4.1 Article

True dry matter digestibility of feeds evaluated in situ with different bags and in vitro using rumen fluid collected from intact donor cows

Journal

ANIMAL PRODUCTION SCIENCE
Volume 52, Issue 5, Pages 338-346

Publisher

CSIRO PUBLISHING
DOI: 10.1071/AN11206

Keywords

filter bags; fistulated cows; in situ digestibility; in vitro digestibility; nylon bags; repeatability

Funding

  1. Italian Ministry of University

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The aim of the study was to determine the comparability of the true dry matter digestibility (TDMd) achieved in situ with either traditional nylon bags (IS nylon) or synthetic filter bags (IS filter), and in vitro with either conventional bottles (CB) or the Daisy(II) incubation technique, using rumen fluid collected by oro-ruminal suction from intact cows. The four TDMd results were compared by linear regression. For each method, 11 feeds were incubated for 48 h in two separate incubations. The reproducibility of TDMd measurements was 97.9%, 95.1%, 98.8% and 96.0% for IS nylon, IS filter, CB and Daisy(II), respectively. The determination coefficient, the slope (b), and the significant difference of the slope from unity, of the linear relationship between TDMd values (g/kgDM) were as follows: IS nylon v. IS filter, R-2 = 0.97, b = 0.86, P = 0.02; IS nylon v. CB, R-2 = 0.90, b = 1.02, P = 0.27; IS nylon v. Daisy(II), R-2 = 0.90, b = 1.06, P < 0.01; and IS filter v. Daisy(II), R-2 = 0.95, b = 0.98, P = 0.13. In situ filter bags and Daisy(II) underestimated the TDMd values compared with IS nylon bags and CB, respectively. In situ, the replacement of nylon with filter bags could simplify the procedure of analysis, with less manipulation of residuals and less labour, and offers the possibility to increase the number of samples analysed simultaneously. The close relationships found among methods suggest that rumen fluid collected from intact cows can produce in vitro estimates of TDMd at 48 h well correlated with those obtained in situ.

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