| Wandong cattle mainly distributes in the hilly areas of eastern Anhui province.Wandong cattle has the good resistance to utilize poor quality roughage due to that local farmers feed cattle with rice straw,corn stalk,wheat straw and other crop straw resources for a long time.Energy is the first limiting nutrient for growth of beef cattle,and the accurate matching between the energy requirement for fulfilling performance potential of beef cattle and the effective energy supply from the formulation diet can be valuable to ensure farm profitability.However,the diet formulation for Wandong cattle was often based on the empiricism or according to other beef cattle breed’s feeding standard due to the absence of accurate information about energy requirement of Wandong cattle and effective energy value of common feedstuffs.Therefore,this study used Wandong cattle and common feedstuffs including corn silage,rice straw,wheat straw,corn grain and soybean meal as subjects,and using feeding trial,digestion and respiratory calorimetry trials to investigate the energy metabolism of Wandong cattle.First of all,the study estimated the effective energy of 5 feedstuffs including corn silage,rice straw,wheat straw,corn grain and soybean meal.Secondly,the study estimated the net energy requirements for maintenance and gain of growing Wandong cattle.Finally,the study validated the accuracy of net energy requirement and net energy value of common feedstuffs of Wandong cattle by a feeding trial.1.Estimation of Effective Energy of Corn Silage,Rice Straw,Wheat Straw,Corn Grain and Soybean Meal for Wandong CattleThis study was to preliminarily compare direct,substitution and regression methods on effective energy evaluation of single feedstuff for beef cattle,and estimate the metabolizable energy(ME)and net energy(NE)of 5 feedstuffs for Wandong cattle,including corn silage,rice straw,wheat straw,corn grain and soybean meal.The study comprised 2 parts:In the first part.20 Wandong bulls with the similar body weight of 281±15.6 kg were randomly assigned to 1 of 5 dietary treatments with 4 animals per treatment.Five dietary treatments included 1 sole corn silage diet(direct method),1 corn silage-concentrate(corn grain-soybean meal)basal diet and 3 test diets(substitution and regression methods)in which the basal diet were partly substituted by corn silage at 10%,30%and 60%.The experiment period lasted for 19 d,including 10 d of pretest period and 9 d of test period.The results showed that the direct method-derived estimates were not different(P>0.05)from those obtained using the regression method.Using substitution method,effective energy values of corn silage varied with the increased corn silage substitution rate(P<0.05).In addition,the corn silage estimates at the substitution ratio of 30%were similar to those estimated by direct and regression methods.According to linear regression equations of corn silage-associated effective energy intake(MJ)against the corn silage substitution amount(DM basis,kg),the respective ME and NE of corn silage were 8.98 and 5.34 MJ/kg DM.In the second part,16 Wandong bulls with the similar body weight of 272.9±11.5 kg were randomly assigned to 1 of 4 dietary treatments.Four dietary treatments included 1 corn silage-concentrate basal diet and 3 test diets in which the basal diet were partly substituted by test feedstuff at 10%,30%and 60%,and test feedstuff contained rice straw,wheat straw,corn silage and soybean meal.The study comprised 4 experiments,and each experiment period lasted for 19 d,including 10 d of pretest period and 9 d of test period.According to linear regression equations of test feedstuff-associated effective energy intake(MJ)against the test feedstuff substitution amount(DM basis,kg),the respective ME and NE of rice straw were 6.76 and 3.42 MJ/kg DM,corresponding values of wheat straw were 6.43 and 3.28 MJ/kg DM.and corresponding values of corn grain were 12.82 and 8.07 MJ/kg DM,corresponding values of soybean meal were 14.23 and 9.24 MJ/kg DM.2.Effects of Feeding Levels on Digestion and Metabolism of Energy and Protein of Wandong CattleThis study was to investigate the effect of different levels of feed intake on nutrient apparent digestibility,digestion and metabolism of energy and protein of Wandong cattle.Twelve Wandong bulls with the similar body weight of 241.0± 22.3 or 281.4 ± 16.6 kg were randomly assigned to 3 groups with 4 animals in each.The study comprised 2 experiments,bulls were fed with a total mixed ration in which the concentrate to forage ratio was 30:70(DM basis)at 3 levels of feed intake:restricted to 40%(IR40)or 70%(IR70)of the ad libitum intake,and ad libitum(AL)in Experiment 1,and were fed with a full corn silage diet at 3 levels of feed intake:restricted to 60%(IR60)or 80%(IR80)of the ad libitum intake,and ad libitum(AL)in Experiment II.Each experiment period lasted for 19 d,including 10 d of pretest period and 9 d of test period.The results showed that the apparent digestibility of dry matter,organic matter,neutral detergent fiber and acid detergent fiber decreased with increasing levels of feed intake in both experiments,and IR40 or IR60 was significantly higher than AL(P<0.05).With increasing levels of feed intake,there was a decreasing tendency in nitrogen(N)apparent digestibility and the difference was not significant among groups(P>0.05),whereas the N retention ratio significantly increased(P<0.05)in both experiments.The gross energy,digestible energy,metabolizable energy intake and fecal energy,methane energy output significantly increased with increasing levels of feed intake(P<0.05),whereas the urinary energy output was not affected by feeding level(P>0.05)in both experiments.The gross energy digestibility and metabolizability significantly decreased with increasing levels of feed intake in Experiment Ⅰ(P<0.05),and there was no significant difference among groups in Experiment Ⅱ(P>0.05).3.Effects of Different Concentrate to Forage Ratios and Roughage Types of Diet on Digestion and Metabolism of Energy and Protein of Wandong CattleThis study was to investigate the effect of different concentrate to forage ratios and roughage types of diet on nutrient apparent digestibility,digestion and metabolism of energy and protein of Wandong cattle.Twenty Wandong bulls with the similar body weight of 398.8 ± 18.9 kg were used in a uncompleted 20×3 Latin square arrangement,and were fed with 15 different experimental diets including 3 roughage types(corn silage,rice straw and wheat straw)and 5 concentrate to forage ratios(0:100,10:90,20:80,30:70 and 40:60).The whole experiment comprised 3 periods,and each period fed 5 experimental diets.Each period lasted for 19 d,including 10 d of pretest period and 9 d of test period.The results showed that the apparent digestibility of dry matter,organic matter,neutral detergent fiber,acid detergent fiber and nitrogen(N)significantly increased with increasing levels of concentrate to forage ratio as well as the N retention ratio(P<0.05),and which in corn silage diet was significantly higher than those in rice straw or wheat straw diet(P<0.05).With increasing levels of concentrate to forage ratio,the digestible energy,metabolizable energy intake and methane energy output significantly increased(P<0.05),whereas the fecal energy output significantly decreased(P<0.05),and the urinary energy output was not affected by concentrate to forage ratio(P>0.05).The digestible energy,metabolizable energy intake and methane energy output in corn silage diet were significantly higher than those in rice straw or wheat straw diet(P<0.05),whereas the fecal energy output in which was significantly lower than those in rice straw or wheat straw diet(P<0.05).The gross energy digestibility and metabolizability significantly increased with increasing levels of concentrate to forage ratio,and which in corn silage diet was significantly higher than those in rice straw or wheat straw diet(P<0.05).In addition,there was a positive correlation relationship between the dietary net energy or retention energy and retention nitrogen/metabolizable energy(RN/ME),and the dietary-net energy and retention energy increased with the level of RN increasing in the same ME concentration of diet.With increasing of level of RN.the variation of net energy and retention energy for corn silage diet was lowest among three groups.and which for wheat straw diet was slightly higher than rice straw-diet.4.Net Energy Requirements for Maintenance and Gain of Growing Wandong Cattle Fed High-forage DietsThis study was to estimate the net energy requirements for maintenance(NEm)and gain(NEg)of growing Wandong cattle,and establish the prediction model of net energy requirement for growing Wandong cattle fed high-forage diets.A database involving 168 cattle with body weight ranging from 211 to 454 kg was obtained from a series of calorimetry experiments integrated with feeding and digestion.The results showed that linear regression equations of the logarithm of heat production(Log10HP)and retention energy(RE)against the metabolizable energy intake(MEI)were produced for this study(R2=0.87 and 0.88,respectively;both n=168;both P<0.001).The combined data indicated that the NEm and metabolizable energy requirement for maintenance(MEm)were 348.1 and 522.2 kJ/k0.75·d-1,respectively,and the partial efficiency of use of ME for maintenance(km)was 0.66.and the partial efficiency for gain(kg)was 0.51.There was also a linear relationship between RE and the average daily gain(ADG)(R2=0.88.n=168.P<0.001).Thus,the requirement for NEg of grow ing Wandong cattle obtained per kg of gain was 291 kJ/kg0.75·d-1.Our estimate of NEm was very similar to the value of the AFRC nutritional system(1993),whereas it was slightly greater than that recommended by the NRC nutritional system(2000).In addition,the NEm and NEg estimates of Wandong cattle were also greater than those recommended by Feeding Standard of Beef Cattle(NY/T 815-2004)from China.5.Validation of Net Energy Value of Common Feedstuffs and Net Energy Requirement Prediction Model for Growing Wandong CattleThis study was to validate the accuracy of the net energy(NE)value of common feedstuffs(obtained from Chapter 1)and the NE requirement prediction model for growing Wandong cattle(obtained from Chapter 4)by a feeding trial.Twenty-four Wandong bulls with initial body weight of 263.5 ± 31.1 kg were randomly assigned to 4 groups with 6 animals per group.Four levels of expected average daily gain(ADG)were designed to be 0,0.3,0.7 and 1.0 kg/d for bulls fed the formed diet based on the NE value of feedstuffs and the NE requirement prediction model for growing Wandong cattle.Fonned diet of each group with the same concentrate to forage ratio was designed to ensure that all animals fed a diet with the same energy to nitrogen ratio(calculated by DE/CP),and the experiment period lasted for 42 d,including 10 d of adaption period and 32 d of feeding trial.The results showed that the ADG progressively increased with increasing of net energy intake of bulls,and the ADG of bulls obtained from the feeding trial was close to the expected ADG value.According to the linear relationship of NE intake against the ADG of bulls,the regression equation without setting intercept was NER(kJ/kg0.75·d-1)=265.78 × △ W+355.48(R2=0.94,n=24,P<0.001)[Eq.1],and the regression equation with a intercept of 348.1 was NER(kJ/kg0.75·d-1)=284.22 × 6 △W+348.1(R2=0.93,n=24,P<0.001)[Eq.2],where NER means requirement for net energy(kJ/kg0.75·d-1)，△W means daily gain(kg/d).The NEg value of 284.22 kJ/kg0.75·d-1 extrapolated by Eq.2 was much closer to the value(291 kJ/kg0.75·d-1)obtained from the prediction model from Chapter 4 than Eq.1(265.78 kJ/kg0.75·d-1).Nevertheless,there was no discrepancy among three equations in estimation of NE requirement of growing Wandong cattle.As stated above,the conclusions are as follow:(1)In determination of the effective energy of single feedstuff by using substitution method,a significant difference is observed when the substitution ratio is different.In current study,the test feedstuff substitution ratio of 30%is better than 10%or 60%.Compared to single point substitution method,the regression method based on multiple point substitution is more practical on energy evaluation of feedstuffs for beef cattle.(2)Feeding levels significantly affected the nutrient apparent digestibility and energy and protein digestibility and metabolizability of Wandong cattle.Feed restriction increased the main nutrient digestion and utilization,whereas decreased the utilization of nitrogen retention.(3)Dietary concentrate to forage ratio significantly affected the nutrient apparent digestibility,energy and protein digestibility and metabolizability of Wandong cattle.In terms of nutrient value and efficiency of protein utilization of roughage,corn silage is significantly better than rice straw and wheat straw,and rice straw is better than wheat straw in the digestion and utilization of nitrogen.(4)The NEm and MEm requirement of growing Wandong cattle(200-500 kg)fed high-forage diets were 348 and 522 kJ/kg0.75·d-1,and the requirement for NEg of Wandong cattle obtained per kg of gain was 291 kJ/kg0.75·d-1.The net energy requirement was expressed as the follow equation:NER=(348+291 × △W)× BW0.75,where NER means requirement for net energy(MJ/d),△W means daily gain(kg/d),and BW0.75 means metabolic body weight(kg).(5)The NE value of common feedstuffs obtained from Chapter 1 and the prediction model obtained from Chapter 4 was accurate,and can be used to guide the diet formulation for growing Wandong cattle in practical production. |
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