Comparison Of Different Methods To Determine Amino Acid Digestibility Of Feed For Yellow-feathered Broilers

This study was conducted to compare the concentration of titanium dioxide（Ti O₂）and amino acid in excreta of cecectomized rooster or ileal digesta of canulated or slaughtered rooster and amino acid digestibility.Then,the amino acid digestibility of corn and soybean meal as well as their additivity were compared between the values determined with excreta of cecectomized rooster or ileal digesta of slaughtered rooster.The results will provide a proper reference to determine digestibility of amino acid.In experiment 1,186 yellow-feathered roosters were cecectomized and 47yellow-feathered roosters were surgically fitted with a T-cannula at the distal ileum.The recovery after operation was evaluated for cecectomy and ileal cannulation.A single factor completely random deign was adopted to estimate the effect of sources of digested samples on the amino acid digestibility.A total of 3 sources of digested samples were excreta of cecectomized roosters,ileal digesta of cannulated roosters or slaughtered roosters.The results showed that the BW gain of cecectomized roosters was not significantly different with that of cannulated rooster at 7,14,21 days after surgery（P>0.05）.The death and cull rates of the first and second batch of cecectomized roosters and cannulated roosters were23.1%,20.4%,33.9%,respectively.There was a significant difference in concentration of Ti O₂,several amino acids and their digestibility in determination with excreta of cecectomized roosters,ileal digesta of cannulated roosters or slaughtered roosters（P<0.05）.Overall,the concentration of Ti O₂and amino acid,digestibility of amino acid and their coefficient of variation determined with excreta of cecectomized roosters were close with ileal digesta of slaughtered roosters.But greater coefficient of variation in concentration of Ti O₂and amino acid,digestibility of amino acid was observed on determination with ileal digesta of cannulated roosters.Experiment 2 was conducted to compare the differences between slaughter and cecectomy method to determine amino acid digestibility of corn and soybean meal and their additivity in a corn-soybean meal diet,which will provide a reference for the accurate determination of amino acid digestibility in chicken feed.A two-sample experiment was adapted to compare slaughter and cecectomy method to determine endogenous amino acid excretion and amino acid digestibility of corn,soybean meal and a corn-soybean meal.Each treatment contained 6 replicates with 3 chickens per replicate.The calculated amino acid digestibility of the corn-soybean meal diet was arithmetically expected according to the digestibility and proportion of individual ingredients in the mixed diet.The additivity of amino acid digestibility between corn and soybean meal was tested by comparing the calculated and determined values of amino acid digestibility in mixed diet.The results showed that the values of slaughter method were 2.2 times in endogenous excretion of 16amino acids and 8.2 times in mean value of SE of cecectomy method.Except for His and Gly,the endogenous excretions of 14 amino acids in slaughter method were significantly higher than those of cecectomy method（P<0.05）.Apparent digestibility of some amino acids in corn（Met and Phe）,soybean meal and corn soybean meal（15 amino acids except Gly）determined with slaughter method was significantly lower than these with cecectomy method（P<0.05）.Mean SE of apparent digestibility of amino acids in slaughter method was 2.6 to 3.5 times of that in cecectomy method.Slaughter method had close standardized amino acid digestibility in maize（except Gly）to that in cecectomy method.Whereas,the standardized digestibility of some amino acid in soybean meal（13 amino acids except Lys,Cys and Gly）and corn soybean meal diet（Arg,Ile,Leu,Val,Asp,Glu,Pro）was lower in slaughter method than cecectomy method（P<0.05）.The mean SE of standardized digestibility of amino acids in slaughter method was 2.4 to 3.1 times of that in cecectomy method.The calculated values were significantly different from the determined values of apparent digestibility of most amino acids（except Ala and Cys）and standardized digestibility of Lys in corn-soybean meal diets using slaughter method（P<0.05）.The calculated values were significantly different from the determined values of apparent digestibility（Leu,Lys,Met,Thr,Val,Ala,Asp）and standardized digestibility（Ile,Leu,Met,Phe,Val,Ala,Asp,Ser）of some amino acids in corn-soybean meal diets using cecectomy method（P<0.05）.In conclusion,slaughter method has higher the endogenous amino acid excretion but lower apparent and standardized digestibility of some amino acids than cecectomy method.The additivity of apparent amino acid digestibility in slaughter method was lower than cecectomy method.The additivity of standardized amino acid digestibility in slaughter method was better than cecectomy method,which may relate to the greater variation among replicates of slaughter method.