Biotechnology in Animal Husbandry 26 (5-6), p 339-346, 2010 ISSN 1450-9156
Publisher: Institute for Animal Husbandry, Belgrade-Zemun UDC 636.087.7
DOI:10.2298/BAH1006339V
THE INFLUENCE OF REPLACING SLOW WITH RAPID
STARCH IN GROWING RAMS’ DIETS ON THE LEVEL
OF RUMEN MICROBIAL PROTEOSYNTHESIS
A. Vasilachi
1
, S. Pop
1
, C. Dragomir
1
, M. Vlassa
2
, M. Filip
2
1
National Research & Development Institute for Animal Biology and Nutrition, Calea Bucureşti no.
1, 077015 Baloteşti, Ilfov, Romania
2
Babes-Bolyai University, Raluca Ripan Institute for Research in Chemistry, 30 Fantanele Street, RO-
400294 Cluj-Napoca, Romania
Corresponding author: andreea.vasilachi@ibna.ro
Original scientific paper
Abstract: The objective of the study was to estimate the level of microbial
proteosynthesis in sheep, following the replacement of a classical ingredient (corn)
with a rapidly fermentable energy source (barley), when protein ingredient of the
compound feed is highly degradable (rapeseed meal).The diets were tested on two
groups of four Merinos rams each, weighing 50-55 kilos. Regular procedure for in
vivo digestibility tests was used and urine was collected for determination of purine
derivatives concentrations. The consumption of the two diets led to similar
nutritional supplies: 1.26-1.29 MFU, 124-129 g IDPN, 112-118 g IDPE; the groups
being distinguish only in terms of the dynamics of energy availability at the
ruminal level. The amount of purine derivatives excreted in urine were 12.58
mmols/day in the corn group and 9.49 mmols/day in the barley group;
consequently, the rumen microbial proteosynthesis was estimated at 43.11 g
IDMP/day for the corn group and 31.3 g IDMP/day for the barley group (P=0,396).
It is concluded that the effect of synchronizing the energy and protein dynamics in
barley group was counteracted by the fact that energy and protein availability were
limited to the first hours after administration of the compound feed, when the
capacity of the ruminal microorganisms to grow was probably exceeded. In order
to maximize their growth potential, it is necessary to extend the period of
synchronized ruminal availability of energy and protein.
Key words: microbial protein, rumen, starch, barley, corn
Introduction
The capacity to accurately predict and to stimulate microbial protein supply is
of prime importance in ruminant nutrition. It is unanimously acknowledged that
A. Vasilachi et al.
340
ruminants use very inefficient the nitrogen from common diets. The usual strategy
aiming to ensure high animal performances is to feed diets exceeding protein
requirements but, as the efficiency of its conversion to animal products is low, the
excess nitrogen is excreted toward environment.
One of the reasons of this low efficiency is the lack of synchronicity of energy
and protein supplies, which can occur at the level of the whole diet (difference
between microbial protein allowed by nitrogen and that allowed by energy) or at
the level of the dynamics of energy and protein availability in the rumen. The first
one is more obvious, as it can be estimated within modern feeding systems, such as
IDP (Verite, 1988); the second one requires taking into account more factors, such
as rate of protein degradation, fermentability of energy, passage rate, etc. Because
microorganisms digest the largest part of the ingested feeds, the interaction
between carbohydrate and protein rumen metabolism is particularly strong. If there
is a deficiency or inefficient utilization of the protein, the digestibility of
carbohydrate can also decrease. If there is insufficient carbohydrate to match
protein supply, nitrogen can be lost as ruminal ammonia (Nocek and Russell,
1988).
Therefore, an approach to ensure better use of dietary nitrogen would be to
match the rapid or slower fermentable energy ingredients with their corresponding
protein ingredients in order to provide a simultaneous release of the nutrients and
simultaneous availability to rumen microorganisms. Thus, diets where protein
source is more degradable may require rapidly fermentable energy in order to
ensure synchronicity of protein and energy supply for microbial proteosynthesis.
The most important source of nonstructural carbohydrates is represented by
grains, corn and barley being the predominant grains of Europe. The starch source
may be of importance, because ruminal fermentation rates vary over a wide range,
with barley being more rapidly fermented in the rumen than corn grain but less
energy dense (Yang et al., 1997).
The objective of this study was to estimate the level of microbial synthesis in
growing rams, when a classical ingredient of the diet (corn) is replaced by a source
of rapidly fermentable energy (barley), while protein supply in the compound feed
is ensured by a more degradable ingredient (rapeseed meal).
Materials and Methods
Eight Merinos rams, weighing 50 – 55 kg, housed in individual digestibility
cages for sheep, allowing separate collection of urine and feces, were assigned
randomly to two groups. During 10 days of adaptation and 6 days collection
period, the animals were fed diets consisting of meadows hay (medium quality)
and ground compound feed based either on corn (group 1) or on barley (group 2),
The influence of replacing ...
341
formulated according to Burlacu, 1996. The structure of the compound feed is
shown in Table 1.
The diets were fed in one meal/day (8:30 a.m.), the compound feed preceding
the meadows hay and the animals had free access to the drinking water.
Consumption of hay and compound feeds was recorded daily and individually.
Feeds samples were taken for proximal analysis, in order to estimate nutritive
values of consumed diets.
Table 1. Structure of compound feed
Group 1
(corn based diet)
Group 2
(barley based diet)
Corn, % 70.8 -
Barley, % - 79.1
Wheat bran, % 3.5 2.4
Rapeseed meal, % 20.9 14.6
Calcium carbonate, % 3.5 2.6
Minerals & vitamins premix, % 0.9 0.9
Salt, % 0.4 0.4
Urine was collected according to Chen and Gomez (1992). Five-liter bins were
used for individual and daily urine collection; sulfuric acid 10 N was used in order
to maintain a low pH of urine samples. According to the authors of the method
(Chen and Gomez, 1992), excess of sulfuric acid does not adversely affect the
analysis of purine bases. After measuring the volume of urine collected over 24
hours, approximately 10% of the total volume was retained for each animal in
plastic containers with screws that were placed in refrigerator, the rest being
discarded. The daily retained volumes were pooled every two days; therefore for an
experimental period of 6 days 3 samples for each animal were taken, leading to 12
observations per group. Of the two days pooled samples, 50 ml were placed in vials
and frozen until analysis of purine derivatives.
Allantoin, uric acid, xanthine and hypoxanthine were assessed using a HPLC
method. A high-performance liquid chromatograph JASCO - 980 was used and
processing of chromatograms was performed with CHROMPASS software. Purine
derivatives standards were prepared with ultrapure water and 1N sodium hydroxide
solution was added until pH reached 7.8. Elution flow was 1 mL / min, detection
was performed at 218 nm, column temperature was 25°C and filtration of samples
was done on Teflon filters. Before determination of purine derivatives the urine
samples were thawed. After checking whether the pH level is within the limits of
the method, samples were stabilized with sodium hydroxide, passed through a 0.45
micrometer filter and injected into the HPLC column.
A. Vasilachi et al.
342
Results and Discussion
Whereas the meadows hay intake was about the same in both groups, the
barley group ingested more compound feed than the corn group. However, the
consumption of the two diets led to similar nutritional contributions: 1.26–1.29
mFU/day, 124–129 g IDPN/day, 112–118 g IDPE/day (Table 2) - the experimental
groups being distinguished only in terms of degree of synchronization of energy
and protein availability at ruminal level.
Table 2. Average consumption and nutritive supply of the experimental diets
Group 1
(corn based diet)
Group 2
(barley based diet)
Consumption of diet ingredients (g/head/day)
Compound feed 563.54 ± 79.15 701.94 ± 61.11
Meadows hay 942.13 ± 118.26 899.06 ± 76.67
Daily nutrient intake:
DM, (g/day) 1294.6 1375.5
mFU/day 1.26 1.29
IDPN, (g/day) 128.5 123.7
IDPE, (g/day) 117.6 111.7
Ca, (g/day) 12.06 11.46
P, (g/day) 6.11 6.82
DM = dry mater; mFU=meat feed units; IDPN = intestinally digestible protein allowed by
nitrogen supply; IDPE = intestinally digestible protein allowed by energy supply
Based on the urine volume and the concentrations of individual purine
derivatives in urine samples, the total amount of excreted purine derivatives (PD)
was calculated (Table 3).
Table 3. Daily output of urine and purine derivatives
Corn Group Barley Group
Specification
xSx ±
xSx ±
Urine volume, (ml) 761.875±58.9 556.450±41.8
Total allantoin, mmols/d 9.828±1.8 7.445±2.3
Total uric acid, mmols/d 1.778±0.2 1.195±0.4
Total xanthine, mmols/d 0.235±0.0 0.248±0.1
Total hipoxanthine, mmols/d 0.735±0.1 0.603±0.2
Total purine derivatives, mmols/d 12.575±2.0 9.490±2.9
Tendency for higher excretion of total purine derivatives was observed in
animals that were fed the corn-based ration, comparing to those fed barley-based
The influence of replacing ...
343
ration: 12.57 versus 9.49 mmols/day (P=0.396). The PD concentrations obtained in
the present study are lower than concentrations reported for sheep by Richardson et
al. (2003) (ranging from 13.1 to 16.4 mmols/day) when a barley based ration is
used.
Table 4 show the daily production of microbial protein, calculated from the
amounts of purine derivatives excreted in urine using the systems of equations
proposed by Chen and Gomez (1992). On this basis, the quantities of synthesized
microbial nitrogen were estimated at 10.78 g/d and 7.82 g/d (for corn and barley
diets, respectively) leading to an average production of 43.11 g/d microbial protein
in group 1 (corn based diet) and only 31.26 g/d in group 2 (barley based diet).
Table 4. Daily production of microbial protein
Corn Group Barley Group
Specification
xSx ±
xSx ±
BW, Kg 52.75±2.7 54.08±1.1
Total 12.58±2.0 9.49±2.9
Endogenous 0.12±0.1 0.46±0.2
Purine derivatives in
urine, mmols/d
Exogenous 12.45±2.1 9.03±3.1
Purine derivatives in microbes, mmols/d 14.83±2.5 10.75±3.7
Microbial N, g/d 10.78±1.8 7.82±2.7
Microbial CP, g/d 67.36±11.3 48.85±16.8
IDMP, g/d 43.11±7.2 31.26±10.8
These results were contrary to the expectations, as in the barley group the
dynamics of rumen availability of energy (supplied by barley) and protein
(supplied by rapeseed meal) were better synchronized than in the corn group. In the
later, the rapidly degradable source of protein (rapeseed meal) was associated with
a slowly fermentable source of energy.
It is known that rumen-produced ammonia exceeding the capacity of ruminal
microbes to incorporate it in the microbial biomass is lost (Lobley et al., 1995). It is
possible that, in the barley group, the peaks of energy and nitrogen early
availability exceeded the growth capacity of microbes in first post-prandial hours.
Another factor which may have interfered is the decrease of rumen pH for a
certain period after the meal, which might had negative influence on microbial
proteosynthesis.
The daily production of microbial N (10.78 g/d and 7.82 g/d) was greater than
that recorded by Witt et al. (1999), who reported a mean value of 6.0 g/d, but was
similar to those reported by Henning et al.(1993), Sinclair et al. (1993, 1995) and
Richardson et al. (2003) in sheep fed at a similar level of intake.
Although there is general agreement that energy source is the primary
influence on microbial protein production (Stern et al., 1978; Henning et al., 1993;
