Influence Of Dietary Energy Levels On Fattening Performance And Mechanism Of Culling Holstein Cows

To explore the effects of dietary energy levels on the fattening performance and related mechanism of culling Holstein cows,the experiment was conducted with 48 culling Holstein cows those were in similar shape?503±65 kg?.With the single factor method,the culling Holstein cows were randomly divided into 3 groups and 16 cattles in each group.This experiment lasted for 100 days that were two stages.In the earlier stage,the crude protein content of the three groups was 12.50% and the combined net energy levels were 6.80,7.00 and 7.20 MJ/kg respectively.In the later stage,the crude protein content of three groups was 12.00% and the combined net energy levels were 6.90,7.10 and 7.30 MJ/kg respectively.The followings were the results of the experiment.?1?The daily gain of Group ? was the highest of three groups,significantly higher than that of Group ??P<0.01?.Material weight ratio of Group ? was lower than that of Group ??P<0.01?.?2?There was no significant effect on apparent nutrient digestibility?P>0.05?of culling Holstein cows by increasing the energy of daily ration.?3?Compared with Group ?,the serum cholesterol of Group ?and Group ?increased significantly?P<0.01?and ?-hydroxybutyric acid decreased significantly?P<0.01?.The glucose content of Group ? was higher than that of the other two groups?P<0.05?.?4?The slaughter rate and net meat rate of Group ? were significantly higher than those of Group?? P<0.01?and Group?? P<0.05?,the back-fat thickness of Group and ? ? was significantly higher than that of Group?? P<0.01?.?5?The breeding benefit of Group ? was the highest of three groups,8.79 yuan,which was 0.47 yuan and 8.47 yuan higher than that of Group ?and Group ?.?6?There was no significant difference on rumen fermentation index among three groups?P>0.05?.?7?There were no significant differences on diversity index,abundance index and community difference among three groups?P>0.05?.At the genus level,the relative abundance of Prevotella₁ in Group ? was the highest and significantly higher than that of Group ??P<0.05?,while the other genus failed to reach the significant level of difference among the three groups?P>0.05?.?8?The activityies of trypsase and lipase in Group ? were significantly higher than those of Group ??P<0.05?,but the differences between Group ? and Group on ? trypsase and lipase were not significant?P>0.05?.?9?There were no significant effects on the meat quality,conventional ingredients and fatty acid composition of longissimus muscle between each group?P>0.05?.?10?The expression of fat metabolism related genes in the liver,muscles and subcutaneous adipose tissues were also affected.It was useful to enhance the fat synthesis and deposition,reduce the fat decomposition and improve the meat quality of Holstein cows by up-regulating the fat biosynthesis related genes FASN,LPL,PPAR?,SREBP1,GLUT4 and SCD1,meanwhile,down-regulating the adipolysis-associated genes HSL,ATGL,HMGCS2,HMGCR,CPT1 A,PPAR?.In conclusion,increasing the energy content of daily ration could improve the growth performance and slaughter performance of culling Holstein cows,promoted the fat deposition and get the meat of better quality.Under the conditions of this experiment,it was more appropriate to feed the culling Holstein cows in medium energy level.The appropriate energy and protein levels were different in the two stages.In the earlier stage,the combined net energy was 7.00 MJ/kg and crude protein 12.50%.In the later stage,the combined net energy was 7.10 MJ/kg and crude protein 12.00%.