| dc.description.abstract | a) Field survey
The present study was designed to establish a profile of gastrointestinal (GI) parasites
and to determine the influence of season, farm, age and sex on their prevalence, burden and
distribution in dairy cattle. A survey of OI parasite infections of young « 6 months old),
yearlings (6-12 months old) and adult (> 12 months old) cattle on 16 farms in Kiambu
District was conducted during an exceptionally dry season (September 1991 to January 1992)
and during a wet season (March to July 1992). The survey was based on monthly
coproparasitological examination of cohorts and worm counts in tracer calves. The effects
of age, sex, farm and season on the prevalence and intensity of helminth and coccidia
infections were determined. Faecal egg and oocyst counts revealed that the overall
prevalences were: strongylids (85.5%), liver flukes (34.0%), coccidia (30.9%) and
tapeworms (9.6 %). Eight species of the protozoan Eimeria were identified and the most
prevalent species were E. bovis and E. zuernii. The most prevalent nematode genera were
Haemonchus, Cooperia, Oesophagostomum and Trichostrongylus. Season, farm and age of
the animals had a significant influence on the intensity (P < 0.05) of infection with
strongylids, liver flukes and coccidia, whereas the sex of the animals had no significant
(P> 0.05) effect on the prevalence or intensity of infections. A higher intensity of infection
with strongylids and coccidia was found in the wet season compared to the dry season
(P <0.05). The age specific intensity was in the following order: for strongylids, yearlings
hadthe highest egg counts, followed by calves and adults. Calves had significantly (P < 0.05)
higher oocyst counts compared to yearlings and adults. Liver fluke egg counts did not differ
significantly (P > 0.05) between yearlings and adult cattle.
b) Case study
The aim of this study was to investigate the cause of poor condition and death among
weaner calves at Iganjo farm. Parasitic gastritis due to H. placei was found at necropsy of
a nine month weaner calf while, clinical signs and history of other sick animals examined
included occasional diarrhoea, unthrifty coats, submandibular oedema, anaemia, weakness
and progressive emaciation. The animals, however, had continued to eat until shortly before
death. At necropsy, lesions were predominantly haemorrhagic gastritis, generalized oedema,
pale mucus membranes and fat degeneration. Adult and immature Haemonchus worms were
recovered in large numbers from the lumen of the abomasum. Relatively small numbers of
other worm species, including T. axei, Cooperia spp. Nematodirus helvetianus, O. radiatum
and Trichuris globulosa were recovered. On treatment of other cases with albendazole and
supportive drugs there was gradual recovery. The cause of the outbreak was attributed to the
release of highly susceptible calves onto a highly contaminated pasture during the wet season.
c) Abattoir survey
The objective of this survey conducted from August 1992 to July 1993 was to provide
information on the spectrum and prevalence of GI nematodes of cattle and to assess the
occurrence of hypobiosis in H. placei. Gastrointestinal (GI) tracts of 672 crossbred cattle
were examined for the presence of GI nematodes. Eight nematode species were found in 583
(86.8%) of the animals. The nematodes were, in order of prevalence: H. placei (67.0%), C.
pectinata (53,0%), c. punctata (41.7%), O. radiatum (38.4%), T. axei (24.3%), N.
helvetianus (19.6%), T. globulosa(9.7%) and Strongyloides papillosus (3.6%). The intensity
of the nematode infections was moderate: the mean burden being less than 7,000 worms. H.
leastduring dry seasons and increased gradually during the rainy seasons. Adult H. placet
persisted in the host throughout the year and there was no indication of hypobiosis. The
heaviestGI worm burdens were detected in 1.5 to 3 year-old animals.
d) One-year epidemiological observations
The purpose of the present work was to more precisely define seasonal prevalence,
abundance and importance of GI nematodes of weaner-yearling cattle over a 13-month
period. The epidemiology of H. placet and other GI nematodes in yearling dairy cattle was
examined monthly in two farms during the period running from April 1993 to April 1994.
In each farm, 32 head of newly weaned dairy calves were given a single dose of albendazole
and then placed on experimental pastures. Twelve of the animals were designated for bimonthly
slaughter (n=2) and analysis of worm population characteristics and 20 were
designatedfor blood and faecal collection and for weighing. Parasite-free tracer calves were
grazedalongside the weaner calves each month (n =2) throughout the study period and were
also slaughtered for analysis of worm populations. Faecal egg counts, haematological and
serumpepsinogen determinations, herbage larval counts, and animalliveweight changes were
recordedmonthly. The study revealed that H. placei, T. axei, Cooperia spp. and O. radiatum
were responsible for parasitic gastroenteritis (PGE) and H. placet was the predominant
nematode present in young cattle of both farms. Faecal egg counts from resident cattle and
necropsy worm counts revealed that pasture larval levels were directly related to the level
of rainfall. Total worm burdens present in the animals were highest during the rainy seasons
(March/June and October/December) and lowest during the dry seasons (July/September and
January/February). The very low recovery of H. placei immature larvae in tracer calves
indicatedthat arrested development is not a feature of the life cycle of this parasite in central
Kenya. The maintenance of the parasite population depended on the continuous cycle of
infection between the host and the pasture. The agro-clirnatic conditions of the study area
revealedthat, in general, favourable weather conditions for the development and survival of
the free-living stages of GI nematodes existed all the year round.
e) Plot studies
The objective of this work was to determine the annual pattern of development of
strongylideggs to infective larvae (L3) on pasture, and relates environmental factors on their
abundance. On a series of pasture plots, 2 kg pats of bovine faeces containing known
numbers of strongylid (Haemonchus, Cooperia, Oesophagostomum and Trichostrongylus)
eggswere deposited at intervals of 4 weeks from July 1995 to June 1996. The plots were
sampled every two weeks after contamination and infective larvae identified and counted.
Larvae of all genera developed throughout the year but the pats exposed during the rainy
seasons yielded abundant larvae on to herbage. Irrespective of season of deposition of the
pats, larval counts were found in larger numbers from 2 to 6 weeks after deposition and
generally declined to below detectable levels within 12 to 16 weeks of contamination. The
comparatively short survival times noted in this experiment may present opportunities for
manipulation of GI nematode population dynamics in the tropical environment of Kenya.
o Control studies using morantel sustained release trilaminate bolus
The aim of this 10-month study was to determine the comparative efficacy of morantel
sustainedrelease trilaminate (MSRT) bolus and conventional anthelmintic treatments against
GI nematodes of cattle under field conditions. Forty weaner calves were randomly divided
similarly contaminated paddocks. Group 1 calves (T-l) served as untreated controls while
group 2 calves (T-2) were dosed at turnout with MSRT boluses designed to release morantel
tartrate continously for 90 days. Group 3 calves (T-3) were drenched with albendazole on
day zero, and group 4 calves (T-4) on day zero and day 14, respectively. The efficacy of
these dosings was assessed by comparison of weight gains, clinical status of the animals and
parasitological data (faecal worm egg counts, herbage larval counts, worm counts from
tracers and set-stocked trial calves, determination of haematological parameters and
pepsinogen levels). Faecal egg counts from the treated groups (T-2, T-3 and T-4) remained
significantly (P<0.05) lower than counts from control T-l calves for the first three months
post-treatment; notably, egg counts were reduced by 100% 28 days after treatment in T-2 and
T-4 groups and by 97% in T-3 treated calves. Egg counts in T-2 calves remained
significantly (P<0.05) lower than counts from T-1, T-3 and T-4 calves up to trial
termination. The use of MSRT boluses resulted in a reduction of 92 % (P < 0.001) in the
number of GI nematodes in set-stocked calves at the end of the study and a 55 to 85.7 %
reduction in herbage larval infectivity as reflected in lowered parasite burdens in tracer
calves. At the trial termination, the control (T-l) calves had gained on average (± S.D) 59.4
± 4.8 kg (200 ± 7.4 g day") and the T-2 ones on average 128.6 ± 10.5 kg (530 ± 13.1
g day"). T-3 calves gained on average 52.5 ± 5.7 kg (170 ± 6.9 g day') and T-4 ones on
average 82.6 ± 6.3 kg (270 ± 9.1 g day:').
g) Duddingtonia flagrans: a study on herbage infectivity
The present investigation, conducted in 1994 was designed to determine the
overwintering residual grass infectivity in a pasture previously grazed by D. flagrans treated
anduntreated calves. Herbage infectivity was monitored by use of tracer calves over a period
of7 weeks. The experimental pasture had previously been divided into two comparable plots,
1 and 2 which were grazed by two sets of calves, groups 1 and 2 respectively. Group 1
calves had been fed fungal material (D. flagrans in barley grains) once daily over a three
monthperiod from turnout. The controls, group 2 calves received barley grains as a placebo.
In the present experiment, 10 parasite naive male Jersey calves aged 6 months were randomly
allocated to either an experimental group (B) or a control group (A). Each group was grazed
on adjacent plots, group B on the previous group 1 plot and group A on the previous group
2 plot for 4 weeks before being housed for three weeks prior to slaughter upon termination
of the experiment. Body weights were recorded and individual faecal samples taken at regular
intervals throughout the experimental period. Pasture nematode contamination was monitored
by larval counts on herbage and worm counts of tracer calves grazed on each plot. The
results demonstrated that fungal treatment did not significantly lower the overwintering larval
population in plot B compared to plot A as tracer calves grazing Plot A acquired worm
burdens roughly comparable, or perhaps slighly lower, than those of the plot B tracers.
h)' Duddingtonia flagrans: fungal dose-nematode larvae interactions
The present esperiment was designed to quantify the influence of egg counts and
fungal dose levels on the nematode-trapping capability of D. flagrans against free-living
stages of GI nematodes of cattle. In an in-vitro experiment, the interactions between freelivingstages
of four bovine GI parasites and the nematode-trapping fungus D. flagrans were
evaluated using a faecal culture assay. Faeces were collected from donor calves infected with
monocultures of H. placei, T. axei, C. oncophora and O. radiatum, and the number of
parasitic eggs per gram of faeces (epg) were determined. The assay consisted of four faecal
wormegg levels: low (40-50 epg) , medium (200-280 epg) , high (600-680 epg) and very high
(1288-4800) and four fungal concentrations: 0 (controls), 1000, 5000 and 25000
chlamydospores g' faeces. The number of infective third stage larvae (L) which developed
in faecal cultures were determined after cultures had been incubated for two weeks in
darkness at 25°C and 95 % relative humidity. Results showed that the nematode-trapping
capability of D. flagrans was dependent on the fungal concentration and number of eggs in
thefaecal cultures. Thus, percent reductions increased with corresponding increase in fungal
concentration and epg levels in all the four species of parasitic nematodes examined. The
average trapping efficacy of D. flagrans at the medium epg level exceeded 80% for H.
placei, T. axei and C. oncophora compared to 53 % for O. radiatum at the 1000 and 5000
fungal spore concentrations.
In conclusion, the results of this study suggest that GI nematode infections, especially
haemonchosis, are major constraints to the health of young dairy cattle of the study area. To
increase the productivity of cattle, helminthosis control should be based on epidemiological
observations and should not rely on anthelmintics only. Alternative ways of control, such as
biological control of free-living stages of strongylid nematodes of cattle by using
nematophagous fungi merit serious consideration. | en |
