Effect And Regulation Of N-3 PUFA On Immune Maturation And Growth Of Piglets

The aim of this study was to investigate the effect of long chain n-3 polyunsaturated fatty acids (PUFA) on immune maturation and muscle growth of piglets, and its potential mechanism involved in n-3 PUFA regulating piglets'growth. The diets of 18 gestating sows were supplemented with 7% lard (C) (n=10) or 7% fish oil (T) (n=8) from 10 d before parturition to weaning on d 28.At farrowing, litters were equalized within dietary treatments to the same number of piglets per litter(-10).At weaning,56 piglets,28 (half female and half castrated male) each from sows fed with fish oil diet or lard diet, were subdivided into four groups of 7 replicates (one female and one castrated male per replicate) based on both sow diet and post-weaning piglet diet (C had 7% lard and T had 7% fish oil):CC, CT, TC, TT, and were fed with the 7% fish oil or lard diet from d 35 to d 70. Milk samples were collected from lactating sows at 21d after farrowing. At d 70, four piglets per group (2 female and 2 castrated male) were sacrificed to collect spleen, longissimus dorsi muscle, biceps femoris muscle and triceps brachii muscle samples. Muscles of triceps brachii, latissimus dorsi, pectoralis profundus, biceps brachii, supraspinatus, infraspinatus, subscapularis, trapezius, longissimus dorsi, posas minor, biceps femoris, quadriceps femoris, adductor, gluteus medius, gastrocnemius, semitendinosus and semimembranosus were separated and weighted. Blood samples of piglets were collected and separated for sera at the end of the experiment.The first part:to investigate the effect of fish oil or lard supplementation to late gestation-lactating sows'and/or weaned piglets'diets on the growth performance, muscle mass of piglet and fatty acids composition in piglet muscle. The fatty acids composition of diets, milk, longissimus dorsi muscle, biceps femoris muscle and triceps brachii muscle were determined by gas chromatography method and growth performance of piglets were measured. C16:0, C18:0, C18:1n-9 and C18:2n-6 composed of the main content of fatty acids in the lard diets, while C16:1,C20:5n-3,C22:5n-3 and C22:6n-3 composed of the main content of fatty acids in the fish oil diets. The n-3 PUFA contents in fish oil diets were 8-9 folds higher than that in lard diets. The lipid contents in milk were not differ (P>0.05).However, C14:0, C16:1,C20:5n-3,C22:5n-3,C22:6n-3,n-3 PUFA and PUFA were extremely higher, while C18:1n-9, C18:2n-6, C20:4n-6, MUFA and n-6 PUFA were extremely lower in milk from fish oil diet fed sows than that from lard diet fed sows (P<0.01).In the lactation period, suckling piglets from fish oil diet fed sows grew more fast (P<0.05) than the controls, and in the post-weaning period these piglets also had higher average daily gain (ADG) (P<0.10), feed intake (P<0.05), and final body weight (P<0.10) than piglets from lard diet fed sows. However, piglets received fish oil diet had lower ADG (P<0.05), lower final body weight (P<0.05), and higher feed:gain ratio (P<0.10) than piglets received lard diet. Late gestation-lactating fish oil supplementation to sows'diet increased the muscle mass of posas minor (P<0.05) in piglets at the end of this experiment. However, longissimus dorsi muscle mass (P<0.05), trapezius muscle mass (P<0.10), biceps femoris muscle mass (P<0.10) and semimembranosus muscle mass (P<0.10) were higher in piglets fed with fish oil diet during post-weaning than that in lard diet fed piglets. Dietary fish oil significantly increased n-3 PUFA content in longissimus dorsi muscle, biceps femoris muscle and triceps brachii muscle. However, the n-3 PUFA content was higher in longissimus dorsi muscle than that in triceps brachii muscle after fish oil feeding. The results suggested that 7% fish oil addition to late gestation-lactating sows'diet was favorable to the growth of piglets. However, it was likely to have negative effect when 7% fish oil was supplemented to piglets'diet during post-weaning period. Dietary n-3 PUFA could increase masses of several muscles in piglet at the end of the experiment. And the effect of n-3 PUFA on muscles' growth was dependent to the enrichment of n-3 PUFA in these muscles.The second part:to investigate the effect of dietary long chain n-3 PUFA on immune maturation. ELISA assay method was employeed to determine the interferon y (IFN-y) and interleukin 10 (IL-10) concentrations in sera and the genes expression of IL-2, IL-12b, IL-12 receptor O2 subunit (IL-12Rβ2), IFN-y, GATA-binding transcription factor 3 (GATA-3), IL-4 and IL-10 in spleen were determined by the method of relative quantitative RT-PCR. IFN-γ/IL-10 ratio of serum was tended to increase in piglets fed with fish oil diet during post-weaning. Dietary long chain n-3 PUFA supplementation increased splenic genes expression of IL-2 (P<0.01),IL-12b (P<0.05) and IL-12Rβ2 (P<0.01)in piglets.IFN-γgene expression was increased (P<0.01),while IL-4 gene expression was decreased (P<0.05) in spleen of piglets fed with fish oil diet in post-weaning period compared with that fed with lard diet. Splenic IL-4 gene expression in piglets from fish oil diet fed sows was higher (P<0.01)than that from lard diet fed sows. The results suggested that long chain n-3 PUFA could increase the mRNA expression of IL-2 and Thl genes in spleen, promote lymphocytes proliferation, Thl polarization and piglets'immune maturation.The third part:to investigate the effect of dietary long chain n-3 PUFA on pro-inflammatory cytokines gene expression and growth of piglets. IL-1β, IL-6 and tumor necrosis factora(TNF-α) expression in longissimus dorsi muscle and spleen and insulin-like growth factor (IGF-Ⅰ) and typeⅠIGF-Ⅰreceptor (IGFIR) expression in longissimus dorsi muscle of piglets were measured by the method of relative quantitative RT-PCR. Piglets from fish oil fed sows had lower genes expression of IL-6 (P<0.05) and TNF-a (P<0.01) but higher gene expression of IGF-I (P<0.05) in longissimus dorsi muscle and had higher TNF-a gene expressio (P<0.05) in spleen than piglets from lard diet fed sows.However, piglets fed with fish oil diet during post-weaning had higher splenic expression of pro-inflammatory cytokines (IL-1β, IL-6 and TNF-a) (P<0.01)and lower expression of IGFIR (P<0.01) in the longissimus dorsi muscle than piglets fed with lard diet. Correlation analysis revealed that splenic IL-6 expression was negatively correlated with longissimus dorsi muscle IGFIR expression (r=-0.6580, P<0.05) and ADG was negatively correlated with longissimus dorsi muscle TNF-a expression (r=-0.6224, P<0.05).The results suggested that supplementation of 7% fish oil to sows' diet during late gestation-lactating period down-regulated the genes expression of pro-inflammatory cytokines and attenuated the suppression of IGF-Ⅰgene expression in longissimus dorsi muscle of their progenies, promoted piglet growth. However,7% fish oil supplemented to piglets'diet during post-weaning period increased splenic genes expression of pro-inflammatory cytokines, decreased IGFIR gene expression in longissimus dorsi muscle, and suppressed piglest growth.The forth part:to investigate the effect of long chain n-3 PUFA on myosin heavey chain isotypes (MyHCs) and myogenic regulatory factors (MRFs) mRNA expression in muscle, and muscle growth of piglets. Multi-PCR was used to determine the ratio of MyHCs mRNA and relative quantitative RT-PCR was used to measure the genes expression of MRFs in longissimus dorsi muscle, biceps femoris muscle and triceps brachii muscle. The MyHC-Ⅰand-Ⅱa were the primary MyHCs in triceps brachii muscle. However, longissimus dorsi muscle and biceps femoris have equal ratios of MyHCs.Fish oil supplemented to sows'dets increased MyHC-Ⅱx mRNA ratio (P<0.01) but decreased MyHC-Ⅱa mRNA ratio (P<0.05) in their progenies'longissimus dorsi muscle at the end of this experiment. The MyHC-IIb mRNA ratio in biceps femoris muscle was also increased by post-weaning fish oil diet feeding in piglets (P<0.05).There was a tendency towards to increase the gene expression of MyoD (P<0.10) in longissimus dorsi muscle of piglets fed with fish oil diet after weaning compared with that fed with lard diet. The results indicated that dietary long chain n-3 PUFA could increase muscle growth via modulating MyoD gene expression, promoting satellite cells proliferation and differetiation and increase the ratio of glycolytic muscle fibre type.Conclusion:1.Dietary long chain n-3 PUFA could promote piglets'immune maturation. Seven percent of fish oil supplemented to sows'diets can decrease genes expression of pro-inflammatory cytokines and their unfavorable effects on IGF-I in longissimus dorsi muscle of their progenies, and in turn promote piglet growth. However, high levels of long chain n-3 PUFA supplementation to post-weaning piglets'diet may increase splenic genes expression of pro-inflammatory cytokines, holdback IGF-I function, and then negatively impact the growth of weaned piglets.2.The long chain n-3 PUFA in diets could deposit in skeletal muscles, increase the gene expression of MyoD and glycolytic muscle fibre type, promote postnatal muscle growth in piglets. However, the long chain n-3 PUFA supplementation in piglets'diets had different effects on muscle growth and growth performance of piglets and it was due to the different amounts of n-3 PUFA deposited in different tissues.