Lack of interactive effects between diet composition and acid addition with drying method on amino acid digestibility values in porcine ileal digesta

Authors: Kerr, Brian; CURRY, SHELBY - Oak Ridge Institute For Science And Education (ORISE); RAMIREZ, BRETT - Iowa State University

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/24/2020
Publication Date: 2/1/2020
Citation: Kerr, B.J., Curry, S.M., Ramirez, B.C. 2020. Lack of interactive effects between diet composition and acid addition with drying method on amino acid digestibility values in porcine ileal digesta. Journal of Animal Science. 98(2):1-8. https://doi.org/10.1093/jas/skaa026.
DOI: https://doi.org/10.1093/jas/skaa026

Interpretive Summary: Accurate determination of nutrients and energy in digesta is critical in digestibility studies. While most studies dry ileal digesta samples by freeze drying, freeze drying requires specialized equipment and is a time consuming process. While oven drying of ileal digesta samples would alleviate these issues, additional research is needed to clarify the effect of drying method (oven drying versus freeze drying) on amino acid digestibility and to determine if an effect is diet dependent or if samples should be pH-adjusted prior to processing to prevent potential microbial growth. Data from this experiment indicates that on average, oven drying of ileal digesta resulted in 2.5% greater estimate of amino acid digestibility compared to samples that were freeze dried, and was not diet-, pH-, or amino acid-dependent. However, because the majority of the data on amino acid digestibility are based on freeze drying, a bias factor may be necessary to adjust amino acid digestibility data obtained on an oven dried-basis relative to a freeze-basis for use in feed formulation. This information is important for nutritionists at universities, feed companies, and pig production facilities determining how drying of ileal samples affect amino acid digestibility and provides a bias factor (2.5%) to adjust samples that have been oven dried compared to samples that have been freeze dried, for use in feed formulation programs.

Technical Abstract: Two experiments were conducted to determine the effect of oven drying (OD) or freeze drying (FD) on apparent ileal digestibility (AID) of AA in diets fed to pigs. In Exp. 1, 15 barrows (BW of 88.4 ± 6.4 kg) were allotted to diets consisting of a corn starch-soybean meal (CST), a potato starch-soybean meal (PST), or a corn-soybean meal (CSBM) diet, over 2 collection periods. Following collection, samples were pooled within pig and subdivided for either OD or FD, resulting in 10 observations per diet by drying method combination. In Exp. 2, 11 barrows (BW of 63.3 ± 3.8 kg) were fed a CST diet and following collection, samples were pooled within pig and subdivided to be either adjusted to pH 4 or remain unadjusted. These subsets of samples were then further subdivided to be either FD or OD, resulting in 11 observations per pH level by drying method combination. Oven drying was accomplished by drying samples in a forced air oven at either 100°C (Exp. 1) or 75°C (Exp. 2). In Exp. 1, there were no diet-type by drying-method interactions noted for any of the AA (P > 0.10). Oven drying resulted in a higher AID of AA compared to samples which were FD (P = 0.10), for all AA except for Gly and Tyr. Averaged across all AA, AID of AA was 3.3% greater if the sample was OD compared to FD. Differences in AID of AA among the 3 diets was noted for all AA (P = 0.07), except for Cys (P = 0.33), due to the CST and PST diets only containing SBM as an AA-providing ingredient while the CSBM diet contained both corn and SBM. Pigs fed the PST diet had greater SID for all AA compared to pigs fed the CST diet (P = 0.05), except for His, Lys, Cys, and Glu. In Exp. 2, there were no pH-adjustment by drying-method interactions noted on AID for any of the AA (P > 0.10). Adjusting ileal digesta to a pH of 4.0 had little effect on AID for most of the AA, except for a lowered AID of Arg, His, Lys, Trp, and Ser (P = 0.10). Oven drying resulted in a higher AID for all AA (P = 0.09) except for Ile, Thr, Val, Ala, Asp, Glu, and Gly. Averaged across all AA, the increase in AID of AA was 1.7% greater if the sample was OD compared to FD. On average, OD of ileal digesta resulted in 2.5% greater estimate of AID of AA compared to samples that were FD, and was not diet-, pH-, or AA-dependent. Because the majority of the data on AA digestibility are based on FD, a bias factor may be necessary to adjust AA digestibility data obtained on an OD-basis relative to a FD-basis for use in feed formulation.