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. 2021 Mar;7(1):64-71.
doi: 10.1016/j.aninu.2020.07.003. Epub 2020 Dec 23.

Acid-insoluble ash is a better indigestible marker than chromic oxide to measure apparent total tract digestibility in pigs

Susanto Prawirodigdo  1   2 , Neil J Gannon  3 , Brian J Leury  1 , Frank R Dunshea  1   4
Affiliations

Acid-insoluble ash is a better indigestible marker than chromic oxide to measure apparent total tract digestibility in pigs

Susanto Prawirodigdo et al. Anim Nutr. 2021 Mar.

Abstract

The aim of this study was to determine the apparent total tract digestibility (ATTD) of nutrients in cottonseed meal (CSM) and soybean meal (SBM) in simple carbohydrate and more complex wheat-based diets using 2 indigestible markers and total faecal collection. Twenty-five Large White × Landrace boars (57.8 kg) were randomly allocated to either a pure wheat diet, 40% CSM or SBM in either a sugar-starch- (1:1) or wheat-based diet for 18 d. Acid-insoluble ash (AIA) and chromic oxide (Cr2O3) were included in all diets as indigestible markers. Diets were offered (1,800 g/d per pig) in 3 meals/d from d 1 to 11 and 8 meals/d from d 12 to 17. On d 9, the pigs were moved to individual metabolism cages to allow total faecal collection. On d 18, the pigs were fed hourly for 8 h. After the 8th meal, pigs were anaesthetized and digesta sampled from the terminal ileum and rectum before lethal injection. There were no differences between ATTD of nitrogen (N) determined using AIA as a marker and measured by total faecal collection. On the other hand, the ATTD of N of diets containing CSM in sugar-starch- or wheat-based diets and the pure wheat diet determined using Cr2O3 as a marker was less (-3.11%, -4.46% and -6.59%; P < 0.001) than that measured by total faecal collection. The ATTD of N determined using AIA as a marker was highly correlated with that measured using total faecal collection (P < 0.001; R 2 = 0.95). Similarly, the ATTD of N determined using Cr2O3 as a marker was correlated with that measured using total faecal collection, although the correlation was not quite as strong as using AIA (P < 0.001; R 2 = 0.87). Also, the slope of the regression line and the intercept were closer to unity and zero for the relationship when the ATTD of N was determined using AIA compared to Cr2O3 as an indigestible marker. The ATTD of organic and dry matter behaved similarly. These data demonstrate that the basal diet and choice of indigestible marker can substantially influence the ATTD and that the use of AIA as an indigestible marker is more suitable than Cr2O3 in digestibility studies in pigs.

Keywords: Cottonseed meal; Digestibility; Nitrogen; Organic matter; Pig; Soybean meal; Wheat.

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Conflict of interest statement

We declare that we have no financial or personal relationships with other people or organizations that might inappropriately influence our work, and there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the content of this paper.

Figures

Fig. 1
Fig. 1
Relationship between apparent total tract digestibility (ATTD) of nitrogen (N) determined using either (A) acid-insoluble ash (AIA) or (B) chromic oxide (Cr2O3) as an indigestible marker and determined using total faecal collection. Data are for individual pigs (n = 5 for each diet) fed either CSM in a sugar-starch-based (Δ), CSM in a wheat-based (□), SBM in a sugar-starch-based (▲), SBM in a wheat-based (■) or a wheat (○) diet. The line of unity is represented by the dashed line while the solid line is the linear regression line. The regression equations are (A) y = 3.25 (SE 3.71) + 0.955 (SE 0.0484)x, R2 = 0.941 and (B) y = 21.1 (SE 4.56) + 0.747 (SE 0.0616)x, R2 = 0.859.
Fig. 2
Fig. 2
Relationship between apparent total tract digestibility (ATTD) of organic matter (OM) determined using either (A) acid-insoluble ash (AIA) or (B) chromic oxide (Cr2O3) as an indigestible marker and determined using total faecal collection. Data are for individual pigs (n = 5 for each diet) fed either CSM in a sugar-starch-based (Δ), CSM in a wheat-based (□), SBM in a sugar-starch-based (▲), SBM in a wheat-based (■) or a wheat (○) diet. The line of unity is represented by the dashed line while the solid line is the linear regression line. The regression equations are (A) y = 1.29 (SE 4.66) + 0.978 (SE 0.0561)x, R2 = 0.927 and (B) y = 29.7 (SE 4.24) + 0.663 (SE 0.0529)x, R2 = 0.867.
Fig. 3
Fig. 3
Relationship between apparent total tract digestibility (ATTD) of dry matter (DM) determined using either (A) acid-insoluble ash (AIA) or (B) chromic oxide (Cr2O3) as an indigestible marker and determined using total faecal collection. Data are for individual pigs (n = 5 for each diet) fed either CSM in a sugar-starch-based (Δ), CSM in a wheat-based (□), SBM in a sugar-starch-based (▲), SBM in a wheat-based (■) or a wheat (○) diet. The line of unity is represented by the dashed line while the solid line is the linear regression line. The regression equations are (A) y = 7.37 (SE 5.39) + 0.910 (SE 0.0680)x, R2 = 0.881 and (B) y = 35.0 (SE 4.98) + 0.594 (SE 0.0661)x, R2 = 0.769.
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