A sampling system was devised and used from 1992 to 1996 in annual grassland and open woodland of the south-west Kenyan Rift Valley. The monitoring was designed to detect vegetation changes consequent on the attempted removal of the tsetse vectors of trypanosomiasis in cattle during a simultaneous trapping programme. The sampled sites covered most vegetation-landscape types, and have led to a better understanding of processes within some. Although fluctuations in pastoralist use and occupancy have been observed, no change in vegetation can be attributed to increased grazing or browsing. Although there is high climatic variability some vegetation types seemed stable over the period studied, and some trends appear to be predictable.

Information was collected on the use of veterinary drugs by Maasai pastoralists in an area of Kenya where tsetse flies and trypanosomosis occur. Three herds of cattle were followed for between 4 and 5 years and records were kept of every veterinary drug treatment given by the livestock owners. Almost all treatments were either with the trypanocides homidium or diminazene, or with oxytetracycline by intramuscular injection. The rate of trypanocide use varied between 0.66 and 1.56 treatments per animal per year, while oxytetracycline use was between 0.20 and 1.00 treatments per animal per year. Farmers were injecting these drugs in the absence of veterinary supervision, obtaining their supplies mainly from local village shops or informal traders. Underdosing with trypanocides appeared to be uncommon and the indications were that farmers generally gave the drugs at dosage rates above the recommended standard dose. Accurate information on the dose rates of oxytetracycline could not be obtained, but it was noted that in most cases farmers gave a single injection rather than a course of treatment. In a proportion of cases, trypanocides and antibiotics were mixed together before injection. The farmers administered the drugs when disease was recognized and were rarely using trypanocides as prophylactics. Although necessity forces the livestock owners to obtain and use these drugs without veterinary supervision, there are concerns with regard to the possibility of drug misuse and the development of drug resistance.

The trypanocidal activity of two commercially available isometamidium-based products, Samorin® (Merial, USA) and Veridium® (Sanofi Santé Nutrition Animale, France), used at a dose rate of 0.5 mg kg−1 bodyweight, was compared in a field trial involving groups of approximately 30 zebu cattle in a trypanosomosis endemic part of south-western Kenya. The trial took place between April 1997 and March 1998 during a time of higher than normal rainfall that resulted in periods of high trypanosome challenge. The trial consisted of five consecutive prophylactic cycles, each of approximately 10 weeks duration. It was demonstrated that there was no significant difference in the prophylactic activity of the two isometamidium-based products, and no significant difference between the relative activity of three different batches of the product Veridium® used during the course of the trial. There was some evidence that drug-resistant strains of trypanosomes may have been present, but it was concluded that isometamidium is still an effective trypanocidal drug in this location.

The Maasai of Kenya are typical of many pastoral communities in that they rely on milk as a major part of their diet. Milk production in three herds of Maasai cattle was studied from 1991 to 1996. Weekly measurements of milk extracted for human consumption were used to estimate lactation length, total offtake and mean daily production. Calf live-weight data were used to estimate total milk yield. Least-mean squares regression and analysis of variance tests were adopted to assess the effect of a number of variables on milk production parameters. Data from a total of 650 lactations and 383 calvings were collected. Mean daily offtake was 891 ml. The length of lactation of frequently milked cows was 372 (s.e. 7·96) days. Total lactation offtake was estimated at 305 I. Herd, parity level and year of calving differences were observed. Multiple regression analyses indicated that some of the variation in daily offtake could be explained by stage of lactation, season of milking, herd, parity and year of calving. An average total yield of 2·73 I/day was estimated for the first 90 days of lactation. Of this, approximately 0·4 was used for human consumption. Overall, seasonality was seen as the major variable influencing production.

An investigation was made into whether recent vaccination of cattle with tissue culture rinderpest virus would cause immunosuppression and lead to more frequent or more severe infection with trypanosomes in animals grazing in tsetse-infested areas. Herds of cattle on Galana Ranch in Kenya were divided, with approximately half of each herd being vaccinated with tissue culture rinderpest virus strain Kabete 'O', while the rest remained unvaccinated. The herds were then exposed to the risk of natural infection with trypanosomes on the ranch. Three experiments were performed during different seasons. Infections with Trypanosoma congolense and Trypanosoma vivax were frequently detected but there was no evidence that vaccinated animals were more likely to acquire trypanosome infections or to show a more severe disease than unvaccinated cattle. It is concluded that tissue culture rinderpest vaccine does not cause immunosuppression and can safely be used in cattle likely to be exposed to tsetse flies and trypanosomosis.

Recent epidemiological studies carried out in East Africa have indicated that some Bos indicus cattle breeds such as the Orma Boran and Maasai Zebu have a degree of trypanotolerance worth exploitation by their introduction into trypanosomosis endemic areas where other cattle breeds cannot survive. However, in most areas of East Africa, trypanosomosis, ticks, and tick-borne diseases occur together. It is therefore important to obtain information on the susceptibility of these breeds to tick infestation and tick-borne diseases. This study was therefore designed to determine the susceptibility of these cattle breeds to tick infestations. They were compared with the Galana Boran (trypanosusceptible) and the Friesian (susceptible to tick infestations, tick-borne diseases, and trypanosomosis). The four breeds of cattle were exposed to natural tick challenge for a period of seven months and whole body weekly tick counts were done on each animal. Significant differences to tick infestations among the four breeds were observed. For both Rhipicephalus appendiculatus and Boophilus decoloratus, susceptibility to infestation increased in the order, Maasai Zebu, Orma Boran, Galana Boran and Friesian.The results generated by this pilot study so far suggest that variation in susceptibility to tick infestations exists among the four breeds. The Orma Boran and Maasai Zebu showed greater resistance to tick-infestations than the Galana Boran and Friesian. This suggests that utilization of these trypanotolerant cattle breeds could be feasible even in the face of tick challenge and should therefore be considered when planning integrated trypanosomosis and tick control strategies.

Studies to assess the differences in susceptibility to trypanosomosis among Bos indicus cattle breeds (Maasai Zebu, Orma Boran and Galana Boran) were conducted under conditions of varying tsetse fly challenge at the Nguruman escarpment in south-western Kenya, for a period of 1 year. It was found that under tsetse challenge quantified as high, Maasai Zebu and Orma Boran were less susceptible than Galana Boran to trypanosome infections, as judged by the significantly lower incidence of infection, development of less severe anaemia, fewer requirements for trypanocidal drug treatments, higher growth rates and fewer mortalities. In the area where tsetse challenge was considered low as a result of a tsetse fly control operation using odour-baited traps, only the Maasai Zebu and Orma Boran were compared. No significant differences in the incidence of infection, degree of anaemia or growth rates were observed between the two breeds, but all were significantly different from their counterparts in the high tsetse challenge area. These results suggest that there is variation in resistance to trypanosomosis among Bos indicus cattle breeds that could be exploited as part of the integrated trypanosomosis control programmes in East Africa.

The size and composition of three herds belonging to Maasai pastoralists were monitored for more than 5 years (1990 to 1996). Animals were categorized as either suckling calves, weaned heifers, weaned males or breeding females. The dates of entries and exits were used to estimate the total number of observed animal days for each category. Fertility rates of breeding females and mortality and disposal rates for each category were estimated using animal days as the denominator. Herd differences were tested using contingency tables. Age to first calving and calving intervals were estimated and examined using analysis of variance tests.The patterns of births and deaths were seasonally influenced. The mean annual calving rate of all breeding females was 65.6% and for females excluding first calvers was 46.9%. No herd effects were observed. The mean observed interval between calvings was 609 days and the calving interval, calculated from the parturition rate, was 649 days with no herd differences. Mean age at first calving was approximately 4 years with no herd differences. Mean annual mortality rates were 8.9% for breeding cows, 7.8% for weaned males, 6.7% for weaned heifers and 22.1% for calves. The mean annual culling rate of cows teas 10.8% and the sale rate of heifers and weaned males was 12.9% and 41.5% respectively. The mean age at disposal of heifers was 655 days and of steers was 801 days. Herd sizes were shown to fluctuate annually with no obvious trend between herds. The main determinants of production identified were the effect of seasonally poor nutrition on the rate of reproduction and the effect of season, herd mobility and disease on mortality.The study describes production levels that can be used to predict future changes to the system. The results are discussed in terms of the factors influencing and their relevance to pastoral development. The findings are compared with those observed in other, similar areas.

The concentrations of isometamidium circulating in poorly nourished Zebu cattle which showed morbidity, mortality, and biochemical and histopathological evidence of hepatotoxicity, following frequent treatments with isometamidium chloride and diminazene aceturate were investigated using the isometamidium-ELISA. As few as two isometamidium treatments one month apart were associated with significant weight loss, and cattle treated with diminazene aceturate after three or four isometamidium treatments suffered a 50% mortality. Although there were no obvious, marked elevations in isometamidium concentration which might have allowed the use of the ELISA as a predictor of a potential toxicity problem, concentrations did increase significantly with the number of monthly treatments administered, suggesting drug accumulation, and the increases were significantly higher in cattle to which diminazene had also been administered. In cattle treated with both trypanocides, weight loss and serum glutamate dehydrogenase levels were correlated with isometamidium concentrations. These observations, together with the histopathological findings, support the hypothesis that the morbidity and mortality observed were related to the repeated treatment with isometamidium in conjunction with diminazene aceturate, and that the pathogenesis involved a component of hepatic damage. It is therefore recommended that cattle, particularly those under nutritional stress, are not subjected to repeated treatments with isometamidium at intervals as short as one month, and particularly not with concurrent administration of diminazene.

A study was undertaken to investigate the influence of trypanosomosis on the outcome of pregnancy in trypanotolerant Orma Boran (Bos indicus) exposed to natural tsetse challenge in an area of Kenya infested predominantly with Glossina pallidipes. Of 73 pregnant Orma heifers, 58 (79.5%) produced live calves at term, 13 (17.8%) aborted and 2 (2.7%) died of trypanosomosis. Of the 71 surviving animals, 22 (31%) were infected with Trypanosoma vivax , 21 (29.6%) T. congolense, and 26 (36.6%) had mixed infections with T. vivax and T. congolense. These results suggest that in areas of high trypanosomosis risk reproductive function is affected even in trypanotolerant cattle, and that both T. vivax and T. congolense can be responsible for the abortions observed in the field. It is suggested that maintenance of pregnancy in the face of trypanosome challenge was dependent on individual variation among the Orma cattle, but as challenge increased beyond the limits of effectiveness of trypanotolerance, disruption of pregnancy occurred.

The duration of prophylaxis provided by isometamidium chloride and homidium bromide, each at a dose rate of 1 mg kg(-1) bodyweight, was compared in a 12-month field trial involving groups of 30 zebu cattle in south-west Kenya. The trial took place between February 1990 and February 1991 and included several months of high trypanosome challenge. Cattle in the prophylaxis groups were retreated on a group basis when 10% of the group had become infected since the previous group treatment. On this basis the mean intervals between retreatment were 7.5 +/- 1.9 and 4.6 +/- 2.1 weeks for the isometamidium and homidium groups, respectively. Weight gains in the two groups were similar. In spite of the need for more frequent treatment in the homidium group as compared to the isometamidium group, total drug costs were lower in the former. There was evidence of Trypanosoma congolense resistant to homidium and some evidence of T. vivax resistant to isometamidium.

A monoclonal antibody-based, enzyme immunoassay (antigen ELISA) for the detection of species-specific invariant antigens of Trypanosoma congolense, T. vivax or T. brucei in the serum of infected animals was evaluated as a means of diagnosis using bovine field sera from a trypanosomiasis endemic area, Nguruman, Kenya. Circulating trypanosome antigens were detected in 126 (96.2%) of 131 serum samples from animals with parasitologically confirmed diagnosis: 74.8% were positive for antigens of two or three trypanosome species, while 21.4% tested positive for one trypanosome species. When 70 sera from animals (at Nguruman), which had tested negative for trypanosomes by the buffy coat technique, were tested, 35 (50.0%) of them were shown to be antigen-ELISA positive: 24 (34.3%) showing infection with a single species and 11 (15.7%) with mixed infections. The predominant trypanosome species diagnosed in the two herds by antigen ELISA was T. vivax, which was detected in 133 (82.6%) of the 161 sera that tested positive for antigens, followed by T. congolense in 122 (75.8%) sera, with 109 (67.7%) showing evidence of mixed infections with two or three trypanosome species. In single infections, T. vivax exceeded T. congolense by a ratio of 2:1, with T. brucei accounting for less than 1.0%. Evidence for the specificity of the test was provided by analysis of field sera from 100 cattle, from a trypanosomiasis-free area, infected with other haemoparasites (anaplasmosis, babesiosis and theileriosis), which all tested negative in the assay.

Homidium bromide was used in a strategic chemoprophylactic regime to control trypanosomiasis in Boran cattle in Kenya. Trypanosome infection rates in cattle receiving homidium bromide prophylaxis were compared with those in control cattle which received no prophylaxis but were treated with diminazene aceturate when infected. Homidium bromide was administered twice during the year after which no infections were detected for periods of nineteen weeks and seventeen weeks respectively. The drug sensitivity of the infecting trypanosomes is believed to be a major factor in determining the duration of prophylaxis.