Effect of a high dose of CLA in finishing pig diets on fat deposition and fatty acid composition in intramuscular fat and other fat depots
Highlights
► High level of CLA does not have any effect on performance or intramuscular fat. ► CLA increases the weight of the liver. ► CLA modifies fatty acid composition in a tissue specific manner. ► Neutral and polar lipids were affected differently by CLA supplementation. ► In 100g of loin, CLA deposited would be 53 mg. The predominant isomer is 9c,11t CLA.
Introduction
Fat and fatty acids (FAs), whether in adipose tissue or muscle, contribute importantly to various aspects of meat quality and are central to meat nutritional value (Wood et al., 2008). It is generally assumed that intramuscular fat (IMF) content positively influences sensory quality traits, including flavor, juiciness and tenderness of meat, whereas a low amount of fat results in a less tasty meat. Accordingly, IMF levels should reach values between 2.2 and 3.4% before any noticeable effects on sensory qualities could be detected (Font-i-Furnols, Tous, Esteve-Garcia, & Gispert, 2012).
Selection against fatness or P2 backfat thickness carried out during the last decades in the pig has been very successful (Kempster, Cook, & Grantley-Smith, 1986). Consequently, IMF content has been also dramatically reduced to less than 1% in some lean genotypes widely used nowadays (Wood, 1990). It is believed that IMF develops later and behaves differently from subcutaneous adipose tissue with regard to development of cellularity and metabolic capacity (Lee & Kauffman, 1974). Hence, an increased IMF content without affecting or reducing backfat through a strategic feeding regimen would be a desirable tool in pork meat production. Several nutritional attempts had been studied during the last years; one of them is the inclusion of conjugated linoleic acid (CLA) in foods for growing/finishing pigs for its distributive effect between fat and lean (Dugan, Aalhus, Schaefer & Kramer, 1997).
The CLAs are a mixture of positional and geometric isomers of linoleic acid (9c,12c C18:2), which were first identified in rumen fluid as an intermediate of the biohydrogenation process (Bartlett & Chapman, 1961). In synthetic CLA preparations the 9c,11t and 10t,12c isomers are predominant (often in a 1:1 ratio; Larsen, Toubro, & Astrup, 2003). It appears that the 9c,11t isomer has positive effects on some types of cancer by inhibiting tumorogenesis (Kelley, Hubbard, & Erickson, 2007), while 10t,12c isomer could be responsible for changes in whole-body fat deposition (Pariza, Park, & Cook, 2000). In first studies with pigs dietary CLA increased lean tissue deposition and decreased fat deposition (Dugan et al., 1997, Ostrowska et al., 1999). Comprehensive reviews on the effects of CLA on growth performance and carcass fat deposition in pigs have been published by Azain (2003), Corino, Di Giancamillo, Rossi, and Domeneghini (2005) and López-Bote, Rey, Ortiz, and Menoyo (2004). In general, the response to CLA was not conclusive and inconsistency could be attributed to the type of pig used in studies or to dietary factors like the source of CLA, the dietary fat content or the duration of feeding. According to Azain (2003), it appears that CLA reduces carcass fat in pigs with more than 23 mm subcutaneous fat thickness at 100 kg body weight, but not when fat thickness was less than 20 mm, suggesting that CLA is more effective in fatter genotypes than the average carcass. Moreover, the response to CLA seems to be greater in barrows than in gilts or entire males (Tischendorf, Schone, Kirchheim, & Jahreis, 2002) and in low-energy diets (Dugan, Aalhus, Lien, Schaefer, & Kramer, 2001). Some authors also report an increase in IMF content of CLA fed pigs (Averette Gatlin et al., 2002, Dugan et al., 1999, Jiang et al., 2010, Joo et al., 2002, Morel et al., 2008) which would be very interesting in terms of pork meat quality. However, as for backfat thickness, results are inconsistent because some other studies did not show any affect on IMF content (Corino et al., 2003, Lauridsen et al., 2005, Martin et al., 2008) and the same reasons could be evoked.
In addition, dietary CLA seems to be highly deposited in body tissues of monogastric animals (Bee, 2001, Corino et al., 2005, Jiang et al., 2010, López-Bote et al., 2004) and as a result, in pork and meat products (Schmid, Collomb, Sieber, & Bee, 2006). An increase of saturated fatty acids (SFA) and a reduction of monosaturated fatty acids (MUFA) in subcutaneous tissue and loin were attributed due to an inhibitory effect on the enzyme delta 9 desaturase (Averette Gatlin et al., 2002, Bee et al., 2008).
Due to the inconsistency of the results of CLA on IMF and backfat thickness and since that most of the studies use a dose of 2% of CLA oil in the diet, one of the goals of the present study is to evaluate if the inclusion of a high dose of CLA oil (4%) as the only dietary fat source during fattening of Duroc × Landrace gilts increases IMF content while reducing backfat thickness in order to determine if the lack of consistency between studies is due to the level of CLA inclusion. A further aim is to determine if CLA is equally incorporated and has the same ability to modify FA composition in different tissues of pig. Longissimus thoracis (LT) was chosen as a typical portion consumed fresh, semimembranosus muscle (SM) as representative of ham muscle, LT subcutaneous fat as the main fat deposit where lipid metabolism takes place in the pig and liver as having an important role in the whole body metabolism and due to implications for further human health benefits.
Section snippets
Animals and diets
Sixteen 73 ± 3 kg gilts, progeny of a Landrace sow and a Duroc boar chosen from a larger group were blocked by weight and housed in adjacent individual boxes (2.25 m2) in a room provided with forced ventilation by extraction. Gilts, from 73 ± 3 kg to slaughter at 117 ± 5 kg live weight (LW) (54 days), were randomly assigned within block to one of the dietary treatments. The basal diets were based on barley (536 g/kg from 73 to 91 kg LW or 601 g/kg from 91 to 117 kg LW) and also included manioc (200 g/kg),
Performance, carcass and meat quality parameters
No significant differences in performance parameters of gilts were found due to the replacement of sunflower oil to CLA for a period of 54 days (average daily feed intake: C: 3.16 kg/day, CLA: 3.20 kg/day; average daily weight gain: C: 0.82 kg/day, CLA: 0.82 kg/day; feed to gain ratio: C: 3.84 kg/kg, CLA: 3.94 kg/kg). Animals fed the CLA ration consumed 62.5 g CLA per day on average (a total of 3.37 kg of CLA for whole experiment) had similar final body weight than those fed the control diet (C: 117.9 kg
Discussion
A higher dose of CLA oil (4%) than in previous studies (normally 2%) was used in order to amplify the possible response to CLA in IMF content. Wiegand, Parrish, Swan, Larsen, and Baas (2001) speculated that if body fat was decreased by CLA supplementation then less energy would be required to maintain animal growth, thus making them more efficient. No modification of performance parameters by dietary CLA was observed, which is in agreement with Bee (2001), although Dugan et al. (1997),
Conclusions
The inclusion of a high dose of dietary CLA oil (4%) in gilts of a conventional genotype (Landrace × Duroc) does not increase IMF content. Growth performance was not affected by CLA inclusion but tended to reduce fat deposition, particularly perirenal and increased liver weight. CLA acted in a tissue specific way, increasing SFA in all studied tissues, reducing the MUFA in LT and LT subcutaneous fat, and PUFA in LT subcutaneous fat, liver and SM. The effect of CLA on FA profile was different in
Acknowledgments
The present work has been financed by MICINN (Ministerio de Ciencia e Innovación) in the project AGL2007-65898-C02-02 and Núria Tous is a recipient of an INIA (Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria) scholarship. CLA was generously provided by Molimen (Barcelona, Spain).
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