| The main objective of the present study was to investigate the difference of Kissl/GPR54 gene expression level on Gonadal (hypothalamus-pituitary-ovary) axis and related hormones in different breed gilts (Meishan and LY), Additionally, whether dietary energy level could induce variation for the age of puberty onset in the breed of late-maturing gilts. Two experiments was conducted:In experiment 1, meishan gilts (at estrus, n=4) and LY gilts (non-estrus, n=4) at age of 70 days were used to collect samples for determination the concentration of serum Leptin and E2 by ELISA, Kiss1 gene sequence clone by RT-PCR, and Kiss1/GPR54 expression in reproductive axis, LeptinR and ERαin hypothalamus, and LHR in ovary by RT-PCR.(1) DNA sequence of Kiss1 gene between meishan and LY gilts were not different.(2) The average puberty onset age of Meishan and LY was 100d and 199d separately, Gene expression encoded by Kiss1 in reproductive axis (including hypothalamus, pituitary and ovary) were significantly higher in LY gilts (P<0.05), but GPR54 mRNA expression level was similar between two breeds (P>0.05). Gene expression level encoded by Kissl/GPR54 in reproductive axis were gradually higher as the advent of first estrus in both meishan and LY gilts (P<0.05)(3) Leptin concentration in meishan gilts at age of 70 days was higher than in LY gilts (P<0.05), but circulating concentration of Leptin at estrus was similar between two breeds (P>0.05). E2 concentration in meishan gilts at estrus was significantly higher than that in LY gilts (P<0.05), but was similar at 70 days of age (P>0.05). Both Leptin and E2 concentration was gradually higher as the increase of age (P<0.05)(4) ERa mRNA expression level was higher in meishan gilts than LY gilts in hypothalamus (P<0.05). LeptinR mRNA expression in hypothalamus was higher in meishan gilts than LY gilts at 70 days of age (P<0.05), but LeptinR mRNA expression was not different between two breeds at estrus (P>0.05). LHR mRNA expression in ovary at estrus was higher than that in LY gilts at 70 days of age and at estrus (P<0.05). LeptinR and ERa mRNA in hypothalamus, LHR mRNA expression in ovary was gradually higher as the increase of age (P<0.05)(5) Person correlation analysis revealed that circulating Leptin concentration was positively correlated with Kiss1 and GPR54 expressions (with exception for GPR54 in ovary) in HPG axis (P<0.05). Circulating E2 concentration was positively correlated with Kissl expressions in hypothalamus (P<0.05), but not for Kissl and GPR54 expression in HPG axis (P>0.05). In experiment 2, twenty LY gilts with initial bodyweight of 50±4.5 kg were randomly allocated to 2 treatment groups based on paired experimental design, ten gilts were fed energy restriction of 70% energy requirement (L) of NRC(1998), remaining ten LY gilts were fed 100% energy requirement (H) of NRC(1998), notably, these two groups of gilts were fed similar nutrients except for the difference of energy intake. Circulating blood samples were collected at the age of 50 kg,80 kg,100 kg and at estrus, for the determination of serum E2 and Leptin concentrations. Estrus check twice per day were conducted when bodyweight of gilts over 80 kg. Occurrence of pink vaginal orifice and mucosal fluid leak was defined as estrus. The age, bodyweight and backfat P2 thickness at estrus initiation were determined.(6) Compared with gilts in L group, gilts in H group was 13 days earlier to reach estrus (177.7±3.4d VS 190.1±10.2 d, P<0.05). Gilts in H group had higher bodyweight, average daily gain, P2 fat thickness(122.6±7.3 kg VS 108.4±4.1 kg; 0.85±0.02 kg/d VS 0.65±0.15 kg/d; 13.50±1.38 mm VS 10.57±1.27 mm, P<0.05).(7) Circulating Leptin and E2 concentrations was higher as the increase of age, which was evidenced by higher Leptin and E2 concentration at bodyweight of 100kg than that at 50 kg and 80 kg (P<0.05). Leptin and E2 concentrations were affected by dietary treatment. Leptin and E2 concentration in L group was significantly lower than H gilts (P<0.05). Kissl expression in hypothalamus was significantly higher than L gilts (P<0.05), but GPR54 expression was not affected by diets (P>0.05)Conclusion:(1) There was no difference of Kissl DNA sequence in meishan gilts and LY gilts, but Kissl/GPR54 expression in reproductive axis was different between breeds, the higher Kissl expression could be beneficial for the initiation of estrus.(2) Higher circulating Leptin and E2 could up-regulate the Kissl expression, and higher Leptin and E2 concentration could promote the initiation of estrus. Dietary high energy level could promote the puberty onset through higher Leptin and E2 level. |
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