Effects Of Rumen-protected Creatine Pyruvate On The Meat Quality And Energy Metabolism Of Beef Cattle Long-distance Transported

Pre-slaughter long-distance transport resulted in a rapid depletion of muscle glycogen and lead to a higher rate of dark,firm and dry（DFD）meat.Therefore,enhancing muscle glycogen reserves is critical for beef cattle prior to transportation.Creatine pyruvate（CrPyr）can provide simultaneous pyruvate and creatine,are both proven to promote the glycogen reserves.This study aimed to investigate the effects of transport treatment and dietary supplymentation of rumen-protected RP-CrPyr on the meat quality,muscle energy metabolism,and hepatic gluconeogenesis of beef cattle,and reveal the mechanism of AMPK signaling pathway mediating CrPyr to regulate the energy metabolism of long-distance transport beef cattle.Twenty 18 months-old male Simmental crossbred cattle（659±16 kg）were allotted to 4 treatments based on a 2×2 factorial arrangement with two RP-CrPyr levels（140 g/d or 0 g/d）and two transport treatments（12 h or 5 min）:NTCrPyr₀,NTCrPyr₁₄₀,TCrPyr₀ and TCrPyr₁₄₀.Three cattle per group were slaughtered after 30 days of feeding.Part 1:Effects of dietary RP-CrPyr supplementation on blood indicators and meat quality in long-distance transport beef cattle.The results show that:the interaction of transport and RP-CrPyr had a significant effect on the muscle p H_{45 min},redness（P<0.05）.Compared with non-transport,long-distance transport significantly increased the LT muscle p H_{45 min} value and drip loss,decreased the muscle a*value and b*value（P<0.05）.Compared with the group without supplementation,supplemented with RP-CrPyr decreased the activities of creatine kinase and lactate dehydrogenase in serum,and muscle p H_{24 h},redness（a*）value,yellowness（b*）value（P<0.05）,and tended to increase the lightness（L*）value（P=0.075）.In conclusion,dietary supplementation of 140 g/d RP-CrPyr can reduce the serum stress indicators level of beef cattle under transport stress,and improve the poor beef quality induced by transport stress.Part 2:Effects of dietary RP-CrPyr supplementation on LT muscle glycolysis and hepatic gluconeogenesis related indicators in long-distance transport beef cattle.The results show that:the interaction of transport and RP-CrPyr had a significant effect on the muscle glycogen content,glycolysis potential,and adenosine monophosphate（AMP）content（P<0.05）.Compared with the group without supplementation,supplemented with RP-CrPyr increased the content of glycogen,glycolysis potential,adenosine triphosphate（ATP）,adenosine diphosphate（ADP）,ATP/ADP ratio,and hexokinase activity in LT muscle,and the content of glucose and pyruvate carboxylase in the liver（P<0.05）;decrease the contents of lactate,AMP,the AMP/ATP ratio in the LT muscle,and the contents of phosphocreatine,creatine,pyruvate in the liver（P<0.05）.Compared with non-transport,long-distance transport significantly decreased the muscle glycogen content,glycolysis potential,and liver glucose content（P<0.05）,increased the content of creatine in LT muscle（P<0.05）.In conclusion,the supplementation of 140 g/d RP-CrPyr could regulate the activity of glycolytic-related enzymes,improve the potential of glycolysis,promote glycogen deposition,promote liver gluconeogenesis,and increase muscle energy level.Part 3:Effects of dietary RP-CrPyr supplementation on the key factors of liver kinase B1/AMP-activated protein kinase（LKB1/AMPK）signal pathway and the glycogen metabolism gene expression in long-distance transport beef cattle.The results showed that:the interaction of transport and RP-CrPyr had a significant effect on the AMPK-a2 m RNA expression in LT muscle.Compared with the group without supplementation,supplemented with RP-CrPyr increased LKB1 and creatine transporter m RNA expression in LT muscle（P<0.05）,decreased glycogen synthase 2 m RNA expression in LT muscle（P<0.05）.Compared with non-transport,long-distance transport significantly increased LKB1 m RNA relative expression level in the liver（P<0.05）.These results suggested that dietary RP-CrPyr supplementation might regulate energy metabolism in long-distance transported beef cattle by increasing muscle glycogen deposition,liver gluconeogenesis,and energy reserve,thereby improving beef quality.Moreover,RP-CrPyr might promote muscle glycogen deposition in beef cattle by activating the LKB1/AMPK signaling pathway,regulating the expression of genes related to glycolysis in this pathway,and improving the beef quality of long-distance transported beef cattle.