Effects Of Heat Stress On Meat Quality And Muscle Metabolites Of Finishing Pigs

The meat quality, nutrition content, myofiber characteristics and antioxidant capacity were assessed to study the effects of constant high temperature stress on meat quality in longissimus dorsi muscle of finishing pigs. Potential biomarkers were detected by metabonomics in longissimus dorsi muscle of finishing pigs under constant heat stress.Castrated24male DLY (crossbreeds between Landrace×Yorkshire sows and Duroc boars) pigs were selected from8litters at a body weight of approximately80kg. Within each litter the three pigs were allocated to one of three treatments:constant optimal ambient temperature at22℃and ad libitum feeding (CON, n=8), constant high ambient temperature at30℃and ad libitum feeding (H30, n=8) and constant optimal ambient temperature at22℃and pair-fed to the HS diets (FP, n=8). Pigs were stunned by an electrical input, and carcass traits were measured. Longissimus dorsi (LD) muscle tissues from the right carcass were snap-frozen in liquid nitrogen and stored at-80℃for myofiber type, muscle nutrition content, enzyme activity and high performance liquid chromatography-mass spectrometry (HPLC-MS) analyses. LD muscles from the left carcass were quickly separated and stored at4℃in45min,24h, and48h for meat quality measurements.1. Effects of constant heat stress on meat quality of finishing pigsThe results showed as follows:the ADG of H30pigs were significantly reduced (P<0.05) and the ADFI of H30pigs were significantly lower (P<0.01) than CON. No significant differences were observed on carcass weight, length, backfat thickness and skin depth among three groups, while the24h marbling score in longissimus dorsi muscle of H30pigs were lower than CON pigs (P<0.1). H30and FP had lower pH24h at24h post-mortem (P<0.05). Higher lightness at45min,24h post-mortem were observed in H30compared to the control and FP treatments (P<0.01), H30had lower redness at45min post-mortem than CON (P<0.05), the yellowness of H30and FP at24h post-mortem were lower than CON (P<0.05). H30had higher drip loss at48h post-mortem compared to the control and FP (P<0.01). The shear force of H30pigs were significantly increased compared with the CON and FP group (P<0.01). The longissimus dorsi muscle of HS pigs had the tendency of lower adhesiveness and hardness than FP pigs (P<0.1).The intramuscular fat (IMF) content in longissimus dorsi muscle of H30and FP pigs were significantly decreased (P<0.01), and the crude protein (CP) content was significantly increased (P<0.05) than CON. The ratio of type Ⅱ x in longissimus dorsi muscle of FP pigs were significantly lower than CON pigs (P<0.05), and the ratio of type Ⅰ in longissimus dorsi muscle of H30group were lower than FP pigs (P<0.1). No differences were observed in myofiber diameter and density among three treatments.Constant heat stress disrupted the pro-oxidant/antioxidant balance in longissimus dorsi muscle with higher MDA content (P<0.01), lower SOD and CAT activities (P<0.01). Muscle LDH activities of H30and FP pigs were higher than those in CON (P<0.1). H30pigs had higher muscle lactic acid level than CON (P<0.05).Constant high temperature stress has a significant influence on pork quality and antioxidant capacity, also leads to the changing of nutrition content and myofiber type in longissimus dorisi muscle of finishing pigs.2. Effects of constant heat stress on metabolites of muscle in finishing pigsIn this study, a metabonomics approach based on ultra-performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight mass spectrometry (UPLC-ESI-QTOF-MS) was performed to characterize the metabolic profile of muscle samples from CON, H30and FP. Acquired metabolic profile data were analysed by multivariate data analysis for differentiation and screening of potential biomarkers.Nine metabolites (Camosine, Acetylcholine, Inosinic acid, Carnitine, L-Anserine, Glycerophosphocholine, Acetylcarnitine, Thiamin triphosphate, Adenosine thiamine diphosphate) among three groups were identified using multivariate data analysis and external search engines (Human Metabolome Database\Metlin Database\KEGG Compound Database). Four of them (Carnosine, Acetylcholine, Inosinic acid and Carnitine) were verified while the rest were not further certified due to lack of corresponding authentic standards. These metabolites are associated with antioxidant mechanism, stress, energy, purine and muscle metabolism, cell signal transduction, and thus play important roles in the function of anti-heat stress.As measured by LC-MS/MS, carnosine and L-carnitine content in H30was significantly lower than that in CON (P<0.01), showing that the carnosine and L-carnitine were the biomarkers between constant heat stress and control pigs.In conclusion, Constant high temperature stress has a significant influence on pork quality (lower pH, higher drip loss and shear force) and antioxidant capacity (higher MDA content, lower activities of SOD and CAT), also leads to the changing of nutrition content (the CP content was significantly increased, while the IMF content in longissimus dorsi muscle of HS group were significantly decreased) in longissimus dorisi muscle of finishing pigs.UPLC-ESI-QTOF-MS was performed to characterize the metabolic profile of muscle samples from CON, H30and FP, nine metabolites were observed, while four of them (Carnosine, Acetylcholine, Inosinic acid and Carnitine) were verified by authentic standards. The carnosine and L-carnitine content in H30was significantly lower than that in CON, showing that constant heat stress results in the changing of metabolites in longissimus dorsi muscle of finishing pigs.