Using the economic surplus model to measure potential returns to international livestock research. The case of trypanosomosis vaccine research

This study illustrates how productivity impacts resulting from livestock research can be measured using a herd simulation model, how the results of this model can be extended spatially using geographic information systems (GIS) to determine the potential increase in livestock production that would result from adoption of a new technology, and how an economic surplus model can be used to value the estimated productivity impacts. The particular problem examined is trypanosomosis in cattle in Africa, and the potential research product is a multi-component vaccine. The results suggest that the potential benefits of trypanosomiasis control, in terms of meat and milk productivity alone are worth over US$ 700 million per year in Africa. The methodology developed in this study can be used to measure the benefits of alleviating constraints to livestock production and the potential returns to research and development approaches addressing those constraints. The results of this study will assist in research priority setting and have highlighted the need for further research aimed at better understanding who the beneficiaries of the vaccine will be, and how it will reach them

Evaluation of criteria of trypanotolerance

Evaluates teh criteria for trypanotolerance including three related characterstics, v.z. the ability to control parasitaemia, the ability to control anaemia, and the ability to develop an effective immune response

Evidence of differences in trypanosusceptibility in East African Zebu cattle

An average of 840 East African Zebu cattle have been monitored in the Ghibe valley, south west Ethiopia since 1986. Despite a high prevalence of drug resistance, regular Berenil treatment appears to have maintained these cattle at reasonable levels of productivity. However, when corrected for frequencies of parasitaemia and treatment, there was significant associations between the PCV maintained by an individual and its productivity in terms of growth rate, calving interval or risk of abortion. For example, there was an average reduction in calving interval of 8.4 + 2.6 (se) days for each percent unit increase in PCV maintained during the first 5 months post partum. Similarly, there was a decrease in abortion rate of 0.8 + 0.3 percent unit for each percent unit increase in PCV maintained during the last 3 months of pregnancy. Despite deficiencies in these data brought about by the high levels of drug resistance, dam-offspring regression analysis indicated genetic associations between dam and offspring PCV when corrected for parasitaemia and treatment frequency. In other words, cows with abilities to maintain PCVs at higher levels than others appeared to pass on this same characteristic to their calves, particularly once calves approached two years of age. The co-heritability between the PCV of a dam and the PCV of her two year old offspring measured simultaneously over a 6-month period was 0.43 + 0.16 when corrected for frequencies of parasitaemia and treatment. These results demonstrate individual differences in the susceptibility of cattle to the effects of trypanosomiasis in this environment

Effects of trypanosomiasis on productivity of East African Zebu cattle exposed to drug resistant trypanosomes

Research has been undertaken since 1986 in the Ghibe valley, southwest Ethiopia, monitoring approximately 840 village East African Zebu cattle monthly to assess the effects of trypanosomiasis on productivity. The average monthly trypanosome prevalence between 1986 and 1989 was about 30 percent. Many cases of parasitaemia that were treated were found parasitaemic again the following month, pointing to the possible existence of drug resistance; this was confirmed in the laboratory with all trypanosome isolates tested showing resistance to diminazene aceturate. With such a high incidence of drug resistance, a higher monthly trypanosome prevalence might have been expected in the village cattle. Thus, whilst treatment was not eliminating infections, it may have helped to limit the trypanosome growth and allowed the cattle to maintain reasonable levels of health and productivity. This was confirmed by statistical analysis of the productivity data. Although there were statistically significant effect of trypanosomiasis appeared to be on calf and foetal mortality, particularly during periods of very high tsetse challenge or increased trypanosomiasis risk brought about by other stress-related factors

Variations in packed red cell volume and trypanosome prevalence and relationships with reproductive traits in East African Zebu cows exposed to drug-resistant trypanosomes

Approximately 320 East African Zebu cows over 36 months of age were monitored monthly from 1986 to 1992 in nine village herds in an area of high trypanosomiasis risk in southwest Ethiopia where there was resistance to all available trypanocidal drugs. Cows were individually treated with diminazene aceturate, either when they were detected parasitaemic and their packed red cell volume (PCV) decreased below 26 percent or when they showed clinical signs of trypanosomiasis. The average annual monthly trypanosome prevalence was 24 percent and the number of treatments of diminazene aceturate per cow per year was 3.1 both of which increased with age. Mean PCV decreased and mean trypanosome prevalence increased during lactation. There was a significant linear association between the time detected parasitaemic during lactation and calving interval. When corrected for frequency of parasitaemia and treatment there was also an average reduction of 8.4 + 2.6 days in calving interval per percent unit increase in PCAge at first calving decreased by 0.44 + 0.26 months per percent unit increase in mean PCV maintained between 24 and 30 months corrected for parasitaemia and treatment. The percentage of pregnancies terminating in abortions significantly increased from 6.8 + 1.0 percent to 10.4 + 1.3 percent when cows detected parasitaemic at least once during the last three months of pregnancy were compared with cows not detected parasitaemic at least once during the last three months of pregnancy were compared with cows not detected parasitaemic. The largest increase to 19.4 +- 4.3 percent was in cows with low mean PCVs < 22 percent. It was concluded that cows which were able to maintain higher than average PCVs when parasitaemic showed superior reproductive performance than those with lower than average PCVs

Genetic variation in packed red cell volume and frequency of parasitaemia in East African Zebu cattle exposed to drug-resistant trypanosomes

Nine hundred and thirty-six East African Zebu village calves in an area of high trypanosomiasis risk in south-western Ethiopia were monitored monthly with their dams from birth to 3 years of age. Mean packed red cell volume (PCV) and the frequency of detected parasitaemia were calculated for each offspring and its dam measured simultaneously over 6 month `wet' and `dry' seasons from March 1986 to February 1992. Six-month residual values for offspring, corrected for solutions of fixed environmental effects, herd, year, season, etc., estimated by least squares analysis of variance, were regressed against corresponding residual values for their dams. The common environment component of variance, not already corrected for and remaining in these residual values, was estimated by regression of offspring values against those for the cows that gave birth closest to the offspring's own date of birth. When corrected for this component, offspring-dam regression coefficients for mean PCV, averaged over calves for each dam, were found to increase from 0.08 + 0.05 (SE) to 0.26 + 0.06 from 4 to 21 months of age. When also corrected for frequency of parasitaemia and treatment, regression coefficients were reduced, but the increasing trend with age was maintained. Offspring-dam regression coefficients for frequency of parasitaemia showed, if anything, an opposite trend. Application of an `animal model' to offspring over 21 months of age and their dams gave heritability estimates of 0.32 + 0.07 for PCV, 0.18 + 0.07 for PCV, corrected for frequency of parasitaemia, and 0.08 + 0.05 for frequency of parasitaemia

Estimating the effects of tsetse control on livestock productivity - a case study in southwest Ethiopia

A tsetse control campaign was started in January 1991 using a synthetic pyrethroid cypermethrin `pour-on' applied monthly to cattle exposed to high levels of drug-resistant trypanosomes in the Ghibe valley of southwest Ethiopia. In December 1992, a cost-recovery scheme was introduced, and thereafter farmers paid for treatment. An average of 100 village Ethiopian Highland Zebu cattle were monitored monthly from March 1986 to February 1997. Individual animals in this herd were treated with diminazene aceturate (Berenil, Hoeschst, Germany) at 3.5 mg/kg when trypanosomes were detected and their packed cell volume was less than 26 percent. Superimposed on this systematic trypanocidal chemotherapy, contol of tsetse resulted in average reductions from 1992 to 1996 of 95 percent and 75 percent in the mean relative densities of tsetse and biting flies, respectively, and of 63 percent in the prevalence of trypanosomal infections in cattle. Despite these reductions, there was no significant increase in the body weight of the cows, calving rate or the mean body weight of calves at 12 months of age. There was, however, an average decrease of 57 percent in calf mortality (including still births) by 12 months of age, an increase of 49 percent in the ratio of live calves under 12 months of age to cows over 36 months of age, and an increase of 8 percent in the body weight of adult males

Productivity of cattle treated with cypermethrin 'pour-on' insecticide to control tsetse in southwest Ethiopia

Approximately 90 village Ethiopian Highland Zebu cattle at Gullele in southwest Ethiopia were ear-tagged in March 1986 and they and their offspring monitored monthly until February 1996. In January 1991 a tsetse control campaign began using a synthetic pyrethroid cypermethrin pour-on applied monthly to cattle. This resulted in reductions of 95 percent in mean relative densities of tsetse and biting flies from 1992 to 1995. A cost recovery scheme was introduced in December 1992, and thereafter, farmers paid for treatment. Cattle from neighbouring herds not affected by this campaign were also monitored and these were used where possible as statistical controls. Tsetse control resulted in a reduction of 64 percent prevalence of trypanosomal infections and 50 percent in the number of treatments of diminazene aceturate given to cattle detected parasitaemic or showing clinical signs of trypanosomosis. Associated with these reductions there were significant increases of 20 percent in mean calf growth rate over the wet season (P<0.05) and an average decrease of 50 percent in abortion rate and calf mortality to 12 months of age (P<0.05). There was an increase of 37 percent in the ratio of live calves under 12 months of age to cows (from 0.49 = 0.03 to 0.66 = 0.08 (P<0.05)) and an average increase of 6 percent in adult body weight (P<0.05 for cows; P<0.01 for oxen). Packed red cell volume was significantly increased only in adult males. Despite the increase in calf growth rate over the wet season there was however, no significant increase in mean body weight at 12 months of age. Calving rate did not change significantly. The major benefit of tsetse control appears to have been the increase in numbers of cattle raised and new owners settling in the area. Generally, however, the significances of the results were difficult to substaniate statistically

Economic benefits to farmers of six years of application of an insecticidal 'pour-on' to control tsetse in Ghibe, southwest Ethiopia

A tsetse control campaign using an insecticidal cypermethrin "pour-on" applied monthly to village Zebu cattle in Ghibe in southwest Ethiopia has been in operation for over six years. For four of these years farmers have paid a cost-recovery price for each animal given treatment. Relative densities of tsetse and biting flies fell by 95 percent during the second year of vector control. Despite very high levels of drug resistance, trypanosomal prevalence in adult cattle has been reduced from 41 percent to 16 percent (a reduction of 61 percent) and the number of curative trypanocidal treatments per animal has been reduced by 50 percent. A 57 percent reduction in abortion rate and calf mortality, a 49 percent increase in calf/cow ratio and an 8 percent increase in adult male body weight occurred as a result of tsetse control. Before tsetse control intervention there were fewer than 500 cattle in the area; now, six years later, up to 6500 cattle may be brought for 'pour-on' treatment in a month. The reduced expenditures on trypanocidal drugs more than offset the cost of the pour-on. The additional benefits of increased output of meat (41 percent) and milk (39 percent) led to an overall benefit/cost ratio of 8:1 spread over five years. Two thirds of households own cattle (one third with 1-3 cattle and one third with between 4 and 56 cattle). When the above net benefits are expressed in terms of average household income they represent increases in annual income of between 10 and 34 percent household

Effects of trypanosomiasis on growth and mortality of young East African Zebu cattle exposed to drug-resistant trypanosomes

Approximately 390 East African Zebu calves from birth to 3 years of age and their dams were monitored monthly from 1986 to 1992 in nine village herds in an area of high trypanosomiasis risk in southwest Ethiopia where there was resistance to all available trypanocidal drugs. Cattle were individually treated with diminazene aceturate when they were detected to be parasitaemic and their packed red cell volume decreased below 26 percent, or when they showed clinical signs of trypanosomiasis. The average monthly trypanosome prevalence among cattle between 6 and 36 months of age was 18 percent. Within this environment, animals achieved averaged body weights of 79+14 (SD) kg, 134+21 kg and 183+22 kg at 12, 24 and 356 months of age respectively. Annual mortalities ranged from 8 to 24 percent, from 6 to 15 percent and from 4 to 16 percent in the age ranges 0-12, 13-14 and 25-36 months respectively. Calves parasitaemic in any one month in 1988, when early rains failed, had a higher average mortality in that month (3.1 percent) than those that were aparasitaemic (1.4 percent). Liveweight gains of calves born to the dams detected as parasitaemic on more than half the occasions during the first 6 months postpartum were 14 percent lower than those of calves from dams not detected as parasitaemic over this period. An effect of parasitaemia in the calf on weight gain to 12 months could not be demonstrated, but animals detected as parasitaemic on more than six of the 12 monthly samples between 13 and 24 or 245 and 36 months of age had growth rates on average 22 percent lower than those of animals not detected as parasitaemic. All these effects of trypanosomiasis on productivity, however, were temporary and animals later compensated for periods of poor growth. Regualr trypanocidal chemotherapy in a situation of high levels of drug resistance may have helped to maintain the health and productivity of these young cattle