE meat than confinement-reared pigs. These authors reasoned free-range pigs had higher levels of muscle glycogen than their penreared counterparts which directly resulted in lower ph readings. Pigs raised during the summer have similar temperature stress, since the confinement barn was essentially ambient temperature. During the winter, free-range pigs were exposed to lower and more variable temperatures than confinement reared pigs (Fig. 1). To compensate, freerange-reared pigs would be expected to have higher glycogen levels than confinement-housed pigs which may account the increased incidence of the soft, exudative pork seen among these pigs (Fig. 2). While L * values (luminosity) were typical for normal pork, the hue angle shifted (P = ) from a nominal 23 to approximately 25, suggesting a slightly less redcoloured pork (Murray 1995), which in turn could be associated with an increased drip loss (P = ) through the subsequent purge of coloured pigments. While a relationship between drip loss and colour reflectance exists, increases in drip and colour reflectance arise through two different mechanisms (Murray 1995). Free-range-reared pigs had 25% less intramuscular fat (P = ) when compared with confinement-housed pigs. Season did not have a substantial effect on intramuscular fat or on shear values. However, Instron shear values were lower for confinement housed pigs (P = ), particularly in the summer (P = ) when compared with free-range-reared pigs. The differences were small and should not influence consumer acceptance. Fat hardness was not affected by housing system or season. Seasonal effects, while statistically significant, had only modest effects on the overall quality of the SM muscle. Initial ph of the SM muscle from free-range pigs reared in the winter were 0.12 units lower than contemporary confinement reared pigs but the L * values were not affected. Hue angle had increased from 22.8 to 29.0 (P = ), with much of the increase attributable to the free-range reared pigs (P = ). As found in LT muscle, but to a lesser extent, chroma values were elevated in the winter among free-range pigs. While an underlying mechanism is not evident, elevated chroma and hue angle values may be related to adaptive measures of the free-range-reared pigs to increased exercise and lowered, more variable temperature. Drip loss while lower when compared with the LT, increased in the SM muscle from 15.5 g kg 1 from summerreared pigs to 21.0 g kg 1 for winter-reared pigs. Soluble protein was higher in winter-slaughtered pigs, these values

6 230 CANADIAN JOURNAL OF ANIMAL SCIENCE Table 4. The effect of housing within season on pork quality attributes of LT and SM muscles Season Contrast Summer Winter Main effect Housing Confinement Free-range Confinement Free-range Season Housing Summer Winter Trait Mean SE Mean SE Mean SE Mean SE P>F P>F P>t P>t Longissimus thoracis Initial ph Ultimate ph CIE L* (%) Hue angle ( ) Chroma Drip loss (g kg 1 ) Soluble protein (mg/g) Moisture (%) Intramuscular fat (%) Shear Instron (kg) Fat hardness meter reading Semimembranosus Initial ph Ultimate ph CIE L* (%) Hue angle ( ) Chroma Drip loss (%) Soluble protein (mg g 1 ) Moisture (%) Intramuscular fat (%) Shear Instron (kg) were not suggestive of DFD. In the adult pig, heat, rather than cold is a cause of greater stress, because of insulating properties of the subcutaneous fat layer (Pond and Houpt 1978). In the winter, free-range pigs would be subject to an acute heat stress as they enter the abattoir just prior to slaughter. In contrast, pigs reared in a relatively warm confinement facility face a cold shock prior to slaughter. While each of these stresses appear to have a modest affect on meat quality, the animals used in this study are also known to be genetically stress-resistant to the halothane gene locus. Warriss et al. (1983) observed slightly darker meat colour as a consequence of outdoor fattening, but Van der Wal (1991) could find no differences in meat quality that could be attributed to feeding pigs indoors or outdoors. In a subsequent study (Van der Wal et al. 1993), which included sensory evaluation of the meat from free-range and confinement reared pigs, no differences were found in any of the parameters studied. A preliminary study reported by Barton- Gade and Blaabjerg (1989) suggested that free-range pigs had a different behaviour pattern to confinement-reared pigs and settled down quickly in the lairage pens after delivery to the abattoir. This resulted in high muscle energy reserves and a higher incidence of PSE meat in ourtdoor housed pigs compared with confinement-housed pigs. To support these observations, the same authors reported that outdoor-fattened pigs showed very little DFD meat when compared to confinement housed pigs. The perception that pigs reared out of doors or under natural conditions would be easier to handle and more resistant to the stressors encountered during marketing and so produce less PSE meat was not supported by the results of the present experiments. Casual observation of behaviour that outdoor pigs had a calmer disposition and were more easily moved to the restrainer for stunning. Further work would be appropriate to examine the effect of different pre-slaughter management regimes on the behaviours of outdoor compared with confinement-reared pigs. Implications The implications of the two different animal rearing systems are complex. The advantage of free-range rearing of animals is the perception by the consumer that animals are raised under natural or traditional conditions. The ethical management of animals is becoming a more important issue throughout the entire animal industry. While placing economic interpretation on ethical management is difficult, it also must not be ignored. This study also reveals more tangible advantages and disadvantages in the outdoor rearing of pigs. The initial investment into outdoor housing facilities is less, but a larger land base is required. Feed costs and labour associated with rearing animals outdoor would be expected to be higher. While diseases associated with higher population density found in confinement housing may be lessened, natural disease vectors (birds, wind, standing water, parasites, etc.) will become more prominent among free-range-reared pigs. In the current study, rearing pigs outdoors increased feed consumption during the winter months by 13% (Table 1).

7 SATHER ET AL. FREE-RANGE REARED PIGS 231 Fig. 2. The distribution of subjective colour and structure scores within housing type and season (LT). Table 5. Implication of housing system on carcass lean yield, composition and value Lean yield (% of cut) Weight of cut (kg) Housing Housing Relative wholesale % change in relative value x Commercial cut Confinement Free-range Confinement Free-range price z Unadjusted Additive Multiplicative Picnic Butt Loin Ham Belly Total carcass value z Realtive whole price: based on 1994 average wholsale value ($ kg 1 ) of commercial cuts (Pers. Commun., Don Sim, Manager, Fletcher s Fine Foods). x %change in relative value = 100 [(free-range commercial value wholesale price/confinement commercial value unadjusted) 1] commercial value = (wholesale price)(weight of commercial) wholesale price: Unadjusted = wholesale price, Additive = wholesale {1 + [(free-range lean yield confinement lean yield)/100]}, Multiplicative = wholesale price (free-range lean yield/confinement lean yield).

8 232 CANADIAN JOURNAL OF ANIMAL SCIENCE However, carcass value increased by at least 2.9% (Table 5), without substantially compromising pork quality attributes. This increase in value is based only on the wholesale value of individual cuts that arise from changes in the distribution of the commercial cuts. If it assumed that the value of a specific cut is also related, in part, by its lean content, then the increased lean content of each cut increased carcass value by 5.7% (additive model). However, if the value of the cut is related more to the proportion of lean within that cut, then a multiplicative adjustment may be more appropriate. Using this model, carcass value increases by 8.1%. This analysis does not reflect carcass value as currently determined by the carcass-grading system, but rather attempts to determine carcass value based in its major components (i.e., weight of cuts and lean yield within each of the primal cuts). Defining carcass value in terms of individual wholesale cuts provides a more comprehensive estimate of carcass value that better reflects the underlying definition of carcass value used for the grading probe. Rearing pigs out of doors resulted not only in changes in carcass conformation, but also in the lean meat yield with the primal cuts. These results may suggest potential for rearing hogs in outdoor facilities in Western Canada. More importantly, they also illustrate the need to revise the current grading system as new technologies develop that better identify differences in carcass conformation. This effect may become more important as specialized meat-type sire lines being developed by hybrid breeding companies become more common. CONCLUSIONS The present study has shown that outdoor-reared pigs had a lower average daily gain than confinement-reared pigs which increased days to market by 15%. While feed conversion was similar in both systems, outdoor-reared pigs required 13.5% more feed during the winter months. Grading data indicate that rearing environment had only a small effect on carcass lean percentage, which tended to be 0.51% higher for outdoor-reared pigs compared with confinement-reared pigs. However, on a carcass dissection basis, confinement-reared pigs were fatter than outdoor housed pigs and carcass value increased by 8.1%. In the same way, meat quality was not substantially influenced by fattening environment, but there was a trend towards higher PSE scores for outdoor-compared with confinement-reared pigs. ACKNOWLEDGEMENTS This work was supported, in part by National Pig Development Corporation, Canada, which provied all breeding stock and assisted with funding of technical support. The authors wish particularly to recognize the dedicated assistance of the Swine Unit staff for the excellent animal care they provided, the Meat Centre staff, and the Unit Managers, Lorne Tannas (Swine Unit) and Don Brereton (Meat Centre). The DNA analysis used to determine genotypes of the pigs was performed by Dr. Austin Murray and Ms Penny Johnson. Barton-Gade, P. and Blaabjerg, L. O Preliminary observations on the behaviour and meat quality of free range pigs. Proc. 35th Int. Cong. Meat Sci. Technol. pp Canadian Council on Animal Care Guide to the care of experimental animals. Vol. 1. Canadian Council on Animal Care, Ottawa, ON. Commission Internationale de l Eclairage Commission Internationale de l Eclairage. 18th Session, London, UK. September CIE Publication 36. Fujii, J., Otsu, K., Zorsato, F., Deleon, S., Khanna, V. K., Weiler, J. E., O Brien, P. and MacLennan, D. H Identification of a mutation in porcine ryanodine receptor associated with malignant hyperthermia. Science (Washington, DC) 253: Grandin, T Environment and genetic effects on hog handling. ASAE Annual Meeting, New Orleans, LA. Paper no Murray, A. C The evaluation of muscle quality. In S. D. Morgan Jones, ed. Quality and grading of carcasses of meat animals. CRC Press, Boca Raton, FL. Murray, A. C., Jones, S. D. M. and Sather, A. P The effect of preslaughter feed restriction and genotype for stress susceptibility on pork lean quality and composition. Can. J. Anim. Sci. 69: Pond, W. G. and Houpt, K. A In The Biology of the pig. Cornell University Press, Ithaca, NY. 76 pp. SAS Institute, Inc SAS/STAT user s guide: statistics, Version 6, 4th ed., Volume 2. Cary, NC: SAS Institute Inc., 846 pp. Van der Wal, P. G Free range pigs: carcass characteristics and meat quality. Proc. 37th Int. Co. Meat Sci. and Tech. pp Van der Wal, P. G., Mateman, G., De Vries, A. W., Vonder, G. M. A., Smulders, F. J. M., Geesink, G. H. and Engel, B Scharrel (free range) pigs: Carcass composition, meat quality and taste panel studies. Meat Sci. 34: Warriss, P. D., Kestin, S. C. and Robinson, J. M A note on the influence of rearing environment on meat quality in pigs. Meat Sci. 9: