Calf mortality and parasitism in periurban livestock production in Mali

Cattle production is very important for the Malian economy. However, the domestic milk
production does not cover the local demand, so that 60% of consumed dairy products are
imported. To increase local milk production, a modernisation of livestock management in
periurban areas has taken place during the last few decades, especially around Bamako. This
change from traditional to modernised management with crossbreeding with European breeds
and increased investments in housing, nutrition and parasite control may have an impact on
calf mortality, for example with regard to the occurrence of ecto- and endoparasites, the main
causes for health problems of cows and calves around Bamako. Calf mortality has a crucial
negative influence on milk production, as local breeds need the stimulus of their suckling
calves for milk let down. West African studies with traditional and on-station managed herds
report calf (0-12 months) mortality rates between 3% and 47%. Although modernised
management becomes more and more important in periurban areas, no information had been
available on calf mortality and its causes in modernised private periurban livestock production
in West Africa. Neither had calf mortality in traditionally managed herds been compared to
calf mortality in modernised managed herds in periurban areas. This is essential for the
economical evaluation of the ongoing modernisation. The overall aim of this study was to
determine mortality rates in different management systems and to elucidate causes and risk
factors for calf mortality in the periurban area of Bamako, with an emphasis on the effects of
endo- and ectoparasites on calf mortality.
Within a longitudinal cohort approach including 762 calves in 38 herds of the periurban zone
of Bamako, newborn calves were followed up from November 2002 until March 2004.
Repeated examination of tick and trypanosome burden and determination of gastrointestinal
egg excretion was done on calves aged 0-1 month, 2-3 months and 5-6 months. If a calf died,
cause of death was assigned based on its death history, postmortem inspection and routinely
collected weight and parasitic data. Gastrointestinal parasite spectrum in dead calves was
investigated as part of the postmortem examinations. Risk factor analysis for calf mortality
stratified in age classes 0-1 month, 1-6 months and 6-12 months was done with demographic
data, calf management-related questionnaire data and routinely collected parasitic and weight
data. To account for clustering of calves in herds and repeated sampling of individual calves,
survival analysis was done with a frailty model and a Bayesian model with two random
factors for herd and calves was used for analysis of parasitic data.
Overall calf mortality rate during the first year of life was 17%. This leads to a partial loss of
lactation of every 6th cow and a loss of one sixth of all potential slaughter cattle, draught oxen
and future dairy and breeding stock. Much higher calf mortality rates occurred in modernised
management (19% in modernised private and 25% in modernised on station) than in
traditional (10%) management (Hazard ratio 2.2, CI 1.2-3.8, p=0.01). This is an alarming
finding in view of the ongoing modernisation of management practices in the periurban zones.
The causes of death were mainly management problems, consisting of accidental losses
(14%), starvation (10%) and sepsis (5%); digestive disorders, consisting of gastrointestinal
parasites (12%), non-parasitic diarrhoea (10%) and ileus (7%); and perinatal mortality (16%).
Minor causes of death were vector-borne diseases (4%), respiratory disorders (4%) and
nervous disorders (2%). The high number of management problems revealed a need for better
herding, control of milk off-take and better hygiene. Digestive disorders were more frequent
in modernised than in traditional management (p=0.02), and were to a large extent responsible
for the higher mortality rates in modernised management. An obvious reason for the high
occurrence of gastrointestinal problems was poor hygiene in stationary enclosures.
Risk factors for the age class 0-1 month were birth complications (Hazard ratio 18.4, CI 4.4-
75.9, p<0.01), birth during the rainy season (Hazard ratio 7.1, CI 2.9-17.8, p<0.01), parity of
dam with calves of multiparous cows having a higher risk of mortality (Hazard ratio 5.2, CI
1.2-22.1, p=0.03), no contact with chicken (Hazard ratio 8.9, CI 2.1-38.1, p<0.01) and large
herd size (Hazard ratio 3.4, CI 1.0-11.7, p=0.05). The risk factor found for the age class 1-6
months was a low number of herdsmen (Hazard ratio 3.5, CI 1.8-6.6, p<0.01). The only risk
factor to occur more often in modernised than in traditional management was a low number of
herdsmen. The risk factors herd size and number of herdsmen underline the importance of
good supervision for calf survival.
Livestock owners and herdsmen had reported trypanosomes to be an important cause of calf
mortality in their herds in the year preceding the study. However their perception was not
confirmed by a Trypanosoma sp. prevalence of 1% in calves aged 0-6 months and only one
identified loss due to trypanosomes. Frequent tick control conducted by the herd owners
probably lowered tsetse fly density and led to the low tick burden of calves aged 0-6 months.
Mean geometric half-body tick count was 3.1 (range 0-65) with most calves being tick-free
(76%). The most common tick genus was Amblyomma sp. (71%), followed by Hyalomma sp.
(23%), Boophilus sp. (4%) and Rhipicephalus sp. (1%). Significant season, age and
management effects on tick counts occurred, with A. variegatum being less frequent in
modernised than in traditional management (Incidence rate ratio 0.4, CI 0.2-0.9). Tick-borne
cowdriosis was not detected in autopsied calves.
The spectrum of gastrointestinal parasites was similar to that found in adult cattle. The
spectrum included 11 nematodes, 1 trematode, 3 cestodes and 1 protozoan parasite. Calves in
the age class 4-13 months carried up to 8 different parasite species. The most frequent
parasites were Haemonchus sp. (Age class 0-1 month: 7%, 1-4 months: 38%, 4-13 months:
69%), Cooperia pectinata (0%, 33%, 44%), Cooperia punctata (0%, 33%, 38%) and
Moniezia sp. (0%, 24%, 38%). Routine coprological examinations of live calves have shown
a moderate prevalence of eggs of Strongyloides papillosus (Age class 0-1 month: 39%, 2-3
months: 59%, 5-6 months: 42%) and strongyle-type (14%, 24%, 36%) and coccidian oocysts
(37%, 68%, 64%) and at low prevalence eggs of Toxocara vitulorum, Moniezia sp, Trichuris
sp. and Paramphistomum sp. Significant season and age effects on egg counts of strongyletype
eggs, S. papillosus and T. vitulorum and on coccidian oocyst counts were found.
Transmission occurred all year round but was lowest during the dry seasons. Gastrointestinal
parasite control was more intensive in modernised than in traditional management. Even
though hygienic conditions were poorer in modernised management, no management effect
on egg counts in living calves was found
In conclusion, overall calf mortality in periurban livestock production is high and has doubled
with modernisation of livestock keeping. Main management problems were hygiene,
surveillance and milk off-take. Vector and vector-borne diseases were of low importance,
while gastrointestinal parasites were important causes of death in modernised management.