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In vivo digestibility of kleingrass from fecal nitrogen excretion

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In vivo digestibility of kleingrass from fecal nitrogen excretion
J. Range Manage.
56: 52-55 January 2003
In
vivo digestibility of kleingrass from fecal nitrogen excretion
CARLOS M. FERRI, NESTOR P. STRITZLER, MIGUEL A. BRIZUELA, AND HORACIO J. PETRUZZI
First author is Graduate Student in the Program of the Doctorado en Ciencias Agrarias, Universidad Nacional de Mar del Plata, Argentina, and Research
Assistant, Facultad de Agronomia, Universidad Nacional de La Pampa, Argentina. Second and fourth authors are Research Animal Scientists, Instituto
Nacional de Tecnologia Agropecuaria, Anguil, La Pampa, Argentina, and third author is Professor, Facultad de Ciencias Agrarias, Universidad Nacional de
Mar del Plata, Argentina, and research scientist of the Comision de Investigaciones Cientificas de la Provincia de Buenos Aires, Argentina.
Abstract
It was proposed that the digestibility of organic matter (OMD)
can be estimated from the relationship between total fecal nitrogen (TFN, as a % of organic matter intake (OMI)) and fecal
nitrogen concentration (FNc) through the equation: OMD =1TFN / FNc. Two assumptions are critical to this equation, total
fecal nitrogen (as a % of OMI) is a constant and does not change
within a range of diet crude protein and fecal nitrogen concentration is proportional to digestibility of organic matter. The
objective of this study was to test if total fecal nitrogen (as a % of
OMI) remains constant over 3 feeding levels, and if fecal nitrogen concentration decreases with decreasing organic matter
digestibility of maturing forages. Total fecal nitrogen did not
change (P = 0.94) with feeding level, but increased (P < 0.05) with
evaluation period. The fecal nitrogen concentration correlated (r
= 0.60; P < 0.001) to digestibility of organic matter. The results
show that digestibility of organic matter cannot be estimated
from total fecal nitrogen, unless time of the year is considered.
Key Words: fecal index, nutritive value, N fecal, rams.
Simple estimates of nutritive value are often of little value if
there is no information regarding the amounts that will be consumed (Qrskov and Ryle 1990). The estimation of forage intake
in grazing systems is, perhaps, the most challenging question of
animal production.
The determination of individual intake can be obtained from
fecal production (F) and diet digestibility. The precision of organic matter digestibility (OMD) determination is affected by the
accuracy with which the forage samples represent the actual diet
of the animals (Burns et al. 1994, Coates and Penning 2000). The
use of the in vitro technique to estimate forage digestibility is
associated with several errors, including the effects of diet composition, between animal variations, intake level and physiological status of animals (Schneider and Flatt 1975). The fecal index
technique, alternatively, does not require diet samples, but only
routine chemical determinations of fecal material, and is currently
being used to estimate intake of wild and domestic herbivores
(Caughley and Sinclair 1996, Hodgman et al. 1996, Mesochina et
al. 1998). Fecal N concentration (FNc) has been widely used as a
fecal index (Le Du and Penning 1982), due to its easy determination and low variation within 24-hour periods (Bartiaux-Thill
1980).
Authors wish to thank Lic. G. Cendoya for technical assistance in data analysis.
Manuscript accepted 3 May 2002.
52
Resumen
Se ha propuesto que la digestibilidad de la materia organica
(DM0) puede ser estimada a partir de la relacion entre el
nitrogeno total fecal (NTF, como un % del consumo de materia
organica (CMO)) y la concentracion de nitrogeno fecal (cNF), en
la ecuacion: DMO = 1 - NTF / cNF. La aplicacion de esta
ecuacion se sustenta en dos supuestos, el nitrogeno total fecal
permanece constante dentro de un rango de proteina bruta de la
dieta y la concentracion de nitrogeno fecal es proporcional a la
digestibilidad de la materia organica. El objetivo de este estudio
fue determinar si el nitrogeno total fecal (como un % del CMO)
permanece constante sobre tres niveles de alimentacion y si la
concentracion de nitrogeno fecal disminuye con la disminucion
de la digestibilidad de la materia organica. El nitrogeno total
fecal no se modifico (P = 0,94) con el nivel de alimentacion, pero
incremento (P < 0,05) con el periodo de evaluacion. La concentracion de nitrogeno fecal se correlaciono (r = 0,60; P < 0,001)
con la digestibilidad de la materia organica. Los resultados
demuestran que no es posible estimar la digestibilidad de la
materia organica, a partir de la utilizacion del nitrogeno total
fecal, sin la consideracion del periodo del ano.
Lancaster (1949a,1949b) proposed that OMD can be estimated
from the relationship between total fecal nitrogen (TFN, as a % of
organic matter intake (OMI)) and FNc through the equation: OMD
= 1- TFN/FNc. Two assumptions are critical to this equation: (1)
TFN (as a % of OMI) is a constant and does not change within a
range to diet crude protein, and (2) FNc is proportional to OMD.
The objective of this study was to test: a) if TFN (as a % of OMI)
remains constant over 3 feeding levels, and b) if FNc decreases
with decreasing organic matter digestibility of maturing forages.
Materials and Methods
The study was performed at the Facultad de Agronomia,
Universidad Nacional de La Pampa, Santa Rosa, La Pampa,
Argentina (36° 46' S, 64° 16' W, 210 m ASL), during 1995. The
forage was obtained from a pasture sown in spring 1994, of pure
Kleingrass (Panicum coloratum L.) cv. Verde. At the beginning
of each growth season (early October), the pasture was cut at 5
cm above ground to eliminate all standing dead forage, and fertilized with 60 kg urea/hectare.
Measurements of intake and digestibility were carried out during 4 experimental periods (I to IV), each one lasting for 16 days,
with 11 days of adaptation and 5 days of data collection.
Beginning day of each period was: 21 March, 2 May, 13 June,
JOURNAL OF RANGE MANAGEMENT 56(1) January 2003
and 25 July, 1995. This was done to obtain
forage of different nutritive value for each
trial.
Seventeen Pampinta rams in each period
(51.3 ± 5.1 kg, 56.7 ± 2.9 kg, 66.4 ± 11.7
kg and 74.0 ± 6.7 kg in period I to IV,
respectively) were grouped by weight, and
then randomly assigned within weight
group, to 3 feeding levels (treatments): 0.5
maintenance level (feeding level = L1; 5
rams), 1.0 maintenance level (feeding
level = L2; 5 rams), and ad libitum, 1.5
the actual intake of 2 days previous to
feeding (feeding level = L3; 7 rams).
Maintenance level was estimated according to the energy requirements (AFRO
1993) of rams, and the in vitro DM
digestibility of the forage (Stritzler et al.
1996). All animals were dewormed 15
days before the beginning of the study and
housed in individual pens under continuous light, with free access to water.
The forage, accumulated from the
beginning of the growing season, was cut
by sickle at 5 cm above ground, before
each feeding time (0800 and 1730 hours).
Samples of offered forage were obtained
before feeding. Refused forage of each
experimental animal was removed from
the manger every day, and weighed immediately. The animals were fitted with feces
bags, secured to harnesses. Total fecal
production was measured for each animal
by weighting feces twice daily. Samples of
forage offered and refused, and feces produced were obtained twice a day, dried at
55° C for 72 hours and ground through a
1-mm screen in a Wiley mill.
Organic matter intake (OMI) was determined by difference between offered and
refused OM of food (Burns et al. 1994). In
vivo organic matter apparent digestibility
(OMD) was estimated by the method of
total fecal collection, using the following
equation
1:
(1)
OMD = [ 1- F / OMI] x 100
Where:
OMD = In vivo OM apparent digestibility,
F = daily OM feces output, and
OMI = OM intake.
Chemical analyses and in vitro OM
digestibility
Dry matter was determined at 105° C
for 48 hours, and ash content was measured gravimetrically by igniting samples
in a muffle furnace at 550° C for 12 hours
in forage and fecal samples. Aliquots of
dried samples were analyzed for total N
concentrations by the semi-micro Kjeldahl
procedure (2040 Digestion Unit and 1026
Distilling Unit, Tecator, Hog anas,
Table 1. Chemical composition and in vivo organic matter digestibility of deferred Kleingrass at 4
periods of evaluation.
Period'
I
II
III
IV
-------------------------------- (%) -----------------------------Ash
8.4
Crude protein
9.7
Neutral-detergent fiber
65.4
Acid-detergent fiber
37.7
Acid-detergent lignin
5.2
In vivo organic matter digestibility 56.0
'I = 21 March to 6 April;
II = 2 to 18 May; III
8.5
6.8
69.4
39.1
3.7
54.3
7.4
6.6
71.1
40.0
4.9
48.6
=13 to 29 June; IV = 25 July to
Sweden). Forage samples were additionally analyzed for crude protein (CP, N x
6.25), neutral-detergent fiber (NDF), aciddetergent fiber (ADF), and acid-detergent
lignin (ADL), as described by Van Soest
and Robertson (1985). In vitro organic
matter digestibility (IVOMD) was estimated as described by Tilley and Terry (1963)
and modified by Alexander and McGowan
(1966). Samples were incubated at 39° C
for 48 hours in a rumen fluid-artificial
saliva solution, followed by an additional
48-hour period in 20% hydrochloric acidpepsin solution. Inoculum for the procedure was obtained from rumen cannulated
steers fed alfalfa hay. The in vitro values
were adjusted by in vivo standards in each
batch. The IVOMD values of consumed
forage were estimated for each experimental animal, from the amount of OM and
Statistical analysis
The trial was carried out within a ran-
domized block design, with a factorial
arrangement of treatments. To test for differences in total fecal nitrogen as influenced by feeding levels and periods, the
following model was used: Y = mean +
block + period + levels + period x levels +
5.9
70.6
40.5
3.6
51.0
10 August.
error, where Y = total fecal nitrogen (as a
% of OMI); period = Periods I to IV, replications of feeding trial, in which 17 rams,
different between periods, were fed at 3
different levels (Ll, L2, and L3), as
explained above, and error = residual error
(Steel and Torrie 1980). Statistical significance was determined using the GLM procedure (SAS Institute Inc. 1999). Mean
separations were made using LSD at P =
0.05. Simple correlation coefficients
between fecal nitrogen concentration and
organic matter intake were determined
using PROC CORR procedure of SAS
Institute Inc. (1999). Paired t-test compared in vitro organic matter digestibility
and predicted in vivo organic matter
digestibility from total fecal nitrogen and
fecal nitrogen concentration.
IVOMD of offered and refused forage
(Meijs et al. 1982).
The total fecal nitrogen (as a % of OMI)
was estimated from the nitrogen concentration, feces production and OMI.
7.6
Results and discussion
The chemical composition and in vitro
organic matter digestibility of the forage
offered in each evaluation period are
shown in Table L All analyses were performed on pooled samples of all days of
data collection. The feed quality declined
with evaluation period (from I to IV), but
the highest differences were found
between periods I and II (Table 1).
The interaction between feeding level
and evaluation period, for total fecal nitro-
Table 2. Total fecal nitrogen (as a % of OMI) at 3 feeding levels and 4 evaluations periods.
Period'
Feeding
Level'
II
I
of OMI) -------------------------------------
Ll
L2
L3
Mean3
SEM
0.569
0.523
0.523
0.627
0.592
0.605
0.537
0.608b
'I = 21 March to 6 April;
0.016
II = 2 to 18 May; III
L1 = 0.5 maintenance, L2
=13 to 29 June; IV = 25 July to
10 August.
=1.0 = maintenance, L3 = ad libitum.
3Means followed by a common superscript are not significantly different at (P > 0.05).
JOURNAL OF RANGE MANAGEMENT 56(1) January 2003
53
each period were also obtained; they were
all significant (P < 0.05) but not high (r =
0.77, 0.67, 0.50, and 0.66 for period I, II,
III and IV, respectively), due to large
between experimental animals variations
of total fecal nitrogen excretion.
Although fecal nitrogen concentration
increased with organic matter digestibility,
the correlation across the 4 periods was
not high. This would allow us to infer that
total fecal nitrogen, as determined in this
study, changes with period. In other
words, for a given value of fecal nitrogen
2.5
2.0
1.5
1.0
concentration obtained in different periods, the organic matter digestibility would
be different. When analyses were run
(%)
within each experimental period, the conrelations were significant.
Fig. 1. Relationship between the fecal nitrogen concentration (FNc) and digestibility organic
The estimations of digestibility by the in
matter. Triangles correspond to 21 March to 6 April, circles 2 to 18 May, squares 13 to 29
vitro technique and the fecal N index were
June, and rhombus 25 July to 10 August period evaluation.
not different (P > 0.05; Table 3) in 3 of the
4 periods. The means of both methods
gen, was not significant (P = 0.70; Table site (rumen or cecum-colon) (Orskov et al. across periods were different (P < 0.05).
1972) and the digestion extent (Arman et However, this difference was only of
2). The total fecal nitrogen did not change
(P = 0.94) with feeding level. This finding
al. 1975). When forages of similar nutri1.5%.
is in agreement with the results found by tive value are considered, total fecal nitroThe comparison of indirect techniques
Lancaster (1949a) and Barrow and gen (as % of OMI) keeps constant with to predict in vivo digestibility of conLambourne (1962) and confirms feeding level because microbial N yield is sumed forage presents limitations. The
Lancaster's first assumption that total propotional to intake.
main problem of the in vitro technique is
The total fecal nitrogen, however, the collection of samples representative of
fecal nitrogen (as a % of OMI) is constant
increased (P < 0.05) from evaluation peri- the diet consumed by the animal. The
and directly proportional to intake.
Insoluble N in feces comes largely from ods I to III. It seems likely that this fecal N index technique requires a feeding
feed (Orskov 1982), although a small con- increase is associated to changes in diges- trial to estimate total fecal nitrogen (as %
tribution of N bound to indigestible cell tion site; according to Thomas (1988), of OMI), using the same forage to be
wall of rumen bacteria should be also with good-quality forages, 5-15% of cell grazed. The nitrogen fecal concentration is
taken into account. The soluble N present wall carbohydrates are fermented in the then assessed in fecal samples from the
in feces is mostly microbial, and includes
cecum-colon. As forages mature, this pro- grazing animals, and diet digestibility can
considerable ammonia produced by portion increases; Hogan et al. (1969) be predicted from the equation: OMD = 1
cecum-colon bacteria (Van Soest 1994). found that up to 25% of the total digestion - TFN I NFc. The usefulness of this techAlthough much of the fecal N may origi- of low quality grasses occurs in the nique is restricted to situations where the
nally have been endogenous, before excre- hindgut. Rumen microbes, but not colon- forage to be grazed can also be cut to run a
tion it has been converted to microbial N cecum microbes, are exposed to the host feeding trial simultaneously. The main
through fermentation in the hindgut animal's enzymes (Mason 1969); there- advantages of the technique are that the
(Mason 1969). The amount of excreted N fore the fermentation site might affect the analytical requirements are low and simdepends, partially, on the microbial N amount of total fecal nitrogen (Qrskov et ple, and does not require diet sampling.
yield (Van Soest 1994), on the digestion al. 1972). The increasing proportion of
Table 3. Estimated organic mater digestibility (OMD) of consumed
herbage using either in vitro organic matter digestibility or fecal N
index in Periods I to IV (n =17).
Period'
I
II
III
IV
Media
In vitro OMD
Fecal N index2
OMD = (1- TFN I FNc)
--------------------------- (%) ------------------------59.5b
54.6a
49.3a
51.5a
53.8b
*
100
62.5a
56.3a
50.31
51.9a
55.3a
Means in the same row followed by a common superscript are not significantly different
at (P > 0.05).
'I = 21 March to 6 April; II = 2 to 18 May; III = 13 to 29 June; IV = 25 July to 10
August.
ZTFN, total fecal nitrogen; FNc, fecal nitrogen concentration.
feed carbohydrates
in
fermented
cecum-colon would
affect mostly the
soluble N in feces
(Qrskov et al.
1972), whilst the
insoluble N should
not be changed.
The fecal nitrogen
concentration was
correlated with
matter
organic
digestibility (r =
0.60; P < 0.001;
Fig. 1) across all 4
p e r i o d
s.
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