COMPROBACION POR COMPONENTES Y NORMAS EN LAS ENTIDADES

As previously reported, the FA composition of pig adipose tissue reflects that of the diet because part of the non-essential FAs are incorporated into the lipid tissues in pigs without further modification or very litter modification (Averette Gatlin et al., 2002; Corino et al., 2002; Rentfrow et al., 2003; King et al., 2004). In the current research, partly corresponding to the intake of different individual FAs, pigs fed CN diets had most SFA including C12 and C14, pigs fed CO diets had most PUFA including C18:2 and C18:3n3, and pigs fed TW diets had most MUFA especially C18:1 in the backfat and belly fat. However, the content of C16 and C16:1 was the highest in the backfat and belly fat of pigs fed CN diets when the intake of these two FAs was the highest in pigs fed TW diets. Besides, the content of C20:2 in the backfat and belly fat of pigs fed CO diets was the highest although the intake was the highest in pigs fed CN diets. These results indicated that FAs are actively modified depending on the FAs intake, especially for those non- essential FAs (Kloareg et al., 2007). As the result, the tissue FA profile did not strictly follow the dietary FA profile.

As the most common FA in grains and oilseeds, the linoleic acid (C18:2n-6) content, which is relatively low in animal fat but essential for animals, is one of the most widely evaluated FA. The changes of linoleic acid with different dietary fat sources follow the difference in the intake through diets (Kloareg et al., 2007). The intake of linoleic acid was the highest in the CO group among the four dietary fat treatments, 2.6 times as much as the intake of linoleic acid in CN groups in the current study. As a result, the concentration of linoleic acid in pigs fed CO diets was 2.9 and 2.8 times as much as in pigs fed CN diets in the backfat and belly fat respectively. The similar relative ratio of increase indicated the concentration dependent deposition of linoleic acid in the adipose tissues. This result is in agreement with previous studies, where the proportion of linoleic acid in subcutaneous adipose tissue and backfat of pigs increased from as low as 10% on a diet with 5% olive oil, which contains around 9.8% linoleic acid, to over 30% on diets supplemented with 5%

greatest among all the FAs, when unsaturated vegetable oil (such as safflower oil, soybean oil, corn oil) were compared to animal fat (such as tallow and choice white grease) as fat sources for pigs (Mitchaothai et al., 2007; Corino et al., 2008; Apple et al., 2009a, b; Apple et al., 2009c; Browne et al., 2013a).

Oleic acid (C18:1) is the most abundant FA in adipose tissues of pigs, it changes in a relatively smaller range with different dietary fat sources, compared to linoleic acid. Although there was also a big difference in oleic acid intake among different fat sources in the current study with the highest intake in TW diets which was 3.9 times as much as that of CS diets, the concentration of oleic acid in adipose tissues from TW goup was 6.8% higher that that of CS group. The result indicated the relative active metabolic activity of oleic acid in pigs. Similar to the result of the current study, when pigs were fed diets containing various fat sources such as corn oil, soybean oil, tallow, poultry fat, sunflower oil, linseed oil, and olive oil, the content of oleic acid in adipose tissues varied from as low as 32% on a no-fat-added diet to as high as 45% when pigs were fed 5% choice white grease (Nuernberg et al., 2005; Benz et al., 2011a, b; Browne et al., 2013a; Kellner et al., 2014, 2015; Kellner et al., 2016).

Additionally, while the intake of oleic acid in the CS group was the lowest, the lowest content of oleic acid in the backfat and belly fat was observed in pigs from the CN group. This demonstrated the effect of the intake of different FAs on lipogenesis, the high intake of SFA inhibited the lipogenesis of oleic acid in adipose tissues. As previously reported, fat deposition increases with increasing dietary fat supplementation, dietary fatty acids inhibit lipogenesis in the adipose tissue. The increasing level of dietary fat as corn oil from 1 to 13% significantly depressed (60 to 70% ) lipogenesis, although body fat content was increased due to the increasing direct deposition of dietary fat (Allee et al., 1971). When pigs were fed with diets of either 5% fat or starch, the fat supplementation decreased the mRNA abundance of FASN in adipose tissue, and mRNA abundance of acetyl CoA carboxylase (ACACA), adipose triglyceride lipase (ATGL), peroxisome proliferator activated receptor-alpha (PPAR-α), AMP-activated protein kinase gamma 1 noncatalytic subunit (PRKAG-1), and stearoyl CoA desaturase (SCD) in the liver compared to the control group with 5% starch (Kellner et al., 2017). Dietary SFA and omega-6 FA (such as linoleic acid) are the most reported factors displaying inhibitive effects on lipogenesis in

adipose tissue. When pigs were fed diets with no added fat or 11% fat (tallow, sunflower oil, linseed oil, blend oil, or fish oil), the mRNA abundances were highest in pigs fed diets with no added fat, while lowest in pigs fed diets with 11% tallow (Duran-Montgé et al., 2009). In most recent studies, the addition of 5% dietary fat in the form of coconut oil, corn oil, fish oil, and tallow all reduced FASN abundance compared to pigs fed a control diet without fat addition (Kellner et al., 2017).

The third most abundant FA in adipose tissues of pigs is palmitic acid (C16), which changes to an even smaller extent than oleic acid and linoleic acid, but did change consistently when dietary fat was switched, depending on the difference among the fat sources. In this study, the intake of C16 was the highest in pigs fed TW diets while lowest in pigs fed CN diets among the four dietary fat treatments, however the content of C16 in the back fat and belly fat was the highest in pigs fed CN diets. The palmitic acid can be synthesized endogenously actively via de novo lipogenesis, and it is the end product of lipogenesis in the cytoplasm of cells. Different from oleic acid and linoleic acid, increasing dietary fat content reduced palmitic acid content in adipose tissues, although the change in tissue palmitic acid content is also positively related with dietary palmitic acid concentration (Rentfrow et al., 2003; Apple et al., 2009a, b; Apple et al., 2009c). A significant change in tissue palmitic acid content was also reported when dietary palmitic acid content differed by supplementation of beef tallow or sunflower oil. There were 23% and 21% palmitic acid in the subcutaneous fat, and 22% and 19% in the backfat when pigs were fed with beef tallow or sunflower oil, respectively (Mitchaothai et al., 2007). A significant difference in adipose tissues was detected even through only around 2% difference in palmitic acid content existed in diets, when supplementation of animal fats (5%) including beef tallow and poultry fat were compared to soybean oil (5%) and no fat- added diets (Apple et al., 2009a, b; Apple et al., 2009c), and when 5% linseed oil supplementation was compared to 5% olive oil supplementation (Nuernberg et al., 2005), and when supplementation of 5% choice white grease was compared to 5% soybean oil

Another FA comprising more than 10% in adipose tissues is stearic acid (C18) which also changes with variations in dietary FA profile, but to a much smaller extent than linoleic acid and oleic acid and a relatively larger extent than palmitic acid. Similar to the pattern of C16, the concentration of C18 was the highest in pigs fed CS diets where the intake of C18 was lowest among the four dietary fat treatments. A similar result was previously reported when animal fats were compared to vegetable oils, significant differences were reported, with lower stearic acid content in adipose tissue of pigs in vegetable oil groups (Apple et al., 2009a). Replacing 5% sunflower oil with 5% beef tallow increased stearic acid from 11% to 13% in adipose tissues (Mitchaothai et al., 2007). Pigs fed diets with 5% beef tallow had higher stearic acid content in adipose tissues compared to pigs fed diets with 5% poultry fat, which was consistent with the stearic acid content of the fat (Apple et al., 2009a, b). However, other research reported no significant difference in stearic acid when different animal fats or vegetable fats were compared as fat sources for pigs, when difference in stearic acid in diets were relatively small (Nuernberg et al., 2005; Corino et al., 2008; Browne et al., 2013a). No difference in adipose tissue stearic acid content was detected when yellow grease supplementation (5%) was compared to beef tallow (5%), due to the lack of dietary difference in this fatty acid (Browne et al., 2013a). Corino et al. (2008) reported a similar result when dietary supplementation of 2.5% sunflower oil was compared to 5% extruded linseed. The difference in tissue deposition of stearic acid is also due to the extent of the variation among different fat sources.

The variation in the concentration of the other PUFAs including C18:3 n-6, C18:3 n-3, and CLA in response to the dietary fat treatments generally followed the difference in the intake of the individual FAs. The increase in the deposition in the adipose tissue was mainly due to the increase in the intake of these FAs or their precurser FAs including C18:2 and C18:3 n-3 (Ramsay et al., 2001; Thiel-Cooper et al., 2001; Tischendorf et al., 2002; Kloareg et al., 2007).

The iodine value in tissues displays similar trends with the FA profile, the highest IV value of backfat and belly fat was observed when pigs were fed CO diets, and the lowest IV value was observed in pigs fed CN diets. It is through the FA profile that dietary fat treatments affect the iodine value of tissues (Wood et al., 2004; Benz et al., 2011a, b). The

current result is in agreement with the previous studies which reported the close correlation between dietary FAs and pork IV (NRC, 2012; Kellner et al., 2016).

As expected, the VE supplementation displayed very limited effect on the FA profile of adipose tissues. The VE supplementation affected concentration of C16:1, C18, and C20 in the backfat, where the concentration of C16:1 increased and the concentration of C18 and C20 decreased with the increasing dietary VE from 11 to 200 ppm. In the belly fat, the VE supplementation affected concentration of C16:1 and C20, wherein the concentration of C16:1 increased and the concentration of C20 decreased with the increasing dietary VE from 11 to 200 ppm. A tendency of increase in CLA content in both the belly fat and the backfat were also detected with the increasing dietary VE. This result has not been reported before, much research need to be done to better interpret the underlying connection in VE supplementation and tissue FA profile.