Ibérico (Iberian) Pig

The main characteristics of the Iberian breed, an autochthonous pig breed of the Iberian Peninsula, are presented in this chapter along with the results of a literature review on productive traits. Reproductive performance was estimated by sow age at first parturition, litters per sow and year, piglets alive per litter, piglet weight at birth and at weaning, percentage of stillborn per litter, mortality at weaning, lactation length and farrowing interval. For growth performance, average daily gain and daily feed intake during lactation and in different growing phases are provided. Carcass traits were evaluated by age and weight at slaughter, hot carcass weight, carcass yield, backfat thickness measurements, muscle thickness and loin eye area. Meat quality traits of longissimus muscle (pH, objective colour measurements and intramuscular fat) were also assessed. The main part of the studies considered simulated practical production conditions in Iberian pig rearing although others evaluated a defined growing period, sometimes quite far from the usual commercial slaughter weight of this breed. Therefore, some figures should be interpreted with caution. Although a considerable number of studies on Iberian pig were included in the current review, scientific papers on reproductive performance and some meat quality parameters are still rather scarce.


History and current status of the breed (census)
The Iberian pig is an autochthonous porcine breed derived from ancestral domestic pig populations of the Iberian Peninsula. For centuries, it was widely spread all over this territory. Nowadays, it can be found in the Southwest of the Peninsula: West Andalusia, Extremadura and Salamanca province. In the Portuguese Alentejo, this porcine breed, with some minor differences, is known as Porco Alentejano.
Until the middle of the XX century, the Iberian pig was the main porcine breed reared in Spain. In the first decades of the last century, the census of reproductive sows could have surpassed 500,000 animals that widely extended all over the country. Since then, a series of sanitary challenges, changes in social and feeding habits, as well as the transformation of the dehesa territory into field crops, lead to a dramatic decline in the Iberian pig population [1] that did not stop until the middle 1980s. The most critical moments of the Iberian pig population crisis took place during the 1960s, in which the breed was at serious risk of extinction.
In the late 1980s, a new period started with the beginning of Iberian pig breeding recovery and the revalorisation of its products. To this recovery contributed not only the increasing demand for traditional food products of high organoleptic quality-a key issue for the definitive recuperation of the Iberian pig populationbut also the social awareness for preservation of the genetic heritage and the natural habitat associated to this breed.
There is no official historical census of the Iberian population as the classification was based on the production system (extensive vs. intensive) and not on genetic discrimination. However, taking into account part of these data, along with own data of the Iberian pig breeders association, we can see the approximate evolution of the Iberian pig population during the last years in Figure 1. At present, with a reliable system of pig population registration, we know that there are 4370 registered Iberian pig farms, with 375,500 breeding sows and 4780 boars in the latest available status (November 2017). The total number of pigs slaughtered during 2017 were 3,240,000, which represent a 35% increment with respect to 2014 when the sector was suffering the effects of the global economic crisis and a specific crisis due to a production excess that led to a decrease in the census.

Exterior phenotypic characteristics
The racial characteristics that identify the Iberian pig are recorded in the racial standard of the genealogical book (order APA/3376/2007). Nevertheless, even today there is a great morphological heterogeneity resulting from the historical genetic isolation of this breed that gave rise to multiple local varieties, many of them already lost or subsumed into the Retinto variety, which is the predominant nowadays. The Iberian breed general morphology information is summarised in Table 1. In general, it is a medium-sized animal with pigmented skin which colour could vary from intense black to blond or reddish. The hair is weak and rather scarce (in entrepelado varieties) or absent (in hairless or lampiño varieties). The legs are thin and resistant, and the hooves are dark and uniformly coloured (Figures 2 and 3), except for the variety Torbiscal which can present depigmented or whitish-striped legs.   Ministry of Agriculture granted AECERIBER the management and development of the genealogical book, since 1992 the genetic selection programme and, more recently, the Conservation programme for several varieties in danger of extinction. Nowadays, more than 2000 breeders in Spain take part in the association.

Growth performance
The basic data on growth performance obtained in this review are presented in Tables 3 and 4. Due to differences among studies concerning the live weight ranges covered and for comparative purposes, we defined the stages for growth performance as lactation (regardless of its length), growing stage (from weaning to approximately 30 kg live body weight) and early, middle and late fattening stages, estimated between approximately 30 and 60 kg, 60 and 100 kg and above 100 kg live body weight, respectively. Sometimes the source provided only the overall growth rate for the whole fattening stage (defined in this case as overall). The recorded data in Table 3 shows heterogeneity. A big part of the collected studies simulated practical conditions of the production systems used in Iberian pig rearing so that they can be considered as field studies. On the other hand, a reduced group of the recorded papers aimed at evaluating the actual growth potential of Iberian pigs in a defined growing period. For this reason, the average growth rates were not calculated. The average daily gain in the early stage that corresponds to the lactation period (approximately 257 g/day, range from 168 to 371 g/day [9,18,23,27,28,60,61,64,67]) could be considered in the range of those described for modern sows [71,72], although the average lactation period in the present studies (approximately 39 days; Table 2) is considerably greater than in sows of conventional breeds (21-28 days). The collected data show that daily gain is characterized by high heterogeneity in the growing (185-524 g/day, [28,43,44,49,50,54,57,58,60,63]), early (228-566 g/day, [26,49,53,54,57,68]), middle (181-800 g/day, [9,26,38,42,48,51,52,57,68]), late (387-1018 g/day, [4, 9, 25, 26, 29-31, 33-48, 55, 59, 60, 62, 65, 66, 68]) and overall (181-800 g/day, [9, 25, 26, 29, 32, 33, 38, 42-44, 48, 49, 51-54, 56, 57, 68-70]) fattening stages, which is related to the fact that this review comprises studies of a        3 ADG birth to slaughter Early Middle Late Overall [4] Ad lib 579 Rest No.-number; ADG-average daily gain in g; Ad lib-ad libitum feeding regime; Semi-semi ad libitum feeding regime; Restrestrictive feeding regime. 1 ADG in period of lactation regardless of how long it was. 2 ADG in growing period estimated from weaning to approximately 30 kg live body weight. 3 ADG in a period of fattening is reported for early, middle and late fattening stages estimated between approximately 30 and 60 kg, 60 and 100 kg and above 100 kg live body weight, respectively. Sometimes the source provided only the overall growth rate for the whole studied period (in that case defined as overall). variety of production systems and, probably more important, feeding levels. In the context of the evaluation of growth performance, it is of interest to point out the extreme values recorded as it can be assumed that the maximum figures obtained for each growing phase correspond to Iberian pig's growth potential determined in ad libitum or close to ad libitum feeding conditions (i.e. 524 g/day in growing stage [50], 800 g/day in overall fattening stage [51,52] and 1018 g/day from 128 kg onwards [65]).
Information on feed intake and feed nutritional composition was mentioned only in few of the considered studies, which limits the evaluation of maximum growth potential as this parameter is directly related to pig nutrition and management (  [55,68]) in the late fattening stage in ad libitum-fed pigs. The maximum value recorded, 5.6 kg/day (determined in individually allocated animals), corresponds to pigs fed ad libitum on acorns in the late fattening stage (from approximately 90 to 140 kg body weight [39]) and shows high intake capacity in Iberian pigs. In comparative studies, the higher intake capacity of Iberian pigs compared to conventional pigs has been confirmed in similar experimental conditions and body weight range [73]. In this respect, according to van Lunen and Cole [74], voluntary feed intake has declined in the development of modern high-selected pigs compared to non-selected animals.

Body composition and carcass traits
The basic data obtained in this review with some of the most common carcass traits are presented in Table 5. As mentioned before, attention should be given to high heterogeneity of the recorded data, because slaughter body weights in the included studies ranged from 1 to 191 kg. A big part of the studies-some of them including high number of pigs-simulated practical conditions of the production systems used in Iberian pig rearing, whereas a reduced group of papers aimed at evaluating different performance and carcass composition parameters in a defined growing period [28,49,53,58,63,64,75,86], in some cases quite far from the usual commercial slaughter weight of this breed (140-160 kg). In studies where final body weight was above 100 kg, pigs were slaughtered at approximate age of 407 days [25, 29, 33, 38, 40-44, 46, 64, 65, 68, 82, 85, 86] and reached around 152 kg live body weight [9, 25, 29-46, 48, 51, 52, 55, 56, 62, 64, 65, 69, 76-86]. In agreement with high slaughter weight, dressing yield in these studies was around 81%. The back fat thickness values measured in all considered studies spanned from 35 to 90 mm on the withers (in average 85 mm in studies with final body weight above 100 kg [55,62,85]), from 10 to 90 mm at the level of the last rib (in average 58 mm in studies with final LW above 100 kg [25, 29-31, 34, 35, 37-44, 46, 51, 52, 55, 64, 65, 68, 69, 76, 77, 82, 85, 86]) and from 48 to 65 mm when measured above gluteus medius muscle (in average 56 mm in studies final body weight above 100 kg [68,76]). Similarly, muscularity measured as loin eye area span from 13 to 29 cm 2 (in average 23 cm 2 in studies with final LW above 100 kg [30,31,34,35,65,76,82]) and muscle thickness measured at the cranial edge of gluteus medius muscle from 11 to 60 mm (in average 40 mm in studies with final body weight above 100 kg [68,76]). Percentage of lean meat content is not reported in the literature as this is not commonly estimated on Iberian pig carcass composition studies, which are focused mainly in the premium cuts obtained from these animals (hams, shoulders and loins). The variation in back fat and muscle thickness of the values recorded is also a consequence of the wide range of final live weights and different feeding No.-number; ADFI-average daily feed intake in kg/day; Ad lib-ad libitum feeding regime; Semi-semi ad libitum feeding regime; Rest-restrictive feeding regime; ME-metabolisable energy; and CP-crude protein. 1 ADFI in growing period estimated from weaning to approximately 30 kg live body weight. 2 ADFI in a period of fattening is reported for early, middle and late fattening stages estimated between approximately 30 and 60 kg, 60 and 100 kg and above 100 kg live body weight, respectively. Sometimes the source provided only the overall daily feed intake for the whole studied period (in that case defined as overall). M is the muscle thickness measured according to ZP method (at the cranial edge of gluteus medius muscle (mm)). 2 S is the back fat thickness measured according to ZP method (above gluteus medius muscle (mm)). Table 5.
Summary of collected literature data on body composition and carcass traits in Iberian pig breed.

Meat quality
The basic data obtained in this review concerning some of the most common meat and fat quality traits measured in longissimus muscle and back fat tissue are presented in Table 6. In the studies reporting meat quality, pH measured in longissimus muscle at 45 min and 24 hours postmortem varied from 6.29 to 6.62 [69,76,96] and from 5.61 to 5.75 [69,76,88,89,93,96], respectively. Intramuscular fat content was very variable and ranged from 3.0 to 19.7% (6.9% in average) [29-33, 37-39, 42, 62, 65-69, 76, 77, 79-83, 87-92, 94]. Colour measured in CIE L, a, b colour space varied from 34 to 54, 7.5 to 14.8 and 1.7 to 13.6 for L, a* and b*, respectively [68, 69, 76, 88-93, 95, 96]. Total SFA, MUFA and PUFA content of intramuscular fat in longissimus muscle, reported for the control groups of animals in the considered studies, were approximately 38, 56 and 7%, with n6-n3 ratio varying from 2 to 20% [30, 31, 33, 35-39, 42, 64, 66, 67, 77, 88-92, 97]. On the other hand, total SFA, MUFA and PUFA content of back fat tissue, reported for control animals in the mentioned studies, were close to 33, 56 and 11%, with n6-n3 ratio varying from 5.6 to 20% [30, 31, 33, 35-39, 41, 42, 62, 68, 69, 77, 91, 97]. Due to wide differences between studies regarding parameters as feeding management, feed composition, final body weight or age and fatness, which are all important factors influencing the fatty acid composition of meat and fat tissue, the results of average fatty acid composition should be interpreted with caution. When comparative studies in which Iberian pigs have been contrasted either with its crosses with Duroc pigs [68] or with pigs from conventional breeds [69,92], the pigs from Iberian genotype show redder (higher values of a*) and darker (lesser values of L) muscles and higher level of intramuscular fat in longissimus muscle than the other pigs types. The red tone is related to greater myoglobin content [91,92] and is generally associated with higher intramuscular fat levels and more oxidative muscle metabolism.

Use of breed and main products
The Iberian pig production is mainly focussed on the elaboration of cured products, with hams, shoulders and loins being those more important, although other charcuterie pieces of lower economic relevance are also produced (chorizo, salchichón, morcón, etc.). More recently, fresh meat either for domestic consumption or for the HORECA sector has gained increasing importance being highly appreciated for its peculiarities in aroma, texture and juiciness, competing in the market with the conventional pig meat and also with specific meat pieces of lamb and beef. Nevertheless, the cured products from the Iberian pig fattened in the traditional montanera system are the commercially strategic products for the whole sector since their high-quality standards provide a prestige that, in a way, favours the rest of productions. All the hams, shoulders and loins produced from Iberian pig in Spain are currently under an official regulation [98] that classify the cured products detailed according to their genetic origin (pure or cross-breed and at what percentage) and system of production (intensive, semi-extensive or montanera), with the aim of offering the consumer a precise information of product origin which is directly related with their market prices. There are currently four protected designations of origin (DPO) for Iberian cured products (Guijuelo, Dehesa de Extremadura, Jabugo and Los Pedroches) that endorse and protect Iberian hams and shoulders. The most typical and well-known product that represents the breed is the bellota cured ham that reaches high prices in the market and acts as a flagship of the increasing export market (EU, Japan and the USA). For fatty acid composition of intramuscular fat tissue in longissimus muscle, only pigs on control diet were considered, and when fatty acid composition was reported separately for neutral and polar lipids, values reported for neutral lipids were considered. Control diets differed among studies, to see diet composition address to the corresponding source. 3 For fatty acid composition of back fat tissue, only pigs on control diet were considered and when fatty acid composition was reported separately for outer and inner layers, values reported for outer layer of back fat tissue were considered. Control diets differed among studies, to see diet composition address to the corresponding source. Table 6.
Summary of collected literature data on meat quality traits in Iberian pig breed.
The quality of the Iberian products from the sensorial and organoleptic, technological, dietetic, biosecurity, commercial and healthy point of view, is due to various meat properties that determine their essence. All of them together are responsible for their commercial success and consumer appreciation. Its sensory characteristics, such as appearance, smell, colour and above all the flavour, justify the conservation of this breed and its ecosystem and the maintenance of its ancient forms of production and processing.