The present experiment showed that the effect of dietary ratios of n-6:n-3 PUFA on the sow and progeny performance, fatty acid composition, and immune component including immunoglobulin and cytokines under conditions of the oil content in the diet is 4.0%.
The content of fat and energy in milk played an important role in keeping piglet alive , and the improvement in litter weight by adding fat to sow diets had been observed previously [13, 14]. In this study, altering maternal dietary ratio of n-6:n-3 PUFA was tended to change the litter average daily gain from d 0 to d 14, and it was greater in 9:1 group compared with the other two groups, but no difference was observed for other performance criterias, some potential effect and the number of sows need to be considered . Reported that offering maize, linseed or tuna oils throughout pregnancy and lactation on sows, the ratio of n-6:n-3 PUFA in maize oil, tuna oil, and linseed oil treatments were 17.4, 3.4, and 3.5, respectively. Piglets suckling maize or tuna oil sows were heavier than piglets suckling linseed oil sows 7 days post weaning. Edwards and Pike (1997) showed that pregnancy length were increased by offering sows n-3 PUFA as fish meal, and piglet born to sows offered n-3 PUFA may have been born more prematurely and less well prepared for birth. But in our experiment. The pregnancy length seems not be affected by the treatment. However,  had demonstrated that an inadequate supply of n-3 PUFA to the pre-term babies is associated with impairment of visual acuity and cognitive development, since commercial sow diets were based on cereals which are lacked of n-3 PUFA, the piglet viability and their growth during lactation may be affected by the imbalance or deficiency of n-3 PUFA. And on the other side, the number of sows should be considered to determine the effect of the ratio of n-6:n-3 PUFA on the performance of lactating sows and their piglets.
Via desaturase-elongase pathway, some long-chain PUFA can be converted in to the linoleate and alpa-linolenate, the precuros of essential fatty acid . Among long-chain PUFA, arachidonic aicd is of particular importance because it is the major regulators of intestinal homeostasis and repair following injury, gastrointestial disturbances rank among the leading cause of neonatal morbidity, and mortality . And research showed that desaturation to 13C-18:3(N-6) increased linearly in pigs fed arachidonate but the alternate elongation to 13C-20:2(n-6) was markedly elevated in pigs fed 0% arachinonate . And on the other hand. Hepatic flux decreased with postnatal age, wherea intestinal flux did not change. In our study, the desaturase-elongase pathway were not analyzed, but the piglet mortaliy during lactation in 3:1 was the least. Additionally, the arachidonic acid content was similar in piglet plasma. It seems the content of precusor in diet and the age of piglets was critical to the effect of those fatty acids.
Colostrum is characterized by a high concentration of IgG and lower concentrations of IgA and IgM . Passive immunity or a sufficient intake of colostral immunoglobulins by piglets plays an important role in the early life . In this study, IgG concentration was highest in 9:1 treatments compared with the other two treatments, and the average daily gain in 9:1 group was also tended to increase. IgM concentration in milk was greater in 9:1 treatment among treatments.This result was consisted with the previous study . Rooke and Bland (2002) reported that IgG synthesis by piglets is positively correlated to the amount of maternal IgG absorbed, thus reinforcing the importance of an adequate IgG intake from colostrum. A highest value of IgG concentration was observed in piglet plasma at d 21 of lactation, which is positively related with the amount of IgG in colostrum . However, there is no clear pattern between the change of immunoglobulin concentrations in piglet plasma and the ratio of n-6: n-3 PUFA. At this time, it is unclear the mechanism that involved n-6 and n-3 PUFA in changing the IgG, IgA, and IgM concentrations. A possible explanation is that n-6 and n-3 PUFA are involved in IL production. Interleukins, as well as isotype specific lymphokines, play an important role in regulation of immunoglobulin synthesis in mouse . IL-2 increased the production of IgG, IgA, and IgM, as reported by . Endres S et al.  reported that the decreased production of interleukin-1 and tumor necrosis factor was accompanied by a decreased ratio of arachidonic acid to EPA in the membrane phospholipids of mononuclear cells. On the other hand, eicosapentaenoic acid, a kind of n-3 PUFA, in membranes competes with arachidonic acids as substrates for cyclooxygenase and lipoxygenase enzymes, decreasing the production of arachidonic acid-derived eicosanoids such as prostaglandin E2, which can affect the production of immunoglobulin directly . Changes in dietary n-6: n-3 PUFA ratios can induce significant alterations in the composition and function of immune cell membranes [26, 27], these can possibly explain the potential effects of ratio of n-6: n-3 on the immunoglobulin.
Cytokines play an important role in immunoregulation. IL-1β, IL-6, and TNF-α is among the most important cytokines produced by monocytes and macrophages. These cytokines can mediate the systemic effects of inflammation such as fever, loss of appetite, mobilization of protein and fat, and acute protein synthesis . Inappropriate amounts or overproduction can be dangerous, these cytokines, especially TNF-α, are implicated in causing some of the pathological responses that occur in inflammatory conditions or some inflammation-associated diseases . An imbalance of the membrane contents of n-6 and n-3 PUFA resulting from dietary deficiency, aging, and diseases may cause abnormalities in neurotransmission and inflammatory responses by changing membrane fluidity, lipid peroxidation, eicosanoid production . In this study, piglet plasma IL-1β concentration were decreased in 9:1 group at d 14 of lactation, and TNF-α was also tended to decrease in this group. It seems the piglet inflammation prevention was improved when dietary ratio of n-6: n-3 was 9:1. Indeed, an increased n-6: n-3 PUFA ratio and decreased n-3 fatty acid fatty acids concentration have been found in patients with inflammatory disorders . Cai S et al.  reported that EPA attenuated IL-1β-induced behavioral changes, and γ-linolenic acid reduced hippocampal PGE2 concentration in rats given IL-1β. It suggested that EPA, γ-linolenic acid, and arachidonic acid play different roles in the neuroendocrine-immune network.
In summary, our study demonstrated that ratio of n-6:n-3 PUFA in plasma, colostrum, milk, and immune components including immunoglobulin and cytokines were well affected by altering the ratio of n-6:n-3 PUFA in lactating sow diets, and it was tended to increase the litter average daily gain from d 0 to d 14 when dietary ratio of n-6: n-3 was 9:1. Further studies might examine whether there is an interaction between dietary energy level and the ratio of n-6: n-3 on performance of sows and their suckling piglets.