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.