Dietary CLA has been reported to decrease backfat and increase marbling in pigs. Our objective was to determine whether the increase in marbling involved changes in intramuscular adipocyte number or size or both. Twenty barrows (53 kg) were penned in pairs and pens were randomly assigned to receive diets containing either 1% soybean oil (SBO) or CLA (60% CLA isomers) for 6 wk. Body weight and feed intake were determined weekly. At slaughter, loin samples were obtained and flash frozen for RNA extraction and real-time reverse-transcription PCR analysis of gene expression. After a 24-h chill, loin eye area and backfat depth were measured and subjective marbling and color scores were assigned. Loin, backfat, and belly fat samples were obtained for fatty acid analysis by gas chromatography. Loin samples were also frozen in ice-cold isopentane for histological analysis of intramuscular adipocytes. Dietary CLA did not affect BW or feed intake at any point (P > 0.10), nor did treatment groups differ in HCW (P = 0.417) or loin color (P = 0.500). The CLA-fed pigs did have less (P = 0.018) backfat and smaller (P = 0.047) loin eye area than SBO-fed pigs and had a trend for an increase (P = 0.069) in marbling score. Relative gene expression for markers of preadipocytes (preadipocyte factor 1; Pref-1), differentiating adipocytes (PPARγ), and mature adipocytes [fatty acid binding protein 4 (FABP4) and perilipin (PLIN)] were determined and normalized to the expression of acidic ribosomal phosphoprotein. No significant differences were detected, but the expression of PPARγ (P = 0.265), PLIN (P = 0.265), and FABP4 (P = 0.148) was numerically greater in CLA-fed pigs than in SBO-fed pigs. Loin samples were stained with Oil Red O to identify intramuscular adipocytes. The average cell area was increased (P = 0.030) in CLA-fed pigs. The cis-9,trans-11 and trans-10,cis-12 CLA isomers were incorporated (P = 0.006) into backfat and belly fat, but only trans-10,cis-12 CLA was increased in the loin (P = 0.004) of CLA-fed pigs. The proportion of SFA was increased (P = 0.006) by CLA in all tissues. These results indicate that the increase in marbling in pigs fed CLA may be related to increased intramuscular adipocyte size, and the combination of increased marbling and degree of saturation could improve the eating quality of CLA-fed pork.

No abstract

Conjugated linoleic acid (CLA) is known to decrease feed intake and body fat in mice. Our objectives were to determine the incorporation of CLA into tissues and the effect on serum hormones during the first 7 d of CLA consumption. Mice (n=150; 9‐wk‐old) were fed 0 (ad libitum or pair‐fed to CLA‐fed mice) or 2% CLA (ad libitum) for 1, 2, 3, 5, or 7 d. A body fat index was calculated; liver, adipose tissue, and brain were analyzed for fatty acid profiles; and serum insulin, leptin, and PYY were measured. CLA and pair‐fed mice ate less (P < 0.05) than control mice on d 1, 2, 3, and 7, but CLA‐fed mice were leaner than control and pair‐fed mice only on d 7 (P < 0.01). CLA was detected in adipose tissue starting on d 2 and in liver on d 1, but CLA was not detectable in the brain. Serum insulin tended (P = 0.11 and 0.13, respectively) to be increased in CLA‐fed mice on d 5 and 7, and serum leptin was non‐significantly reduced in CLA‐fed mice compared to control mice on d 7. The CLA‐induced reduction in feed intake was not sufficient to cause the loss of body fat as pair‐fed mice were not leaner than controls. The lack of CLA in the brain indicates that the effect on feed intake may be indirect.