| The purpose of this study was to investigate the effects of low temperature on growth performance,skeletal muscle fiber types and mitochondrial functions,and to explore the lower limit of temperature in weaned piglets.This work may provide a reference for the winter management of weaned piglets.Two experiments were included in this study.Exp.1 Effects of low temperature on growth performance,muscle fiber types and mitochondrial functions in weaned piglets.The purpose of this experiment was to investigate the effects of low temperature on growth performance,skeletal muscle fiber types and mitochondrial function in weaned piglets.A total of 16 health male DLY barrows at 21-d old age were divided into control group and low temperature group with 8 replicates in each.The weaned piglets were randomly submitted to either cold(from 15±1?;n = 8)or thermoneutral(from 26±1?;n = 8)environmental temperatures.The trial period was 21 d.The growth performance,antioxidant capacity,muscle fiber types,the expressions of mitochondrial function related genes were investigated.The results showed that:1)Compared to control group,low temperature significantly increased the average daily feed intake(P<0.05),increased the ratio of feed to gain(P=0.07).There were no significant effects on average daily gain(P>0.05).2)Compared to control group,low temperature significantly increased diarrhea incidence and diarrhea index of weaned piglets in early stage of experiment(P<0.01).There were no significant effects on diarrhea in later stage of experiment(P>0.05).3)Low temperature significantly increased the relative weight of heart(P<0.05).4)Low temperature significantly decreased the apparent digestibility of CP and DM(P<0.05),decreased GE apparent digestibility(P=0.05).5)Low temperature significantly increased the mRNA expression of MyHCIIa in LM(P<0.05),increased the mRNA expression of MyHCI in PM(P<0.01),decreased the mRNA expression of MyHCIIx in PM(P<0.05).6)Low temperature increased the mRNA expression of mitochondrial function related genes CS and SDHB in LM and PM(P<0.05),increased the mRNA expression of CPT-1b in PM(P<0.01).7)Low temperature significantly increased the total antioxidant content TAOC in serum and LM(P<0.01),increased total superoxide dismutase TSOD activity in PM(P<0.05).Therefore,low temperature decreased the nutrient apparent digestibility,increased the ratio of feed to gain,the diarrhea incidence,increased the relative weight of heart,and the proportion of oxidative muscle fibers in skeletal muscles,enhanced the expression of mitochondrial functions related genes and antioxidant capacity in weaned piglets.Exp.2 Exploration of the Lower Limit Temperature in weaned pigletsThe purpose of this experiment was to investigate the exploration of the lower limit temperature in weaned piglets.A total of 30 health male DLY barrows at 21-d old age were selected and divided into control group and four cold exposure groups with 6 replicates in each.The weaned piglets were randomly submitted to the cold group IV(11±1?;n = 6),the cold group III(15±1?;n = 6),the cold group II(19±1?;n = 6),the cold group I(23±1?;n = 8)or thermoneutral(27±1?;n = 6)environmental temperatures.The trial period was 21 d.The growth performance,antioxidant capacity,muscle fiber types,the expressions of mitochondrial function related genes were investigated.The results showed that:1)The ratio of feed to gain increased with the decreasing temperature,19? group,15? group and 11? group was significantly higher than 27? group(P<0.01),there was a very significant linear and quadratic regression relationship between low temperature and the ratio of feed to gain(P<0.01).Low temperature had a tendency to increase average daily feed intake.There were no significant effects on average daily gain among these groups(P>0.05).2)Compared to 27? group,19? group,15? group and 11? group significantly increased diarrhea incidence and diarrhea index of weaned piglets(P<0.01).3)Compared to 27? group,15? group and 11? group significantly increased the relative weight of heart(P<0.05),and there was a significant linear and quadratic regression relationship between low temperature and the relative weight of heart(P<0.05).4)Compared to 27? group,11? group significantly increased the mRNA expression of MyHCI in LM(P<0.05),and there was a significant linear and quadratic regression relationship between low temperature and the mRNA expression of MyHCI in LM(P<0.05).There had a tendency to increase the mRNA expression of MyHCIIa in LM in each cold group(P=0.09).5)Compared to 27? group,15? group and 11? group significantly increased the mRNA expression of mitochondrial function related genes CS and SDHB in LM(P<0.01),and there was a very significant linear and quadratic regression relationship between low temperature and the mRNA expression of CS and SDHB in LM(P<0.01).Compared to 27? group,11? group significantly increased the mRNA expression of PGC-1? in LM(P<0.05)and the mRNA expression of CPT-1b in PM(P<0.01).There was a significant linear and quadratic regression relationship between low temperature and the mRNA expression of PGC-1? in LM(P<0.05),and there was a very significant linear and quadratic regression relationship between low temperature and the mRNA expression of PGC-1? in LM(P<0.01).6)Compared to 27? group,15? group and 11? group significantly increased TAOC in serum(P<0.01),.and there was a very significant linear and quadratic regression relationship between low temperature and TAOC in serum(P<0.01).Therefore,the lower limit temperature for significant change in the growth performance of weaned piglets was 19.1?,and the lower limit temperature for changing mitochondrial function and antioxidant capacity was 12.4~12.9?.Taken together,low temperature decreased the nutrient apparent digestibilities,increased the diarrhea incidence,the ratio of feed to gain,the relative weight of heart,the proportion of oxidative muscle fibers and mitochondrial functions in skeletal muscles,and antioxidant capacity of the body in weaned piglets.Under the condition of this experiment,the lower limit of temperature for significant change in the growth performance of weaned piglets was 19.1?,and the lower limit of temperature for changing mitochondrial function and antioxidant capacity was 12.4~12.9?. |
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