Effects Of Dietary Energy Level On Growth Performance,Metabolism,Meat Quality And Energy Requirement Of Jinjiang Cattle In Fattening Period

In this study,the effects of dietary energy level on growth,metabolism and meat quality of Jinjiang cattle during fattening stage were studied by feeding test,digestion and metabolism test and slaughter test,The energy requirement of Jinjiang cattle during fattening period was determined and a mathematical model was established.The present study was designed to improve the feeding level of Jinjiang cattle during fattening period,make full use of its production potential,and provide theoretical basis and technical support for formulating the feeding standard of Jinjiang cattle and improving China's"beef cattle feeding standard".The study was divided into four experiments:Experiment 1:Effects of dietary energy level on growth performance and rumen fermentation of Jinjiang cattle in fattening periodThe experiment was conducted to study the effect of dietary energy level on growth performance and rumen fermentation of Jinjiang cattle during fatten stage.Fifty steers with good body condition and similar weight?301.74±30.98 kg?were randomly divided into 5groups with 10 heads in each group,Each treatment group was divided into 4 replicates,with2³ cows in each replicate.The experiment was divided into two stages,namely the early stage and the late stage.The preparation of basic diet before and after fattening refers to China's beef cattle feeding standards?2004?.The basic diet was fed in group A,and the comprehensive net dietary energy of group B,C,D and E was increased by 6%,12%,18%and 24%respectively on the basis of group A.The crude protein level was consistent.The results showed that:?1?with the improvement of the comprehensive net energy level of diet,the average daily weight gain?ADG?of Jinjiang cattle increased gradually in the early stage of fattening,but the difference was not significant?P>0.05?.the ADG was the highest in group B and group E.The diets of C,D and E at the early stage and B,C,D and E at the later stage of fattening significantly reduced the feed weight ratio of Jinjiang cattle.?2?There was no significant difference in nutrient digestibility between the two groups in two stages?P>0.05?.In the later stage of fattening,the high energy level of diet might inhibit the nutrient digestibility of Jinjiang cattle.?3?Before and after fertilization,the rumen pH of Jinjiang cattle in each group decreased with the increase of dietary energy,and there was a certain risk of rumen acidosis in the high-energy diet at the later stage of fertilization.The content of NH₃-N in the diet C group at the early stage of fattening was the lowest?P<0.05?,while the content of?microbial protein?MCP was significantly higher than that in the control group?P<0.05?.In the late stage of fattening,the content of NH₃-N in diet B group was the lowest,?P<0.05?,and the MCP content was the highest.The total volatile fatty acids?TVFA?in the rumen in the early and late stages of fattening showed an increasing trend with the increase of dietary energy level.To sum up,under the conditions of this experiment,higher dietary energy level improved the growth performance of Jinjiang cattle and the feed conversion rate.The cattle in group C at the early stage of fattening?NEmf=6.74MJ/kg?and group B at the later stage of fattening?NEmf=6.58MJ/kg?had better nitrogen balance than those of the other groups,which could promote the synthesis of microbial proteins and the utilization of nitrogen.Experiment 2:Effects of dietary energy level on blood indexes and metabolic hormone indexes of Jinjiang cattle in fattening periodOn the basis of experiment 1,this experiment aims to further study the effect of dietary energy level on blood indexes and metabolic hormone indexes of Jinjiangcattle in fattening period.Blood samples were collected at empty stomach state before morning feeding on the third day before the end of feeding experiments at all stages,and centrifuged for the determination of relevant indicators.The results showed that:?1?with the improvement of the dietary comprehensive net energy level,the serum glucose?Glu?content in Jinjiang cattle showed an increasing trend in the early stage of fattening.The content of urea nitrogen?BUN?and high-density lipoprotein?HDL?in the group C and E were significantly lower than that in the control group?P<0.05?,and the content of urea nitrogen?BUN?was significantly higher than that in the control group?P<0.05?.?2?At the later stage of fattening,serum glucose?Glu?content in diet group B and group C were significantly increased by 19.37%and 14.73%compared with control group?group A??P<0.05?.The alanine transaminase?ALT?and high-density lipoprotein?HDL?content of cattle in group B,C and D were significantly higher than that of the other groups?P<0.05?,while urea nitrogen?BUN?content of cattle was significantly lower than that of the other groups?P<0.05?.?3?With the improvement of the comprehensive net energy level of the diet,the growth hormone content of cattle fed diet E at the early stage of fattening was significantly higher than those fed diet A,B and C?P<0.05?,and the insulin content of cattle fed diet E was significantly higher than those fed diet A?P<0.05?.The leptin content of cattle in C group was significantly decreased by 47.85%?P<0.05?compared with control group?group A?,and adiponectin content of cattle was significantly increased by 19.76%?P<0.05?compared with control group?group A?.There was no significant difference in T3,T4 and insulin growth factor content between the two groups.?4?In the later stage of fattening,the growth hormone levels of cattle in the group B and E were significantly higher than those in other groups?P<0.05?.The leptin content of cattle in group B was significantly lower than that in other groups,and the adiponectin content of cattle in group B was significantly higher than that in other groups?P<0.05?.There was no significant differences in T3,T4,insulin,insulin growth factor?IGF-1?between the test groups?P>0.05?.To sum up,with the improvement of the comprehensive net energy level of the diet,the metabolism in Jinjiang cattle during the fattening stage was at normal state,and the body's sugar metabolism was enhanced in the early fattening stage,which promoted the digestion and absorption of nutrients and increased the growth rate of the body.In the early and later fattening period,the HDL and LDL in the blood of Jinjiang cattle were increased,indicating that the energy intake level and fat metabolism increased.It was speculated that the group C?NEmf=6.74MJ/kg?in the early fattening stage and the group B?NEmf=6.58MJ/kg?in the later fattening stage had better effects on regulating body fat deposition than other groups.Experiment 3:Effects of dietary energy level on carcass quality and meat quality of Jinjiang cattle in fattening periodOn the basis of experiment 1 and 2,the present experiment further explored the influence of dietary energy level on carcass quality and meat quality of Jinjiang cattle during fattening period.On the day at the end of feeding test in each stage,three cows with body weight close to the average were repeatedly selected from each treatment,slaughtered routinely,and the carcass quality and meat quality of Jinjiang cattle were determined.The longissimus dorsi muscle of the left side was taken from each cattle to determine the meat quality.The results showed that:?1?there was no significant difference in preslaughter live weight,carcass weight and slaughter rate of Jinjiang cattle in each group at the fattening stage.With the increase of the comprehensive net energy level,the backfat thickness of Jinjiang cattle decreased first and then increased in the early and late fattening stage,The backfat thickness of diet C in the early stage of fattening and diet B in the late stage of fattening were the lowest,and the eye muscle area increased with the increase of energy level in the early stage of fattening,but the difference between each group was not significant,In general,in the later stage of fattening,with the increase of energy level,the eye muscle area of jinjiang cattle was greatly increased.?2?In the early stage of fertilization,with the improvement of the comprehensive net energy level of the diet,the muscle pH45_minin value and shear force of Jinjiang cattle were decreased significantly?P<0.05?.However,dietary treatment had no significant effect on pH_24h4h value,meat color?L*,a*,b*?,dripping loss and cooking loss of Jinjiang cattle.In the later fattening period,the muscle drip loss and shear force of Jinjiang cattle fed with diets B and C longissimus dorsi were significantly lower than the other groups?P<0.05?,whereas muscle pH_{45 min}5 min and pH_{24 h} value,meat color?L*,a*,B*?,cooking loss had no significant difference.?3?With the improvement of diet comprehensive net energy level,in the early stage fattening,the muscle crude fat concentration of Jinjiang cattle fed with diet C was significantly higher than those in other groups?P<0.05?.At the later stage of fattening,the mucle crude fat concentration of Jinjiang cattle fed with diet B was significantly higher than those in other groups?P<0.05?.Combined with various indicators,The energy level required for high quality beef production by feeding jinjiang cattle in the early fattening stage was compared between the diet group C?NEmf=6.74 MJ/kg?and the diet group B?NEmf=6.58 MJ/kg?.Experiment 4:Study on Energy requirements of Jinjiang cattle during fattening period and establishment of modelThe purpose of this study was to investigate the energy requirements of Jinjiang cattle at different stages of fattening.The composition of the experimental animal and the diet is the same as that of experiment 1.After the feeding test in each stage,three cows with similar body weight were selected from each group for a 3-day digestion and metabolism test.All feces and urine of each cow were collected every day for the determination of relevant indicators.The results showed that:?1?with the increase of the comprehensive net energy level of the diet,the food intake of Jinjiang cattle in the fattening stage showed a gradually decreasing trend.In the later fattening stage,the total energy intake of Jinjiang cattle fed with diets D and E were significantly lower than that of the other groups?P<0.05?.In the early stage of fattening,the digestibility and metabolic rate of Jinjiang cattle fed with diet C were highest,while,in the later stage of fattening,the digestibility and metabolic rate of Jinjiang cattle fed with diet B were highest?P<0.05?.?2?Under the conditions of this experiment,the digestibility and metabolic energy requirements of Jinjiang cattle in the early and late stages of fattening were highly positively correlated with the average daily weight gain,with high correlation coefficient.The total requirements of digestive energy and metabolic energy in the two stages were as follows:DE=0.638W^0.75+36.837*ADG in the early stage of fertilization?R²=0.996,P<0.05?;ME=0.494W^0.75+33.843*ADG?R²=0.989,P<0.05?.Late fattening stage:DE=0.770W^0.75+40.088×ADG?R²=0.997,P<0.05?;ME=0.645W0.75+38.603×ADG?R²=0.993,P<0.05?.To sum up,in the early stage of fattening under this experiment,when the energy level is 112%of the net energy required for the daily weight gain of 1.2kg/d of 300kg beef cattle in the"beef cattle feeding standard"?NY/T 815-2004??group C,NEmf=6.74MJ/kg?,the energy utilization rate is the highest in the early stage of fattening?NY/T 815-2004?.In the later stage of fattening,when energy levels for the beef cattle breeding standards?NY/T 815-2004?of 350 kg of beef cattle daily gain of 1.2 kg/d required 106%of the net energy?group B,NEmf=6.58 MJ/kg?,the highest energy utilization,by the energy of each stage need models can exit:Jinjiang cattle fattening upfront can maintain digestion?DEm?and metabolic energy?MEm?general requirements were 0.638,0.494 MJ/(kg W^0.75·d);The digestibility and metabolic energy requirements for weight gain per kg in the early stage of fattening were 36.837 and 33.843MJ,respectively.The DEm and MEm requirements of Jinjiangcattle at the later stage of fattening were 0.770 and 0.645 MJ/(kg W^0.75·d),respectively.The digestibility and metabolic energy requirements for weight gain per kg at the later stage of fattening were40.088 and 38.603 MJ,respectively.