Selection of study villages, households and data collection
The intervention was undertaken from June 2012 to December 2013 in Tororo District, south-eastern Uganda. Tororo is semi-arid with small-holder crop-livestock systems dominating. It is estimated that there are over 400 villages keeping more than 37,345 cattle most of which are males used for draft work, usually referred to as work oxen, whether castrated or uncastrated [32]. The selection of villages for the economic study was based on a concurrent epidemiological study evaluating the effectiveness of controlling trypanosomiasis by spraying different proportions of the cattle population using RAP [27]. Fifty-seven villages were selected for evaluation to meet eligibility for the RAP epidemiological study. The parameters included: i) cattle AAT prevalence of 15% or more, ii) a population of 50 or more cattle in the village, and iii) villages being at least 5 kilometers apart. Of the 57 villages investigated, 20 villages met the criteria for RAP intervention [27].
The sample size (number of households to be studied) was determined using CSurvey software version 2.0 [33] where the prevalence of AAT was set as 30%, rate of homogeneity at 0.15 and the average eligible persons per household as 1. Thereafter, a sample size of 600 households (30 per village) comprising a total of 5,534 individuals was determined for the economic baseline survey.
The 20 selected villages were randomly allocated to five RAP treatments [27]. All cattle were given two doses forty days apart of Veriben B12 (CEVA Santé Animale, containing diminazene aceturate, vitamin B12 (cyanocobalamin) and B12a (hydroxocobalamin) at 0.01 g/kg live body weight) to treat any pre-existing trypanosome infection [27], [34]. Treatment 1 (T1) cattle received no further treatments whereas treatments 2 to 4 (i.e. T2, T3 and T4) consisted of villages where 25%, 50% and 75% of the cattle population were sprayed using RAP at 28 days interval. Treatment 5 (T5) comprised villages whose cattle were dewormed once every three months but received no other treatment. T1 and T5 were considered as control groups for the graded (25%, 50% and 75%) RAP regimes [27]. For this study T1 villages were used as the control for comparing benefit-cost ratios as well as the incremental cost benefit ratios.
Prior to data collection, two study enumerators were provided with 10 days training as to how to approach farmers, to identify study cattle (using ear tag numbers) and to appropriately complete questionnaires. Enumerators were deployed to the villages depending on their understanding of the local language with each covering 10 villages. Semi-structured questionnaires were pre-tested in two villages that were not included among those randomly selected for this study. Data were collected detailing whether the cattle in the household had had a blood sample taken by the epidemiology team, household characteristics (number of people, livestock kept, type of dwelling, animal health measures used) and components of livestock income.
Data were collected from 600 households in the 20 villages eligible for RAP intervention using six months recall over a period of 18 months (a total of 2,400 interviews before and during the RAP intervention). Six months recall enabled data on cattle ‘exits’ and ‘entries’, productivity, mortality, fertility, cattle-related expenses and revenues, the number of times farmers took their cattle for spraying and the related costs to the household to be updated.
Economic analysis
In the study villages, gross margin analysis and marginal analysis were used to establish the benefit of using RAP to control trypanosomiasis at the household/farm level. For a livestock enterprise, the gross margin is given by the value of livestock output, which includes not just production, but also all entries and exits of livestock and the change in the herd valuation, less the variable costs. This reflects the impact of disease, via mortality, fertility, draft days worked, etc. Marginal analysis consists of analyzing the relationship between small increases in costs and in output; formula for change in net benefit as adapted from [35] was as follows:
Change in net benefit = marginal benefit - marginal cost
where change in net benefit refers to change in income gained by the farmer with each increase in the proportion of the cattle population sprayed using RAP (from T1 to T2, T2 to T3 and T3 to T4). The marginal benefit referred to the difference between the annual income per bovine between the treatments whereas the marginal cost referred to the difference between the annual cost per bovine between the treatments. The annual income per bovine was calculated as a gross margin based on the questionnaire data and compared to the total annual costs to farmers and to the project for implementing the intervention under each treatment.
The marginal analysis involved analyzing the costs and benefits from stepwise increases in the proportion of cattle sprayed (the measure of output) up to the point at which the marginal cost is either equal to or greater than the marginal benefit. Until then it is considered economic to continue increasing output even though the ratio of marginal benefits divided by marginal costs may be reducing (diminishing returns). After this when the additional benefits received are less than the cost of achieving them, negative returns are experienced, and it is no longer profitable to increase output.
The gross margin information was combined with the total societal costs of each treatment to determine the incremental net benefit of spraying an extra 25% of the cattle using RAP i.e. 0% to 25%, 25% to 50% and 50% to 75%. The cost of implementation (delivery cost) for the epidemiological study on the RAP intervention have been previously calculated in detail [36]. Interviews with farmers in this study enabled their own costs to be collected over the 18-month period, to complete the calculation of the full societal cost of the intervention. The costs to the farmer included time required to collect animals and to take them for spraying, money spent on ropes, on maintenance of a crush, on hired labor, etc.
Monetary data collected from the household questionnaires was in Ugandan shillings which were converted to United States Dollars (USD) at 1 USD being equivalent to 2,575 Ugandan shillings (sourced from OANDA, historical currency exchange rates). It represents the average rate applicable for the period when the study was undertaken and is also the same rate used for the project costs [36].