Effects Of Different Crude Protein Levels In High Concentrate Diet On Fattening Performance And Meat Quality Of Holstein Bulls

In order to study the effects of different crude protein levels in high concentrate diet on fattening performance and meat quality of Holstein bulls,90 Holstein bulls with?197.07±11.11?kg body weight?BW?and similar body conditions were selected and designed by a single factor completely randomized trial.They were randomly divided into three groups with 30 calves in each group.The difference in average body weight and body condition between the groups was not significant?P>0.05?.The group I,II and III were fed low-protein,medium-protein and high-protein diets,respectively,and the energy levels of the diets were the same in each group.The test was divided into three body weight stages.The comprehensive net energy(NE_mf)of 200³00 kg stage was 7.05MJ/kg,the protein levels were 14.05%,15.00%and 16.04%,respectively;the NE_mf of 300⁴00 kg stage was7.10MJ/kg,the protein levels were 13.03%,14.01%and 15.00%,respectively;the NE_mf of400⁵00 kg stage was 7.16MJ/kg,and the protein levels were 12.01%,13.01%and14.00%,respectively.The ratio of concentrate to roughness was 90:10.The pre-trial period lasted 10 d and the formal trial period lasted 193 d.The results showed as follows:1)The average daily gain?ADG?,dry matter intake?DMI?,digestible dry matter intake?DDMI?,ratio of digestible dry matter intake to weight gain?DDMI/ADG?and feed/grain?DMI/ADG?in all stages and the whole period of the experiment were not significantly different?P>0.05?.In the stage of 200³00 kg body weight,the feed/grain?DMI/ADG?index in group?and group III was the lowest?P>0.05?.The breeding income of the group?was the highest,which was 0.78?yuan/head/d?and 0.22?yuan/head/d?higher than that in group?and group?,respectively.The DMI/ADG indexes of other stages and the whole period were the lowest in group III?P>0.05?,and the breeding income of the group?was the highest.2)In the stage of 200³00 kg body weight,the apparent digestibility of neutral detergent fiber?NDF?in group I was significantly higher than that in group III?P<0.05?;In the stage of300⁴00 kg body weight,the apparent digestibility of crude protein?CP?in group III was4.27%higher than that in group I?P<0.05?.The apparent digestibility of NDF in group I was 16.06%and 10.42%higher than that in group II and III?P<0.05?,respectively.3)In the stage of 200³00 kg body weight,the CP digestion of group III was significantly higher than that of group I?P<0.01?;in the stage of 300⁴00 kg body weight,there was a significant difference in CP digestion among groups?P<0.01?.The digestion of NDF in group I was significantly higher than that in group?and group??P<0.05?;the digestion of CP in the stage of 400⁵00 kg body weight and whole period was significantly different among groups?P<0.01?.4)The concentration of blood glucose?GLU?and growth hormone?GH?increased with the increase of dietary CP levels,but there was no significant difference in the experimental group?P>0.05?.In the stage of200³00 kg body weight,thyroxine?T₄?in group?was significantly higher than that in group??P<0.05?,and had no effect in other stages.In the stage of 300⁴00 kg body weight,the concentration of GLU in the group III was significantly higher than that in the group I?P<0.05?.The aspartate aminotransferase?AST?content in group II and III was8.63%?P<0.05?and 10.98%?P<0.05?higher than that in group I.5)The longissimus muscle area in group III was significantly increased by 6.69%?P<0.05?compared with group I,but there were no effects on dressing,meat-bone ratio,net meat percentage and carcass yield under different treatments?P>0.05?.6)The dehydration rate in group?were significantly lower than those of group I by 9.01%?P<0.05?;With the increasing of dietary CP level,the shear stress and cooking loss decreased slightly,but the difference was not significant?P>0.05?,and there was no significant difference in meat pH,meat color,chroma and hue angle among groups?P>0.05?.7)Dietary CP levels had no significant effect on conventional ingredients of longissimus muscle?P>0.05?.8)The content of saturated fatty acid?SFA?in group III was 14.58%?P<0.01?and 9.68%?P<0.05?lower than that of group I and group II,respectively,and the content of palmitic acid?C16:0?in group III was significantly lower than that in group I?P<0.05?.There was no significant difference in other SFA content?P>0.05?;Compared with group?,the content of monounsaturated fatty acid?MUFA?in group II and group III was increased by 14.16%and 17.42%?P<0.01?,respectively,and the content of oleic acid?C18:1n9c?was increased by 28.89%and 30.19%?P<0.01?,respectively.With the increase of dietary CP levels,there was no significant difference in other indicators in MUFA?P>0.05?;The polyunsaturated fatty acid?PUFA?content of longissimus muscle decreased with the increase of dietary CP levels,but the difference was not significant?P>0.05?.Dietary CP levels had no significant effect on linolenic acid?C18:3n3?,linoleic acid?C18:2n6c?,arachidonic acid?C18:4n6c?,eicosatrienoic acid?C20:3n3?and eicosatrienoic acid?C20:4n6??P>0.05?.The M/S in group II was significantly higher than that in the group??P<0.05?,and the M/S in group III was significantly higher than that in group??P<0.01?.There was no significant difference in P/S among the groups?P>0.05?.9)With the increase of dietary CP levels,there was no significant difference in the pH of the rumen fluid between the groups I,II and III?P>0.05?.The ammonia nitrogen concentration in the rumen fluid in group III was significantly higher than that in group I?P<0.01?,which was 15.54%higher than that in group I.The concentration of microbial protein in group II and III was significantly higher than that in group I?P<0.05?,which was 19.95%and 14.53%higher than that in group I,respectively.Dietary CP levels had no significant effect on the rumen fluid acetic acid,propionic acid,butyric acid,total volatile fatty acid concentration and ethylene-propylene ratio in group I,II and III?P>0.05?,the ratio of ethylene to propylene decreased with the increase of dietary CP levels.10)The trypsin activity increased with the increase of dietary CP levels,the difference between the three groups was significant?P<0.05?,and group III was significantly higher than that in group I by 8.94%?P<0.05?,which was higher than group II by 5.10%?P>0.05?.Alpha-amylase activity and lipase activity are not affected by dietary CP levels.In summary,increasing the CP level of the diet can improve the fattening performance of dairy bulls,increase the longissimus muscle area,increase the MUFA content and reduce the SFA content.Under the conditions of this experiment,the recommended value of dietary CP at each stage?DM basis?:at BW of 200³00 kg,the appropriate CP level is15.00%;at BW of 300⁴00 kg,the appropriate CP level is 15.00%;at BW of 400⁵00kg,the appropriate CP level is 14.00%.