Degree of Breed Purity and Farm Sustainability: Effects on the Quality of Iberian Pork

Abstract

The sustainability of livestock farming is becoming a key consideration in the European pork industry, particularly regarding the balance between intensive and extensive farming practices. This study focuses on the Iberian pig breed, assessing the pure breed and the Iberian × Duroc crossbreed and three production systems: intensive indoor fattening, outdoor intensive fattening, and free-range fattening, with an emphasis on their impact on both sustainability and pork quality. The quick-scan sustainability assessment tool developed within the H2020 project mEATquality was used to evaluate the environmental, social, and economic performance of each system. The results revealed that the free-range system performed best in environmental and economic sustainability, while the intensive indoor system showed higher economic stability. Significant differences in meat quality were observed based on the production system, including pH, fat and protein content, colour, texture, and fatty acid profiles. Notably, the free-range system produced pork with higher levels of MUFA and omega-3 fatty acids while intensive indoor showed a more favourable texture, while the intensive systems were associated with paler meat and higher SFA content. Indeed, the results highlighted a significant interaction between the production system × breed, indicating that the 100% Iberian is better adapted to the extensive systems. This study highlights the importance of integrating sustainability assessments with meat quality parameters to identify production methods that are both environmentally responsible and capable of meeting the consumer demand for high-quality pork.

1. Introduction

European citizens believe that current pig farming practices are too intensive and, by contrast, associate extensive breeding practices with the idea of sustainability and meat quality [1,2,3]. Among the factors associated with greater extensification are the availability and complexity of space to enhance the animals’ exploratory behaviour, the possibility of foraging and the use of diverse raw materials for animal feed [4], and the breeding of native breeds [5,6], which are considered to be extrinsic traits. In contrast, intrinsic traits are those that, through sensory qualities such as colour, texture, or flavour, depend on the physical and chemical composition of the meat and determine the actual quality of the product obtained. Since intrinsic traits may depend on extrinsic traits [7], a relevant achievement would be the possibility of correlating the quality of a product through physical and chemical parameters with the degree of extensification.

Regarding the quality of pork, this is defined by a group of complex traits that, in turn, depend on the perspective of each of the factors involved [1,2,3]. From the consumer’s point of view, quality is the result of visual perception, colour, percentage of lean meat and the amount of visible water, along with characteristics that emerge during meat consumption, such as flavour, tenderness, and juiciness, and are evaluated after the thermal processing of meat cuts [8,9,10]. These sensory attributes of pork are, in turn and a priori, the result of other quality traits that are important from a scientific and technological point of view: pH, water holding capacity, texture, and other parameters [10,11]. Previous studies and their thorough review have shown that quality can be affected by factors such as the use of local breeds, space allocation during fattening, and environmental enrichment [7], all of which are related to extensification and sustainability factors.

In Spain, the Iberian pig breed is the most widespread autochthonous swine breed, and it is mainly raised outdoors in the southwest of the Iberian Peninsula. Traditionally, this breed was linked to pasture-based and extensive systems. However, nowadays, the finishing phase is mainly intensive and indoors. There is a regulation in place to differentiate the Iberian pig breed fattening systems [12], which establishes three different categories depending on the rearing system:

• Intensively fattened pigs (white label): indoor rearing of Duroc crossbred animals, which are slaughtered at ≥150 kg live weight (LW) and at ≥10 months old.
• Outdoor intensively fattened pigs: outdoor rearing with a diet based on feed and occasional grazing. Up to 100 pigs/ha are allowed, and they are slaughtered at 150 kg LW and at ≥12 months old.
• Free-range fattened pigs: outdoor rearing for at least 60 days to gain ≥45 kg LW exclusively by grazing acorns and grass in dehesa grasslands, which is an agroforestry system with scattered oaks (Quercus sp.) [13]. The stocking rate ranges from 0.25 to 1.25 pigs/ha, depending on acorn availability [14]. They are slaughtered at ≥14 months of age with ≥165 kg LW; although in traditional systems, they may reach up to 2 years old [15].

Although the Iberian breed represents only 10.7% of total pig production in Spain [16], the exceptional quality of its products, known for their high levels of unsaturated fats and premium market prices, makes the Iberian breed a crucial species in farm economic sustainability [17]. Moreover, within that breed, free-range fattened pigs represented only 16.9% in 2024 [18].

In this context, it is necessary to assess and improve the sustainability of livestock farms by promoting extensive practices that are both profitable and environmentally responsible [19]. Sustainability, understood as meeting present needs without compromising viability, is based on three interrelated dimensions: the environmental, focused on responsible resource use; the social, linked to well-being and equity; and the economic, centered on the viability and efficiency of production systems. These dimensions are especially relevant in pig production, one of the most consumed types of meat in Europe. Although quick-scan tools exist to assess aspects such as herd health [20], biosecurity [21], or management practices [22,23,24], there is a need for simple, objective and applicable instruments that enable an integrated evaluation of sustainability.

However, it is not only necessary to evaluate sustainability; it is also necessary to correlate the effect of production methods with the quality of the meat obtained, and to establish which factors have the greatest influence on the final quality. With this premise in mind, the project mEATquality (“Linking extensive husbandry practices to the intrinsic quality of pork and broiler meat”) seeks to analyze meat quality in relation to sustainable meat production. Specifically, in this work, the main objective was to correlate the degree of sustainability of the different production systems of Iberian pigs, intensive fattening, outdoor intensive fattening, and free-range fattening pigs (montanera or acorn-fed system), with the quality of the meat obtained, and simultaneously establish the influence of breed (pure Iberian vs. Iberian × Duroc). Therefore, the aim is to determine which production method is more sustainable and produces higher quality pork, trying to elucidate which production parameters have the greatest influence on this quality.

2. Materials and Methods

2.1. Farms

For this study, three farms were selected to retrieve the meat samples:

• Farm 1: Intensively indoor-fattened Iberian × Duroc crossbred pigs (Ib × Dc) (see feed composition in

  Table 1. Compound feed composition.

  Raw Material	% Composition
  Barley	44.80
  Wheat	41.50
  Sunflower seed	6.70
  Sunflower oil	2.90
  Soybeans	1.70
  Calcium carbonate	0.95
  Dicalcium phosphate	0.55
  Salt	0.50
  Others	0.40

  ).
• Farm 2: Outdoor intensively fattened Iberian purebred (Ib) and crossbred pigs (Ib × Dc) fed compound feed (see composition in Table 1) with free access to outdoor pen runs with dirt floors.
• Farm 3: Free-range fattened Iberian purebred (Ib) and crossbred pigs (Ib × Dc). During the finishing period, the animals foraged in a dehesa, where they mainly consumed acorns and grass.

The animals stayed in these finishing systems for 60 days. For more information about these systems, see Reyes-Palomo et al. [25] and Rodríguez-Estévez et al. [4,13].

When the animals reached the slaughter weight (≈150 kg for intensive, ≈156 kg for outdoor intensive and ≈165 for free-range) they were transported to commercial abattoirs.

2.2. Sustainability Calculation Methods

Two quick sustainability calculators (QSCs) have been developed within the mEATquality project to assess the sustainability of pig production farms, one specifically adapted to intensive systems, and another tailored to extensive or free-range farms [26]. Both calculators are publicly available at https://meatquality.eu/ for consultation and use. These QSCs aim to provide a standardized, practical and comparative framework for evaluating environmental, social and economic performance at the farm level.

These QSCs follow a quick-scan approach, combining ease of use with technical evaluation about stockmanship, animals, farm and environment management. They are structured around a set of best practices identified through expert consultation and scientific literature review, enabling the systematic identification of strengths and improvement areas in pig farm management. These QSCs are structured into thematic blocks or attributes that group related sustainability practices/questions. The intensive QSC includes 8 blocks, whereas the extensive QSC covers 10 blocks, incorporating 2 blocks with additional aspects relevant to outdoor systems. The 8 blocks common to both systems are: certifications; water management; feed; energy efficiency; socioeconomic contribution to the territory; farm-associated business; animal management; and waste and residues management. The two additional blocks of the extensive QSC include specific indicators to capture sustainability dimensions that are not applicable to intensive indoor farms: stocking density and grazing management, pastures, soil management, and biodiversity. In general, the intensive QSC includes 72 questions, while the extensive one includes 69, with most questions being binary (yes/no) or based on predefined categorical responses, designed to be intuitive and minimize respondent burden. Each question is linked to one or more dimensions of sustainability (environmental, social, and economic) and contributes proportionally to the overall sustainability score.

For each farm, the tool generates: (1) a global sustainability score (on a 0–100 scale) and (2) partial scores for each of the three main dimensions (environmental, social, and economic). The scoring system is based on a predefined weighting matrix, derived from expert consensus, and enables benchmarking between farms.

2.3. Samples

A total of 117 samples of pig loins were analyzed: 25 samples from the indoor intensive farm from Ib × Du pigs; 42 samples from the outdoor intensive farm (17 samples of Ib and 25 samples of Ib × Du) pigs and 50 samples from the free-range farm (25 samples of Ib and 25 samples of Ib × Du pigs).

Upon arrival at the abattoir, the pigs were weighed and slaughtered using standard commercial methods and a CO₂ stunning system. The carcasses were cooled at 4 °C for 24 h, after which the left loins were removed and transferred to the laboratory for the corresponding analyses of the Longissimus thoracis et lumborum (LTL) muscles.

2.4. Meat Quality Analyses

After arrival at the laboratory, the meat samples were stored at 4 °C for 24 h. Therefore, 48 h after slaughter, pH, EZ-DripLoss, colour and moisture analyses were performed. All the samples, wrapped in plastic to avoid dryness, were then left to mature in cold storage (4 °C) until 72 h post-mortem, at which time they were vacuum-packed and frozen at −20 °C for subsequent analyses: total fat and protein, fatty acid profile, texture analysis and cooking losses.

2.4.1. pH and Drip Loss

The pH was measured 48 h post-mortem of the animal, after thawing (24 h at 4 °C) and just before texture analysis, using a pH meter (Crison Basic 20, Barcelona, Spain) equipped with a penetration probe electrode inserted into the left longissimus thoracis et lumborum (LTL) (loin) at the last rib (T13-L1 level) three times. Drip loss was determined by the EZ-DripLoss method [27]. At 24 h post-mortem, one slice of 2 cm in thickness was cut from the longissimus dorsi between T13-L1. Then, two samples of approximately 10 g of the loin eye were cut with a circular knife (2.5 cm diameter). Sample A was always taken from the ventral part of the M. longissimus dorsi and sample B from the dorsal part. The samples were placed in pre-weighed drip loss containers (KABE Labortechnik, Nümbrecht-Elsenroth, Germany) and stored for 24 h at 4 °C. Afterwards, each container was weighed with the meat sample, and weighed once again to determine drip loss. All drip loss measurements were expressed as a percentage of the initial weight.

2.4.2. Colour

The colour was measured 48 h post-mortem using a HunterLab MiniScan EZ45/LAV (Hunterlab, Reston, VA, USA) equipped with a 25 mm measuring head and the CIELab parameters determined were L* (lightness), a* (redness), b* (yellowness), chroma and hue, using an observer of 10° and the illuminant D₆₅. To measure the colour of the loin, two fillets of 2.0 cm each were cut across the grain, from the LT between T7 and T9. The fillets were placed in the refrigerator at 4 °C for 30 min. Colour was measured by placing the colorimeter directly on the surface of the meat, in five different positions on the exposed surface of each steak. Therefore, 10 replicates were obtained from each sample.

2.4.3. Proximate Composition

Chemical analysis of the loin was performed according to the AOAC methods (Meat and Meat products Preparation of Sample Procedure for Association of Official Analytical Chemists). At 48 h after slaughter, moisture was determined by oven-drying (AOAC 950.46) [28] with fresh pork that was finely ground for each sample using a chopper. Total fat and protein were determined on grounded and frozen meat. Before analysis, the samples were thawed for 24 h at 4 °C. Total fat was determined by the Soxtec extraction unit (Gerhardt Soxtherm, Königswinter, Germany) using ethylic ether (AOAC 960.39 crude fat in meat) [29], and total protein was determined by the Kjeldahl method using 6.25 as a conversion factor (AOAC 981.10 Kjeldahl method) [30], using a heating digester (DK 20 Heating Digester, VELP SCIENTIFICA, Usmate, Italy) and a Kjeltec™ 2300 (based on Tecator™ Technology) (FOSS Group, Hoeganaes, Sweden). All the analyses were performed in duplicate.

2.4.4. Fatty Acids

A total of 39 fatty acids were quantified, and their sums were calculated based on the degree of saturation and type. To quantify these fatty acids, the first total lipid extraction was carried out according to the Folch et al. [31] method. Next, the transmethylation was performed according to the standardized acid-catalysed transmethylation method (UNI EN ISO 12966-2:2017) [32]. And finally, 1 μL was injected into the gas chromatography system (GC 6890 N, Agilent Technologies, Santa Clara, CA, USA) equipped with a 100 m × 0.25 mm × 0.20 mm capillary column (SP-2560, Supelco, Inc., Bellefonte, PA, USA) and with a split/splitless injector and an FID detector, using the following conditions: injector temperature 250 °C, detector temperature 250 °C, and carrier gas (helium) at a flow rate of 1.3 mL/min. The oven temperature program was 100 °C, increasing temperature at 25 °C/min until reaching 200 °C, then increasing at 5 °C/min until reaching 220 °C, then increasing by 0.50 °C/min until reaching 230 °C, and then increasing by 4 °C/min until reaching 250 °C, where it was maintained for 5 min. Fatty acids are identified according to their retention times by comparison with an external quantitative standard mixture (FAME Mix 37 components C4–C24, Supelco Inc., Bellefont, PA, USA), added with all cis-methyl 7,10,13,16-docosatetraenoate (C22:4) and methyl all cis-7,10,13,16,19-docosapentaenoate (C22:5) analytical standards (Supelco Inc., Bellefont, PA, USA). The quantification is carried out according to the method described in UNI EN ISO 12966-4:2015 [33]. The methyl nonadecanoate analytical standard (Supelco Inc., Bellefont, PA, USA) is used as an internal standard. Quantification is expressed as a percentage (g/100 g) of total fatty acid methyl esters. The determinations were carried out in duplicate.

2.4.5. Texture Analysis: Warner–Bratzler Shear Force and Slice Shear Force

Meat samples between T9 and T13 were kept at 4 °C for 72 h post-mortem and then vacuum packed, frozen and stored below −20 °C up to a maximum of 3 months. Slices of 3.5 cm in thickness were used for WBSF, SSF and cooking losses analysis. Before carrying out the analysis, the samples were thawed in darkness at 4 °C for 24 h.

For the SFF test, samples were grilled in a double plate grill (KGJ442, GGM Gastro Inter., Ochtrup, Germany) preheated to 200 °C. The internal temperature of each slice was monitored by inserting a thermometer (Checktemp1 Hanna Instruments, Eibar, Spain) in the center of the piece. When the center reached 40 °C, the sample was turned over until it reached 68 °C, and then the temperature was allowed to stabilize at 70 °C. The SFF kit was used to cut each of the two samples, first making a cut across the width of the muscle at a point approximately 2.0 cm from the lateral end. Then, a cut was made parallel to the first cut of the loin at 5.0 cm from the first cut. Using a double-bladed knife (two parallel blades 1.0 cm apart), a cut was made along the 5.0 cm long steak position at a 45° angle to the long axis of the tenderloin and parallel to the muscle fibres. Two slices (samples) were taken per muscle, one slice per steak.

The slices were sheared using a flat blunt-point blade with a thickness of 1.1684 mm and a half-round beveled cutting edge attached to a TA-XT2i texturometer (Stable Micro Systems, Godalming, UK), using a crosshead speed of 2 mm/s.

Samples for WBSF analysis were vacuum packed and then immersed in the water bath at 76 °C. The samples were cooked until they reached an internal temperature of 72 °C, immediately after which they were transferred to an ice bath for 10 min to stop the cooking and then they were refrigerated for 6 h. Samples of each steak were obtained with a cork borer, cutting round scores of 1.27 cm in diameter, parallel to the muscle fibre and with an inclination angle of 45°, and a minimum of six round scores were measured per sample. Each core was sheared once in the perpendicular direction of muscle fibres by a texture meter TA-XT2i (Texture Technologies Corp./Stable Micro Systems, Godalming, UK), equipped with a 2.97 mm thick Warner–Bratzler blade, adjusted for a crosshead speed of 2 mm/s.

The recorded values were shear force, which is the maximum force recorded (N), and shear energy, which is the area under the force deformation curve (N × sec) from the start of the test to the maximum force.

2.4.6. Cooking Loss

Meat samples used for WBSF analysis were also used for determining cooking losses. The cooking loss values were determined by calculating the difference in weight between the fresh fillet and after cooking the loin in the water bath, and the losses were expressed as a percentage of the initial weight.

2.4.7. Statistical Analysis

The significant effects of breed, production system and their interactions were obtained by using General Linear Model (GLM). Means and standard error of the mean were calculated for all variables. The statistical significance of each factor was assessed at a 95% confidence level (α = 0.05) using Snedecor’s F as the contrast statistic. For the differentiation of homogeneous subsets, Tukey’s test was used.

Correlations between the different parameters were studied using a two-tailed Pearson significance correlation. All the statistical analyses were carried out using the SPSS Package 28 (IBM, Chicago, IL, USA).

3. Results

3.1. Quick Scan

The intensive farm (farm 1) obtained the lowest overall sustainability score (54.17), with the lowest social impact (37.30) and an intermediate environmental performance (50.30), standing out in energy efficiency (7.00) but showing deficiencies in waste management (3.50) and lacking certifications (0.00). In contrast, extensive farm 2 had the highest social sustainability (50.83) due to its strong farm–business association (9.00), and its punctuation excels in waste management (8.00) and water consumption (8.89), but with a low socioeconomic contribution to the territory (1.00). Extensive farm 3 achieved the highest overall sustainability (59.90), with the best environmental (68.14) and economic performance (59.02) due to its high energy efficiency (9.60) and proper grazing management (9.48), although it had poor waste management (1.25) (

Table 2. Punctuation of the mEATquality project quick scan sustainability calculators for each topic, partial and total scores.

Farm	Certifications	Water Management	Feed	Stocking Rate and Grazing Management	Energy Efficiency	Socioeconomic Contribution to Territory	Farm Associated Business	Animal Management	Pastures and Soil Management and Biodiversity	Waste and Residues Management	Environmental Impact	Social Impact	Economic Impact	Total Sustainability Score
Indoor intensive	0.00	7.89	5.14	-	7.00	5.00	4.00	6.67	-	3.50	50.30	37.30	49.47	54.17
Outdoor intensive	1.18	8.89	5.03	8.40	1.00	6.00	9.00	4.09	8.00	0.00	53.07	50.83	53.98	55.65
Free-range	0.00	7.78	9.48	9.60	10.00	6.00	1.00	3.18	5.00	1.25	68.14	44.59	59.02	59.90

). These results suggest that extensive systems offer advantages in environmental and social sustainability, while the intensive system maintains greater economic stability, highlighting the need for strategies that balance these aspects to improve the overall sustainability of pig production.

3.2. Physicochemical Composition

Table 3. Mean values of the physicochemical parameters for the different production systems and breeds.

Production System	Indoor Intensive	Outdoor Intensive		Free-Range Dehesa		SEM	p Value
Breed	50%	50%	100%	50%	100%		PS	B	PS×B
pH48h	5.81 b	5.71 c	5.68 c	5.79 b	6.09 a	0.023	0.000	0.012	0.002
pHthaw	5.84 c	5.69 c	5.71 c	5.90 b	6.18 a	0.018	0.000	0.000	0.002
EZ-DripLoss	0.92 c	2.10 a	1.23 b	1.29 b	0.39 c	0.085	0.000	0.000	0.940
Moisture %	69.21	68.73	67.45	69.18	68.78	0.209	0.157	0.078	0.349
Protein %	23.32 a	21.14 c	21.78 c	22.20 b	22.05 b	0.120	0.000	0.377	0.150
IMF %	7.24 c	11.47 a	11.79 a	7.49 c	9.07 b	0.249	0.000	0.093	0.268

^a,b,c Different letters mean statistically significant differences between groups at p < 0.05. SEM: Standard error of the mean. PS: Production system. B: breed. 50%: Iberian × Duroc breed. 100%: Iberian breed.

shows that the farming system had a statistically significant effect on all parameters analyzed, pH, drip loss, protein, and fat, except for moisture. On the other hand, the breed factor showed a statistically significant effect for pH_48h, pH_thaw and drip losses, but not for the composition parameters.

Regarding pH, the free-range group presented significantly higher mean values (5.94 and 6.04 for pH_48h and pH_thaw, respectively), followed by the indoor intensive system (5.81 and 5.84), while the outdoor intensive group presented the lowest mean values (5.69 and 5.70). In the case of the breed, the highest pH corresponded to the 100% Iberian breed, with mean values of 5.88 and 5.94 vs. 5.77 and 5.81 (pH_48h and pH_thaw) for the 50% Iberian. The interaction of both factors produced significant differences for both pH measures owing to the high values of the 100% Iberian free-range group. An increase in pH values was observed due to the freezing and thawing process, which was especially noticeable in the case of free-range animals. The drip loss parameter presented the highest mean value for the intensive outdoor system (1.66), followed by the intensive indoor system (0.92), while the free-range group (0.84) presented the lowest value. As far as breed is concerned, the 50% Iberian showed the highest drip loss value (1.44 vs. 0.81) while the interaction between both factors was not significant.

Fat and protein showed an inverse correlation. Thus, the intensive indoor system presented the significantly highest protein and lowest fat values (23.32% and 7.24%, respectively), while the intensive outdoor system presented the lowest protein and highest fat values (21.46% and 11.63%, respectively), showing that the effect of the farming system was statistically significant. The free-range group therefore showed intermediate values for both parameters (22.12% and 8.28%). No significant effect of the breed was observed, although the highest protein value and lowest fat value corresponded to the 50% Iberian breed, with values of 23.32% for protein and 7.24% for fat.

3.3. Cooking Loss and Instrumental Colour and Texture

Table 4. Mean values of the instrumental colour and texture parameters for the different production systems and breeds.

Production System	Indoor Intensive	Outdoor Intensive		Free-Range Dehesa		SEM	p Value
Breed	50%	50%	100%	50%	100%		PS	B	PS×B
L*	56.83 a	50.91 c	50.91 c	55.52 b	48.88 c	0.303	0.000	0.000	0.000
a*	8.40 c	10.95 b	11.78 a	9.55 c	11.89 a	0.099	0.000	0.000	0.001
b*	15.44 a	13.89 c	14.28 b	15.26 a	13.84 c	0.095	0.000	0.019	0.000
C	17.63	17.73	18.56	18.04	18.42	0.104	0.595	0.012	0.335
H	61.57 a	51.90 c	50.59 c	58.03 b	49.13 c	0.318	0.000	0.000	0.000
WBSF max. force (N)	40.12 b	35.41 b	37.40 b	42.57 b	88.96 a	2.688	0.000	0.000	0.000
WBSF energy (N/mm)	129.17 b	58.21 c	63.92 c	135.81 b	181.48 a	3.474	0.000	0.001	0.012
SSF max. force (N)	142.69 b	141.48 b	113.86 c	164.10 a	171.87 a	3.502	0.000	0.213	0.027
SSF energy (N/mm)	519.52 b	496.90 b	369.34 c	593.35 a	601.18 a	13.514	0.000	0.052	0.029
Cooking loss (%)	11.48 b	14.66 a	14.33 a	14.42 a	13.15 b	0.393	0.011	0.368	0.598

^a,b,c Different letters mean statistically significant differences between groups at p < 0.05. SEM: Standard error of the mean. PS: Production system. B: breed. 50%: Iberian × Duroc breed. 100%: Iberian breed.

shows that the rearing system had a statistically significant effect on all colour and texture parameters, except for chroma. Regarding the breed factor, significant differences were observed in all colour parameters and WBSF force and energy, but not in SFF texture parameters or cooking losses.

The intensive indoor group had the highest values of L*, b* and hue followed by the free-range group showing mean values of 52.2, 14.52 and 53.58 for L*, b* and hue, respectively, which means that the meat was paler and yellower, while the intensive outdoor system had the lowest values (50.91, 14.08 and 51.24). In contrast, the a* parameter (redness) reached the highest values for the intensive outdoor group (11.37), followed by the free-range system (10.72), while the intensive indoor system had the lowest values. In terms of breed, the highest values of L*, b*, and hue corresponded to the Ib × Du, while for the a* parameter, the highest value corresponded to the 100% Iberian. The interaction between both factors produced significant differences for these colour parameters. This is mainly because the 50% Iberian intensive indoor animals had significantly lighter, less red, and more yellow meat than the 100% Iberian free-range animals.

With regard to texture, the free-range group showed significantly higher values (65.76 N, 158.64 N/mm, 167.98 N and 597.26 N/mm for WBSF force, WBSF energy, SFF force, and SFF energy, respectively), followed by the intensive indoor system, while the intensive outdoor system showed the lowest values (36.40 N, 61.06 N/mm, 127.67 N and 433.12 N/mm). Regarding breed, the highest texture value when measured with the Warner–Bratzler probe (WBSF force and energy) corresponded to the 100% Iberian. However, breed did not have a significant effect on the texture parameters measured with the SSF. The interaction between both factors produced significant differences in these texture measurements. It was found that when the WBSF probe was used, the 100% Iberian raised in free-range showed higher values and for the SSF probe, the 100% Iberian intensive outdoor showed the lowest ones. Finally, for the cooking loss parameter, the group raised in the intensive outdoor system had the highest mean value (14.49%), while the intensive indoor system (11.48%) had the lowest value. Neither breed nor the interaction between the two factors produced significant differences for this parameter.

3.4. Fatty Acid Profile

The results related to the fatty acid profile of the analyzed groups (

Table 5. Mean values of the individual fatty acids for the different production systems and breed.

Production System	Indoor Intensive	Outdoor Intensive		Free Range Dehesa		SEM	p-Value
Breed	50%	50%	100%	50%	100%		PS	B	PS×B
C6:0	0.08 a	0.06 b	0.02 c	0.09 a	0.22 c	0.02	0.01	0.20	0.01
C8:0	0.02	0.01	0.01	0.01	0.01	0.00	0.10	0.54	0.95
C10:0	0.15 a	0.12 b	0.11 b	0.13 b	0.13 b	0.00	0.00	0.44	0.30
C11:0	0.00 b	0.01 a	0.00 b	0.01 a	0.01 a	0.00	0.04	0.44	0.73
C12:0	0.12 b	0.08 b	0.08 b	0.11 a	0.10 a	0.00	0.00	0.28	0.70
C13:0	0.04 c	0.12 b	0.03 c	0.04 c	0.16 a	0.01	0.42	0.66	0.00
C14:0	1.59 a	1.44 b	1.49 b	1.53 a	1.51 a	0.01	0.00	0.59	0.19
C14:1	0.05	0.06	0.05	0.05	0.06	0.00	0.59	0.53	0.13
C15:0	0.29 a	0.03 c	0.04 c	0.15 b	0.16 b	0.01	0.00	0.65	0.92
C15:1	0.21 a	0.03 c	0.01 c	0.14 b	0.16 b	0.01	0.00	0.93	0.26
C16:0	26.26 a	25.11 b	25.62 b	25.96 a	25.11 b	0.11	0.03	0.49	0.01
C16:1	4.46	4.32	4.12	4.31	4.53	0.09	0.52	0.96	0.31
C17:0	0.20 c	0.49 b	0.74 a	0.17 c	0.21 c	0.08	0.05	0.42	0.55
C17:1	0.25 a	0.21 b	0.16 c	0.23 b	0.26 a	0.01	0.00	0.60	0.01
C18:0	12.06 a	11.33 b	11.45 b	12.12 a	10.87 b	0.10	0.40	0.01	0.00
C18:1n9t	0.34 b	0.40 b	0.28 c	0.34 c	0.52 a	0.02	0.15	0.53	0.00
C18:1n9c	46.53 b	48.16 a	48.64 a	48.21 a	48.10 a	0.16	0.00	0.62	0.41
C18:2n6t	0.00	0.06	0.05	0.01	0.11	0.02	0.73	0.27	0.21
C18:2n6c	4.05 a	4.02 a	3.47 b	3.56 b	4.13 a	0.07	0.32	0.96	0.00
C18:3n6	0.03 b	0.07 a	0.05 b	0.04 b	0.06 a	0.00	0.02	0.86	0.03
C18:3n3	0.25 b	0.14 c	0.15 c	0.20 b	0.32 a	0.01	0.00	0.00	0.00
C20:0	0.18 a	0.19 b	0.20 b	0.18 b	0.22 a	0.00	0.14	0.00	0.02
C20:1	0.80	0.81	0.83	0.78	0.83	0.01	0.86	0.20	0.59
C20:2	0.31 a	0.21 b	0.17 c	0.18 c	0.20 b	0.01	0.00	0.30	0.01
C20:3n6	0.12 b	0.15 a	0.13 a	0.08 c	0.09 c	0.00	0.00	0.55	0.11
C20:3n3	0.06 b	0.05 b	0.03 c	0.08 a	0.08 a	0.00	0.00	0.88	0.00
C20:4n6	0.01	0.05	0.11	0.02	0.12	0.02	0.84	0.06	0.65
C20:5n3	0.01 b	0.06 a	0.05 a	0.00 c	0.01 b	0.00	0.00	1.00	0.20
C21:0	0.03 b	0.07 a	0.07 a	0.03 b	0.04 b	0.00	0.00	0.62	0.44
C22:0	0.07 b	0.14 a	0.13 a	0.03 c	0.06 b	0.00	0.00	0.40	0.03
C22:1n9	0.38 a	0.31 b	0.33 b	0.32 b	0.31 b	0.01	0.05	0.73	0.57
C22:2n6	0.01	0.03	0.04	0.02	0.09	0.02	0.75	0.31	0.36
C22:4n6	0.08 a	0.02 c	0.06 b	0.05 b	0.07 a	0.00	0.00	0.01	0.16
C22:5n3	0.10 c	0.26 a	0.12 c	0.11 c	0.17 b	0.02	0.22	0.41	0.05
C22:6n3	0.01	0.04	0.02	0.02	0.06	0.01	0.24	0.70	0.06
C23:0	0.83 c	1.20 a	1.04 b	0.59 c	0.74 c	0.03	0.00	0.98	0.05
C24:0	0.05	0.05	0.05	0.06	0.07	0.00	0.11	0.45	0.22
C24:1	0.01 c	0.08 a	0.06 a	0.04 b	0.09 a	0.01	0.12	0.38	0.05
SFA	41.96 a	40.44 b	41.08 a	41.21 a	39.64 c	0.18	0.04	0.25	0.01
MUFA	53.03 b	54.39 a	54.48 a	54.43 a	54.86 a	0.18	0.01	0.51	0.67
PUFA	5.00 b	5.17 b	4.45 c	4.36 c	5.50 a	0.12	0.66	0.43	0.00
n6	4.69 c	4.88 b	4.19 c	4.08 c	5.03 a	0.11	0.75	0.59	0.00
n3	0.31 b	0.29 c	0.25 c	0.28 c	0.47 a	0.01	0.00	0.01	0.00

^a,b,c Different letters mean statistically significant differences between groups at p < 0.05. SEM: Standard error of the mean. PS: Production system. B: breed. 50%: Iberian × Duroc breed. 100%: Iberian breed. SFA: saturated fatty acids. MUFA: monounsaturated fatty acids. PUFA: polyunsaturated fatty acids. Values are expressed as a percentage (g/100 g) of total fatty acid methyl esters.

) showed significant differences due to the production system in 21 out of 39 fatty acids quantified and in three of their sums, while breed had a significant effect on a total of four individual fatty acids and the n3 sum.

In the case of the saturated fatty acids (SFA), the highest values corresponded in general to the intensive indoor group, followed by free-range and finally the outdoor intensive, except for C6:0, C20:0 and C22:0. It is worth noting that in the case of odd-numbered SFAs, the highest values corresponded in general to the outdoor intensive (C17:0, C21:0 and C23:0) or the free-range (C13:0). Due to these results, the production system showed significant differences for the total SFAs, with the indoor system presenting the highest values. For the breed, however, significant differences were only found for C18:0, for which the 50% Iberian breed showed a higher mean value than the 100% Iberian breed (11.83% vs. 11.16%), and for C20:0, for which the highest mean value was found in the 100% Iberian group (0.21% vs. 0.18%). For the total SFA, no significant effect of breed was found. Moreover, significant interactions were observed due to the differences between the 100% free-range and 50% indoor intensive for C16:0, C18:0, and C20:0, the highest values in the outdoor intensive for C22:0, and the highest values in the 100% Iberian free-range for C6:0.

As for the monounsaturated fatty acids (MUFAs), significant differences were found due to the production system for C15:1 and C17:1, with the lowest values for the outdoor intensive group, and for C18:1n9c (oleic acid), with the lowest values for the indoor intensive group. Since oleic acid is the main fatty acid, this caused the MUFA sum to show significant differences due to the production system. However, breed did not significantly affect any of the unsaturated fatty acids, nor did it affect their sum. The interaction of both factors produced significant differences only for C17:1 and for C18:1n9t.

Finally, C18:3n3 and C20:3n3 polyunsaturated fatty acids (PUFA) showed a significant effect of the production system, with the outdoor intensive system having the lowest values and the free-range having the highest (0.14% vs. 0.26% vs. 0.25% and 0.04% vs. 0.07% vs. 0.06%), while for C20:5n3 the highest values corresponded to the intensive outdoor system (0.05%). The total sum of n3 fatty acids also showed a significant effect of production system, with the free-range group presenting the highest values. However, for the sum of n6 fatty acids, no significant effect of this factor was found, mainly due to the lack of a significant effect of this factor on C18:2n6, which is the main fatty acid in this group. Differences were observed for C20:3n6, with the highest values for the outdoor intensive samples, and for C22:4n6, with the lowest values for this group of animals. As a result, there was no significant effect of the production system on the total PUFA.

The breed factor significantly affected only C18:3n3 and C22:4n6, with the highest values found in the case of the 100% Iberian breed in both cases, but no significant effect of the breed was observed for the n3 and n6 sums or the total PUFAs.

4. Discussion

4.1. Sustainability in Livestock Production

The sustainability assessment of the three types of farms reveals substantial variability across the evaluated areas, highlighting both strengths and opportunities for improvement. It should be notice that the different items evaluated go beyond the minimum legal requirements established by the European Union, and each management system (intensive and extensive) has their own best practices and goals. Therefore, the result of the different indicators cannot be compared between extensive and intensive systems.

In global terms, water management was highly rated in all systems, an aspect of particular importance in southern European regions where efficient water use is essential due to the risk of desertification [34]. The intensive indoor system shows moderate performance, with solid scores in water management, energy efficiency and animal management, but lower values in waste management and social impact. Its relatively low environmental and social scores indicate the potential for strengthening ecosystem stewardship and farmer–community engagement.

Outdoor systems, including the outdoor intensive fattening and free-range systems, achieved very high scores in stocking rate and grazing management. These results confirm the application of good grazing practices, ensuring adequate herbaceous cover and maintaining stocking rates aligned with the grassland carrying capacity [14]. Exceeding this capacity could generate ecological imbalances such as pasture and soil degradation and a decrease in covered surface [35,36,37], which heightens erosion risk [38]. The outdoor intensive fattening system also presents high values in farm-associated business, reflecting strong integration with the local economy. However, its poor performance in energy efficiency and especially in waste and residues management is critical, as it threatens environmental integrity [39,40] and increases carbon footprint [25].

The free-range system stands out for its excellent feed management, grazing management and energy efficiency, indicating well-optimized resource use. Its higher score in feed management is partly explained by its reduced dependence on external feed sources, which constitute one of the main contributors to the environmental impact of pig production [25,41] and its carbon footprint [25]. The use of on-farm feed resources, including pasture, also increases economic sustainability by reducing vulnerability to fluctuating feed prices [42]. Nevertheless, its lower score in farm-associated business suggests limited economic diversification.

Overall, while each farm excels in specific sustainability dimensions, none achieves a uniformly high performance across all pillars. The most recurrent weakness is waste and residues management, which consistently reduces environmental performance. Addressing this limitation, together with improving animal management and social engagement where needed, would greatly enhance the overall sustainability of the systems evaluated.

4.2. Meat Quality Characteristics

The analysis of meat quality results showed a significant influence of the production system, but also a significant effect of breed, which, in turn, for some parameters, depended on the production system. Therefore, the intensive indoor production system was characterized by high protein and low-fat content, paler, more yellowish and less red meat colour, and a fatty acid profile characterized by the highest levels of SFA and the lowest levels of MUFA. This meat also showed the lowest cooking losses. On the other hand, the intensive outdoor system showed the lowest protein and pH_48h values and the highest fat and drip loss values of the three production systems. Its meat was the darkest, reddest, but also the most tender, although this group showed significantly higher cooking loss. In terms of fatty acid profile, intensive outdoor meat showed the lowest PUFA values. Finally, the meat from the free-range group showed the highest pH and lowest drip loss and was characterized by greater toughness and higher MUFA and n-3 PUFA content.

However, not only the production system must be taken into account, but also the breed. On the one hand, there are parameters that depend solely on the breed, as the 100% Iberian breed showed lower EZ-DripLoss and cooking losses and SFA, along with higher values of a* and WBS strength and energy, regardless of the production system. On the other hand, for other parameters, the effect of the production system depended largely on the breed. Thus, in the intensive outdoor system, no significant differences were observed between the 50% and 100% Iberian in terms of pH, protein, IMF, L*, b* and MUFA, while the 100% Iberian showed lower PUFA values. Finally, when considering the free-range production system, the 100% Iberian showed a higher pH, higher IMF content, lower b* and SFA content, along with a higher PUFA content (both n3 and n6), pointing to a greater influence of breed on meat quality for this system.

These results were not always in agreement with those previously published. Thus, previous results did not show significant differences in pH between production systems (intensive versus free-range), highlighting that the discrepancies could be related to the Iberian breed itself [43]. Drip loss was remarkably low in animals raised in the free-range system, as previously observed [44], which could be related to the low pH of this group, as it is well known that higher pH correlates with greater water retention capacity [45]. Therefore, the lack of significant differences in pH is the reason why no differences in drip loss and cooking losses were observed in the study by Ortiz et al. [43]. The higher water retention capacity of pasture-raised pigs has been attributed to the consumption of tocopherols from acorns and grass [5].

Furthermore, the significantly higher pH of the Iberian breed was due to the results obtained for the 100% free-range group, indicating that this breed may exhibit different pH behaviours compared to other improved pig breeds, and that this parameter could be affected differently depending on specific production conditions [43]. Therefore, although 100% Iberian pigs tend to have a higher pH [46], this rustic breed could be more affected by pre-slaughter conditions when reared in a free-range system as genetics together with preslaughter handling are critical for the muscle glycogen content and therefore for the final pH [47]. However, the water retention capacity of both raw and cooked meat was always higher in the 100% Iberian pigs, pointing to a greater influence of breed, as has also been observed in different strains of the Iberian breed [46], than of diet.

As far as the proximate composition is concerned, it has been reported that IMF is higher in intensive indoor production [43] than in free-range production, which has been associated with the growth rate of the animals [48], which is consistent with the actual results; however, other authors found no significant differences in the muscles of Iberian pigs reared in different production systems [49,50]. This contradictory result could be explained by the fact that different levels of the protein:energy ratio can affect the level of IMF [51]. Therefore, changes in the formulation of concentrated feed contribute to regulating IMF in intensively reared pigs [44]. Regarding the effect of breed, previous studies have shown that crossbreeds had lower intramuscular fat levels than 100% Iberian breeds [46,52], as the Iberian pig is a fast-maturing and anabolic breed with a high tendency to accumulate fat [53], while diet does not seem to influence this [52]. However, in this case, the results point to an effect of breed on the free-range rearing system, which shows an increase in intramuscular fat in the 100% Iberian group.

It has been reported that the rearing system affects the sensory characteristics of meat. A significant effect of the free-range rearing system on the colour of pork was observed, with animals reared in pasture having darker, redder meat than intensively reared animals [43,44], while the differences between intensive indoor and outdoor systems were negligible [44], which is not entirely consistent with the results of this study, in which all outdoor groups were characterised by their darker, redder colour. The higher L* and a* values of free-range Iberian pigs have been correlated with the combined effect of feed and environmental characteristics [54], while the effect of exercise remains unclear. Some studies do not correlate colour and exercise [55], but others point out that both haem pigment content and instrumental colour parameters increase [50]. In addition, breed had a significant effect on meat colour, with the 100% Iberian meat being darker and redder, as previously described [46,52]. These results partially agree with those described by Andrés et al. [56], who reported a higher myoglobin content in 100% Iberian muscles, but this did not correlate with the higher L* and a* values. The notable differences observed in 100% Iberian animals raised on free-range grazing would therefore be the result of all the factors mentioned above: diet, environment, exercise and breed. On the other hand, the b* value showed significant variability between breeds and rearing conditions, while the a* value did not, as previously observed by Andrés et al. [56].

Texture was also shown to be a significant effect of the rearing system, with meat from the free-range rearing system presenting significantly higher values in the instrumental texture parameters determined by the Warner–Bratzler device than meat from the intensive system, in line with the observations of Ortiz et al. [43]. This phenomenon has been attributed to the higher proportion of type I fibres in LT muscles reared on pasture [43,50], as they would be associated with a high oxidative capacity to withstand sustained muscle contractions associated with greater exercise in the free-range system [57]. However, the intensive indoor system showed significantly higher texture values than the intensive outdoor system, pointing to the influence of other factors, such as the lower IMF content of this group, as reported by Ortiz et al. [43]. In addition, WBSF parameters were higher for the 100% Iberian, and the differences were very noticeable in the free-range system. In this regard, Ventanas et al. [58] observed that pure Iberian pigs had less structured intramuscular fat than Iberian × Duroc crossbred pigs; therefore, lower texture parameters are expected for pure Iberian pigs. However, other studies found no significant differences between 100% Iberian pigs and crossbreeds when carried out in an intensive system [46]. When the slice shear force was used, no significant effect of breed was observed; in fact, no significant differences in SSF force and energy were observed for free-range pigs, and values were lower for 100% Iberian pigs in the intensive outdoor system. Previous studies have shown that SSF parameters correlate better with sensory hardness than WBSF parameters [59].

The effect of raising Iberian pigs in different production systems has been extensively studied, and the results indicate that the more extensive the production system, the higher the MUFA and n-3 PUFA content and the lower the SFA content [44,50,60]. These changes have been attributed to the high oleic acid content of acorns, whereas the main fatty acid in grass is linoleic acid [61], so the longer the time spent in the pasture, the greater the changes observed [62]. Although previous studies have shown that, under similar feeding regimes, purebred Iberian pigs tend to accumulate higher levels of oleic acid than 50% Iberian × Duroc crosses [63], as well as a higher PUFA content and a lower SFA content [46,64], this result was only observed in the free-range breeding system, while the 100% Iberian breed showed a higher SFA content and a lower PUFA and n-3 PUFA content in the intensive outdoor system, as reflected in the significant interaction between both factors observed in this study. Variations in fatty acid composition are highly relevant, as the sensory quality of Iberian pork depends largely on the fatty acid profile [44], as well as the antioxidant products from grass and acorns [65] that will affect oxidative phenomena during the production of Iberian meat products.

The above results show that production systems based on the native Iberian breed, characterized by its low growth rate and high fat content, and the free-range rearing system, which allows pigs to express their genetic potential, demonstrate the positive effects of genotype × rearing system interactions on meat quality, as suggested by Lebret [51].

This research underscores the need for integrated approaches that combine sustainability assessments with meat quality parameters. By aligning sustainable practices with consumer preferences for higher quality, particularly in terms of nutritional content, pork production systems can be optimized for both profitability and environmental stewardship.

5. Conclusions

This study revealed significant differences in meat quality between the different production systems: the free-range system produced pork with a higher content of monounsaturated and n-3 fatty acids and greater water retention capacity, but also with greater toughness, while the intensive outdoor system stood out for the tenderness of the meat, but also for its darker colour and higher fat content. On the other hand, the intensive indoor system was associated with paler meat and low-fat content, characterized in turn by a higher proportion of saturated fatty acids. However, it is not only the production system that must be considered, but also the breed, as the results have highlighted that the 100% Iberian local breed reared in extensive systems, especially free-range which showed the highest scores for sustainability, had the best meat quality characteristics compared to the 50% Iberian breed.

Therefore, extensive systems, particularly free-range fattening which showed strengths in grazing and feed management, contribute to better pork quality, especially for the 100% Iberian, with improved nutritional profiles as well as interesting technological properties such as higher IMF amount, firmer texture and lower losses during cooking. These characteristics, combined with the high sensory appreciation of this meat, highlight its suitability for use as a raw material in the production of high-quality meat products with high economic value. On the other hand, intensively fattened pigs show greater efficiency but less desirable meat characteristics together with weaknesses in waste management, negatively impacting their environmental performance. Addressing these weaknesses could significantly improve the overall sustainability of pork production systems.