Determination of ileal endogenous nitrogen losses and true ileal nitrogen digestibility during non-steady-state conditions of the ¹⁵N-isotope dilution technique

Figures & data

Table 1. Composition of the control and quebracho tannin diets^ǂ.

	Control	Quebracho tannin
Ingredients	g/kg diet	g/1.04 kg diet^§
Enzyme-hydrolysed casein^# (84% CP)	180	180
Cornstarch	521	521
Sugar (meritose/dextrose)	148	148
Soybean oil	25	25
Cellulose^¶	50	50
Quebracho extract^$	–	40
Premix^¤	10	10
Mineral mixture^¥	61	61
DL-Methionine	3	3
L-Threonine	1	1
Antibiotic^ƚ, ppm	40	40
Chromic oxide	1	1

^ǂCalculated contents of the diets 157.4 g/kg crude protein (CP), 902.3 g/kg DM, 55.6 g/kg ash, 25.8 g/kg crude fat, 50.8 g/kg crude fibre, 2479 kcal/kg net energy; ^§The quebracho diet was fed at 104% of the feed intake for the control diet; ^#Hyprol 8369, Quest International Nederland BV (Netherlands); ^¶Arbocell B800, Fr Jrettenmayer und Söhne (Germany); ^$Unitan Saica, Quebracho Superior ATO, 120 g/kg catechin equivalents, 650 g/kg total phenols, 9 g/kg crude protein; ^¤The premix provided per kg diet: 0.27 mg all-trans retinol equivalents (9000 IU vitamin A), 45 µg (1800 IU) cholecalciferol, 40 mg vitamin E, 5 mg riboflavin, 30 mg nicotinamide, 12 mg D-pantothenic acid, 100 mg choline chloride, 40 µg vitamin B-12, 3 mg vitamin K; 50 mg vitamin C, 1 mg folic acid, 0.1 mg biotin, 2 mg vitamin thiamine, 3 mg vitamin B-6, 2.5 mg CoSO₄·7 H₂O, 0.2 mg Na₂SeO₃·5 H₂O, 1 mg KI, 400 mg FeSO₄·7 H₂O, 100 mg CuSO₄·5 H₂O; ^¥The mixture provided per kg diet: 0.5 g NaCl, 14.5 g CaCO₃, 21 g CaPO₄, 2 g MgO₂, 2 g; NaHCO₃, 16.5 g KHCO₃, 1 g CuSO₄·5 H₂O; ^ƚTylosine, Elanco.

Table 2. Apparent (AD-N) and true (TD-N) ileal nitrogen digestibility, dilution factor and ileal endogenous nitrogen losses (ENL) in pigs fed an enzyme-hydrolysed casein (EHC) and EHC+quebracho tannin (QT) diet determined over a 4-d period after ¹⁵N labelling.

Parameter	Diet		Significance level
	EHC	EHC+QT	Diet	^15N-method^ǂ	Day	Diet x Day
AD-N [%]	86.3 ± 2.89^§	60.8 ± 3.24	0.001	0.274	0.209	0.465
Dilution factor	0.71 ± 0.056	0.82 ± 0.063	0.233	0.278	0.001	0.661
ENL [g/kg DMI]^#	2.41 ± 0.405	8.69 ± 0.455	<0.001	0.248	0.209	0.078
ENL [g/d]	1.62 ± 0.222	5.93 ± 0.251	<0.001	0.111	0.210	0.081
TD-N [%]	95.1 ± 1.71	92.0 ± 1.93	0.273	0.278	0.003	0.434

^ǂThe effect of method of ¹⁵N administration was not significant, therefore LSMeans per method are not reported; ^§Values are least square means ± standard error; ^#DMI, dry matter intake.

Figure 1. Daily apparent nitrogen (N) digestibility (AD-N, panel a), dilution factor (DF, panel b), endogenous N losses (ENL, panel c) and true N-digestibility (TD-N, panel d) at the terminal ileum of pigs fed an enzyme-hydrolysed casein (EHC, □) and EHC+quebracho tannin (QT, ■) diet, determined over the four subsequent days directly after ceasing ¹⁵N labelling. Values are least square means ± standard error. Different subscripts within panels represent significant differences (p < 0.05) between diets (panels a and c) or days (panels b and d).

Table 3. Apparent (AD-N) and true (TD-N) ileal nitrogen digestibility, dilution factor and ileal endogenous nitrogen losses (ENL) in pigs fed an enzyme-hydrolysed casein (EHC) and EHC+quebracho tannin (QT) diet determined over the four subsequent days (non-steady-state) directly after ceasing ¹⁵N labelling and determined from the combined 3 d, 12 h collections and the 3 h collection on day 10 of Steendam et al. (Steendam et al. 2004, steady-state)^ǂ.

Parameter	Non-steady-state^§,#		Steady-state^¶
	Current study (3 h for 4d)		12 h for 3d^$		3 h on d10
	EHC	EHC+QT	EHC	EHC+QT	EHC	EHC+QT
AD-N [%]	86.3 ± 2.65^¤	61.0 ± 2.96	86.2 ± 2.65	70.0 ± 2.96	83.4 ± 2.65	60.0 ± 2.96
Dilution factor	0.71 ± 0.047	0.83 ± 0.055	0.53 ± 0.051	0.70 ± 0.052	0.47 ± 0.051	0.63 ± 0.052
ENL [g/kg DMI]^¥	2.41 ± 0.410	8.78 ± 0.483	2.06 ± 0.439	5.75 ± 0.457	1.93 ± 0.439	6.86 ± 0.457
ENL [g/d]	1.62 ± 0.239	5.96 ± 0.285	1.38 ± 0.260	3.93 ± 0.267	1.30 ± 0.260	4.67 ± 0.267
TD-N [%]	95.1 ± 1.79	92.3 ± 2.11	93.4 ± 1.92	91.2 ± 2.00	90.7 ± 1.92	85.1 ± 2.00

^ǂThe effect of method of ¹⁵N administration was not significant, therefore LSMeans per method of ¹⁵N administration are not reported; ^§3 h collections for 4 subsequent days post steady-state conditions; ^#Some LSMeans and SE values differ from Table 2 due to differences in the statistical models used; ^¶Data from Steendam et al. (2004); ^$As only values from period 2 of Steendam et al. (2004) were used, values differ slightly from the latter study; ^¤Values are least square means ± standard error; ^¥DMI, dry matter intake.

Table 4. Significance^ǂ,§ of the difference in apparent (AD-N) and true (TD-N) ileal nitrogen digestibility, dilution factor and ileal endogenous nitrogen losses (ENL) in pigs fed an enzyme-hydrolysed casein (EHC) and EHC+quebracho tannin (QT) diet determined over the four subsequent days (non-steady-state) directly after ceasing ¹⁵N labelling non-steady-state and determined from the combined 3 d, 12 h collections and the 3 h collection on day 10 of Steendam et al (Steendam et al. 2004, steady-state).

Parameter	Steady-state^# 12 h for 3d vs 3 h on d10		Non-steady-state^¶ vs
			Steady-state^# (12 h for 3d)		Steady-state^# (3 h on d10)
	EHC	EHC+QT	EHC	EHC+QT	EHC	EHC+QT
AD-N [%]	0.776	0.007	1.000	0.017	0.760	0.998
Dilution factor	0.786	0.731	0.032	0.274	0.003	0.033
ENL [g/kg DMI]^$	0.999	0.137	0.946	<0.001	0.834	0.007
ENL [g/d]	0.942	0.129	0.942	<0.001	0.825	0.007
TD-N [%]	0.708	0.052	0.919	0.991	0.214	0.029

^ǂTukey adjusted p-values; ^§The effect of method of ¹⁵N administration was not significant; ^#Determined from data of Steendam et al. (2004); ^¶3 h collections for 4 subsequent days post steady-state conditions; ^$DMI, dry matter intake.

Steendam CA, Verstegen MW, Tamminga S, Boer H, van ‘t End M, Verstappen B, WR C, Visser GH. 2004. Route of tracer administration does not affect ileal endogenous nitrogen recovery measured with the 15N-isotope dilution technique in pigs fed rapidly digestible diets. J Nutr. 134:3068–3075.

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Data availability statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.