Effects Of Dietary Energy Levels On Growth Performance,Rumen Fermentation,and Gene Expression Of Hepatic Energy Metabolism In Chinese Holstein Heifers

The objective of this study was to investigate the effect of diets energy levels on the apparent digestibility of nutrients,growth performance,rumen fermentation,serum indices,and relative expression of energy metabolism genes in the liver of Holstein heifers.Forty-five Chinese Holstein heifers aged 240 days were selected and randomly divided into three groups of 15 heifers each.Group I was fed a low-energy diet?NE_L5.64 MJ/kg?,Group II was fed a medium energy diet?NE_L 5.94 MJ/kg?,and Group III was fed a high-energy diet?NE_L 6.21 MJ/kg?.Dietary protein levels were the same in each experimental group?CP14.04%?.The experiment lasted for 110 days.The results showed as follows:1)Comparing with groups I and II,the apparent digestibility of neutral detergent fiber?NDF?and acid detergent fiber?ADF?in group III was significantly decreased?P<0.05?.Compared with group I,the apparent digestibility of neutral detergent fiber?NDF?in group II and group III were decreased by 4.84%and7.03%,and the apparent digestibility of acid detergent fiber?ADF?were decreased by2.99%and 7.35%.In comparison to group I,there was no significant effects of group II,group III on the apparent digestibility of crude protein?CP?,crude fat?EE?,calcium?Ca?and phosphorus?P??P>0.05?.2)There was no significant differences between groups I,II and III on dry matter intake was not significantly different?P>0.05?;The average daily gain?ADG?of the heifers of groups I,II,and III was 0.70 kg/d,0.80 kg/d,and 0.91 kg/d;compared with group I,group II and group III increased by 14.28%and 30.00%,respectively?P<0.05?.There was no significant differences between groups I,II and III on body measurements?withers height,body length,heart girth,circumference of cannon bone?were not significantly different?P>0.05?.Index of body structure of group II was best?P>0.05?.3)Comparing with groups I and III,mammary gland development was significantly better in group II?P<0.05?.4)There was no significant differences between groups I,II and III on rumen p H,microbial protein content?MCP?,acetic acid,butyric acid,total volatile fatty acids?T-VFA?and the concentration of acetic acid/propionic acid?A/P?was not significantly different?P>0.05?;the content of ammonia nitrogen?NH₃-N?was the lowest in group II,which was significantly lower than group I by 3.70%?P<0.05?,here was no significant difference in group III?P>0.05?.Compared with group I and II,the propionic acid concentration in group III was significantly increased?P<0.05?.5)Compared with group I,serum glucose?Glu?levels in group II and III was significantly increased by 19.95%and 27.89%?P<0.01?;serum cholesterol?CHO?levels increased significantly by 5.76%and 8.27%?P<0.05?;there was no significant differences between groups I,II and III on urea nitrogen?BUN?,total protein?TP?and triglyceride?TG??P>0.05?.6)Compared with group I,serum growth hormone?GH?levels in group II and III was significantly decreased by 3.83%and 8.51%?P<0.05?;serum concentrations of Insulin?Ins??Insulin-like growth factor?IGF-1?and Leptin?LP?in group II increased by 15.12.%,10.10%and 12.15%,group III significantly increased22.09%,13.85%and 16.14%?P<0.05?.7)The diet with NEL of 6.21 MJ/kg significantly increased the relative mRNA expression of Mammalian Target of Rapamycin?mTOR?,Melanocortin-4 receptor?MC4R?and Leptin?LP?genes in the liver of broilers?P<0.01?,and decreased the relative mRNA expression of AMP-activated protein kinase?1?AMPK?1?mRNA?P<0.01?.In conclusion,when the dietary NE_L is 5.94 MJ/kg,it could not only ensure that the body figure and mammary glands were well developed,but also maintained the normal fermentation of the rumen,and could increase the utilization rate of energy and reduce waste of feed.