| Two feeding trials and milk composition analysis were conducted to investigate the effect of dietary fish oil (rich in DHA and EPA) levels on milk composition and performance of sows and piglets during later gestation (103d) and lactation of sows. The objective of the study is to provide theroy basis for the application of n-3 PUFA to diet for sows and piglets.In two trials, twenty later gestation (103d) of multiparous LandracexLarge White sows were randomly allotted to two groups with ten pens of one sow each. Piglets were weaned at 21d of age. In trial 1, sows had free access to either corn-soybean meal diet (control group) or the same diet except supplementation with 5% fish oil, and in trial 2, sows fed the basal diet supplemented with either 7% of lard or fish oil. The results were as follows:1. In trial 1, compared with the control group, dietary 5% fish oil during lactation decreased loss weight by 39.13% (P＞0.05), backfat loss by 15.63% (P＞0.05), and shortened weaning to estrus interval of sows by 0.3d (P＞0.05), respectively. In trial 2, in contrast to diet supplemented with 7% lard, dietary 7% fish oil lowered backfat loss (P＜0.10), and improved sows' body status, and shortened weaning to estrus interval of sows by 0.3 d (P＞0.05) during lactation, respectively. The ADFI was not significantly affected by treatment diets in two trials (P＞0.05).2. Milk composition analysis results showed that dietary 5% or 7% fish oil significantly increased the percentage of n-3 PUFA (P＜0.001), and significantly decreased the percentage of n-6 PUFA (P＜0.001) in milk, respectively. Meanwhile, the percentage of fatty acids in milk were significantly affected by the duration of lactation (P＜0.05). The percentage of n-3 PUFA (especially for DHA and EPA) were linely increased with the duration of lactation, while n-6 PUFA were linely decreased. Furthermore, the interaction between dietary fatty acid and the duration of lactation significantly(P＜0.05) influenced the percentage of AA, DHA, EPA and n-6 PUFA in milk.3. Dietary 5% fish oil significantly increased the fat content in milk in trial 1 (P＜0.05), but there was no significant difference between treatments with 7% fish oil or 7% lard in trial 2. The content of total solids and protein in milk were not significantly affected (P＞0.05)in trial 1 and 2.4. In trial 1, dietary 5% fish oil significantly increased the percentage of weaning survival (P＜0.05), increased ADG of 21d piglets (P＜0.10), and improved the percentage of fetal survival (P=0.12) by improving the content of fat and the percentage of n-3PUFA in milk, respectively. It also increased 21d average litter gain by 8.99% (P＞0.05) and 21d average body weight by 7.91% (P＞0.05), respectively. In trial 2, higher fish oil level was supplemented in diet, and the result showed sows fed the 7% fish oil diet had higher ADG (P＜0.05)and the percentage of weaning survival (P=0.08)of 21d piglets than 7% lard diet. It also increased 21d average litter gain by 11.84% (P＞0.05) and 21d average body weight by 4.40% (P＞0.05) of 21d piglets, respectively. Furthermore, growth performance of piglets were positive correlation with the percentage of n-3 PUFA in milk, and were negative correlation with the percentage of n-6 PUFA in milk.5.χ2 test was used to further analyse the distribution of newborn piglets' body weight and weaning survival in trial 2. Compared with the 7% lard diet, diet supplemented with 7% fish oil significantly decreased the percentage of piglets with initial body weihgt equal or lesser than 1200g (P＜0.05), and significantly increased the percentage of weaning piglets with initial body weihgt equal or lesser than 1500g (P＜0.05), especially increased the percentage of weaning piglets with initial body weihgt equal or lesser than 900g by 31%.The results indicated that 1) sows fed diet supplemented with fish oil during sows' later gestation (103d) and lactation improved reproductive performance of sows and enhanced growth performance of piglets. It also may be benefit for improving the percentage of fetal survival and weaning survival of pigs. However, it's better for maternal diet supplemented with fish oil with 7%. 2) Diet supplemented with 5% or 7% fish oil increased the percentage of DHA, EPA and n-3 PUFA in milk, and they were also increased in a dose-dependent manner with increasing level of dietary n-3 PUFA, which was benefit for the growth of the piglets.
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