Influence Of Different Dietary Energy Levels On Fattening Performance, Rumen Fermentation And Nutrient Metabolism Of Simmental Hybrid Bulls

The objective of this study was to investigate the effects of different dietary energy levels on the production performance,nutrient metabolism,rumen fermentation characteristics and rumen microflora of the Simmental hybrid bulls during stage of fattening.Forty-five Simmental hybrid bulls with good body condition and body weight(363±23 kg)were selected and randomly divided into 3 groups by single factor design.The test period was 137 days,of which the pre-feeding period was 15 days.Formal experimental period was divided into three phases: Early: the crude protein level of the three groups diet were 12.03%,the comprehensive net energy of beef cattle was 6.27(group I),6.38(group II),6.48(group III)MJ/kg,feeding 45 days;Medium-term: the crude protein level of the three groups diet were 11.59%,the comprehensive net energy of beef cattle was 6.43(group I),6.53(group II),6.63(group III)MJ/kg,feeding 45 days;Late: the crude protein level of the three groups diet were 11.01%,the comprehensive net energy of beef cattle was 6.70(group I),6.80(group II),6.90(group III)MJ/kg,feeding 32 days.The results showed that: 1)Among the three experimental groups,the average daily gain of group II was the highest,which was higher than 7.91% in group I(P>0.05)and 11.11% in group III(P<0.05).The dry matter intake of the group II was the highest,which was higher than 2.06% in group I(P>0.05),which was higher than that 6.75% in group III(P<0.05).The feed conversion efficiency of group II was the highest,but it did not reach significant difference with group I and group III(P>0.05).2)There was not significant difference in apparent digestibility among groups(P>0.05).3)With the increase of dietary energy level,the rumen pH and acetic acid content of group III was decreased,the content of propionic acid increased,the ratio of ethylene to propylene was the lowest,the energy utilization efficiency was the highest,and the synthetic fat was the most;but the ammonia nitrogen content of group II was the lowest.Microbial protein content is the highest,the protein utilization was the most.4)The species observation index,the Zhao index,the ACE index,the PD_whole_tree of group III were higher than group I and group II(P<0.05),but group I was not significant difference with group II(P>0.05).5)The dominant flora of group I was significantly higher than that of group III(P<0.05),but they were not significant with group II(P>0.05).Vibrio succinate gradually decreased with the increase of dietary energy level(P<0.01).The proportion of Bacillus in group II was the lowest,which was significantly different from that in group I(P<0.01),but they were not significantly different with group III(P<0.05).6)The energy level of the diet had not significant effect on the diversity of rumen microflora(P>0.05).7)The contents of cholesterol,low~density lipoprotein and high~density lipoprotein in the serum of group III were significantly higher than those in group I(P<0.05),but they were not significantly different with group II(P>0.05).The other serum biochemical indexes were not significantly different(P>0.05).8)The back fat thickness of group III beef cattle was significantly higher than that of group I(P<0.05),but the back fat thickness of group II was not significant difference with group I and group III(P>0.05).With the increase of dietary energy level,the net meat rate,carcass meat production rate,fat color and eye muscle area gradually increased,but they were not significant difference in apparent digestibility among groups(P>0.05).9)The longest muscles in group III had the strongest water~strengthening ability and the weakest shear force,but they were not significant difference in apparent digestibility among groups(P>0.05).10)The crude protein was the highest in the longest muscle of group II,the content of fat was the highest in the longest muscles of group III,but they were not significant difference in apparent digestibility among groups(P>0.05).11)With the increase of dietary energy level,the saturated fatty acid in the meat showed a trend of decreasing first and then increasing(P>0.05).The monounsaturated fatty acids in meat showed a trend of increased first and then decreased(P>0.05).but the polyunsaturated fatty acids in meat of group II were significantly higher than those in group I(P<0.01),they were not significant difference with group III(P>0.05).12)Group II had the best economic benefit,which was higher than 15.08% in group I and 24.85% in group II.In summary,the Simmental hybrid bulls with the middle energy level group,which had the highest daily gain and the highest feed conversion rate,the highest apparent digestibility of nutrients,the best rumen fermentation effect,and the crude protein in the meat,the saturated fatty acids in the meat decreased the most.the highest saturated fatty acid,the highest economic benefits.the Simmental hybrid bulls with high energy level group,which had the highest content of cholesterol,low density lipoprotein and high density lipoprotein,the largest eye muscle area and the thickest back fat thickness.The longest muscle in the back muscle had the strongest water capacity and the highest fat content;the shear force was the weakest and the effect on the rumen microflora was more positive.After comprehensive consideration,it can be concluded that the appropriate protein energy level under the conditions of this experiment was: At the early stage the crude protein was 12.03% and comprehensive net energy was 6.38 MJ/kg of beef cattle.Medium term the crude protein was 11.59% and comprehensive net energy was 6.53 MJ/kg of beef cattle.At the later stage the crude protein was 11.01% comprehensive net energy was 6.80 MJ/kg and of beef cattle...