|JANG, YOUNG - University Of Kentucky|
|LINDEMANN, MERLIN - University Of Kentucky|
|AGUDELO, JORGE - University Of Kentucky|
|ESCOBAR, CARLOS - University Of Kentucky|
|INOCENCIO, NOEL - University Of Kentucky|
|CROMWELL, GARY - University Of Kentucky|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/13/2014
Publication Date: 10/1/2014
Citation: Jang, Y.D., Lindemann, M.D., Agudelo, J.H., Escobar, C.S., Kerr, B.J., Inocencio, N., Cromwell, G.L. 2014. Comparison of direct and indirect estimates of apparent total tract digestibility in swine with effort to reduce variation by pooling of multiple day fecal samples. Journal of Animal Science. 92:4566-4576.
Interpretive Summary: Apparent total tract digestibility of nutrients is traditionally assessed by either the total collection method or the indicator method. Although the total collection method has long been considered the “gold standard” because it collects all voided nutrients, the indicator method saves labor by measuring the concentration of an indigestible indicator (such as chromium) in feed and feces, purportedly resulting in similar digestibility values as those obtained by the total collection method. Results from this research demonstrated that the total collection method results in higher digestibility values than the indicator method, and that for the indicator method, apparent total tract digestibility values and fecal chromium concentration require five days to stabilize after initial feeding of diets containing chromic oxide as the source of chromium. In addition, at least two days of pooling of feces was needed when using the indicator method to provide greater accuracy and lower variations in digestibility estimates compared to a single grab sample. This information is important for nutritionists at universities, feed companies, and livestock production facilities for assessing energy and nutrient digestibility of various feedstuffs utilized in diet formulation.
Technical Abstract: The intent of this study was to establish a fecal sampling procedure for the indicator method (IM) to provide digestibility values similar to those obtained by the total collection (TC) method. A total of 24 pigs (52.6 kg) were fed 1 of 4 diets with a 2 × 2 factorial arrangement of virginiamycin and phytase (PHY) added to a low P basal diet. Pigs were housed in metabolism crates for a 5-d TC period after 7-d of adaptation. Immediately after TC, a fecal collection period followed using the IM by including 0.25% of Cr2O3 in the feed for 10 d. Fecal collection for the IM started the day after diets containing Cr2O3 were first fed and continued for 9 consecutive d with a single grab sampling per day. Similar portions of feces from d 5 to 9 were also composited into 4 samples to evaluate multi-day pooling combinations. Highly variable means and CV among samples for apparent total tract digestibility (ATTD) were observed at d 1 and d 2 using the IM. The mean ATTD for all nutrients tended to stabilize by d 5 or d 6 for all nutrients in all dietary treatments. The TC data tended to have lower CV than the IM data for many nutrients. Fecal Cr concentration per day and diet had a similar trend compared with the ATTD values. Based on linear broken-line analysis, fecal Cr concentration plateaued at d 3.75 (P < 0.001) after the first feeding of Cr. Mean ATTD values by the IM were lower than those by TC for DM (P < 0.05), GE (P < 0.01), P (P < 0.01) and Ca (P < 0.001). The PHY supplementation improved ATTD of P (P < 0.001) and Ca (P < 0.001) in both collection methods, whereas the PHY effect on ATTD of DM was observed only for IM (P < 0.05) but not for TC. Differences related to PHY effect on ATTD were detected from d 4 to 9 in a single grab sampling for P and DM, but the ATTD of DM had inconsistent P-values by day. Feces sampling after 4 d of initial feeding of marker always detected the treatment effect on ATTD of P but not on ATTD of DM. Results indicate the TC method offers higher digestibility values than IM. For IM, ATTD values and fecal Cr concentration stabilize at least on d 5 after initial feeding of diets containing Cr2O3. At least 2 d pooling of feces for IM is needed to provide greater accuracy and lower variations than a single grab sampling.