Parasit Vectors. 2016; 9: 329.
Published online 2016 Jun 10. doi: 10.1186/s13071-016-1617-z
PMCID: PMC4901493
Parasitology
and Aquatic Diseases, Department of Veterinary Disease Biology,
University of Copenhagen, Dyrlægevej 100, DK-1870 Frederiksberg C,
Denmark
Section of
Bacteriology, Pathology and Parasitology, National Veterinary Institute,
Technical University of Denmark, Bülowsvej 27, DK-1870 Frederiksberg C,
Denmark
Norwegian Veterinary Institute, PO Box 750, Sentrum, N-0106 Norway
Olivier Desrues, Email: kd.uk.dnus@dreivilo, Email: moc.liamg@seursed.reivilo.
Corresponding author.Abstract
Background
Increasing
anthelmintic-resistance in nematodes of ruminants emphasises the need
for sustainable parasite control. Condensed tannin-containing legume
forages such as sainfoin (Onobrychis viciifolia) have shown
promising anthelmintic properties in small ruminants but this has never
been explored in cattle. Therefore, our aim was to examine the efficacy
of sainfoin against cattle nematodes in vivo.
Methods
Fifteen
Jersey male calves (2–4 month-old) were allocated into two groups and
fed isoproteic and isoenergetic diets mainly composed of sainfoin
pellets (Group SF; n = 9, three pens) or concentrate and grass-clover hay (Group CO; n
= 6, two pens). After 16 days of adaptation, all animals were
experimentally infected with 10,000 and 66,000 third-stage larvae of Ostertagia ostertagi and Cooperia oncophora,
respectively. Egg excretion, blood parameters and bodyweights were
recorded throughout the study. Worms were harvested by sieving for
quantification and scanning electron microscopy (SEM) 42 days
post-infection (dpi) when the calves were necropsied.
Results
The number of O. ostertagi adults in the abomasum was reduced by 50 % in Group SF compared with Group CO (P < 0.05). This was further reflected in higher albumin (P < 0.1) and lower pepsinogen levels (P
< 0.05) in Group SF at 21 dpi, and structural damage of the worm
cuticle could be visualised by SEM. Yet, the nematode egg excretion in
Group SF was not significantly different from that of the controls (P > 0.05). Likewise, no statistical difference in total worm burdens of C. oncophora was found between the groups. Weight gains were lower for Group SF (P
< 0.05), which may reflect lower digestibility and phosphorus levels
in the SF diet, despite similar feed intake at pen-level.
Conclusions
Overall,
the effect of sainfoin on abomasal nematodes corroborates results from
studies with small ruminants and encourages further investigations of
the use of this crop for control of cattle nematodes.
Keywords: Sainfoin, Condensed tannins, Nematodes, Ostertagia ostertagi, Cooperia oncophora, Cattle
Background
Gastrointestinal
nematode (GIN) infections in grazing ruminant livestock remain an
important problem, which affect health and welfare of the animals and
cause serious economic losses. While anthelmintic (AH) drugs are still
considered a keystone for GIN control in ruminants, the awareness of the
impact of drug resistance among nematode populations [1]
urges farmers and researchers worldwide to explore new strategies,
including feeding of bioactive forages containing plant secondary
metabolites (PSM) with AH properties. While PSM can be administered on a
short term as herbal remedies, we opted for a “nutraceutical” approach,
which also consider bioactive plants for their nutritive value and
require long term consumption to obtain substantial health benefits,
including AH effects [2].
Plants with condensed tannins (CT; syn. proanthocyanidins) have been
thoroughly investigated in small ruminants, particularly the use of
CT-rich temperate/subtropical leguminous forages: sulla (Hedysarum coronarium), lotus species (Lotus corniculatus and L. pedunculatus), sericea lespedeza (Lespedeza cuneata) and sainfoin (Onobrychis viciifolia).
Due to their nitrogen fixating capacity, legumes have an essential role
to play for the sustainability and competitiveness of
grassland-livestock systems in Europe [3].
CT
are polyphenolic PSMs found throughout the plant kingdom resulting from
the polymerisation of flavan-3-ols units; using either epi-/catechin,
known as procyanidins (PC), or epi-/gallocatechin, known as
prodelphinidins (PD). Both PC and PD have the ability to reversibly bind
proteins and other macromolecules. They have shown beneficial effects
on animal health through lower GIN parasitism and bloat prevention, on
animal nutrition due to better use of dietary protein and by reducing
the environmental impact of livestock by mitigating emissions of
greenhouse gases [4].
However, the bioactivity of CT in vivo against GIN of small ruminants
is known to be highly variable depending on the plant source, the
parasite and the host [5].
Plants have different concentration and composition of CT according to
species, cultivar, season and general growth conditions. Also, it seems
that a CT concentration of 3–4 % of dry matter (DM) in plant material is
a lower threshold for AH effects [5],
albeit different methods were used to estimate CT and may give variable
results. Moreover, CT with a higher proportion of PD units have been
associated with a higher efficacy both in vivo and in vitro [6–10]. Forage preservation processes, e.g. ensiling [11]
or pelleting, releasing CT from the plant cells, have been shown to
alter the status of CT from “free” to “bound”, notably to proteins, but
may also positively influence the AH activity. Moreover, parasite
species and stages have different susceptibilities to CT [12–14].
In addition, different host species are differently adapted to CT
and/or various gut environments ensuring the formation or release of
CT-protein complexes [5]. This has been illustrated, e.g. in sheep and goats using wattle tannin [15]. Although most in vitro assays and short-term CT feeding trials have demonstrated a direct AH effect of CT [5],
the high nutritive value of some temperate legumes and the protection
of protein by CT from microbial degradation in the rumen (rumen by-pass
protein) can improve the immune response and be indirectly detrimental
to the parasites [16, 17].
To
the best of our knowledge no data are available on potential AH effects
of CT against cattle nematodes in vivo. However, sainfoin seems to be a
good candidate based on in vitro studies [8, 18].
It is a crop known for its appealing features such as high
palatability, high protein levels and importance in biodiversity
preservation. In GIN infected small ruminants intake of sainfoin has
been consistently associated with a reduction in faecal egg counts
(FEC), except when CT levels were lower than 2 % of DM intake [19–23].
Several studies have indicated reduction in worm burdens at CT dietary
concentrations of 5.1 % and 8 %, without negative effects on animal
performance [21, 22].
Our
main objective was to assess whether feeding sainfoin has an effect on
pathophysiological and parasitological measurements in calves
experimentally infected with the most pathogenic and prevalent GIN of
cattle in temperate regions: Ostertagia ostertagi and Cooperia oncophora.
Methods
Animals
Fifteen
Jersey male calves with no grazing history (2.5−4.5 month-old,
91.4 ± 24.0 kg [mean ± standard deviation, SD]) were acquired from a
commercial farm. Upon arrival they were orally treated with fenbendazole
(Panacur®Vet 10 %, MSD Animal Health, 5 mg/kg bodyweight [BW]) to
ensure helminth-free condition (later confirmed with negative FEC one
week post treatment). During the whole study period the calves were
reared indoor in solid concrete floored pens with straw bedding and
external feeders. All animals were allowed an acclimatisation period of
16 days and were clinically assessed on a daily basis throughout the
study.
Feed constituents and nutritional analysis
Sainfoin (O. viciifolia) pellets were provided by Multifolia/MG2MIX (Viâpres-le-Petit, France) Ltd., and consisted of a pure-stand 3rd
cut (cultivar: Perly) harvested in 2012 and processed to obtain
dehydrated pellets. The other feed sources included grass-clover hay and
a commercial concentrate (Danish Ragna Grønmix©, Danish Agro
Ltd., Karise, DK). The level of DM, crude protein (CP), neutral
detergent fibre (NDF) and ash was analysed in all feed components by an
accredited, authorised laboratory (Eurofins Steins Laboratorium Ltd.,
Holstebro, DK). Digestible organic matter (DOM) was calculated
considering OM content in feeds and OM digestibility (OMD) of hay,
sainfoin and concentrate that was analysed by near-infrared (NIR)
spectroscopy, an in vitro method [24] and in vitro enzymatic method (EFOS [25]),
respectively. The values for OMD of sainfoin and concentrate were
corrected to in vivo OMD (OMD %) using the following regression
functions: OMD %sainfoin = 4.1 + (0.959 × in vitro digestibilityTilley & Terry %) (used for most forages) and OMD %concentrate = 22.0 + (0.752 × in vitro digestibilityEFOS %) [25].
Metabolisable energy levels, expressed in MJ/kg of DM, were calculated
from the net energy lactation values, which were provided by
manufacturers or laboratory, and divided by 0.65 [26].
Mineral composition values were obtained from suppliers. Feeds were
analysed for CT content by the acetone-butanol-HCl assay [27] with pure fraction of CT from dried sainfoin as standard. In addition, CT in sainfoin pellets were characterised after in situ thiolysis [28] and LC-MS analysis [29].
This gives information on the content and composition of CT: their mean
degree of polymerisation (mDP)-values (i.e. size), percentages of PC
versus PD type tannins, and cis versus trans flavan-3-ol subunits.
Experimental infections
Infective third-stage larvae (L3) for inoculations were isolated from donor calves experimentally infected with O. ostertagi and C. oncophora
following standard larval culture procedures (14 days at 21 °C). The
larvae were stored at 13 °C for 3 months until evaluation of
ensheathment and viability 1–3 days prior to inoculation. Hundred
baermannised L3 were then morphologically differentiated [30], and a batch comprising 13 % O. ostertagi and 87 % C. oncophora was used. All calves (n = 15) were orally inoculated with a total dose of 10,000 L3 of O. ostertagi and 66,000 L3 of C. oncophora per calf, given as three sub-doses for three consecutive days.
Experimental design, diets and sample collection
Sixteen
days prior to the experimental infection the calves were randomly
allocated into two groups after stratification by BW. The Sainfoin group
(SF) (n = 9; 90.9 ± 28.1 kg) was allocated to three pens, each
containing three animals with almost similar BWs in order to allow a
better estimation of the feed consumption and to avoid bullying (i.e. a
pen for the smaller, intermediate and larger calves). The Control group
(CO) (n = 6; 92.1 ± 18.5 kg) was allocated to two pens of three calves. All calves were weighed weekly except for the last time point.
In
Group SF sainfoin pellets were gradually offered in addition to hay
until becoming the main feed component (> 90 %) after a period of
12 days. Calves from Group CO received commercial concentrate (ranging
from 55 to 65 % of the diet) and hay of ryegrass-clover. The intakes of
sainfoin pellets, hay and commercial pellets were calculated every day
for each pen (feed offered - feed refusals). Four days prior to
infection, the diets were formulated in order to fulfil requirements of
CP and energy and to obtain similar levels adjusted for BW in both
groups. Diet in Group SF was offered close to ad libitum and
the diet in Group CO was adjusted with concentrate every second day to
match the diet of Group SF, with a maximum of 2 and 3 kg of DM for small
and larger animals, respectively. All animals had free access to water.
Straw bedding consumption was observed in both groups but could not be
recorded. Individual faecal samples were rectally collected once weekly
during the pre-patency period and every 2–3 days from 14 days
post-infection (dpi) onwards. Faecal egg counts (FEC) and larval
cultures were prepared as described in the next section. Individual
blood samples were collected by jugular venipuncture at weekly
intervals, and the recovered serum was stored at -20 °C until use. At
40−42 dpi all calves were euthanized with captive bolt pistol followed
by exsanguination.
Serum and faecal samples analysis
Serum samples obtained from week 0 to 6 were analysed for pepsinogen as previously described [31]
and for total protein (TP), albumin (ALB) and inorganic phosphate (IP)
using an ADVIA1800 analyzer (Siemens). A more detailed biochemical
profile analysis was performed at necropsy: alkaline phosphatase,
alanine aminotransferase, total bilirubin, cholesterol, creatinine,
creatinine kinase, iron, aspartate aminotransferase, urea,
gamma-glutamyl transpeptidase, calcium, magnesium, sodium and potassium.
FEC were determined using a modified McMaster technique with a sensitivity of 5 eggs per gram faeces [32].
Faecal DM from each animal was determined during the patency period
from 3 g subsample dried at 60 °C for 24 hours, and FEC were expressed
as the number of eggs per gram of dried faeces (FECDM). Species-specific
FECDM was estimated from larval cultures that were prepared at selected
time points from pooled faecal samples (10 g of faeces per animal) for
each pen, which were mixed with vermiculite and incubated for 13 days at
20–22 °C.
Recovery and analyses of adult nematodes
Immediately
after euthanasia, the abomasum and the whole small intestine from each
animal were opened separately and washed with 5 and 10 l of 38 °C warm
saline (0.9 % NaCl), respectively. For each organ, one subsample of
500 ml of washed digesta content (i.e. representing 10 % of the abomasum
and 5 % of the small intestine contents) was passed through a 38 μm
metallic sieve and retained material was stored in 70 % ethanol. Worm
counts and sex determination were performed. Sex ratio was reported as
the percentage of male worms in the total worm burden. Changes in sex
ratio are a good indicator of worm expulsion for C. oncophora because expulsion initially includes male worms [33].
Worm fecundity was assessed by counting the number of eggs from 16
female worms of both nematode species per calf. These worms were
recovered from individual animals and lysed in 200 μl of a 20 %
household bleach solution. Eggs were enumerated 10 min after lysis for O. ostertagi and after 30 min for C. oncophora
female worms. Finally, the cleaned mucosa of the abomasum from one
animal in each group was scraped and digested in pepsin/hydrochloric
acid for 2–3 hours [34]. Each digested mucosa was passed over a 38 μm sieve, and the retained material was examined for inhibited fourth-stage larvae.
Scanning electron microscopy (SEM)
Adult O. ostertagi were examined by SEM. The worms were collected from randomly selected animals (CO: n = 2; SF: n
= 4) after washing with tap water, and fixed in PBS with 2 %
glutaraldehyde. They were merged per Group and post-fixed in 1 % OsO4 and 0.05 M K3FeCN6
in 0.12 M cacodylate buffer for 2 hours at room temperature and
stirred. Then, the samples were rinsed with 0.15 M cacodylate buffer and
distilled water, followed by dehydration in a gradient of ethanol
concentrations in a critical point dryer. The worms were coated with
4 nm gold with a coating instrument (Leica EM ACE200) and loaded in a
scanning electron microscope (Phillips XL 30 FEG) for visual analysis
using Scandium software.
Statistical analyses
The
effects of feeding sainfoin were assessed by linear mixed-effects
models fitted with maximum likelihood. BW, faecal DM and biochemical
markers were analysed as repeated measures as described by [35].
These models included Pen as random effect and the fixed effects were
Group and Time, and the interaction between Group and Time if
significant. Baseline measurements were used as covariates for
biochemical markers (week 0 value) and BW (initial BW). Pepsinogen data
were log-transformed prior statistical analysis but presented as
back-transformed means. The variance homogeneity between observations of
the models was also tested. The residual plots were used to validate
the final models. Likewise, statistical differences between groups in
relation to: worm counts (for O. ostertagi), sex ratio, fecundity of female worms (i.e. number of eggs in utero),
and additional blood parameters (42 dpi) were analysed by mixed effects
models including post-hoc comparison of means by Tukey’s test, with
Group as fixed effect and Pen as random effect. Counts data for adult
worms of C. oncophora and FECDM were over-dispersed therefore
we used generalised linear mixed-effects models for the negative
binomial family with Group as fixed effect and Pen as random effect.
Statistical analyses were carried out with R (version 3.2.0).
Results
Feed composition and diets
The
CT content of sainfoin pellets was 65 g/kg DM with the
acetone-butanol-HCl method and 19.6 g/kg DM with the thiolysis LC-MS. CT
had a high proportion of PD (81 %) and cis-conformation (77 %)
and a mDP of 11. No CT were found neither in hay nor in concentrate. CP
was low in hay compared to sainfoin and concentrate (8.4, 17.2 and
20.4 % of DM, respectively) (Table 1). The feed intakes for the week of experimental infection were 2.89 ± 0.05 for Group SF versus
2.87 ± 0.12 for Group CO (mean of pens ± SD kg/100 kg of BW). The feed
intake in both groups increased gradually during the first 3 weeks
post-infection and then stabilised around 3.5 kg/100 kg of BW for the
last three weeks (mean of pens ± SD on the last week: 3.53 ± 0.06 in
Group SF versus 3.58 ± 0.19 in Group CO). Dietary intakes are presented in Table 1
as pooled means per feeding group during the experimental infection
period. CP dietary intake was marginally lower in Group CO
(0.52 ± 0.06 kg/100 kg of BW) compared to Group SF (0.54 ± 0.04) but the
energy intake was similar in both groups. Yet, diet for Group CO had
higher DOM (2.31 ± 0.22) and NDF (1.36 ± 0.10) compared with Group SF
(DOM: 1.92 ± 0.19; NDF: 0.92 ± 0.14).
Nutrient contents of experimental feeds and daily dietary intake
Health and bodyweights
Overall,
the general condition of the animals was good during the study period
although the youngest animals in Group CO had soft faeces to mild
diarrhoea for most of the study period. The faecal DM was significantly
higher in Group SF (F(1,3) = 17.48, P =
0.025) across the patency period (pooled means [± SD] in Groups SF and
CO, respectively: 18.2 ± 0.8 % and 15.2 ± 1.1 %). Although the effect of
Time was not significant (P > 0.05), a gradual decrease in
faecal DM was observed in Group CO from 14 to 28 dpi (16.0 ± 2.8 % and
12.8 ± 4.3 %, respectively) and then increased until 42 dpi
(16.9 ± 3.1 %), which was not seen in Group SF.
The BW of calves were significantly lower in Group SF as compared with Group CO from 5 dpi onwards (P < 0.05) with a significant interaction of Group × Time (F(6,87) = 4.58, P = 0.0004). Moreover, the effect of the baseline was also significant (initial BW; F(1,87) = 5189, P
< 0.0001), as lower growth was observed in smaller animals.
Cumulative weight gains (mean ± SD) for the whole period were
18.3 ± 11.3 and 31.2 ± 8.0 kg for Group SF and CO, respectively (Fig. 1).
Cumulative weight gains (kg) of calves per group. Control group (CO; n = 6; dotted line) and Sainfoin group (SF; n = 9; solid line). Error bars represent the standard deviation. *P < 0.05
Blood parameters
Serum PEP levels remained very low throughout the study in both groups (mean < 1 UTyr, Fig. 2a), indicating low infection levels with O. ostertagi. Nevertheless, the PEP levels were consistently lower in Group SF compared with Group CO, and significant differences (t(3) = -3.74, P = 0.033) were observed 21 dpi. Serum IP values were significantly lower in Group SF (F(1,3) = 71.14, P = 0.0035) throughout the study (Fig. 2b). Moreover, the baseline was not significant (P
> 0.05) and the means in both groups seemed to level out after a drop
around start of the patency period. Serum ALB levels decreased in both
groups (Fig. 2c) but with significant effect of baseline (F(1,74) = 6.06, P = 0.016) and interaction Group × Time (F(5,74) = 3.27, P = 0.010); levels were higher in Group SF 21 dpi (t(3) = 2.77, P
= 0.069) as compared with Group CO. Serum protein levels gradually
decreased during the study in both groups without any significant effect
of Group (initial values: 71.2 ± 3.9; 68.0 ± 3.4 g/l; final values:
52.4 ± 4.4 and 55.7 ± 7.4 g/l for Groups SF and CO, respectively).
Additionally, the levels of iron (20.2 ± 7.5 and 37.1 ± 9.6 μmol/l in
Group SF and CO; GLH-test: Z = -3.84, P = 0.0001; Tukey) and gamma-glutamyl transpeptidase (8.9 ± 1.5 and 14.2 ± 3.7 U/l in Group SF and CO; GLH-test: Z = -3.94, P < 0.0001; Tukey) differed significantly between the groups.
Mean serum levels of biomarkers in calves experimentally infected and fed various diets. a Pepsinogen (PEP). b Inorganic phosphate (IP). c Albumin (ALB). Control group (CO; n = 6; dotted lines) and Sainfoin group (SF; n = 9; ...
Faecal egg counts
The means of FECDM were not significantly different between the groups (Fig. 3).
Specific egg excretion of each nematode species was estimated from the
pooled larval cultures, despite high individual variability of FECDM,
and showed a similar trend as FECDM. Yet, an overall predominance of C. oncophora
was found, particularly during the peak of excretion (mean % ± SD:
64 ± 6; 80 ± 15; 88 ± 10 and 86 ± 19 at 19, 22, 26 and 28 dpi,
respectively), which was observed between 21 and 28 dpi for all calves
except one in Group CO, in which it occurred around 35 dpi.
Mean faecal nematode egg counts during the patency period. a Faecal egg counts (FEC). b
FEC adjusted for dry matter (FECDM). Control group (CO; dashed line:
arithmetic mean; hatched orange area: 95 % confidence interval) and
Sainfoin group (SF; ...
Adult worms
The mean worm count of adult O. ostertagi was significantly lower in Group SF compared with Group CO (GLH-test: Z = -2.34, P = 0.019; Tukey; Table 2);
a high worm burden (3,300) was found in the smallest animal in Group SF
while all others had less than 1,500. The comparison of the statistical
models with or without pen as a random effect was not significant with
ANOVA. No significant differences were seen in sex ratio or fecundity of
the female worms. Analysis of O. ostertagi adult worms by SEM (Fig. 4) showed some aggregates of particles and few localised damages of the external structure of 1/3 of the worms from Group SF (n = 3). In comparison, the cuticle of the worms from CO (n = 3) appeared clean and smooth (Fig. 4a, ,b).b). No inhibited fourth-stage larvae were recovered from the abomasal mucosa of the six animals.
Parasitological data from worms recovered 42 days post-infection
External structural changes of adult Ostertagia ostertagi
recovered from calves fed sainfoin for 58 days. Scanning electron
microscopy of representative worms recovered 42 days post-infection from
Control group (CO) (a, b) or Sainfoin ...
For C. oncophora, no significant differences between Group SF and CO (P
> 0.05) were found regarding total worm burden, sex ratio and female
fecundity. However, these results showed a strong variation within each
group (Table 2). In Group SF, three animals (one in each pen) had close to none adult C. oncophora 42 dpi (≤ 100), and were therefore not included in the analysis of sex ratio and female fecundity.
Discussion
This
study showed that calves fed pelleted sainfoin as the sole, continuous
diet had a significant reduction by 51 % in the worm burden of O. ostertagi
42 days after experimental inoculation, as compared with animals fed a
control diet. Our results confirm AH effects of sainfoin observed in
earlier studies of abomasal nematodes in sheep. In one study, sainfoin
(6.1 % CT of dietary DM) consumption for 16 days significantly reduced
the number of worms in an already established population of adult H. contortus [21]. Similar results have been reported for Teladorsagia spp. in naturally infected animals fed sainfoin containing 8.3 % CT for 13 days [22]. Moreover, the pelleting of sainfoin may have influenced the AH activity as shown by Terrill et al. [36].
These researchers found that consumption of the pelleted form of
sericea lespedeza was even more potent as compared with hay of the same
bioactive forage (both containing 6.4 % total CT) in reducing the worm
burden of H. contortus. This was, however, not the case for T. colubriformis.
Further, it has been highlighted that the molecular structure (e.g.
PD/PC ratio) of CT may have a greater importance than the ratio of
bound/unbound forms of CT in the diet [37].
This hypothesis was substantiated by our results. In fact, although
bound CT were not determined directly in our study, the lower CT %
obtained with thiolysis compared with acetone-butanol-HCl may indicate
that CT have a low accessibility in the pellets. However, CT in sainfoin
is mainly of the PD type and especially in our case (PD % > 80) that
is known to greatly influence the AH activity of CT in vitro [8, 10].
Although
the majority of feeding trials with sainfoin have been associated with a
significant reduction in FEC, the non-significant egg count reduction
in our study was presumably due to the apparent lack of effect on C. oncophora
which was the dominant species in the inoculum and responsible for the
majority of the egg output throughout the trial. A few studies found
that a lower female worm fecundity, rather than a lower worm burden, was
responsible for FEC reduction in goats and sheep [20, 23]. Other studies have reported reduced numbers of adult H. contortus in lambs without any accompanying significant effect on worm fecundity after feeding sainfoin for 16 or 70 days [21, 38].
We expect that the effect of sainfoin against O. ostertagi
is mainly related to direct effects of CT rather than an
immunologically induced expulsion, since it is known that the
acquisition of protective immunity against O. ostertagi needs a continuous larval exposure for longer than the first grazing season to arise [39].
Moreover, it has been shown that the loss of adult worms was very
limited even 50 dpi after a single infection with 10,000 L3 of O. ostertagi [40].
Our study was not designed to pinpoint which stage of infection was
affected by sainfoin. The levels of serum-pepsinogen indicated a low
infection level [41] and the albumin values were in all cases within the range of healthy calves [42], although significant differences were found between groups. However, the lower pepsinogen in Group SF at 21 dpi, when O. ostertagi
young adults had emerged from the gastric glands, could indicate an
effect of sainfoin at this stage of infection, or perhaps even on
establishment. In fact, Brunet et al. [18] found that the larval exsheathment of O. ostertagi
was reduced in vitro in the presence of sainfoin extracts. Furthermore,
sainfoin has been shown to reduce the larval exsheathment process of H. contortus in the rumen of cannulated sheep fed with fresh sainfoin [43], and to inhibit the following penetration into the abomasal mucosa after in vitro incubation with sainfoin extracts [44].
The authors linked these effects with structural alterations of the
infective larvae at both external and internal levels, depending on the
presence of the sheath [45]. Moreover, we also found local cuticular damage by SEM on adult O. ostertagi of sainfoin-fed calves (Fig. 4).
Previously, structural damage of worms at intestinal and muscular
levels have been visualised by transmission electron microscopy of adult
female H. contortus from goats fed sainfoin [46]. The external surfaces of worms from goats was also damaged when animals were fed sainfoin, tzalam (Lysiloma latisiliquum) [47] and more recently sericea lespedeza [48].
Interestingly, the latter study concluded that the degree of cuticle
damage was influenced by the length of exposure to CT; all worms were
affected after 77 treatment days whereas only a smaller proportion was
affected after 28 days. In our case, adult worms were in contact with CT
for approximately 25 days which may explain the inconsistencies between
worms. In addition, adult worms were pooled per group and calves may
have had different CT concentrations in the digestive tract considering
the variation in straw consumption.
Our study showed no influence of sainfoin-feeding on the worm counts of C. oncophora in the small intestine. This is in accordance with a previous study of established populations of C. curticei in experimentally infected sheep fed sainfoin (6.1 % CT in DM) [21].
The same study reported a significant reduction of abomasal species. In
addition, they found a significantly lower fecundity of C. curticei, although no data in utero were presented [21]. However, a reduction in numbers of adult C. curticei has been reported in naturally infected lambs fed sulla (Hedysarum coronarium) which had a high CT content (12 % CT of DM in the leaves) [49].
Despite these examples, there seems to be an apparent lack of
bioactivity of CT in sainfoin against nematodes in the small intestine.
This may be due to a lower availability or binding capacity in the small
intestine where the local conditions are different from the abomasum [5].
Accordingly, the majority of studies in sheep have reported a greater
effect of sainfoin against abomasal versus small intestinal nematodes [21, 38, 50], but similar AH effect of sainfoin in the two gut compartments has also been reported [23].
The opposite case: a better effect against small intestinal nematodes,
was only reported in studies of sheep fed with quebracho as a source of
CT that contains profisetinidins, another type of flavanol basic units [51].
Controlled in vivo and in vitro studies with tannins against cattle
nematodes at species level are very limited. Recently, it has been
reported that O. ostertagi was more susceptible to CT than C. oncophora in vitro [10], although such difference was not found in other studies [8, 18]. In vivo studies may yield a different result. The low number of adult C. oncophora
recovered from some calves in both groups, 42 dpi, was likely related
to the expulsion of worms in those animals. In fact, a primary infection
with C. oncophora has been shown to elicit a Th2-biased immune
response against adult worms in high responder type animals, which
confers a rapid protective immunity [33].
Moreover, in the same study the worm sex ratio proved to be a good
indicator of the worm expulsion as males were first expelled, which was
also observed in our case.
In general,
calves appeared healthy and showed no signs of clinical disease. Group
SF and had less soft faeces compared with Group CO. Although we found
higher levels of iron and gamma-glutamyl transpeptidase in serum of
calves of Group CO compared with Group SF 42 dpi, only one value of
serum iron in Group SF was slightly lower than the reference range for
calves [42, 52].
Therefore we did not consider this biologically significant. However,
the mean levels of inorganic phosphorus in Group SF were ≤ 1.3 mmol/l
from 21 dpi which is at the lower marginal threshold for calves [53].
This emphasizes the need for possible supplementation with phosphorus.
In previous studies, infected small ruminants fed sainfoin hay had
similar or improved weight gain with CT concentrations up to 8 % [21–23].
Yet, the relatively low number and variable size of animals in our
study preclude firm conclusions on performance. Moreover, it was
challenging to maintain similar levels of CP and energy in the diets of
CO and SF groups with the low replication of feed intake. Therefore the
feed intake adjustments and nutritional differences in favour of the
concentrate-rich diet in Group CO including higher digestible OM, NDF,
and phosphorus need to be considered as explanatory factors of the
relatively large difference in animal performance observed in this
study.
Conclusion
Pelleted sainfoin as a sole feed significantly reduced the population of O. ostertagi
in young calves. Our promising results confirm the potential value of
sainfoin and perhaps other tannin-rich forages with a high percentage of
prodelphinidins in integrated control of bovine ostertagiosis. Although
O. ostertagi is the main species responsible for reduced productivity in grazing calves, the apparent lack of effect against C. oncophora
is a drawback and may hamper the practical use of sainfoin as a
“broad-spectrum” anthelmintic forage. More research is needed to address
the background of the lacking effect against C. oncophora.
Abbreviations
AH,
Anthelmintic; ALB, Albumin; CP, Crude protein; CT, Condensed tannins;
DM, Dry matter; FEC, Faecal egg counts; GIN, Gastrointestinal nematodes;
IP, Inorganic phosphate; OMD, Organic matter digestibility; PC,
Procyanidins; PD, Prodelphinidins; PEP, Pepsinogen; SEM, Scanning
electron microscopy
Acknowledgments
The
authors gratefully acknowledge P. Lund and all animal caretakers
(Tåstrup, Denmark) as well as colleagues from our groups for their great
assistance with sampling on the last day, A.R. Williams for his help
with electron microscopy and the Core Facility for Integrated
Microscopy, University of Copenhagen. Sainfoin pellets were kindly
provided by Multifolia/MG2MIX Ltd., FR.
Funding
This research was supported by the EU Marie Curie Initial Training Network (‘LegumePlus’; PITN-GA-2011-289377).
Availability of data and materials
Not applicable.
Authors’ contributions
OD,
MPE, HLE and SMT conceived and designed the study. OD, MPE and TVAH
performed the sampling and recordings throughout the study. OD counted
the samples and analysed the data. OD wrote the paper. All the authors
contributed to improve the manuscript and approved the final version.
Competing interests
The authors declare that they have no competing interests.
Consent for publication
Not applicable.
Ethics approval and consent to participate
The
experiment was approved by the Animal Experiments Inspectorate of the
Ministry of Food, Agriculture and Fisheries of Denmark (j. No.
2013-15-2934-00763).
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