Study On Energy And Protein Requirements Of20to35kg Dorper And Thin-tailed Han Crossbred Lambs

Experiment1: Effects of feeding levels on growth, carcass traits and organ indexes of Dorper×thin-tailed Han crossbred lambsThis experiment was conducted to investigate the growth patterns, carcass traits and organ indexesof Dorper×thin tailed Han crossbred lambs from20to35kg of live weight. The same experimentaldesign was used in two experiments. Twenty-one lambs were randomly assigned to three groups withone group fed ad libitum （AL）, and the other two groups fed either70（IR70） or40%（IR40） of ad libitum.A slaughter trial was performed when the lambs in AL group reached35kg of live weight. The resultsshowed that there were significant differences in net gain, average daily gain and dry matter intake amongthree groups. ADG of ram lambs were higher than ewe lambs and the F/G was also lower. No significantdifference was found between AL group and IR70group in the ratio of relative rumen weight to totalstomach （P>0.05）. Besides, the relative liver weight in AL group was higher than that in either of theother two groups （P<0.05）. No significant differences were found in meat percentage and meatpercentage of carcass （P>0.05）. Feeding levels had different effects on growth performance, feedconversion ratios, weight of the four stomach and other main organs of the lambs. Results of growth,carcass traits and organ indexes of Dorper×thin-tailed Han lambs were different from therecommendations of NRC （2007）.Experiment2: Effect of feeding levels on digestion and metabolism of energy and protein inDorper×thin-tailed Han crossbred lambsThis study was conducted to investigate the effect of different levels of feed intake on digestibilityof main nutrients in Dorper×thin-tailed Han crossbred lambs, and provide some basic parameters forthe slaughter experiment. The same experimental design was used in two experiments. Fifteen Dorper×thin-tailed Han crossbred ram or ewe lambs were assigned to3levels of dry matter （DM） intake: adlibitum, or restricted to70%（IR70） or40%（IR40） of the ad libitum intake. Digestibility trial andrespiratory trial were conducted to determine the metabolic parameters of protein and energy, as well asCH4, CO2and O2. The values of digestibility of DM, OM increased with decreasing levels of feed intakeand the difference was not significant among ram lambs （P>0.05）. There is no significant difference inN digestibility among three feed intake levels in ram lambs. The digestibility of DM, OM and N in IR40was higher than AL and IR70（P<0.05）. The digestibility of NDF and ADF in IR40was significantlyhigher than AL （P<0.05） and showed no significantly difference compare to IR70in ram lambs and ewelambs （P>0.05）. The gross energy intake, fecal energy, methane energy, carbon dioxide emissions andmethane production were significant difference among three groups in ram lambs and ewe lambs（P<0.05） The ratio of methane energy to gross energy increased from7.45to8.75in ram lambs andfrom7.55to8.85in ewe lambs, respectively, but the value was not significant （P>0.05）. The respiratoryquotient ranged from0.68to0.84in ram lambs and0.82to0.98in ewe lambs. The apparentdigestibility of main nutrients was higher in intake restriction groups than the group fed ad libitum, but the N retention was lower in intake restriction groups. The feeding levels did not affect the ratio ofmethane energy to gross energy and the metabolic rate of digestible energy, but significantly influencedthe methane emissions of lambs.Experiment3: The distribution of energy and protein in body tissues and mathematical modelsfor predicting body composition of Dorper×thin-tailed Han crossbred lambsThis study was aimed to determine the content and distribution of energy and protein in differentbody tissues of20-35kg Dorper×thin-tailed Han crossbred lambs, and to develop mathematicalmodels to predict body composition and chemical composition from live weight of lambs. Twenty-oneanimals were randomly assigned to three groups with one group fed ad libitum （AL）, and the other twogroups fed either70（IR70） or40%（IR40） of ad libitum. Each group had7lambs. A slaughter trial wasperformed when the lambs in AL group reached35kg of live weight. Dry matter, crude protein, fat, aswell as gross energy were measured in bone, muscle, fat, blood, viscera, hide, and fleece. For bodycomposition, AL group lambs had the highest proportion of fat to moisture and showed a significantdifference from IR40group （P<0.05）, while the proportion of protein/fat was higher in IR40group thanin AL group （P <0.05）. No significant difference was found in the ratio of the muscle, blood plusviscera or hide weight to fleece-free empty body weight （P>0.05）, but the ratio of bone to fleece-freeempty body weight was significantly different （P<0.05） among three treatments. There were nosignificant differences （P>0.05） in energy or protein content among three feeding levels. The ratio ofdry matter or protein to fleece-free empty body weight was not significantly different among the threegroups （P>0.05）. However, IR40group had a higher ratio in moisture and ash contents than that in ALand IR70group （P <0.05）. The feeding level significantly affected the proportion of crude protein, fatand moisture in Dorper×thin-tailed Han crossbred ram lambs growing from20to35kg of live weight,and a highly negative correlation was found between body fat and moisture. The parameters of E/GEand CP/GCP in different tissues were affected by the feeding levels, but the effects were different. Theprotein content was relatively stable while the fat content was largely affected by age and feeding levels.There was a strong correlation between empty body weight and the weight of different tissues andorgans, and a strong correlation relationship was also found between fleece-free empty body weight andthe main chemical composition of the body.Experiment4: Energy requirements of20-35kg Dorper×thin-tailed Han crossbred lambsThe study aimed to define the energy requirement of metabolizable energy （ME） and net energy（NE） for maintenance and growth for20-35kg Dorper×thin-tailed Han crossbred F1lambs. The trialwas conducted according to a completely random design. Fifty Dorper×thin-tailed Han ram lambs wereselected, thirty five lambs were used for a comparative slaughter trial and15lambs were used for adigestibility trial. Seven lambs were randomly chosen and slaughtered at20kg BW for measuring theinitial body composition. The remaining28ram lambs were offered a pelleted mixture diet at ad libitumintake, or70or40%of the ad libitum intake. Seven of the ram lambs were randomly chosen and slaughtered when the14ram lambs fed ad libitum reached28kg. The remained21ram lambs wererandomly divided into3intake levels and fed a pelleted mixture diet, and the lambs were all slaughteredwhen the lambs in ad libitum treatment group reached at35kg of BW. In a digestibility trial, fifteenlambs were randomly divided into three groups （five lambs in each group） with the same feeding regimeas the comparative slaughter trial. Total feces and urine was collected. Methane production, carbondioxide output and oxygen consumption were measured by open-circuit respirometry. The resultsshowed that the maintenance requirements for NE and ME were250.6and374.2kJ·kg^-1metabolicshrunk BW （SBW0.75） for ram lambs and247.74and386.65kJ·kg^-1metabolic shrunk BW （SBW0.75） forewe lambs. The efficiency of ME utilization for maintenance were0.67and0.64, respectively. Netenergy and metabolic energy requirements for growth ranged from1.10to5.04MJ·d^-1and2.43to11.13MJ·d^-1for ram lambs and1.18—5.18MJ·d^-1and2.68—11.71MJ·d^-1of ewe lambs, respectively. Theefficiency of ME for growth was0.45and0.44, respectively. These parameters were lower than thoserecommended by NRC and AFRC.Experiment5: Protein requirements of20-35kg Dorper×thin-tailed Han Crossbred lambsThis experiment was conducted to determine the protein requirements for maintenance and growthof Dorper×thin-tailed Han crossbred lambs growing from20to35kg of live weight. A feeding trialand a comparative slaughter trial were used. According to the data of ruminal microbial proteinsynthesis from other trials of our studies, the results showed that the maintenance requirements of netprotein （NP） for ram lambs and ewe lambs were1.86and1.82g/kg SBW0.75, respectively, and thecorresponding values of requirement for metabolizable protein （MP） were2.80and2.86g/kg SBW0.75.The utilization efficiency of MP for maintenance was0.66and0.64for ram lambs and ewe lambs. Theresults also showed that NP and MP requirements for growth ranged from12.43to42.35g·d^-1,18.17to61.92g·d^-1for ram lambs and12.12to38.12g·d^-1,18.34to57.67g·d^-1for ewe lambs that gained100to350g/d. Estimated efficiencies of MP use for body weight gain were0.68and0.66, respectively. Theram lambs shows a higher net protein requirements and MP requirements than ewe lambs with the samelive weight and ADG.