| dc.description.abstract | An epidemiological study of gastroinLestinal nematodes
of cattle was conducted in Tetu Division of Nyeri District,
Kenya. This area has a trcpical climQte, being within the
tropics. The aim of the study was to assess the ~nfluence
of weather factors, stocking rate and herbage cover on the
larval pasture contamination as indicated by the populations
of infective larvae recovered from pasture herbage over a
period of one year. Herbage was sampled at two week
intervals.
The study was carried out in five farms selected by the method
of stratified sampling to cover a representative crosssection
of the farming community within the division. Three
age groups of cattle (under 6 months, 6 - 12 months, and over
12 months) were used for this study. Their faecal egg counts
were used as an index of their worm.burdens. At any given
period of time, the corresponding pasture larval contamination
was considered as the source of the worm burden in the herd
.at the time.
Weather parameters which included rainfall, temperature,
evaporation and relative humidity were recorded in a meteorological
station located in the area of study. All the
farms were within 10 - kilometre radius from the recording
station.
A W-transect method of herbage sampling was adopted.
About 500gm of herbage was collected from each paddock and
thoroughly washed with water containing a small amount of
detergent. Larvae were recoveY'2d by a combination of
sedimentation, flotation with concentrated solution of
magnes iWI;sulphate, and finally by centrifugation to
concentrate the larvae in about 0.5ml of water. Herbage
was then dried to constant weight at 70°C. Infective
larvae recovered were counted on a simple ordinary glass
slide with calculating columns in doses of 0.1ml after
adding a drop of Lugol IS iodine to kill the larvae.
They were recorded in numbers of infective larvae per
kilogramme of dry herbage at 70°C. During the counting,
larvae were also identified to genus level.
For the deter~ination of herbage cover, foliage from
three quadrants per paddock and selected at random was cut
to ground level and dried separately in an oven· to constant
weight at 700e. The quadrants were 30cm. by 30cm. in size.
The final dry weights were recorded, their mean calculated
and herb~ge cover of each paddock recorded as dry weight
of folia.ge per 30cm2.
Faecal samples were collected per rectum. The modified
McMaster egg counting method was adopted for the analysis of
the egg counts. Faecal and herbage sampling in all the farms
were done the same day.
Calves under 6 months of age had the highest egg counts
and were the main source of pasture contamination followed
by the 6-12 months age group. The egg counts of the over
12 months age group remained constantly low throughout the
year. The highest egg counts ~ere recorded during the dry
seasons. The output went down during the rains. Larval
populations were lowest during the dry periods (to a minimum
of 8 L3/kg dry herbage) but went up to a maximum of 2728
L3/kg dry herbage during the rain seasons.
The highest pasture larval count was recorded in the
month of February when there was a brief rainfall following
a prolonged dry period. This observation was made immEdiately
after the onset of the rains and the eggs on pasture had not
had adequate time to hatch and develop to third stage larvae.
It was therefore concluded that there was a ready source of
infective larvae that caused the sudden rise immediately the
rains came. With continued rainfall, there was a gradual
decrease in the number of infective larvae recovered. This
meant that either the infective larvae were carried down into
the ground by percolating rain water or there was an apparent
dilution effect due to increasing amount of herbage.
Rainfall and temperature were found to bave .apos it ive
influence on the level of larval popul a cion in fns"'CuY·e.A
rise in rainfall was accompanied by a rise in herbage larval
population while a fall was followed by a decrease in pasture
larval count. A regression line of temperature drawn against
pasture larval count showed a positive correlation. Similar
results were obta ined for herbage cover, stock in9 rate t·nd
evaporation. A negative correlation was obtained between
relative humidity and pasture larval. count.
In this study, a negative correlation was observed
between rainfall and faecal egg counts in all the three age
groups of cattle. During the rains the herbage became ;,,
abundant and lush. Animals grazing bn this herbage were
passing out copious soft faeces. This was thought to
dilute eggs passed in faeces and cause a frtlse decrease
in faecal egg counts. Although not investigated in this
work, the possibility of self-cure taking place and
causing the decrease in faecal egg-counts during the
rein season was also consideredalikelyexplanation.
Nematodes of the genus· Cooperia were the most predominant
while those of the genus Strongyloides were the least
dominant. Other genera found were Haemonchus, Trichostrongylus
and Oesophagostomum, in that order of prevalence;
this was observed throughout the year. It was therefore
concluded that no genus was more favoured or adversely
affected by any seasons than others.
A wide discrepancy was always observed between the - percentages of infective larvae of the genus Strongyloides
recovered from herbage and those recovered from coproculture.
It was further noted that the infective larvae of this genus
did not survive as long as other larvae under laboratory
conditions. This could mean that they were more susceptible
to certain environmental conditions, thus leading to
their short lifespan. It was suggested that under field
conditions this could reduce Strongyloides larval population
\ in herbage, thus leading the discrepancy between herbage /
cover larval rscovery and coprocu1turc recovery.
It was concluded that to control the problem of
gastrointestinal parasitism, cont~mination of pastures that
occurs during the dry period shouid be avoided or reducFd
by deworming animals curing this period. Deworming during
the rainy period, as is the common practice in this area,
would be of temporary relief to the animals as the
pastures at this time are heavily infested with
infective larvae. | en |
