| Calves are the basis of the adult herd,dietary protein level plays an important role in calves growth and development.Therefore,investigating the propor dietary protein level and raising method for calf are of great importance.The rumen is the first stomach of ruminants,in which 60%～80% of dietary nutriment was degraded including protein..From birth to weaning,it is the key period for calves to establish rumen function which is directly influenced by its epithelium development.Translational tumor regulatory protein(TCTP),a highly conserved protein,can promote cell proliferation and growth by regulating cell growth-related signaling pathways.Studying the roles of TCTP in the rumen epithelial cells’ development will help to better understand the molecular mechanism of rumen development andexplore the regulation methods of rumen development.In this thesis,we first explored the proper dietary protein level for calves of 3 to 4 months old.Using Hu sheep as a animal model,the rumen development was studied,and the expression and function of TCTP during rumen epithelial development in ruminants were explored.The results of this study are as follows:1.Effects of different dietary protein levels on growth performance,digestibility and blood indexes of Chinese Holstein calves during 3～4 months old.The purpose of this study was to investigate the appropriate dietary protein levels of Chinese Holstein calves during 3 to 4 month old.Using a single factor randomized trial design,Twenty-four healthy and similar-weight(84.77 ± 3.0 kg)weaned calves were randomly divided into three groups,with energy(NE)levels of 6.82 MJ / kg and fed diet containing 19.00%,21.00% or 23.00% crude protein respectively.Growth performance,nutrient digestibility and serum biochemical indices were then analyzed.Results showed that average daily weight gain of calves from groups fed with 19.00%,21.00% and 23.00% crude protein were 1.19±0.16 kg/d,1.23±0.16 kg/d and 1.24±0.13 kg/d respectively.Calves body side length was significantly influenced by dietary protein level(P<0.05),and body length of the calves consumed ration with 23.00% protein were significantly higher than 19.00% protein group.Serum urea nitrogen content increased significantly with dietary levels increasing(P<0.01),and the group fed with 23.00% protein was significantly higher than groups fed with 21.00% and 19.00% protein.The content of triglycerides and free fatty acids increased significantly with dietary levels increasing(P<0.01),and the group fed with 23.00% protein was significantly higher than the group fed with 19.00% protein.Dietary protein levels have no significant effect on total protein,albumin,lactate dehydrogenase,alkaline phosphatase,aspartate aminotransferase,total cholesterol,high density lipoprotein cholesterol,low density lipoprotein cholesterol,glucose,etc.The digestibility of crude protein,dry matter,crude fat and neutral detergent fiber decreased with the increase of dietary protein levels(P<0.05),and the group fed with 19.00% protein was significantly lower than 23.00% protein group.Based on various factors such as calf daily weight gain,body size index,blood index and nutrient digestibility,the daily ration containing 19.00% protein is most suitable for 3-4 months calves.2.The rumen development and the expression and function of TCTP in rumen epithelial cells before weaning.The purpose of this experiment was to investigate the effect of TCTP on rumen epithelial cell proliferation in ruminants.The rumen weight and the length of rumen nipple of lambs grow and develop gradually from newborn to 60 days of age.The length of rumen nipple of lambs reached 4169.0±174.2 μm at 60 days of age.Compared with ten-month old Hu sheep,there was no significant difference in the rumen nipple length(4664.1±131.2 μm)(P <0.05).The growth rate of rumen papillae was the fastest during 30 to 45 days of age,while the ratio of acetic acid to propionic acid in rumen fluid reached 13.29.This ratio then decreased following the growth of age.The expression level of TCTP protein gradually increased from 0 to 45 days of age,and it reached a peak at 45 days of age,and decreased significantly at 60 days of age(P<0.05).The proportion of Ki67 positive cells in basal layer cells at the age of 30 days and 45 days was the highest in Hu sheep,and it was slightly higher at 30-days old than that at 45-days old,but there was no significant difference.The proportion of Ki67 positive cells in rumen basal cells of 60-day-old lake sheep was significantly lower than that of 30-day and 45-day-old lake sheep(P<0.05).Akt phosphorylation level was the lowest in primary rumen epithelial cells.It gradually increased at 30 and 45 days of age and decreased slightly until 60 days of age subsequently.In summary,the peak of rumen epithelial growth and development appeared during 30 and 45 days of age in Hu sheep.The proliferation level of rumen epithelial basal cells is related to the expression of TCTP.TCTP may promote rumen epithelial basal cell proliferation through phosphorylating Akt protein.To conclude,the best dietary protein level for 3-4 months old calves was 19.00%.The growing speed of rumen papillae reached the peak during 30-45 days old,while the ratio of acetic acid to propionic acid in rumen fluid also reached its peak.The rumen papillae almost established its full function before day 60.TCTP might promote rumen epithelial basal cell proliferation through AKT phosphorylation. |
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