Effects Of Body Condition On Follicular Development And Integration Of Ewes And Kidlets During Lactation In Goats

The number of goats are 145 million in China,ranking first in the world.However,the precise nutrient regulation of goats has not yet been achieved,resulting in its reproductive potential not being fully utilized.In large-scale self-supporting goat farms,the low annual productivity of goats(LEY)has become a bottleneck restricting its effectiveness.Fertility of dams is influenced by many factors,such as genetics,environment,nutrition and management.Among them,litter size depends mainly on the number of ovulated oocytes,which is greatly determined by the body condition around estrus and mating period.While the interval of postpartum estrus return of dams mainly depends on the recovery of body condition during the lactation period.Therefore,the body condition of female livestock at different physiological stages plays vital roles on reproduction.Obese or too thin will affect the reproductive potential.The growth and development,including recruitment,selection and dominance,of follicles are regulated not only by reproductive hormones in the hypothalamus-pituitary-ovary axis,but also precisely regulated by internal genes and signal pathways of follicles.The concept of folliculome was first proposed in dairy cows.The goal was to establish a follicle gene expression profile from small follicles to preovulatory follicles and atresia follicles in dairy cows,but the folliculome study on goats has not been reported.In short,body condition affects follicular development and ovulation in goats.However,the nutritional regulation mechanism of improving ovulation rate and litter size at different physiological stages need further investigate in goats.Study on the effect of body condition on follicular development of goats and the molecular regulation mechanisms during follicular development are of great significance to improve ovulation rate and shorten lambing interval.The main contents of this paper include:(1)Seventy-two goats were fed with Total Mixed Rations(TMR)for 5 months,and they were divided into four groups according to body condition scores on puberty:A thin group(2.0-2.7),B normal group(control group,2.8-3.2),C medium-upper body condition group(3.3-3.5)and D obese group(3.6-4.0).Their body condition scores,age and weight of puberty were measured.Slaughtering tests were also carried out to study the effect of body condition on growth and slaughter traits of goats.These results showed that the number of follicles with diameter>1.0 mm,1.0-1.9 mm,2.0-3.0 mm and 1.0-3.0 mm were not affected by BCS.However,with the increase of body condition scores,the number of follicles with diameter>3.0 mm increased significantly.Especially in the mid-upper body condition group,the number of dominant follicles with diameter>4.0 mm was significantly greater than those of the normal group and the thin group.The BSC of goats was highly correlated with backfat thickness,body weight,carcass weight and slaughter rate.The puberty age of high-BCS-goats was 7-10 days earlier than those of the normal group and the thin group.These results showed that keep moderate or higher BCS in goats during the growing period was beneficial to the development of large follicles,the increase of ovulation number of adult goats,and the increase of lambing of goats.The "TVUOC"scoring method of goats' body condition was refined according to the body shape of goats,and referred to the scoring standards of cattle and sheep,which provide reference for keeping the best body condition of goats by staged specific feeding.(2)The 2.0-3.5 mm follicles of goats with different body conditions were used.The transcriptome was sequenced by RNA-Seq technology.Bioinformatics was used to screen key pathways and differentially expressed genes that regulate reproduction and to verify their functions.The results showed that,compared with 2.0-3.5 mm follicles of normal BCS goats,2019 differentially expressed genes were screened in the follicles of obese goats,of which 381 genes were up-regulated and 1638 genes were down-regulated.KEGG pathway enrichment analysis showed that body condition may affect follicular development and ovulation rate by affecting steroid hormone production,Arginine and proline metabolism,apoptosis,gap junction and progesterone secretion.The results of qRT-PCR showed that the expression of 3?-HSD in 2.0-3.5 mm follicles of obese goats increased significantly,while the expression of PRLR,cholesterol APAF1,PDE5A,IGF-1 and Leptin R decreased significantly.In addition,the level of P4 in follicular Fluid of obese group was significantly lower than that of normal group,adiponectin level had a downward trend(P>0.05),leptin and estrogen had a upward trend(P>0.05).In this study,we established a transcriptome database of goat follicles in different body conditions,which provided a reference for screening key genes and molecular mechanisms that affect follicular development in goats.(3)The small follicles(1.0-1.9 mm),medium follicles(2.0-3.5 mm)and large follicles(5.0-8.0 mm)of goats in normal body condition were selected as the research object.The key regulatory genes and pathways related to follicular development in goats were screened and verified by RNA-Seq sequencing and bioinformatics analysis.KEGG pathway enrichment analysis revealed that differentially expressed genes during follicular development were mainly enriched in Focal adhesion,Cell adhesion molecule,Cytokine-cytokine receptor interaction,ECM-receptor interaction,D-Arginine and D-ornithine metabolism and TGF-? signaling pathway.Based on the results of RNA-Seq and previous reports,39 genes related to follicular selection and dominance were screened out,and the relative expression of genes in small,medium and large follicles of goats and their trends were studied.Ten genes closely related to follicular development(FoxL2,Nobox,GDF-9,KIT,INHBA,CYP19A1,BCL-2,FSHR,LHR,ESR)were selected for trend analysis and qRT-PCR validation to further prove their roles in follicular development.In this study,we established the transcriptome libraries of follicles with different diameters,screened differentially expressed genes and related regulatory pathways that play an important role in follicular selection and dominance,which could provide a reference for further exploring the regulation mechanism of follicular development in goats.(4)The results of follicular sequencing showed that arginine and its metabolites(polyamines,NO,etc.)played important roles in follicular development in goats.To study the effect of N-carbamoyl glutamic acid(NCG)on goats,thirty-two lactating goats with twin lambs were selected and divided into four groups randomly.The dietary NCG supplements of lactating goats were 0 g/d,1 g/d,2 g/d and 3 g/d in each group respectively for 42 days.The results showed that the average daily gain of lactating lambs supplemented with NCG was significantly higher than that of the control group.On the d 21st day and d 42 day,the milk yield in the 2g/d NCG supplementation group was higher than that in the control group.Addition of NCG increased the concentration of NO,insulin,arginine,citrulline and ornithine in ewe's plasma,and decreased the concentration of NH3 and urea in plasma.The contents of milk protein,putrescine,insulin,NO and GH in goat milk supplemented with 2 g/d NCG were significantly higher than those in control group.Slaughtering lambs on the 42nd day showed that adding NCG significantly increased lamb body length,rumen muscle thickness and papillary density.The body weight loss of lactating goats decreased and the body condition improved at the end of lactation.This study showed that adding NCG in the diet of lactating goats improved the body condition during lactation,milk yield and growth performance of kidlets,and provided a reference for the application of NCG in early estrus return and shortening reproductive interval of goats.