Fish Oil Promote Muscle Growth In Weaned Pigs By Up-regulating Expression Of Muscle Fiber Tapes And Related Genes

In the current study,7%fish oil(rich in LCn-3PUFA) or lard(rich in saturated fatty acid) was added to the diet for sows during pregnancy and lactation and for weaned pigs to test the hypothesis that dietary long-chain n-3PUFA has the effects on muscle mass,the mRNA abundances of four myosin heavy chain(MHC) isoforms and muscle development related genes(MRF4,MyoG and PGC-1α) in weaned pigs.In addition,we investigated the effect of maternal nutritional of fish oil on skeletal muscle development in weaned pigs.The objective of the study is to provide theroy basis for the effects of n-3PUFA on skeletal muscle growth and related genes in piglets.Experiment 1:the experiment uses the two factors design,divides to three stages, late gestation,lactation and nursing.Twenty later gestation(103 d) multiparous sows (Landrace×Large White) were randomly allocated into two groups:control group(C) and treatment(T),respectively.Ten sows were allocated into per treatment,with a sow as one experimental unit.Two isoenergetic and isonitrogenous diets were formulated to meet the nutrient requirements of late gestation and lactation of sow,and one of which was the control diet including lard at the level of 7%and another one was the treatment diet including fish oil at the level of 7%.For the postweaning growth phase of the experiment, barrows and gilts(n=56) selected from each litter of two groups were randomly allocated into two groups,control group(C) and treatment(T).Two diets were formulated to meet NRC requirements for nursery and growing pigs,and one of which was the control diet (including lard) and another one was the treatment diet(including 7%fish oil), respectively.Thus,there are four groups,CC,CT,TC and TT of nursery piglets,with seven replications per treatment and one barrow and one gilt as an experimental unit.At the 70 d,16 pigs(2 barrows and 2 gilts of each group) were slaughtered and dissected, and most of skeletal muscle in anterior part,middle and posterior part of body were weighed.The results were as follows:1.Dietary 7%fish oil of weaned pigs significantly increased the mass of Longissimus and Semimembranosus(P＜0.05),and improved the mass of Trapezius and Biceps femoris muscles(P＜0.10) in 70d weaned pigs;2.The results showed that,7%fish oil adding to the diet for sows during pregnancy and lactation significantly increased the mass of Lesser posas(P＜0.01),and improved the mass of Gluteus medius and Gastrocnemius muscles(P＜0.10),but there was no significant difference on skeletal muscles in anterior part of body we measured(P＞0.05); Experiment 2:skeletal muscle samples of the Triceps brachii(TB),Longissimus muscle(LM) and Biceps femoris(BF) were immediately removed after slaughter and exsanguination,wrapped in foil,and frozen in liquid nitrogen to be stored at -80℃for subsequent total RNA extraction.Total RNA was extracted from the skeletal muscle samples using the Trizol regent.The mRNA expression of IGF-1,GHR,MRF4,MyoG and PGC-1 was measured using semi-quantitative reverse transcription PCR,and relative expressions of four MHC isoforms(MHC-Ⅰ,MHC-Ⅱa,MHC-Ⅱx and MHC-Ⅱb) were using a multiplex PCR procedure in threes muscles,respectively.The results as follows:1.Supplemented 7%fish oil in diet for sows during pregnancy and lactation and weaned pigs all resulted in an significant influence expressions of MHC in the Triceps brachii(TB),Longissimus muscle(LM) and Biceps femoris(BF)(P＜0.05),especially up-regulated MHC-ⅡmRNA level,including MHC-Ⅱα,MHC-Ⅱb and MHC-Ⅱx.In addition,the effects of fish oil adding to the diet for weaned pigs on expressions of MHC in skeletal muscles in 70d was higher than adding to the diet for sows,and depended on anatomic location of muscles.2.In our experiment,adding 7%fish oil to diets of sows and weaned pigs diet all resulted in an significant increase expressions of IGF-1 and GHR in the Triceps brachii (TB),Longissimus muscle(LM) and Biceps femoris(BF)(P＜0.05),and there was a significant interaction between two stages(P＜0.01).These data indicated that,the effects of dietary fish oil for sows on expressions of growth-axis genes affected the effectiveness of dietary fish oil for weaned pigs.3.The level of MyoG in in threes muscles were not affected by 7%fish oil adding to sows diet or weaned pigs(P＞0.05).Dietary fish oil of weaned pigs significantly increased expressions of MRF4 in the Triceps brachii(TB) and Biceps femoris(BF)(P＜0.01),and significantly increased expressions of PGC-1αin the three muscles(P＜0.01),while MRF4 mRNA in Longissimus muscle(LM)had a trend of decrease(P=0.079).Furthermore, dietary fish oil of sows significantly up-regulated abundance of MRF4 mRNA in Longissimus muscle and PGC-1αmRNA in the Triceps brachii(TB)(P＜0.01), meanwhile,the levels of MRF4 mRNA in Biceps femoris(BF) and PGC-1αmRNA in Biceps femoris(BF) and Longissimus muscle(LM) had a trend of increase(P=0.107, P=0.088,P=0.081).The following conclusion of this study can be drawn from:1) Supplemented 7%fish oil to the diet for sows during pregnancy and lactation and for weaned pigs enhance growth of skeletal muscles,which were located in middle and posterior part of body especially,by modifying muscle phospholipid.In addition,there was significant maternal nutritional effectiveness of fish oil on skeletal muscle development in weaned pigs.2) Dietary long-chain n-3 fatty acids increased skeletal muscle mass in different part of body by altering composition of muscle fiber tapes,especially increased proportion of MHC-Ⅱb and MHC-Ⅱx.The effects of n-3PUFA in muscle on muscle fiber tapes may be mediated,at least in part,by up-regulating expression of muscle development and muscle fiber tapes transformation related genes,including growth-axis genes,MRF4,MyoG and PGC-1.