Gene expression of beta-adrenergic receptors and myosin heavy chain isoforms induced by ractopamine feeding duration in pigs not carrying the ryanodine receptor mutation

Performance, Carcass Traits, Pork Quality and Expression of Genes Related to Intramuscular Fat Metabolism of Two Diverse Genetic Lines of Pigs

We aimed to evaluate the performance, carcass and pork quality traits, as well as the mRNA expression of genes related to intramuscular fat deposition in female pigs from different genetic lines. A total of eighteen female pigs (Large White × Landrace × Duroc × Pietrain) × (Large White × Landrace) (Hybrid) averaging 88.96 ± 3.44 kg in body weight and twelve female pigs (Duroc) × (Large White × Landrace) (Duroc) averaging 85.63 ± 1.55 kg in body weight were assigned to a completely randomized design experimental trial that lasted 45 days. Pigs from both genetic lines received the same diet, which was initially adjusted for their nutritional requirements from 0 to 17 days of age and subsequently adjusted for nutritional requirements from 17 to 45 days of age. The performance of pigs did not differ among groups (p > 0.05). Duroc pigs showed a lower backfat thickness (p < 0.03) and greater intramuscular fat content (p < 0.1). A greater mRNA expression of the peroxisome proliferator-activated receptor gamma gene (PPARγ, p = 0.008) and fatty acid protein translocase/cluster differentiation (FAT/CD36, p = 0.002) was observed in the Longissimus dorsi muscle of Duroc pigs. Similarly, a greater expression of PPARγ (p = 0.009) and FAT/CD36 (p = 0.02) was observed in the Soleus muscle of Duroc pigs. Overall, we observed that despite the lack of differences in performance between the genetic groups, Duroc pigs had greater intramuscular fat content than hybrid pigs. The increased intramuscular fat content was associated with an increase in the mRNA expression of key transcriptional factors and genes encoding enzymes involved in adipogenesis and lipogenesis in glycolytic and oxidative skeletal muscle tissues.

Ractopamine-induced fiber type-specific gene expression in porcine skeletal muscles is independent of growth

Feeding ractopamine (RAC), a β-adrenergic agonist (BAA), to pigs increases type IIB muscle fiber type-specific protein and mRNA expression. However, increases in the abundance of these fast-twitch fiber types occur with other forms of muscle hypertrophy and thus BAA-induced changes in myosin heavy chain (MyHC) composition may simply be associated with increased muscle growth known to occur in response to BAA feeding. The objective of this study was to determine whether RAC feeding could change the MyHC gene expression in the absence of maximal muscle growth. Pigs were fed either an adequate diet that supported maximal muscle hypertrophy or a low nutrient diet that limited muscle growth. RAC was included in diets at 0 or 20 mg/kg for 1, 2, or 4 wk. Backfat depth was less (P < 0.05) in pigs fed the low nutrient diet compared with the adequate diet but was not affected by RAC. Loin eye area was greater (P < 0.05) in pigs fed an adequate diet plus RAC at 1 wk but did not differ among remaining pigs. At 2 and 4 wk, however, pigs fed the adequate diet had greater loin eye areas (P < 0.05) than pigs fed the low nutrient diet regardless of RAC feeding. Gene expression of the MyHC isoforms, I, IIA, IIX, and IIB, as well as glycogen synthase, citrate synthase, β 1-adrenergic receptor (AR), and β 2-AR were determined in longissimus dorsi (LD) and red (RST) and white (WST) portions of the semitendinosus muscles. MyHC type I gene expression was not altered by RAC or diet. Feeding RAC decreased (P < 0.01) MyHC type IIA gene expression in all muscles, but to a greater extent in WST and LD. MyHC type IIX gene expression was lower (P < 0.05) in WST and LD muscles in response to RAC but was not altered in RST muscles. RAC increased (P < 0.05) MyHC type IIB gene expression in all muscles, but to a greater extent in RST. β 1-AR gene expression was unaffected by RAC or diet, whereas the expression of the β 2-AR gene was decreased (P < 0.001) by RAC. No significant RAC * diet interactions were observed in gene expression in this study, indicating that RAC altered MyHC and β 2-AR gene expression in porcine skeletal muscles independent of growth.

Effects of dietary hop (Humulus lupulus L.) β-acids on quality attributes, composition and oxidative stability of pork meat

BACKGROUND

The effects of dietary levels of hop β-acids on physical attributes, lipid oxidation and chemical composition of pork meat were evaluated. Thirty-two castrated male pigs obtained from a complete block design feeding experiment (6.23 ± 0.42 kg initial body weight (BW) to 20.45 ± 0.95 kg final BW) and fed diets supplemented with 0, 120, 240 or 360 mg kg^-1 hop β-acids during 35 days were slaughtered to sample longissimus dorsi muscle for meat analysis.

RESULTS

No effects (P > 0.05) of dietary hop β-acids were observed on meat physical attributes. Quadratic effects (P < 0.05) of hop β-acids were observed on lipid and protein contents and on thiobarbituric acid-reactive substance (TBARS) values of meatballs, whose equations allowed the estimation of dietary hop β-acid levels of 176, 169 and 181 mg kg^-1 to provide up to 16.20% lipid reduction, 1.95% protein accretion and 23.31% TBARS reduction respectively.

CONCLUSION

Dietary hop β-acids fed to pigs might reduce lipid, increase protein and reduce lipid oxidation without affecting physical attributes of the pork meat. © 2017 Society of Chemical Industry.