Effect Of Highly-limiting Rumen-protected Amino Acids On Protein Utilization In Goats

Lysine and methioine are the first-or second-limiting amino acids for ruminants,and can be called highly-limiting rumen-protected amino acids?HLRPAA?.Low protein technique has been giving more and more attention in the academic scope.There is insufficient information on the feeding effect of HLRPAA for goats,therefore,the study is conducted to evaluate the effect of feeding HLRPAA for goats,consumed low protein diet,on protein utilization,blood metabolites,and rumen fermention.There are 3 experiments in the paper.Trial 1:Effects of RPMet supplement on protein utilization,plasma metabolites,and rumen fermentation parameters of goats fed low protein level diet.Eighteen Qianbei brown goats were randomly divided into 3 groups with 6replicates in each group and 1 goat in each replicate.The control was fed with basal diet,and its dietary protein level was 2 percentage points higher than treatment 1 and treatment 2.However,treatment 1 and treatment 2 was added 0.2%and 0.4%RPMet,respectively.The growth performance,dietary nutrients digestibility,plasma metabolites and rumen fermentation parameters were tested.There was no significant difference in the final weight,dry matter intake?DMI?,average daily gain?ADG?,and ratio of feed to gain?F/G?of each group of goat?P>0.05?.Digestibility of CP and EE in treatment 2 was higher than that in control and treatment 1?P<0.05?.There was no significant difference in plasma metabolites among the groups?P>0.05?.Rumen fermentation parameters?pH,NH₃-N concentration,and VFA?and cellulase activity for each group were not significantly different?P>0.05?.It is suggested that adding RPMet in the low protein diet can effectively improve the utilization of feed protein.The best addition level is 0.4%.Trial 2:Effects of RPLys supplement on protein utilization,plasma metabolites and rumen fermentation parameters of goats fed low protein level diet.The experimental design is similar to trial 1 except for RPLys level at 0.5%and1%.There was no significant difference in the final weight,DMI,ADG,and F/G of each group of goat?P>0.05?.Digestibility of CP and EE in treatment 2 was higher than that in control and treatment 1?P<0.05?.There was no significant difference in plasma metabolites among the groups?P>0.05?.Rumen fermentation parameters?pH,NH₃-N concentration,cellulase activity,and VFA?of each group were not significantly different?P>0.05?.It is suggested that adding RPLys in the low protein diet can effectively improve the utilization of feed protein and have no effect on growth,plasma metabolism,and rumen health.The best addition level is 1%.Trial 3:Evaluation of synergetic effects of RPLys and RPMet supplementation on protein utilization,plasma metabolites and rumen fermentation parameters of goats fed low protein diet.Experimental design is similar to trial 1.Ratio of RPLys and RPMet is scheduled to be 2.5:1 and their adding level is 0.5%and 0.2%for treatment1 and 1%and 0.4%for treatment 2,respectively.There was no significant difference in the final weight,DMI,ADG and F/G of 4 groups of goats?P>0.05?.Digestibility of CP in treatment 1 was higher than that in control?P<0.05?.Digestibility of NDF and ADF in treatment 1 were higher than those in control and treatment 2?P<0.05?.Plasma UN in treatment 1 and treatment 2 was lower than that in control?P<0.05?.Rumen fermentation parameters?pH,NH₃-N concentration,VFA?and cellulase activity,of each group were not significantly different?P>0.05?.It can be seen that addition of appropriate level of RPLys and RPMet to low protein diet is synergetically beneficial to increase of protein utilization and improving plasma N metabolism.The suitable addition levels of RPLys and RPMet are 0.5%and 0.2%,respectively.It can be concluded that,supplementation of RPLys and/or RPMet to low protein diet can improve the digestibility of protein.There is a synergetic association for half-dosage addition of RPLys and RPMet simultaneously indicated by reducion of plasma UN level.