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Evaluating the relationship between in vitro and in situ starch degradation rates.

C. B. Gleason




Evaluating the relationship between in vitro and in situ starch degradation rates.
C. B. Gleason*1, L. M. Beckett2, B. R. dos Reis1, M. B. Hall3, R. R. White1. 1Virginia Tech Blacksburg, VA, 2Purdue University West Lafayette, IN, 3US Dairy Forage Research Center, USDA ARS Madison, WI.

Determining starch degradability is important because of its implicit relation to gut health, energy availability, feed intake, and animal productivity. In vitro assays for protein and fiber degradability have been useful tools for ration formulation; however, analogous assessments of starch degradability have limited update. Our objective was to test how an in vitro starch degradation assay compared with the traditional in situ method. Samples of 28 livestock feeds were obtained from 3 feed mills and subjected to in vitro and in situ starch degradation analyses. Seven ruminally cannulated wethers (Suffolk, Dorset or Suffolk x Dorset) were used for the in situ procedure. In vitro starch degradation was assessed using the acetate buffer technique with modified enzymatic incubation times: amylase (AML) 5 min and amyloglucosidase (AGS) 10 min, AML 10 min and AGS 20 min, AML 15 min and AGS 30 min, AML 30 min and AGS 60 min, AML 45 min and AGS 90 min, and AML 60 min and AGS 180 min. R statistical software was used for all analyses. In situ rates were determined using the �rskov method and in vitro rates calculated assuming exponential decay. Relationships were analyzed as a linear mixed-effects model with in situ degradation rate as the response variable and in vitro degradation rate, percent starch, percent crude protein, percent neutral detergent fiber, percent fat, and feed type as fixed effects. Interactions between in vitro degradation rate and the nutrient percentages were also included. Feed mill was included as a random effect. In situ degradation rates ranged from 2.5 to 620.0%/h and in vitro degradation rates ranged from 12.0 to 610.0%/h. A relationship (P = 0.031) between in vitro and in situ methods was observed but an interaction (P = 0.042) between in vitro degradation rate and neutral detergent fiber content was also significant, suggesting the consistencies among methods are influenced by fiber content. Additional work is needed to confirm the usefulness of this in vitro screening technique.

Keywords: in situ incubation, in vitro assay, ruminal starch degradability.

Biography: Claire Gleason hails from a farming background and has always had a passion for the beef and dairy industries. She obtained her Bachelor's of Science in Animal & Poultry Sciences at Virginia Tech and is currently pursuing a PhD in Ruminant Nutrition at the same institution. Claire researches the effects of diet on fermentation dynamics and the rumen microbiome under the direction of Dr. Robin White.