Effect Of Dietary Protein Level On Mammary Development Of Tibetan Sheep During Pregnancy

In this study,Tibetan ewes in late pregnancy were taken as the research object.The purpose of this experiment was to detected the differences of serum reproductive hormone concentration,breast histomorphology,breast transcriptome and expression of genes related to breast development by feeding different protein levels of diets,and to elaborated the mechanism of the effect of dietary protein levels on the development of Tibetan ewes in pregnancy,which provided a theory for the reasonable protein intake of Tibetan ewes in pregnancy.A total of 120 Tibetan ewes with similar age,parity and body condition were selected for grazing and feeding at 0-84 days after conception.At the 85 th day after pregnancy,the gravid ewes were randomly divided into four groups,30 in each group.According to the nutritional needs of the sheep,NRC(2013)was fed with the same level of digestive energy and different protein levels(7.5%,9.5%,11.5%,13.5%)in quantitative diet.The serum concentrations of progesterone,luteinizing hormone,follicle stimulating hormone,prolactin and growth hormone were measured on the 90 th,120th and 150 th day of gestation;the length of milk pool,acinus,basement membrane,myoepithelium and mitochondria were measured on the breast tissue samples of Tibetan ewes;the gene expression level of Tibetan ewes was measured by transcriptome technology,and the difference gene was verified by q PCR.The results showed that: 1)in the late pregnancy,when the dietary protein level was 11.5%,the concentration of reproductive hormones related to the development of mammary gland was relatively high,which promoted the development of mammary gland.2)Among the four experimental groups,the group with 11.5% protein level exhibited better acini,basement membrane,myoepithelium and mitochondria.3)Based on the data of mammary gland phenotype,we compared the transcriptome data of 7.5% and 13.5% levels,14 differential genes were screened by q PCR analysis,including CSN2,LALBA,CSN1S1,PAEP,FABP3,CSN1S2,CSN3,RPS17,FASN,SPP1,ATF4,PGD,LTF,VEGFA.In conclusion,we found that effect of feeding was optimum under the 11.5% protein level for gravid ewes,and speculated that dietary protein level might affect the development of breast via changing the expression of target gene.This study will provide a scientific basis for the regulation mechanism of diet on breast development and lactation.