| This research was designed to evaluate the nutrient requirement（Energy and Protein requirement）and evaluate the feed efficiency for Dorper and Hu crossbred F1 lambs.First of all,feeding experiment,comparative slaughter and digestibility trials were conducted to determine nutritional parameters,and provide a theoretical basis of scientific supply of net energy（NE）,metabolizable energy（ME）and net protein（NP）for this breed of ewe and ram lambs.Secondly,this study adopt residual feed intake（RFI）,an emerging feed efficiency evaluation indicator,to calculate the feed efficiency and evaluate the divergence in body composition,growth performance,metabolic variables and meat quality traits between different RFI group ewe lambs,in order to reveal main biological factors that contributes to the difference in feed efficiency and growth performance between RFI selected phenotypes.Finally,we try to investigate how and what extent the blood metabolic variables,growth performance and transcription profiles coding for somatotropic axis components of different RFI animals are responded to different nutritional levels,looking forward to explain the phenomenon that animals classified as different RFI phenotypes showed different growth performance,which were reported by previous research.1.Energy requirement of Dorper and Hu crossbred F1 ram and ewe lambsThis study was aimed to define the energy requirement for maintenance and growth for Dorper and Hu crossbred F1 lambs during fattening periods.The whole study was consisted of four phases of experiment.Each phase of the experiment was included feeding trial,comparative slaughter trail and digestion and metabolism trail,to determine the corresponding energy requirements parameters.In comparative slaughter trail,Thirty lambs（N = 18）were divided into ad libitum intake group（AL,N = 6）,low-restricted feeding group（LR,N = 6）and high-restricted feeding group（N = 6）,and were slaughter when they reach the appropriate body weight.In digestion and metabolism trail,at least 12 lambs were selected and divided into 3 feed intake levels according to the design of comparative slaughter trail,to determine methane production and metabolizable energy intake levels of lambs under 3 feed intake levels.Our results showed that,for both female and ewe lambs,net energy requirement for growth（NEg）,metabolizable energy requirement for growth（MEg）and partial efficiency of use of ME for maintenance（km）increased with increasing of age,while net energy requirement for maintenance（NEm）,metabolic energy requirement for maintenance（MEm）,and partial efficiency of use of ME for growth（kg）decreased with increasing of age.In the same body weight,NEm and MEm of ram lambs were greater than ewe lambs;while at the same body weight and ADG,NEg and MEg requirement of this breed ewe lambs were higher than ram lambs.Energy requirement parameters of this breed lambs were shown as below:①NEm and MEm of ewe lambs of 20-35 kg BW were 260.62 and 400.61 kJ·kg-0 75 of SBW,values of km and kg were 0.65 and 0.43,NEg and MEg were 1.25-4.55 MJ/d and 2.88-10.49MJ/d,repectively.②NEm and MEm of ewe lambs of 35-50 kg BW were 254.10 and 386.49 kJ·kg-0 75 of SBW,values of km and kg were 0.66 and 0.42,NEg and MEg were 1.53-5.57 MJ/d and 3.65-13.28 MJ/d,repectively.③NEm and MEm of ram lambs of 20-35 kg BW were 267.30 and 414.59 kJ·kg-0 75 of SBW,values of km and kg were 0.65 and 0.44,NEg and MEg were 1.06-4.13 MJ/d and 2.41-9.39 MJ/d,repectively.④NEm and MEm of ram lambs of 35-50 kg BW were 259.42 and 399.91 kJ·kg-0 75 of SBW,values of km and kg were 0.65 and 0.42,NEg and MEg were 1.59-6.03 MJ/d and 3.79-14.36 MJ/d,repectively.2.Protein requirement of Dorper and Hu crossbred F1 ram and ewe lambsThis study was aimed to define the net protein requirement for maintenance and growth for Dorper and Hu crossbred F1 lambs during fattening periods.The whole study was consisted of four phases of experiment.The design was in accordance with the experiment 1.Our results showed that net protein requirement for maintenance and growth decreased with the increasing of age,under the same body weight and ADG,net protein requirement for maintenance and growth of ram lambs were slightly greater than those of ewe lambs,and the divergence of net protein requirement for maintenance between ram and ewe lambs of 20-35 kg BW were greater than those of ram and ewe lambs of 35-50 kg BW.Net protein requirement parameters of this breed ewe and ram lambs were shown as below:NPm of ewe lambs of 20-35 kg BW was 1.85 g/kg of SBW0.75,NPg was 13.07-32.95 g/d.NPm of ewe lambs of 35-50 kg BW was 1.63 g/kg of SBW0.75,NPg was 9.83-25.08 g/d.NPm of ram lambs of 20-35 kg BW was 1.92 g/kg of SBW0.75,NPg was 15.94-44.32 g/d.NPm of ram lambs of 35-50 kg BW was 1.70 g/kg of SBW0.75,NPg was 10.41-26.28g/d.3.A comparative study of growth performance,plasma metabolic variables and hormones and meat quality traits between different RFI ewe lambsThis study aimed to evaluate the phenotypic effect of residual feed intake（RFI）on growth performance,body composition,blood metabolic variables,and meat quality traits.The 54 growing ewes（BW=17.50±0.48 kg,8 weeks of age）offered ad libitum access to TMR diets at 0800 h over 63 d.During these days,data of DMI（recorded daily）and BW（recorded every 10 days）were recorded were collected and were ranked on RFI phenotypes.The 12 ewes with highest and lowest RFI values（six ewes each RFI group）were chosen to use in further study.At 0900,1100,1400 and 1700 hours of 15th,30th,45th and 60th day,collected blood plasma through the jugular vein serum to determine the plasma metabolic variables and hormones.At the end of the trial（day 63th）,6 animals in each RFI group were slaughtered to determine various tissues fresh weight,body composition and body chemical components proportion and distributions between high and low RFI phenotypes.Collected longissimus muscle,lumbar and gluteal to measured meat quality traits.Our results showed that RFI was positively associated with DMI（r = 0.68,P<0.001）and FCR（r = 0.64,P<0.001）,but independent of ADG,initial BW,or final BW.Ewes with low RFI exhibited a higher carcass lean percentage（P<0.05）than that with high RFI,but no significant difference of the other body composition traits were detected between high and low RFI phenotypes.Similar plasma IGF-1,NEFA,TG,Urea,T3,T4 and Glucose concentration were detected between different RFI phenotypes（P>0.05）.Ewes with high RFI exhibited a higher trenderness of longissimus muscle and lumbar（P<0.05）than that with low RFI,high RFI ewe lambs have lower value of longissimus muscle pHu than that of low RFI ewe lambs（P<0.05）,but no significant difference of L*,a*,b*and pH1 were detected（P>0.05）between high and low RFI phenotypes.In conclusion,our study provided certain references to reveal the mechanism in influence animal feed efficiency between different RFI phenotypes 4.Effect of residual feed intake phenotype-nutritional treatment interaction on growth performance,plasma metabolic variables and somatotropic axis genes expression in growing ewesThe objective of current study was to evaluate the effect of RFI phenotype and nutrition treatment interaction on growth performance,plasma variables and gene expression level within somatotropic axis.The growing ewes（n= 52,Initial BW=17.50±0.48 kg,2 months of age）offered ad libitum access to diets over 63 d and were ranked on RFI phenotype.Thirty of them that have the highest and lowest RFI values were selected and randomly assigned to ad libitum（AL）,low restriction（LR）and high restriction（HR）group,respectively.Each nutritional treatment group included ewes with high（n-5）and low RFI（n=5）,time period for feeding treatment were 74 days（from 64 to 138th day）.During nutritional treatment,BW was recorded weekly,plasma samples were taken for measuring metabolic variables and hormones concentration.Tissues of hypothalamus,pituitary,liver,and longissimus dorsi muscle（LM）were harvested at the end of the experiment（138th day）to measure the gene expression level within somatotropic axis.Results showed that growth inhibited by negative energy balance associated with increasing of plasma NEFA,GH concentration and pituitary GH mRNA expression,whereas with decreasing of plasma IGF-1,TG,T4 concentrations and mRNA abundance of hepatic IGF-1,GHR（Growth hormone receptor）and muscle IGF-1.Under AL feeding,muscle GHR mRNA abundance of low RFI ewes tend to be greater（P = 0.09）,however,this difference was abolished by underfed（P>0.10）.Growth performance did not differ among RFI groups ewes under ad libitum and LR feeding conditions.In contrast,when under HR treatment（DMI was restricted to 45%of the average ad libitum intake）,low RFI ewes showed slightly greater growth performance,which was accompanied with lower pituitary SSTR2 mRNA abundance（P<0.05）,plasma NEFA concentration（P<0.05）,and greater concentration of TG（P<0.05）,compared with ewes classified as high RFI group.Furthermore,RFI was positively associated with pituitary SSTR2 mRNA（r = 0.58;P<0.01）,and tend to negative correlated with muscle GHR（r =-0.33;P = 0.09）.Expression level of pituitary SSTR2 mRNA was negatively associated with pituitary GHRHR（r =-0.43;P<0.01）;and positively correlated with hepatic IGF-1（r = 0.36;P = 0.07）.In conclusion,Ewes categorized as low RFI grew more under high feed restriction might attribute to the less intensity of fat mobilization under negative energy balance on an equal basis,and presumably through action of SSTR2 and potentially mediated by inhibitory effects of somatostatin on GH release but not basal GH secretion. |
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