Objective To investigate the effect of docosahexaenoic acid (DHA) on the body weight growth and lipid metabolism of neonatal rats during lactation.Methods The specific pathogen free Sprague-Dawley neonatal rats were randomly assigned into 4 groups (high-dose group,medium-dose group,low-dose group and control group) by random number table method.The rats in 3 experiment groups received intragastric administration with DHA 600 mg/kg,300 mg/kg and 100 mg/kg,respectively,while the control group were given 9 g/L saline,totally for 21 days.Body weight was monitored and compared among groups on postnatal day 1,7,14 and 21.And body weight growth rates at each time point were calculated.The serum concentrations of high density lipoprotein cholesterol (HDL-C),low density lipoprotein cholesterol(LDL-C),triglyceride (TG) and total cholesterol were measured and compared at 6-week and 8-week ages.The pathological and histological changes in the heart,the large vessel and the liver were observed at same time.Results The mean body weight of the neonatal rats were significantly different among 4 groups on postnatal day 7,14 and 21 (F =17.334,4.159,6.485,all P ＜ 0.01).Comparisons were made between every 2 groups,the low-dose group was higher than the control group on postnatal day 7 [(21.60 ±0.89) g vs.(18.57 ± 0.76) g] and day 21 [(58.52 ±6.62) g vs.(53.01 ± 11.75) g];the medium-dose group was lower than the control group on postnatal day 7 [(14.23 ±0.49) g vs.(18.57 ±0.76) g] and lower than the low-dose group on postnatal day 21 [(52.47 ±8.18) g vs.(58.52 ±6.62) g];the high-dose group was lower than the low-dose group on postnatal day 7[(16.13 ± 1.02) g vs.(21.6 ±0.89) g],and it was lower than the control group and the low-dose group on postnatal day 14[(31.69 ± 1.77) g vs.(37.60 ± 1.32) g and (36.24 ±0.84) g],and lower than all the other 3 groups on postnatal day 21 [(45.9 ± 13.17) g vs.(53.01 ± 11.75) g,(58.52 ±6.62) g and (52.47 ±8.18) g];all the differences above were statistically significant (all P ＜ 0.05).During the first and the second week after birth,there were significant differences in the mean body weight growth rate among 4 groups (F =8.369,8.331,all P ＜ 0.01),but there was no significant difference during the third week (F =0.603,P ＞ 0.05).Compared with 2 groups,the mean body weight growth rate of the low-dose group was higher than that of the control group in the first week [(184.96 ± 63.16) ％ vs.(141.02 ± 72.07) ％],but which was lower than that of the control group in the second week [(72.60 ± 35.37) ％ vs.(103.20 ± 40.11) ％];the medium-dose group was lower than the low-dose group at the first week [(116.78 ± 51.59) ％ vs.(184.96 ± 63.16)％],but higher than the low-dose group and lower than the control group at the second week[(139.93 ± 67.4) ％ vs.(72.60 ± 35.37) ％ and (103.20 ± 40.11) ％];the high-dose group was lower than the low-dose group in the first week [(137.33 ± 34.42) ％ vs.(184.96 ± 63.16) ％] and lower than that of the medium-dose group in the second week [(98.22 ± 65.86) ％ vs.(139.93 ± 67.4) ％];all these differences were statistically significant (all P ＜ 0.05).At 6 weeks of age,the mean serum concentrations of total cholesterol,TG and LDL-C were not significandy different (F =1.899,1.450,2.581,all P ＞ 0.05) among 4 groups,but the mean concentration of HDL-C was statistically different (F =7.801,P ＜ 0.01).In detail,the mean concentration of HDL-C in medium-dose group was higher than that of the control group,the low-dose group and the high dose group [(1.66 ± 0.08) mmol/L vs.(0.97 ± 0.16) mmol/L,(1.20 ± 0.09) mmol/L and (0.82 ± 0.09) mmol/L,all P ＜ 0.05],and which in the high-dose group was lower than that in the low-dose group (P ＜ 0.05).At 8-week age,the mean serum concentrations of HDL-C,LDL-C and total cholesterol were not significantly different among 4 groups (F =0.935,0.300,1.299,all P ＞ 0.05),but the mean concentration of TG was significantly different (F =2.875,P ＜ 0.05).The mean concentration of TG in the medium-dose group was lower than that in the control group [(0.98 ± 0.11) mmol/L vs.(1.36 ± 0.09) mmol/L,P ＜ 0.05].There were 5 (15.62％) neonatal rats in the high-dose group which were found to have adipose tissue accumulation around the large vessel walls and the heart and were confirmed by histological examination.The liver cells in these rats were found to have mild fatty changes.No similar changes were found in the other groups.Conclusions Neonatal rats supplemented with DHA during lactation can affect their body weight growth and lipid metabolism.Supplemented with high dose may bring risks,while moderate dose may bring benefits.