| This research was conducted to study the effect of feed intake level on the embryonic survival and secretion of Leptin and expression in embryos during early pregnancy in gilts. A total of 63 Landrace/Yorkshire crossed-breed gilts, every of which body weight was 113.40±9.58kg on mating, were randomly allocated to one of the three different feed intake level (high, middle, low), and allowance of 2, 1.2, 0.6 times requirement of maintenance after mating. There were three replicates each replicate including seven gilts in every feed intake level. The gilts were weighted, collected blood samples and slaughtered on d12, d25, d35 of pregnancy respectively. Then, ELISA was applied to determine the Leptin concentration in serum and uterine flushing of difference gilts, and real time-quantitative RT-PCR was applied to determine the Leptin, obese receptor (obR), signal transducer and activator of transcription -3 (STAT3) and DNA methyltransferase -1 (DNMT1) gene expression difference in embryos. The results were as follows:1. Feed intake level significantly influenced embryonic survival on early pregnancy in gilts. Total embryonic survival on d12, 25 35 of pregnancy in middle feed intake were significantly greater than high and low feed intake (P＜0.05). There was not difference between high and low feed intake (P＞0.05).2. Feed intake level significantly influenced Leptin concentration in serum and uterine flushing on early pregnancy in gilts. On day 12 of pregnancy, Leptin concentration in serum and uterine flushing of high feed intake was significantly greater than middle feed intake (P＜0.05), and very significantly greater than low feed intake (P＜0.01). On day 25 and 35 of pregnancy, Leptin concentration in serum and uterine flushing in high feed intake was very significantly greater than middle and low feed intake (P＜0.01), and Leptin concentration in serum of middle feed intake was very significantly greater than low feed intake (P＜0.01), and there was no difference of Leptin concentration in uterine flushing between middle feed intake and low feed intake (P＞0.05). There was a positive correlation between Leptin in serum and uterine flushing concentration and feed intake on day 12, 25 and 35 of pregnancy, showing a very significant exponential and cubic change (P＜0.01). There was a positive correlation between serum Leptin concentration and feed intake on day 25 and 35 of pregnancy, showing a very significant exponential and cubic change (P＜0.01). Leptin concentration would increase during early pregnancy of gilts. In the same feed intake level, Leptin concentration in serum was increased following the extension of pregnancy time(P＜0.05).3. Feed intake level significantly influenced the gene expressions of Leptin,obR,STAT3 and DNMT1 in embryos on early pregnancy. The results of every gene expression difference, which were normalized using the H2A gene as internal control, were presented as follows:On day 12 of pregnancy, Leptin gene expression of high feed intake was very significantly greater than middle and low feed intake (P＜0.01), and obR gene expression of high feed intake was very significantly greater than low feed intake (P＜0.01), and DNMT1 gene expression of high feed intake was significantly greater than low feed intake (P＜0.05), STAT3 gene expression of high feed intake was very significantly greater than middle and low feed intake (P＜0.01) and the expression of middle feed intake was significantly greater than low feed intake (P＜0.05).On day 25 of pregnancy, Leptin gene expression of high feed intake was very significantly greater than middle and low feed intake (P＜0.01), and obR gene expression of high feed intake was significantly greater than middle and low feed intake (P＜0.05), and STAT3 gene expression of high feed intake was very significantly greater than low feed intake (P＜0.01) and middle feed intake was significantly greater than low feed intake (P＜0.05), DNMT1 gene expression of high and middle feed intake was very significantly greater than middle and low feed intake (P＜0.01) and the expression of high feed intake was significantly greater than middle feed intake (P＜0.05).On day 35 of pregnancy, Leptin and DNMT1 gene expression of high feed intake was significantly greater than middle feed intake (P＜0.05), and very significantly greater than and low feed intake (P＜0.01) for Leptin, and obR gene expression of high feed intake was significantly greater than low feed intake (P＜0.05), and STAT3 gene expressions of high and middle feed intake were very significantly greater than middle and low feed intake (P＜0.01)Conclusions:1. Feed intake level significantly influnced embryonic survival on early pregnancy in gilts. Gilts were fed with allowance of 1.2 times requirement of maintenance in d0-35 of pregnancy, but high feed intake and serious restricted feeding would depress embryonic survival in early pregnancy.2. Feed intake level significantly influnced Leptin concentration in serum and uterine flushing on early pregnancy in gilts. Leptin concentration in serum and uterine flushing was increased following the feed intake level of gilts, and had positive relation to feed intake level and slaughter weight. Leptin concentration would increase during early pregnancy of gilts. In the same feed intake level, Leptin concentration in serum and uterine flushing was increased following the extension of pregnancy time. Much higher or lower secretion of Leptin had detrimental effects on the development of early embryo.3. Feed intake level significantly influenced the gene expressions of Leptin,obR,STAT3 and DNMT1 in embryos on early pregnancy. High feed intake (2 times requirement of maintenance) could upregulate the expression of these genes and low feed intake(0.6 times requirement of maintenance) could downregulate the expression of these genes. The downregulation of these genes was not favourable for embryonic survival.
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