Free-range rearing of pigs during the winter: Adaptations in muscle fiber characteristics and effects on adipose tissue composition and meat quality traits1

Abstract

This research aimed to determine whether outdoor free-range rearing during the winter (average ambient temperature of 5 degrees C) vs. indoor housing (22 degrees C) affects meat quality, muscle metabolic traits, and muscle fiber characteristics. Forty Large White gilts and barrows were blocked by weight within each gender (20 per gender) and allotted randomly into two groups of pigs, with one reared indoors (IN) in individual pens (2.6 m2) and the other reared outdoors (OUT) from December to March in a 0.92-ha pasture. Both groups had free access to the same grower-finisher diet from 23 to 105 kg. At slaughter, adipose (backfat [BF] and omental fat [OF]) and muscle tissues (longissimus muscle [LM], rectus femoris [RF], and semitendinosus [ST]) were obtained from the right side of each carcass. Muscle fibers were stained and classified on the basis of stain reaction as slow-oxidative (SO), fast oxidative-glycolytic (FOG), and fast glycolytic (FG); fiber area and distribution were determined. Also assessed were carcass characteristics, initial and ultimate pH, L*a*b* values, drip loss percent, glycolytic potential (GP), and intramuscular lipid content, as well as the fatty acid profile of each muscle and adipose tissue. The OUT pigs had lower (P < 0.05) ADG and leaner (P < 0.05) carcasses than IN pigs. Rearing environment did not (P > 0.63) affect the intramuscular lipid content of the ST, but intramuscular lipid content was lower (P < 0.01) in the LM and tended to be higher (P = 0.06) in the RF of OUT than in those of IN pigs. In the BF outer layer of the OUT pigs, the higher PUFA content was compensated by both a lower (P < 0.01) saturated and monounsaturated fatty acid (MUFA) content, whereas in the OF, LM, and dark portion of the ST, only the percentage of MUFA was decreased (P < 0.01). In all tissues of the OUT pigs, the linolenic acid content was higher (P < 0.01) and the n-6:n-3 ratio was lower (P < 0.01). The GP of all muscles was higher (P < 0.01), and the ultimate pH of the RF and ST was lower (P < 0.01), in OUT compared with IN pigs. Lightness (L*) values were lower (P < 0.01) in the LM. Percentages of drip loss were higher (P < 0.05) in the LM and light portion of the ST of OUT than in those of IN pigs. The LM and RF of OUT pigs had more (P < 0.01) FOG and fewer (P < 0.01) FG fibers than muscles of IN pigs. Results suggest that rearing pigs outdoors increases aerobic capacity of glycolytic muscles but has little concomitant influence on meat quality traits.

Influence of production system in local and conventional pig breeds on stress indicators at slaughter, muscle and meat traits and pork eating quality

“…Deeper investigations would be helpful to better characterize the influence of extensive rearing conditions on p.m. muscle physiology and metabolism. In contrast with our findings, the literature generally reports no effect of extensive v. indoor rearing on the pH1 value in local (Labroue et al, 2000 in Basque and Gascon; Pugliese et al, 2005 in Cinta Senese pigs) or conventional breeds (Bee et al, 2004;Terlouw et al, 2009). Besides, the higher pre-slaughter physical activity of BE than BC pigs, which requires consumption of muscle energy (glycogen) store, would have probably contributed to their higher pHu values.…”

“…Moreover, the higher level of physical activity of extensively reared pigs that is generally associated with increased muscle oxidative metabolism (Gondret et al, 2005 for review) could also partly explain the darker colour of BE pork, in accordance with reports of Millet et al (2005). In agreement with our results, reduced meat lightness and water loss have been observed in outdoor pigs by Pugliese et al (2005), whereas Bee et al (2004) reported lower meat lightness but higher drip in outdoor v. indoor pigs. Despite higher pH1 and pHu and lower drip, which have all been positively associated with mechanical tenderness of pork (Huff-Lonergan et al, 2002;Bee et al, 2007), BE pigs had higher meat shear force values than BC pigs.…”

“…This also suggests that during their rearing period, the BE pigs probably had a higher muscle GP than the BC pigs, as suggested by their tendency for higher level of glucose issued from glycogen hydrolysis at 30 min p.m. Increased muscle glycogen or GP in extensive conditions, especially during the winter season to fulfil high muscle energy requirements has already been reported, but was not accompanied by lower ultimate pH (Bee et al, 2004;Terlouw et al, 2009). Accordingly, Pugliese et al (2005) found similar loin pHu in Cinta Senese pigs reared outdoors or indoors, whereas Labroue et al (2000) showed lower pHu in the LM of Basque and Gascon pigs reared in free-range compared with semiconfined systems.…”

Effects of deep-bedded finishing system on market pig performance, composition and pork quality

“…The replication differences in ambient temperature were more pronounced in hoop systems compared with confinements. Fluctuations in ambient temperature due to alternative production systems have been shown to influence fatty acid composition in pigs (Lefaucheur et al, 1991;Lebret et al, 2002;Bee et al, 2004). Overall, outdoor-produced pigs have been shown to deposit more PUFA than their confinement counterparts (Bee et al, 2004).…”

“…Substantial variation in growth performance and pork quality has been noted in opposing seasons, as well as between confinement and deep-bedded systems (Lebret et al, 2002;Honeyman and Harmon, 2003). Seasonal alterations in fatty acid profiles (Cava et al, 2000;Bee et al, 2004), flavour attributes of fresh pork, including intensity and pork flavour (Gentry et al, 2002b), and overall flavour acceptability (Enfalt et al, 1997) have also been noted between pigs finished in deep-bedded and outdoor systems compared with indoor systems.…”