Study On Protein Metabolism And Requirement Of Dezhou Donkeys During Growing Period

Dezhou donkey is one of the 24 local donkey breeds in China,which has the characteristics of high feed utilization,roughage resistance and strong disease resistance,and is a high-quality local donkey breed in Shandong,China.The donkey industry is changing from the original extensive and scattered breeding mode to large-scale and intensive donkey breeding mode,and the large-scale and intensive efficient breeding mode is inseparable from scientific feeding management and nutrition needs.At present,there are few studies on donkey nutrition in the world,and there are no corresponding feeding standards and nutritional needs.Therefore,this study took Dezhou donkeys in the growing period as the research object,and combined feeding experiments,digestion and metabolism tests and nitrogen balance tests to explore the effects of diets with different protein levels on the growth performance,blood indexes,apparent digestibility of nutrients and nitrogen metabolism of Dezhou donkeys during the growing period,and established a factorial model of crude protein requirements of Dezhou donkeys during the growing period,which provided reference for the formulation of their feeding standards.Effects of different protein levels on performance,blood index and economic benefits of growing Dezhou donkeys.The study started with 9-month-old Dezhou donkeys weighing141.38 kg and ended with 189.53 kg.The experiment lasted for 105 days and was divided into three phases:the preliminary phase of the experiment lasted for 45 days,including 15 days of adaptation and 30 days of trial.In the middle stage of the experiment,the experimental period lasted for 30 days.At the later stage of the experiment,the experimental period lasted for 40days.Forty growing Dezhou donkeys,half male and half female,were selected for the experiment.After weighing the foals,they were grouped and numbered according to the principle of similar weight.Donkeys were divided into 5 treatment groups（groupsⅠ,Ⅱ,Ⅲ,ⅣandⅤ）with 8 replicates in each treatment group and 1 donkey in each replicate.Five diets were fed,TMR1（CP%:9.98）,TMR2（CP%:11.46）,TMR3（CP%:13.02）,TMR4（CP%:14.43）and TMR5（CP%:16.06）,respectively.A single factor design was used in this experiment,and the total energy was similar to other nutrient levels,but the protein levels were different.The donkeys were fed 3.25 kg/d TMR granules in the early stage of the experiment,4.00 kg/d TMR granules in the middle stage and 5.50 kg/d TMR granules in the late stage.The results showed as follows:1)There were significant differences in the effects of different protein levels on daily gain,feed to gain and economic benefit of Dezhou donkeys during growing period（P<0.05）.The daily gain and economic benefit of Dezhou donkeys in groupⅢwere significantly higher than those in the other four groups,and the feed to gain ratio was significantly lower than those in the other four groups（P<0.05）.2)Different protein levels had no significant effects on body size development and blood physiological indexes of Dezhou donkeys during growing period（P<0.05）.3)At the early stage of the experiment,the contents of serum albumin,urea nitrogen and high-density lipoprotein of Dezhou donkeys in test groupⅤwere the highest.There were no significant differences in serum biochemical indexes in the middle and late stages of the experiment（P>0.05）.Effects of different protein levels on nutrient availability and nitrogen metabolic of Dezhou donkeys during growing period.At the end of each period of the feeding experiment,4 experimental donkeys were randomly selected from each treatment group and fed in a digestive cage for 5 days of digestion and metabolism experiment,with 1 day of adaptation period and 4 days of trial period.Each treatment group was fed the same diet as the feeding experiment.During the experiment period,all excrement and urine were collected,and digestion and metabolism tests were carried out by total feces collection and total urine collection.Acid detergent lignin（ADL）were used as an endogenous indicator to determine the apparent digestibility of dietary nutrients at the later stage of each feeding stage.The results showed as follows:1)The crude protein digestibility of donkeys increased with the increase of dietary protein level during the experiment period;At the early stage of the experiment,the digestibility of digestible energy（DE）,organic matter（OM）,crude protein（CP）,crude fiber（CF）and acid detergent fiber（ADF）in test groupⅤwere the highest.At the middle stage of the experiment,the digestibility of dry matter（DM）,organic matter（OM）,carbohydrate（CHO）and nitrogen free extract（NFE）in test groupⅠwas the highest.At the later stage,the digestibility of crude fat in test groupⅡwas the highest,which was significantly higher than that in test groupsⅢandⅤ（P<0.05）,had no significant difference with experimental groupsⅠandⅣ;The digestibility of crude fiber in test groupⅡwas the highest,which was significantly higher than that in other four groups（P<0.05）;The digestibility of carbohydrate and nitrogen free extract in test groupⅠwas the highest,and significantly higher than that in test groupsⅢ,ⅣandⅤ（P<0.05）was not significantly different from test groupⅡ.2)Different protein levels had significant effects on nitrogen intake（NI）,urinary nitrogen（UN）,digestible nitrogen（DN）,deposited nitrogen（RN）,biological value of protein（BV）and net protein utilization（NPU）of Dezhou donkeys during growing period（P<0.05）,with the increase of dietary protein level NI,UN,DN and RN,BV and NPU decreased.At the early stage of the experiment,different protein levels had no significant effect on fecal nitrogen（FN）.At the middle and late stages of the experiment,FN increased with the increase of dietary protein levels.Estimation of crude protein maintenance requirement by zero nitrogen balance test and nitrogen free diet test.Four Dezhou donkeys with the body weight of 186.38 kg and four Dezhou donkeys with the body weight of 134.13 kg were divided into two treatment groups A and B with four replicates in each group and one donkey in each replicate.Four Dezhou donkeys with the body weight of 185.25 kg and 139.63 kg were divided into C and D treatment groups with 4 replicates in each group and 1 donkey in each replicate.The weight of Dezhou donkeys in group A during the growing period was 186.38 kg,that of Dezhou donkeys in group B during the feeding period was 134.13 kg,that of Dezhou donkeys in group C during the growing period was 185.25 kg,and that of Dezhou donkeys in group D was 139.63 kg.The piglets in groups A and B were fed TMR1,the piglets in groups C and D were fed nitrogen-free diet,the piglets in groups A and C were fed 2.30 kg/d,and the piglets in groups B and D were fed 1.80 kg/d.The experimental donkeys were all fed in digestive and metabolic cages.The pre-trial period lasted for 7 days and the trial period lasted for 4 days.Total fecal collection method collected feces and urine to measure nitrogen metabolism and estimate crude protein maintenance requirements.Zero nitrogen balance test results showed that the deposited nitrogen in groups A and B was close to 0,and the deposited nitrogen was corrected according to the net protein utilization rate,that is,CPm=（NI-RN/NPU）/W^0.75:Group A CPm=4.2251 g/(kg W^0.75·d);Group B CPm=4.3761 g/(kg W^0.75·d);Average the two groups:CPm₁=4.3006 g/(kg W^0.75·d)The experimental results of nitrogen-free diet showed that metabolic fecal nitrogen（MFN）,endogenous urinary nitrogen（EUN）and crude protein maintenance requirement（CPm）of Dezhou donkey during the growing period were as follows:MFN（g/d）=0.1143W^0.75;EUN（g/d）=0.2209W^0.75;According to the formula CPm=（EUN+MFN+SLN）×6.25/（BV×TD）:CPm₂=4.3201 g/(kg W^0.75·d)Zero nitrogen balance test and no nitrogen diet test have similar results,and the average value is taken:Dezhou Donkey During Growing Period:CPm=4.3104 g/(kg W^0.75·d)The prediction models of crude protein requirement（CPR,g/d）and digestible crude protein requirement（DCPR,g/d）of growing Dezhou donkeys（140～190 kg）were as follows:CPR（g/d）=4.3104W^0.75+0.5048ADG（r=0.9359,n=80,P<0.01）;DCPR（g/d）=3.1740W^0.75+0.3983ADG（r=0.8977,n=80,P<0.01）Under the conditions of this experiment,with the increase of dietary protein level,the digestibility of organic matter,carbohydrate,biological value of protein and net protein utilization tended to decrease gradually.When the dietary protein level was 13.02%,it could meet the normal growth and development requirements of the growing Dezhou donkey,and had better daily gain and economic benefits.CPm and DCPm were 4.3104 and 3.1740 g/(kg W^0.75·d),respectively,and the crude protein and digestible crude protein requirements were0.5048 and 0.3983 g per 1.00 g of weight gain,respectively.