Effects Of Dietary Energy Levels On Growth,slaughter Performance And Meat Quality Of Holstein Steers

In this experiment,feeding and slaughter experiments were conducted to explore the effect of dietary energy level on growth,slaughter performance and meat quality of 13?18 months old Holstein steer,and to select the appropriate dietary energy level,so as to provide reference for the fattening of Holstein steer.Sixty 13-month-old Holstein steers with good health and average body weight of 501.47±40.09 kg were selected and randomly divided into three groups with 20 replicates in each group and 1 steer in each replicate.The three groups were low energy group(LE),medium energy group(ME)and high energy group(HE).The comprehensive net energy(NEmf)of the diets in the early stage of the experiment(97d)was 5.90 MJ/kg,6.10 MJ/kg and 6.30 MJ/kg respectively.The NEmf of the diets in the later stage of the experiment(47d)was 6.10 MJ/kg,6.30 MJ/kg and 6.50 MJ/kg,respectively.The crude protein level of the diets in the whole experiment was 11.50%.The pretest period was 10 days,and the formal test period was 144 days.At the end of the feeding experiment,the production performance and other indicators were measured.Five steers were randomly selected from each group to collect blood for determination of blood biochemical indicators and slaughter for determination of slaughtering performance and meat quality.The results showed as follows:1)The average daily gain(ADG)of Holstein steers was not significantly affected by the increase of dietary energy level(P>0.05).Compared with LE group and ME group,the ratio of feed to gain(F/G)of HE group was the lowest in the early and the whole period of ADG.Compared with LE group and ME group,the feed weight ratio of HE group decreased by 11.90%(P<0.05)and 4.38%(P>0.05)in the early period,while that of HE group decreased by 8.47%(P<0.05)and 1.23%(P>0.05)in the whole period.2)With the increase of dietary energy levels,the apparent digestibility of dry matter in the early ME group was the highest,and there was no significant difference from the LE group,which was 1.74%higher than the HE group(P<0.05);the protein,fat and The apparent digestibility of neutral detergent fibers was significantly lower than that of LE group(P<0.05),while the apparent digestibility of acid detergent fibers also decreased but the difference was not significant.In the later period,the apparent digestibility of dry matter,protein,neutral detergent fiber and acid detergent fiber in the LE group was significantly higher than that in the HE group(P<0.05),and there was no significant difference from the ME group.The apparent digestibility of dry matter was higher than that in the HE group The group increased by 9.28%(P<0.05);the digestibility of fat in the later HE group was significantly lower than that of the LE group(P<0.05)and the ME group(P<0.05).3)With the increase of dietary energy level,the serum glucose content in the HE group was the lowest,which was 16.04%(P<0.05)and 8.99%(P<0.05)lower than that of LE group and ME group,respectively.The content of serum urea nitrogen of ME group was the lowest,which was 8.52%lower than that of LE group(P<0.05),and there was no significant difference between ME group and HE group(P>0.05).The content of ?-hydroxybutyric acid and growth hormone decreased significantly with the increase of dietary energy(P<0.05),and the activity of serum lipoprotein lipase increased with the increase of dietary energy level(P<0.05);4)With the increase of energy level,body height decreased significantly(P<0.05),but there was no significant effect on body length and heart girth(P>0.05);5)The income of ME group was the highest,which was 0.97 yuan/(day/head)and 1.02 yuan/(day/head)higher than that of LE group and HE group;6)The loin eye area of Holstein steers increased significantly with the increase of dietary energy level(P<0.05),but the energy level had no effect on dressing percentage,net meat rate and meat bone ratio(P>0.05);6)The content of ether extract in longissimus dorsi muscle was significantly increased(P<0.05)and the content of water was significantly reduced(P<0.05)with the increase of dietary energy level;Raising the dietary energy level increased the daily feeding profits.7)The dietary energy level had no effect on the rumen fermentation parameters.Using high-throughput sequencing technology,the Von region of the 16Sr DNA gene of each rumen sample was sequenced on the IonS5TMXL platform.The dominant phylum in the rumen;the ME group had the highest relative abundance of Pseudomonas,which was significantly higher than those in the LE and HE groups;the genus Stenotrophomonas decreased significantly as the dietary energy level increased,and the LE group was relatively abundant The relative abundance of Brevibacterium,Methanobacteria,and Anaerobic Vibrio in the ME group was significantly higher than that in the LE group,which was not significantly different from that in the HE group.Increasing the energy level of the diet had no significant effect on the relative abundance of core flora among the experimental groups,such as unidentified_Bacteroidales,unidentified_Prevotellaceae.In summary,under the conditions of this experiment,when the dietary CP level of 13?18 month old Holstein steer was 11.5%,the suitable NEmf level in the early period(501?612kg BW)was 6.10 MJ/kg,and the later period(613?674kg BW)was 6.30 MJ/kg.