Revista Computadorizada de Producción Porcina
Calorific content of pig urine/Contenido calorífico de orina de cerdos
Volumen 12 (número 1) 2005
AN APPROACH TO THE RELATIONSHIP BETWEEN N AND ENERGY IN URINE OF PIGS FED SUGAR CANE
PRODUCTS
J. Ly
Instituto de Investigaciones Porcinas, Gaveta Postal No. 1, Punta Brava, La Habana, Cuba
email: iip@enet.cu
SUMMARY
Data from a total of 17 trials for determining balance of N and energy using 78 female growing pigs (20-50 kg were used to determine the
calorific value of urinary N. In all trials the sources of energy were sugar cane products, including sucrose, syrup off and molasses. All
diets contained 16% crude protein (Nx6.25) and daily feed intake was 0.10 g DM/W 0.75.
It was found a highly significant (P<0.001) and a direct, very strong (R2 = 0.919) correspondence between the urinary concentration of N
(in g/dL) and its calorific value. The regression coefficient and the constant value (x, 0) were 54.309 kjoule/g N and 1.789 kjoule/dL
respectively. In data from trials using starch or cereals as source of energy, the calorific value of N accounted for between 41.46-42.87
and 42.98 kjoule/g N, and this index was higher when sugar and molasses were used (refined sucrose, 56.05; syrup off, 54.11; high-test
molasses, 58.66-67.41 and molasses type A, B and C or final, 62.96, 71.33-73.30 and 86.59-90.93 kjoule/g N in this same order).
It is suggested that the increase in the calorific value of the urinary N appears to be a consequence of the presence in urine of fructose
and probably non nutritive compounds present in molasses, which are excreted after being absorbed to some extent.
Key words: urine, energy, nitrogen, sugar cane molasses, pigs
Short title: Calorific content of pig urine
UNA APROXIMACION A LA INTERRELACION DEL N Y LA ENERGIA EN ORINA DE CERDOS ALIMENTADOS CON
PRODUCTOS DE CAÑA DE AZUCAR
RESUMEN
Se usaron datos de 17 pruebas de balance de N y energía en las que se utilizaron 78 cerdas en crecimiento (20-50 kg) para determinar
el valor calorífico del N urinario. En todas las pruebas la fuente de energía fue productos de caňa de azúcar. Todas las dietas contenían
16% de proteína bruta (Nx6.25) y el consumo diario de alimento igual a 0.10 g MS/W 0.75.
Se halló una correspondencia altamente significativa (P<0.001), directa y muy estrecha (R 2 = 0.919) entre la concentración urinaria de N
(en g/dL) y su valor calorífico. El coeficiente de regresión y la constante (x, 0) fueron 54.309 kjoule/g N y 1.769 kjoule/dL. Mientras que
en las pruebas con almidón o cereales como fuente de energía el valor calorífico del N estuvo entre 41.46-42.87 y 42.98 kjoule/g N, con
el azúcar y con las mieles fue más alto (azúcar refinado, 56.05; sirope final, 54.11; miel rica, 58.66-67.41; mieles A, B y final, 62.96,
71.33-73.30 y 86.59-90.93 kjoule/g N en ese mismo orden).
Se sugiere que el incremento en el valor calorífico del N urinario parece estar originado por la presencia en la orina de fructosa y
probablemente compuestos no nutritivos presentes en las mieles, que se excretan en cierta medida por la orina después de ser
absorbidos.
Palabras claves: orina, energía, nitrógeno, mieles de caňa de azúcar, cerdos
Título corto: Contenido calorífico de orina de cerdos
INTRODUCTION
Since the very early report of Rubner (1902) and other
from Eriksson (1950) and Elliot and Loosli (1959), several
investigations have been advanced in order to establish
the calorific value of urine from different farm animals. The
efforts have been directed to obtain a reliable predicting
equation in order to calculate the gross energy in urine,
and therefore, avoid the tedious and time-consuming
procedure of urine preparation for combustion in a bomb
calorimeter.
Reports from Street et al (1964) and Paladines et al (1964)
for cows and sheep followed the earlier results from Elliot
and Loosli (1959) and afterwards, other articles have been
published on this subject, for example, predicting
equations concerning rats (May and Nelson 1972) and
rabbits and sheep (Sanz et al 1987). In the particular case
of pigs, some reports are available related to the energy
content of urinary N (Fuller and Cadenhead 1967;
Simeček 1968; Morgan et al 1975; Hoffmann and Klein
1980).
35
Revista Computadorizada de Producción Porcina
Calorific content of pig urine/Contenido calorífico de orina de cerdos
Volumen 12 (número 1) 2005
The present report provides information related to this
subject.
Values from a total of 17 sets of data from trials conducted
in our laboratory for determining balance of N and energy
using 78 female growing pigs (20-50 kg) were used to
estimate the calorific value of urinary N. In all considered
experiments the major source of energy was sugar
products: raw and refined sucrose, syrup off, sugar cane
high-test molasses, intermediary molasses of type A and
B, and final molasses.
All diets contained 16% crude protein (Nx6.25) from either
torula yeast or soybean meal. Details related to routine
work concerning the balance trial in this laboratory have
been described elsewhere (see for example, Ly et al
1998). In all cases, daily feed intake was 0.10 kg
DM/W 0.75.
Il all cases the calorific value was determined in aliquots of
concentrated urine by drying the samples prepared in
poliyethylene bags at room temperature (25oC) in vacuum
dessicators over concentrated sulfuric acid, following
recommendations of Nijkamp (1969). An adiabatic bomb
calorimeter was used for measurements of heat of
combustion by triplicate.
In all cases, data were adjusted to kjoule, assuming that 1
kcal = 4.1855 kjoule (Brouwer 1965). The urinary N
concentration was determined by duplicate in thawed,
untreated samples by the well known Kjeldahl procedure
(AOAC 1990).
Regression analysis was conducted to investigate the
possible relationship between N and energy content in
pig’s urine (Steel and Torrie 1980). The Harvey (1990)
software was employed for computation purposes.
It was found a highly significant (P<0.001) and direct
correspondence, very strong (R2 = 0.919), between the urinary
concentration of N (in g/dL) and its calorific value (figure 1).
The regression coefficient and the constant value (x, 0) were
54.309 kjoule/g N and 1.789 kjoule/dL respectively (S yx = ± 2.6).
50
45
40
Urine energy, kjoule/dL
MATERIALS AND METHODS
Table 1. Some calorific values of urinary N (in kjoule/g)
in growing pigs fed different sugar cane
products
Type of feed
Urinary N
Source of data
Maize starch1
42.87
Ly (1998)
Cassava starch1
41.46
Figueroa et al (1990)
Maize meal1
42.98
Pérez et al (1988)
Raw sucrose
52.51
Figueroa et al (1990)
Refined sucrose
56.05
Ly (1998)
Syrup off
54.11
Ly et al (2001)
High-test molasses
67.41
Pérez et al (1988)
Molasses type A
62.96
Figueroa et al (1990)
Molasses type B
71.33
Macías and Ly (1995)
Molasses type B
73.30
Pérez et al (1988)
Final molasses
86.59
Ly (1998)
Final molasses
90.93
Pérez et al (1988)
1
Not included in the regression equation
35
30
25
20
y = 1.789 + 54.309 x
R2 = 0.919
15
10
5
RESULTS AND DISCUSSION
0
0
In trials using cereals as source of energy, the calorific
value of N accounted for 41.46 kjoule/g N, and this index
was higher when sugar and molasses were used (refined
sucrose, 56.05; high-test molasses, 67.41 and molasses
type A, B and C or final, 62.96, 71.33-73.30 and 86.5990.93 kjoule/g N in this same order).
A summary of these results is presented in table 1. As a
rule, all products derived from sugar cane molasses
determined a high calorific value in the examined samples,
as opposed to those values related to maize-based feeds.
0,2
0,4
0,6
0,8
1
Urine N, g/dL
Figure 1. Linear relationship of urine N to urine
energy in pigs fed sugar cane products
It could be assumed that there was a trend of the calorific
value of the urine of pigs fed sugar cane products to vary
in a wide range of values, although this range is in
agreement with other data from other farm animals (table
2).
36
Revista Computadorizada de Producción Porcina
Calorific content of pig urine/Contenido calorífico de orina de cerdos
Table 2. Some data concerning the calorific value
of urinary N (in kjoule/g) in several farm
animals
Animal
Urinary Source of data
species
N
Cow
58.5
Street et al (1964)
Rat
42.3
May and Nelson (1972)
Rabbit
56.1
Sanz et al (1987)
Sheep
56.7
Sheep
76.7
Paladines et al (1964)
Sheep
61.0
Street et al (1964)
Swine
52.6
Fuller
and
Cadenhead
(1967)
Swine
23.91
Nehring et al (1963)
Swine
33.41
Just Nielsen (1970)
Swine
40.7
Morgan et al (1975)
Swine
38.3
Swine
33.5
Jentsch et al (1991)
Swine
37.6
Swine
54.31
This report
1
Value of the regression coefficient
It was evident that an increase occurred in calorific value
of urine from pigs consuming high proportions of sugar
cane products in the diet, if compared to conventional or
starch based diets. In connection to possible causes for
urinary fluctuations in the calorific value of N, Cook et al
(1952) reported that winter range plants provoked a
noticeable increase in the heat of combustion of sheep
urine, due to unmetabolizable essential oils consumed by
the animals.
It is apparent that some factors may influence the calorific
value of urinary N in pigs, too. As illustration, Jentsch et al
(1991) observed that diets very high in crude protein
content (44-47%) could determine a slight increase in the
calorific content of urine’s N as compared to a rather low
crude protein content (17-24%), values being moving from
33.5 to 37.6 kjoule/g N (table 2). On the other hand,
Morgan et al (1975) claimed that a slight decrease in the
gross energy to N ratio took place in urine when pig were
fed 16 and 20% crude protein-based conventional diets,
40.75 and 38.36 kjoule/g, respectively, as calculated by
regression analysis. In the particular case of pigs fed sugar
cane products, it has been suggested that the increase in
the calorific value of the urinary N appears to be a
consequence of the presence in urine of fructose (see for
example, Ly and Macías 1979; Ly 2001) and probably non
nutritive compounds present in molasses (McLaren 1950;
Ly et al 1985), should be excreted after being absorbed, to
some extent. In this respect, Cook et al (1952) reported
high values for the heat of combustion in urine of sheep
fed certain essential oils which not being metabolized,
were eliminated by the kidney route. This last hypothesis
should be of interest to explore.
ACKNOWLEDGEMENTS
The author would like to express his gratitude to Mrs. Nidia
Victores for her technical assistance in the conduction of
the N analyses.
Volumen 12 (número 1) 2005
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