Feasibility Evaluation On Slow-Release Urea In Substitution Of Dietary Alfalfa Protein In Goat

Slow-release urea（SRU）is a common replacement of concentrate protein feed such as soybean meal.The shortage of high quality hay such as alfalfa can not be changed in short time and has been the bottleneck restricting the efficiency of cattle and goat feeding.It is of great significance to find the replacement of alfalfa protein.This study is conducted to investigate the effects of SRU replacement of alfalfa protein on growth,blood metabolism,ruminal fermentation,and meat quality of goats.The aim is to explore the feasibility of SRU replacing alfalfa protein in goat diet.There are4 experiments in the study.Experiment 1.Evaluation of slow-release urea replacement of alfalfa protein by in vitro gas productionExperiment design:Four goats were used as rumen fluid donors in the study.The ANKOM system was used to detect the in vitro gas production.The in vitro rumen fermentation substrates were control（no SRU with 48%alfalfa in the diet）,treatment 1（0.5%SRU,replacing 50%alfalfa）,and treatment 2（1.0%SRU,replacing 100%alfalfa）,respectively.Experiment results:（1）Treatment 1 and treatment 2 resulted in higher GP₂₄,GP₄₈,GP₇₂,slow fermentation partial gas production（b）,potential gas production（a+b）,digestibility organic matter（DOM）,and metabolizable energy（ME）than control（P<0.05）.The rapid gas production partial（a）of in treatment 1 was lower than that in control and treatment 2（P<0.05）.The gas production rate（c）values of treatment 1,treatment 2,and control were successively decreased（P<0.05）.（2）The rumen p H value of control,treatment 2,and treatment 1 were successively decreased（P<0.05）.Level of NH₃-N in treatment 1 was lower than that in control and treatment 2（P<0.05）.（3）The level of propionic acid in treatment 1 and treatment 2 were higher than that in control（P<0.05）.The ratio of acetate to propionate in control,treatment 1,and treatment 2 were successively decreased（P<0.05）.Experiment 2.Effect of slow-release urea on digestion and metabolism of alfalfa protein in goatsExperiment design:Six Guizhou local male goats were divided into 6 replicates of 1 goats and were successively fed a TMR pelleted diet of alfalfa protein diet（no SRU with 48%alfalfa in the diet）,SRU protein diet（1.0%SRU,replacing 100%alfalfa）,and alfalfa protein+SRU diet（0.5%SRU,replacing 50%alfalfa）,respectively.Experiment results:Levels of F/G and NDF digestibility in SRU protein diet were higher than those of alfalfa protein diet（P<0.05）.（2）The protein efficient ratio of SRU protein diet was lower than that of alfalfa protein diet（P<0.05）.There were no differences for other nitrogen metabolism and energy metabolism among the 3 treatments diets（P>0.05）.Experiment 3:Effects of slow release urea replacement of alfalfa protein on growth,blood metabolism,and ruminal fermentation in goats.Experiment design:Thirty Guizhou black goats were divided into 3 treatments（control,treatment 1,and treatment 2）with 5 replicates per treatment of 2 goats each and were fed 1 of 3diets:control（no SRU with 48%alfalfa in the diet）,treatment 1（0.5%SRU,replacing 50%alfalfa）,and treatment 2（1.0%SRU,replacing 100%alfalfa）,respectively.The experiment lasted for 126days,including 14-day pretrial period and 112-day trial period,which consisted of 4 stages 28 days.Experiment results:（1）There was no difference in growth performance among the 3 treatments（P>0.05）.（2）Plasma metabolites were unaffected（P>0.05）,with the exception that ALT level in treatment 2 was higher than that of control and treatment 1 in the second stage（P<0.05）.（3）There was no difference in blood routine indexes among the 3 treatments at each stage（P>0.05）.（4）The activities of SOD and GSH-Px in treatment 1 and treatment 2 were lower than those in control（P<0.05）,and there were no difference in other antioxidant indexes among the 3 treatments（P>0.05）.（5）Goats fed treatment 1 had higher NH₃-N level than control and treatment 2（P<0.05）.There were no differences in rumen p H,MCP,cellulase activity,VFA,and CH₄ among the 3 treatments（P>0.05）.（6）There was no difference for rumen microbial diversity by 3 dietary treatments（P>0.05）.In general,the replacement of alfalfa protein with slow-release urea had no effects on growth performance,blood biochemical measurements,and rumen fermentation parameters of goats,and could improve the feeding efficiency.Experiment 4.Effects of slow-release urea replacement of alfalfa protein on slaughter performance,meat quality and amino acid composition in goatsExperiment design:On the basis of the feeding trial in Experiment 3,a total of 18 goats in 3treatment of 6 goats in each replicate were selected for slaughter sampling and analyze the slaughter performance,meat quality and amino acid composition.Experiment results:（1）The spleen index of treatment 1 was higher than that of control and treatment 2（P<0.05）.There were no differences in other slaughter performance among the 3treatments（P>0.05）.（2）No difference was observed in the quality of the longest dorsal muscle among the 3 treatments（P>0.05）.（3）Treatment 1 and treatment 2 had lower activities of SOD and GSH-Px in the longissimus dorsi muscle（P<0.05）.There was no difference in T-AOC and MDA among the 3 treatments（P>0.05）.（4）The level of arginine in treatment 2 was lower than that in control（P<0.05）.There were no differences in other amino acid levels in the longissimus dorsi muscle among the 3 treatments（P>0.05）.It is suggested that,from the above-mentioned results,slow-release urea can be used as a high-quality protein source for goats.Under the conditions of this study,it is feasible for slow-release urea to replace 50%alfalfa protein in the diet for goats.