Animals
and Housing
Six Cotswold barrows with an average initial
BW of 52.5 ± 2.7kg were obtained from Glenlea
Research Farm and housed in individual metabolism crates (118 cm x 146 cm) with
smooth transparent plastic sides and tender foot floors in a temperature
controlled room (200C). After a 7-day adjustment period to their
environment the pigs were surgically fitted with simple T-cannulae
at the distal ileum according to the procedures of Sauer et al. (1983). Feed was removed in the afternoon of the day
preceding the surgery. After each surgery the pig was immediately returned to
its crate. They were allowed 11-days to recover and regain their pre-surgery
appetites. On the 1st day of surgery the pigs were fed 50g of their
commercial grower diet in the evening after regaining their consciousness and
thereafter feed allowance was gradually increased by 50g by the next feeding
daily until they attained their pre-surgery appetites fully. Pigs had unlimited
access to water. A day prior to and three days after surgery each pig received Excenel (Upjohn company, Orangeville, Ontario, Canada)
intramuscularly at a dose of 1 ml/17 kg live weight. Pigs were cleaned twice
daily at 8:00 h and 16:00 h except the two days of digesta
collections with Hibitane skin cleaner (Ayerst Laboratories, Division of Wyeth-Ayerst Canada Inc.
Montreal, Canada) and then skin smeared with zincoderm
(Rhone Merieux Canada Inc.) to minimize skin
irritation due to the emissions of digesta around the
cannula. The University of Manitoba Animal Care Committee approved the use of
the pigs and experimental procedure of study and pigs were cared for according
to the guidelines of the Canadian Council on Animal Care (CCAC, 1993).
Experimental
Design and General Conduct of Study
The experiment was designed and carried out
as a replicated 3 x 3 Latin Square Design (LSD). However, the experiment was
initially planned to be 6 x 6 LSD with the six simple T-fitted ileal cannulae pigs involving the
three intact DON-contaminated barley diets and their pearled counterpart diets.
However, the experiment was re-designed to a replicated 3 x 3 LSD because the
pigs refused to ingest the intact-DON barley diets even the low 1.2ppm DON
diet; confirming the anorectic effects of DON in swine nutrition.
Each
experimental period lasted 8-days. Pigs received their daily feed allowance in
two equal portions at 08:00 and 16.00 h, respectively. Feed intake was closely
monitored especially for orts to be able to measure actual feed intake. Daily
feed allowance was maintained at 2.6 x daily maintenance energy requirements
based on the BW of the pigs at the beginning of each experimental period
(Agricultural Research Council, 1981). Pigs had unlimited access to water at
all times throughout the study period. During study, at the end of each period animals
were usually removed from their individual metabolism crates to individual
exercise pens for three days during which they were fed standard commercial
grower diet. This was necessary to neutralize any possible stress the animal
might have experienced due to confinement in the crates. Pigs were usually
weighed before the beginning of each of the periods consisting of 8-days of
4-days adaptation period to diets, 2-days of fecal collections and 2-days of digesta collections, respectively. This means during any
one period, pigs were fed their respective diets from day 1 to 4 (adaptation
period to diet), followed by 2-days (d 5 and 6) fecal collections from 08:00 to
16:00 and another 2-days (d 7 and 8) of digesta
collections starting from 08:00 to 20:00 h every 2 h intervals, respectively. Digesta were collected into plastic bags containing 10 ml
of 10% formic acid solution to minimize microbial activity. Bags were usually
attached to the cannulas with hose clamps and were changed every 2 h throughout
the 2-days of digesta collections. Both fecal and digesta collected were immediately snap frozen at -230C
for later analyses.
Sample
Processing and Chemical Analyses
Both fecal and digesta
samples were thawed and pooled for each pig within a collection period. Digesta samples were thoroughly mixed for 15 s using a
heavy duty blender (Model 38BL56, SERIAL No. 536024, Torrington, Connecticut,
USA). After mixing 400 ml of each mixed digesta
sample was collected in sample bags and they as well as the entire pooled fecal
samples were freeze-dried. For the pooled and mixed digesta
samples the remnants were collected in large sample bags and immediately frozen
again at -230C in case there would be a need for further analyses. Diet
samples, freeze-dried fecal and digesta samples were
ground in a Wiley mill through a 1-mm screen and thoroughly mixed before being used
for the analyses.
Diet,
fecal and digesta samples were analyzed for dry
matter (DM) and chromic oxide. Fecal samples were further analyzed for gross
energy (GE) by Adiabatic Bomb Calorimeter (Parr Instrument Company Inc. Moline,
Illinois, USA). DM contents for diet, fecal and digesta
were determined by weighing out 2 g of sample into a pre-weighed silica dish
and dried to a constant weight at 1050C for 24 h (AOAC, 2000).
Samples were then removed and allowed to cool down in a desiccator and re-weighed.
DM determined as: (%DM = final weight / initial weight x 100). Crude protein
(N) contents were determined as: (N x 6.25) for diets and ileal-digesta
using Leco NS 2000 Nitrogen Analyzer (Leco Corporation, St. Joseph, MI, USA, and Model No.
602-000-500, Serial No. 3611). Chromium concentration in diets, digesta and faeces was determined
according to the procedure of Williams et
al. (1962). Amino acids (AA) concentration in diet and digesta
was determined using the standard procedure of AOAC (2000). Tryptophan was not
measured because it is destroyed by acid hydrolysis.
Digestibility
Calculations
DE value for each barley type diet was
calculated as described by Adeola (2001) using the
index method. Accordingly, the digestibility coefficient (DC) of each diet was
calculated as:
DC (%) = 100 – [100 (Mfeed/Mfeces) x (Nfeces/Nfeed)]
where:
Mfeed = marker
(chromic oxide) concentration in the feed; Mfeces
= marker concentration in the feces; Nfeces
= concentration of energy component in feces (%) and Nfeed
= concentration of energy in feed (%). The component of interest in feces and feeds
was gross energy (GE). The % DC obtained for the diets using the pig fecal
samples from the diets within periods for individual pigs were converted to DE
values for the three DON-contaminated pearled barley-based diets as: DE = %DC x
gross energy (GE) of the diet.
Similarly, the
apparent N digestibility and ileal AA digestibility
of each AA acid for individual pigs were calculated for each diet using marker
content in feed and digesta as: N digestibility
coefficient = 100 – [100 (Mfeed/Mdigesta) x (Ndigesta/Nfeed)] where Mfeed
is the concentration of marker in feed; Mdigesta
is the concentration of marker in digesta; Ndigesta is the concentration of
nutrient in digesta and Nfeed
is the concentration of nutrient in feed. Apparent ileal
AA digestibility (AID) was derived as: AID = 100 – [100 (AAd/AAf) x (Crf/Crd)] where AAd
is the AA content in ileal digesta;
AAf is the AA
content in feed; Crf is chromium content
in feed and Crd is the chromium content in
the ileal digesta. All
analyses were performed on dry matter basis.
Statistical
Analysis
Analysis of variance was carried out using
the GLM of SAS (SAS Institute Inc., 1988). Bonferoni’s
test was used to compare means at α- level for significance of P ≤ 0.05. The model used was Yijk = µ + Di + Pj
+ Ak + Eij(k):
where Yijk = the digestibility of the kth pig fed the ith
diet in the jth period; µ = the population
mean; Di = the effect of the ith
diet; Pj = the effect of the jth period; Ak
= the effect of the kth pig and Eij(k) = the residual error. The
premise for comparisons of the actual DE values (sample means) obtained in the
in vivo studies from the pigs for the three barley-based diets belong to the
population mean (predicted or calculated DE values) obtained in vitro. A t-test
was therefore conducted to compare the sample means with the population means
using t8 degree of freedom from the ANOVA table obtained from the proc GLM procedure (Table 2) and the standard error of the
means (11.35). The null hypothesis was: there is no difference between sample
and population means for each of the three barley diet types (Ho: X
- µ = 0); while the alternative hypothesis is that sample and population means
are not the same (Ha: X - µ ≠ 0); α = 0.05. Since the
test is 2-tailed, the value of α/2 = 0.025 was used as the two-side
critical region. Critical region of t0.025(8)
= 2.306. Accordingly, the decision rule was reject the H0 if tcalculated ≥ 2.306; formula = X - µ/SEM.
For the 1.2 ppm DON diet: 3803.5 – 3756.9/11.35 = 4.1; 4.4 ppm DON diet =
3741.1-3752.8/11.35 = -1.033 and 7.6 ppm DON diet = 3771.07-3662.69/11.35 = 9.549.
RESULTS
The animals appeared healthy throughout the
experimental duration and readily consumed their daily feed allowance without
any feed rejection and thus were seen to be growing during the study period.
This also confirmed that commercial pearling was effective in removing DON from
the pearled barleys resulting in the elimination of anorectic effect of DON
from the diets. This is further supported by the fact that the pigs grew as
feed intakes were not perturbed during the experimental period leading to
increased final average body weight of the pigs at the end of the study to 69.4
± 3.5 kg. These observations are further cemented by the refusal of the pigs to
consume the intact-barley diets but not their pearled counterpart diets. The DE
contents of the three pearled barley-based diets are presented in Table 2. The
DE contents of 1.2 ppm DON pearled barley diet was significantly (P < 0.05) greater than that of 4.4
ppm but not the 7.6 ppm DON pearled diet. Nevertheless, the DE of 4.4 ppm DON
pearled diet was not different (P >
0.05) from that of 7.6 ppm DON diet.
Apparent ileal N digestibilities were not different (P > 0.05) amongst diets. There were also no differences (P > 0.05) in the ileal
digestibilities of indispensable AAs amongst diets except
for arginine and methionine where significant (P < 0.05) differences were observed. Arginine lowest value was
with the 1.2ppm diet while the 7.6 ppm diet had the highest value. However, for
methionine the lowest value was found with the 7.6 ppm diet while the 4.4 ppm
diet demonstrated the highest value. For the dispensable AAs, there were no
differences (P > 0.05) amongst diets except for glutamic
acid, glycine and proline where significant (P < 0.05) differences were observed.
From these results it could be seen that AID for N and AA were high. This might
be related to the high N and AA contents of the pearled barley. This is true
because it is known that the apparent digestibility of AA increases
exponentially with the ingested quantity because endogenous excretion as a
percentage of total excretion decreases proportionally.
DISCUSSION
The results obtained in this study might be
connected with DON and fibre components of each of
the barley-based diets. Charmley and Prelusky (1994) demonstrated that DON during infection of
the barley grain is evenly distributed and is mostly found predominantly near
the exterior surface of the kernel. This pattern of DON distribution therefore
would have resulted in the removal of most of the DON in the 1.2ppm diet compared
with those of 4.4ppm and 7.6 ppm diets; although there was no sign of feed
refusal amongst the diets. Removal of DON from these diets made them palatable
and metabolizable by the pigs as a result of the
eradication of impairment of nutrient metabolism associated with DON in swine
nutrition (Rotter et al. 1996). DON
interferes with metabolism of glucose and other nutrients in animals that
ingested DON-contaminated diets (Hunder et al. 1991; Rotter et al. 1996).
The determined and
the predicted DE values were compared primarily to measure the similarity
between the actual DE values of the diets with their predicted counterparts
based on the prediction equation of Fairbairn et al. (1999) derived for swine with barley where DE = 3,526 – 92.8
x %ADF. This equation depends largely on the amount of ADF in the barley. The
4.4ppm barley diet sample mean (determined DE value) was not significantly (P > 0.05) different from its population
mean (predicted DE value). However, significant differences were found between
the sample and population means for the 1.2ppm and 7.6 ppm diets. A number of
factors could have contributed to the observed differences, including the
appropriateness of the prediction equation and variables associated with
analyses and biological phenomenon. Sample means were obtained from six pigs (3
x 3) replicated LSD whereas population means were derived with just a duplicate
sample of ADF analyses suggesting that accuracy of the chemical measurement of ADF
is of essence (Noblet and Perez, 1993). This however,
does not erode the fact that individual pig differences in the digestibility of
the diets could also be an important factor contributing to the differences
observed between the actual and predicted DE values for diets 1.2ppm and 7.6ppm,
respectively.
The differences
observed was not also surprising because in the study of Fairbairn et al. (1999) the mean DE value for the
barley used diets ranged from 2,686 to 3,133 kcal/kg with an
overall mean of 2,934kcal/kg. The lower DE values obtained in the study
of Fairbairn et al. (1999) could be
due to high fibre contents in the barley types used
in their study; whereas in our study pearling significantly polished away the
fibrous hulls from the barley much in the same fashion as reported by Trenholm et al.
(1991) and House et al. (2003). The
high NDF and ADF contents of grains in pig rations reduce energy and nutrient digestibilities. Therefore, their removal would have enhanced
energy and nutrient digestibilities in the pig. This
would have also resulted in the higher energy digestibility observed in this
study leading to the improvements observed in the actual or in vivo DE values.
It is also worthy of note that the prediction equation of Fairbairn et al. (1999) was developed based on
intact hulled barley and not pearled barley and therefore would also be
important in explaining some of the observed differences.
In the pig biology, BW
and age affect energy and nutrient digestibilities.
Energy digestibility is improved with increased BW as the pig grows. In
Fairbairn et al. (1999) from which
the prediction equation was developed the initial and final BW of the pigs used
were 35.3kg and 38.7kg, respectively. Thus, the wide BW differences between
their pigs and ours could have contributed to the improvement in the actual DE
values obtained in our study. Although we could not determine the actual DE
values of the intact DON-barleys whose pearled counterparts were used in this
study due to feed refusal of the intact DON-barley diets, it is not a
gainsaying that commercial pearling was effective in removing DON and fibres from the DON-contaminated barleys resulting in
improved energy digestibility.
The results obtained
with AID of N and AAs in this study are in agreement and in some cases better
than values found in the literature for regular barley for growing pigs. For
instance, Green et al. (1987), Stein et al. (1999) and in this study, AID of
N was 71.3%, 61% and 74.4%, respectively. Similar trends in favour
of pearled barley were also observed for AA digestibilities.
Nevertheless, for methionine the highest levels of digestibility were observed
with the 1.2 and 4.4 ppm barley diets compared with the 7.6 ppm diet. This
finding might be related to the interference of DON with methionine metabolism
(Hunder et al.,
1991). Hunder et
al. (1991) showed in male mice that DON inhibited nutrient metabolism
leading to impaired intestinal absorption of essential nutrients, such as
D-glucose and 5-methyltetrahydrofolic (5-MTH) acid. Removal of DON via pearling
from the diets of the pigs would therefore alleviate these effects of DON and
better support nutrient metabolism. Effective uptake of 5-MTH is very important
in the metabolism of methionine. It was possible that more of the DON were
removed from the 1.2ppm and 4.4ppm diets compared with the 7.6pmm diet.
Therefore, the enhanced digestibility of methionine in the low and medium DON
barleys was not surprising.
CONCLUSIONS
Commercial pearling is effective in removing
both DON and fibre from DON-contaminated barley.
Therefore, pearling can make DON-contaminated barley even up to 7.6 ppm
possible for effective utilization by the growing pig when first pearled
without deleterious effects, such as feed refusal and reduced nutrient
digestibility. DE value of pearled DON-contaminated barley was improved over
intact barley from literature data and in this study. Therefore, apart from
removing the anorectic properties of DON-barley, pearling has the additional
advantage of increasing the DE value with improved nutrient digestibilities.
Thus, pearling technology can serve as an effective strategy for managing DON
in barley for swine in any DON endemic region.
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