Effects Of Vitamin A On Growth Performance And Mechanism Of It Regulating Hair Follicle Development Of Mink(Neovison Vison)

This experiment was conducted to investigate the effects of supplemental vitamin A(Vit A)on the growth performance,nutrient digestibility,serum biochemical parameters,gut microbiota and hair development of mink(Neovison vison)during the growing period(late growing period and fur growing period),and explore the molecular mechanisms of ATRA inhibit hair follicle growth in vitro.The main research contents and results are as follows:1.Late growing period test: 90 healthy mink were randomly assigned to 6 treatment groups with 15 animals in each group and fed a diet supplemented with0 k IU/kg(Vit A0)?5 k IU/kg(Vit A5)?20 k IU/kg(Vit A20)?80 k IU/kg(Vit A80)?320 k IU/kg(Vit A320)and 1 280 k IU/kg(Vit A1280),the pretest period lasted for 7 days and the formal period lasted for 63 days.The results showed that: Final body weight,average daily gain(ADG)were exhibited a quadratic relationship(quadratic,P<0.05).Compared with Vit A0 group,vitamin A could improve the digestibility of nutrients(P<0.05),Vit A20 group was all the best.With the inclusion of vitamin A,the level of albumin(ALB)in serum had exhibited a quadratic relationship(P < 0.05).Serum triglycerides(TGs)and low-density lipoprotein cholesterol(LDL-C)levels showed a quadratic relationship(P < 0.05)with increasing level of vitamin A.The serum concentrations of highdensity lipoprotein cholesterol(HDL-C)and total antioxidant capacity(T-AOC)were significantly affected by increasing dietary vitamin A(linear,P < 0.05;quadratic,P < 0.05).Vitamin A had a significant effect on concentrations of lactic dehydrogenase(LDH)?aspartate aminotransferase(AST)?alkaline phosphatase(ALP),alanine aminotransferase(ALT)(P<0.05).2.Fur-growing period text: 90 healthy male mink were randomly assigned to 6 treatment groups,with 15 mink per group.Mink in the 6 groups were fed diets supplemented with vitamin A acetate at dosages of 0 k IU/kg(Vit A 0),5 k IU/kg(Vit A5),20 k IU/kg(Vit A20),80 k IU/kg(Vit A80),320 k IU/kg(Vit A320)or 1,280 k IU/kg(Vit A1280)of basal diet.A 7-day pretest period preceded a formal test period of 60 days.At the end of the experiment of the fur-growing period,5 mink from each treatment were selected randomly,the samples of jejunum for intestinal morphology analysis and its contents for microbiological examination were collected.Intestinal morphology analyses were stained with hematoxylin and eosin(H&E)for evaluation of their general histological structure.Gut microbiota were identified using 16 S r RNA sequencing.The results showed that the final measurements of ADG exhibited a quadratic relationship(P < 0.05)to the dosage of dietary vitamin A.With the inclusion of vitamin A,the digestibility of nutrients exhibited a quadratic relationship(P < 0.05).Vitamin A improved the digestibility of nutrients(quadratic,P < 0.05).Serum concentrations of total cholesterol(TC),LDL-C and ALP showed a quadratic relationship(P < 0.05)according to the treatment.The serum concentrations of TGs were significantly affected by increasing dietary vitamin A(linear,P < 0.05;quadratic,P < 0.05).The serum concentrations of total protein(TP),ALB,HDL-C,LDH,AST and ALT were increased(P < 0.05)linearly.With the dietary inclusion of vitamin A,the levels of retinol in the liver increased(P < 0.05).Prominent lipid vacuoles were observed in the liver tissue sections of mink in the Vit A0 and Vit A1280 groups.Our results indicated that vitamin A could promote the development of jejunum villus.Vitamin A supplementation can influence the richness and diversity of mink gut microbiota,the ratio of Firmicutes to Bacteroidetes,as well as modulate the relative abundance of some genera,including Akkermansia.The bacterial abundances of Anaerovibrio,Succinivibrio and Prevotella were positively correlated with amylase activity.The bacterial abundance of Corynebacterium?1,Clostridium?sensu?stricto?1,Streptococcus were negatively correlated with trypsin activity.3.This study is performed to investigate the effects of supplemental vitamin A(Vit A)on the hair follicle development and TGF-?2 gene expression of mink.During the anagen period(September),catagen period(October)and telogen period(November),3 mink from each treatment group were selected randomly,small dorsal skin pieces were surgically excised.The results showed that the primary and secondary hair follicles of mink were in the anagen period,the dermal papilla(DP)were clearly visible,the DP and bulb reside in the middle of the subcutis.In October,the bulb and dermal papilla of mink gradually degenerate and shrink upwards,the hair follicles were in the catagen phase,whereas those of Vit A20 group mink were in the anagen phase.In November,both the primary and secondary hair follicles in the telogen phase,and the length of hair follicles in Vit A20 group were significantly greater than those in the other groups.The relative expression of TGF-?2 in the Vit A0 group during the anagen period was significantly higher than that in the Vit A20 and Vit A1280 groups(P <0.05).During the catagen period,the relative expression of TGF-?2 in the Vit A0 group was significantly different from that in the Vit A20 group(P <0.05),and there was no significant difference between Vit A0 and Vit A1280(P>0.05).During the telogen period,the relative expression of TGF-?2 in the Vit A1280 group was significantly higher than that in the Vit A20 and Vit A1280 groups(P <0.05).Therefore,vitamin A could prolong the anagen period.Deficiency or excessive vitamin A could increase the relative expression of TGF-?2 gene.4.In this study,the effects of ATRA on cultured mink hair follicle growth were studied by administration of different concentrations of ATRA for 12 days in vitro.In addition,the proliferation and apoptosis of DPC were measured after treating with ATRA.The m RNA and protein levels of hair follicle growth associated factor transforming growth factor-?2(TGF-?2)and the phosphorylation level of Smad2 were determined.Moreover,TGF-? type I and type II receptor inhibitor LY2109761 was administered to investigate whether it would abate the effects of ATRA on DPCs.The results showed that ATRA inhibited hair follicle growth,promoted TGF-?2 expression and activated phosphorylation of Smad2.In addition,ATRA inhibited cell proliferation by arresting the cell cycle at G1 phase and induced apoptosis of DPCs by enhancing the ratio of Bax/Bcl-2 and promoted the cleavage of caspase-3.Furthermore,LY2109761 partially reserved the decreased cell viability,increased apoptosis and phosphorylation of Smad2 that were induced by ATRA.In conclusion,,this results showed that supplementation of vitamin A with 20 k IU/kg in diet via improving the development of intestinal villi,the body's antioxidant capacity,and the structure of intestinal microflora,thereby improving the digestibility of nutrients and the health of the body state,and thus improve the growth performance of mink during the growth period(late growing and fur-growing phase).;however,deficiency or excessive vitamin A may negatively affect growth and lipid metabolism of mink.Excessive vitamin A(1280 k IU / kg)could cause the hair follicle anagen period to shorten and the categen period to come early,the mechanism is that it could inhibit hair follicle growth via inhibiting proliferation and inducing apoptosis of DPCs partially through the TGF-?2/Smad2 pathway.