Date of Award

Fall 2008

Project Type


Program or Major

Animal and Nutritional Sciences

Degree Name

Doctor of Philosophy

First Advisor

Charles G Schwab


Soybean meal, SoyPlusRTM, dried distillers grains with solubles (DDGS), and fish meal samples were used in the evaluation of the modified three-step, the immobilized digestive enzyme assay ( IDEA), the guanidination, and the furosine in vitro procedures to estimate intestinal digestibility of amino acids in rumen undegraded protein ( RUP-AA). Identifying an in vitro method to estimate RUP-AA digestibility will allow for routine analysis of feeds for this parameter, which can lead to more accurate formulation of dairy rations. To determine the adequacy of these procedures, in vivo RUP-AA digestibility estimates were obtained using the precision-fed cecectomized rooster assay. Rumen undegraded residues ( RUR) were generated, and intact feeds and RUR were analyzed for AA and crop-intubated to cecectomized roosters. Results of the rooster experiments indicate that AA digestibility differs from RUP-AA for DDGS samples, and RUP-AA digestibility differs within samples. For the modified three-step procedure, digestibility of all AA in all feedstuffs was highly correlated to in vivo data. For the IDEA analysis, IDEA values of intact feeds were highly correlated to RUP-AA digestibility, which indicates that the ruminal incubation step can be eliminated with this method. The guanidination and furosine methods can be used to predict lysine digestibility only, which is often a limiting AA in dairy rations. Blocked lysine was calculated from furosine concentrations, and the guanidination procedure was used to calculate reactive lysine. Blocked and reactive lysine estimates were highly correlated to in vivo lysine digestibility. Of these two methods, the guanidination procedure was a better approach for predicting lysine digestibility across feedstuffs. To increase the number and type of sample analyzed, 5 BM samples were later obtained. Blood meal was only analyzed via the rooster assay, the modified three-step procedure, and the guanidination method. Among the BM samples, digestibility of AA was similar to RUP-AA. For the modified three-step procedure, the use of intact BM provided more accurate estimates of RUP-AA digestibility than the RUR. The guanidination method was not a good approach to predict lysine digestibility in BM. In conclusion, the modified three-step procedure appears to be the best in vitro approach to estimate RUP-AA digestibility.