Effects Of Lysine On Growth And Reproduction Performance In New Zealand Rabbits And Its Molecular Mechanism

This study was conducted to investigate the effects of dietary lysine on production performance, N metabolism, blood metabolites, hormone and GH-IGF axis gene expression of growing and reproductive New Zealand White rabbits. Growing period was divided into two growing phases, which were from weaner to 70 days of age and from 70 days to 90 days age. One hundred weaned rabbits were allocated in individual cages for five treatments in which they were fed each diet with lysine level at 0.55%, 0.65%, 0.75%, 0.85% and 0.95%, respectively. Sixty parous female rabbits were used for five treatments in which the experimental dietary lysine level was at 0.65%, 0.80%, 0.95%, 1.10% and 1.25%, respectively. This study were finished by five trials as follows:Trial one was carried out to discover the effect of dietary lysine on growth performance, N metabolism, blood metabolites and hormone of weaner to 70 days and 70 to 90 days of age NZW rabbits. The results in trial one indicate that dietary lysine effected the daily gain and feed conversion rate of weaner to 70, but not 70 to 90 days of age NZW rabbits (P<0.05). Daily gain in 0.75%-0.95% lysine level treatment were highest but feed conversion rate were lowest, which were 30.48-33.42g/d and 3.46-3.85:1 respectively. Dietary lysine level had quadric effect on RN and NBV of weaner to 90 days while only had quadric effect on SUN of 70 to 90 days of age rabbits (P<0.05). Serum hormone contents were affected by dietary lysine (P<0.05), and the highest serum IGF-I were in 0.75%-0.95% lysine treatments, which were 46.7-49.7 and 54.3-57.0mg/mL of weaner to 70 and 70 to 90 days of age, respectively. Serum IGF-I (y) and daily gain (x) were correlated greatly, and regression equation as follows : y = -0.5917x2 + 7.0279x + 28.982,R2 = 0.9426.Trial two is the semiquantitative study about GHR, IGF-I and IGFBP1 gene expression in the liver and skeletal muscle of rabbits fed each diet with lysine level at 0.55%, 0.65%, 0.75%, 0.85% and 0.95%, respectively. The relative contents of GHR, IGF-I and IGFBP1 gene to GAPDH indicated that dietary lysine level increasing may promote the GHR gene expression in the liver but repress in the skeletal muscle of rabbits, so the effect of dietary lysine on GHR gene expression is tissue specific. Dietary lysine may up-regulate the expression of IGF-I mRNA and down-regulation the expression of IGFBP1 mRNA in the liver and skeletal muscle of weaner to 90 days of age NZW rabbits.Real time fluorescent quantitative PCR was used in trial three to quantize the IGF-I mRNA expression in the liver and skeletal muscle of growing NZW rabbits. And the results were that IGF-I mRNA expression amount increased significantly in the liver and skeletal muscle of 70 and 90 days of age NZW rabbits with the increasing dietary lysine level.Trial four was carried out to discover the effect of dietary lysine on reproductive performance, blood metabolites and hormone of female rabbits in gestational period and lactation. The results in trial four indicate that with the dietary lysine increasing, total litter weight at birth, total litter size, live litter size, milk secretion power, total litter weight at wean increasing significantly NZW rabbits (P<0.05). Total litter weigh at birth, total litter size and milk secretion power in 1.10% lysine level treatment were highest, which were 561g, 11 and 1378g respectively. While the total litter weight at wean in 0.996% lysine level treatment was highest, which was 2724g. Dietary lysine level had quadric effect on SUN of female rabbits(P<0.05), and the lowest SUN in 0.95% lysine level treatments were all lowest in gestation period and lactation, which were 4.94 and 5.79 respectively. Serum Ins and IGF-I contents were affected by dietary lysine (P<0.05) at gestation period and lactation, and the highest serum IGF-I were in 1.10% lysine treatments, which were 293 and 203mg/mL at the last day of gestation period and lactation, respectively. Dietary lysine level had significant effects on serum LH and E2 (P<0.05), but not on other reproductive hormone such as FSH, P and PRL.Trial five Trial two is the quantitative study about GHR, IGF-I and IGFBP1 gene expression in the liver, mammary gland and ovary of female rabbits in gestation period and lactation fed each diet with lysine level at 0.65%, 0.80%, 0.95%, 1.10% and 1.25%, respectively. In this trial semi quantitative PCR and Real time fluorescent quantitative PCR were used. The relative contents of GHR, IGF-I and IGFBP1 gene to GAPDH indicated that dietary lysine level increasing may promote the GHR and IGF-I gene expression, but repress the expression of IGFBP1 mRNA in the liver, mammary gland and ovary of female rabbits in gestation and lactation period. The results by Real time fluorescent quantitative PCR indicated that the expression contents of IGF-I in the liver, mammary gland and ovary of reproductive female rabbits increased significantly (P<0.05), but the over-high dietary lysine maybe repress the expression of IGF-I in the liver of female.The results of this study illuminate that lysine is added into diet at suitable level is good for the growth and reproductive performance of New Zealand White rabbits. The increasing hormone contents and expression of some gene which were all relative with the GH-IGF axis at higher dietary lysine level, and their correlation provide a latent mechanism about the lysine promote the production performance of rabbits. By all round consideration, the suitable dietary lysine level is 0.75% in growing period, is 1.10% in gestation period, is 0.95% in lactation period, and is 0.95% in total reductive period.