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The epidemiology of H. placei and of other gastrointestinal nematodes in yearling dairy cattle was examined on two farms in Kiambu District, central Kenya during each of 13 one-month periods from April 1993 to April 1994. On each farm, 32 newly weaned dairy calves were given a single dose of albendazole and then placed on experimental pastures. Twelve of the animals were designated for bimonthly slaughter (n = 2) and analysis of worm population characteristics and 20 were designated for blood and faecal collection and for weighing. Two parasite-free tracer calves were grazed alongside the weaner calves each month throughout the study period and were also slaughtered for analysis of worm populations. Faecal egg counts, haematological and serum pepsinogen determinations, herbage larval counts, and animal live weight changes were recorded monthly. The study revealed that Haemonchus placei, Trichostrongylus axei, Cooperia spp. and Oesophagostomum radiatum were responsible for parasitic gastroenteritis and that H. placei was the predominant nematode present in the young cattle on both farms. Faecal egg counts from resident cattle and necropsy worm counts revealed that pasture larval levels were directly related to the amount of rainfall. The total worm burdens in the animals were highest during the rainy season (March-June and October-December) and lowest during the dry seasons (July-September and January-February). The very low recovery of immature larvae of H. placei from the tracer calves indicated that arrested development is not a feature of the life cycle of this parasite in central Kenya. The maintenance of the parasite population depended on continuous cycling of infection between the host and the pasture. The agroclimatic conditions of the study area were such that, in general, favourable weather conditions for the development and survival of the free-living stages of gastrointestinal nematodes existed all year round.

The gastrointestinal tracts of 672 crossbred cattle were obtained from various abattoirs in Kiambu District, Kenya from August 1992 to July 1993, and examined for the presence of gastrointestinal nematodes. Eight nematode species were found in 583 (86.8%) of the animals. The nematodes were, in order of prevalence: Haemonchus placei (67.0%), Cooperia pectinata (53.0%), Cooperia punctata (41.7%), Oesophagostomum radiatum (38.4%), Trichostronglyus axei (24.3%), Nematodirus helvetianus (19.6%), Trichuris globulosa (9.7%) and Strongyloides papillosus (3.6%). The intensity of the nematode infection was moderate; the mean burden being less than 7000 worms. H. placei accounted, on average, for 52.3% of the total burden. The total burden was least during the dry seasons and increased gradually during the rainy seasons. Adult H. placei persisted in the host throughout the year and there was no indication of hypobiosis. The heaviest gastrointestinal worm burdens were detected in 1.5- to 3-year-old animals. These findings are discussed with regard to their relevance for strategic control of gastrointestinal nematodes in cattle.

The efficacy of morantel sustained release trilaminate (MSRT) bolus against gastrointestinal nematodes was evaluated under field conditions over a 10-month period. Twenty weaner calves were randomly divided into 2 groups of 10 calves each and grazed from March to December on adjacent, similarly contaminated paddocks. Group 1 calves (T-1) served as untreated controls while group 2 calves (T-2) were dosed at turnout with MSRT bolus designed to release morantel tartrate continuously for 90 days. The efficacy of MSRT was assessed by comparison of parasitological data (faecal worm egg counts, herbage larval counts, worm counts from tracer calves and set-stocked trial calves, determination of haematological parameters and pepsinogen levels), weight gains and clinical status of the animals. Faecal egg counts from the treated group (T-2) were reduced by 100% (P < 0.001) following treatment and remained significantly (P < 0.05) lower than counts from T-1 calves up to trial termination. The use of MSRT bolus resulted in a reduction of 92% (P < 0.001) in the number of gastrointestinal nematodes in set-stocked calves at the end of the study and a 55 to 85.7% reduction in herbage larval infectivity as reflected in lowered parasite burdens in tracer calves. At the trial termination, the control calves had gained on average (+/- s.d.) 59.4 +/- 4.8 kg (200.0 +/- 7.4 g day-1) and the treated ones on an average 128.6 +/- 10.5 kg (530.0 +/- 13.1 g day-1).

An attempt was made to controlOstertagia ostertagiby feeding the nematode-trapping fungusDuddingtonia flagrans(DSM 6703) to grazing calves. One group of calves (group E) was fed the fungal material in the first two months of the grazing season while another group was a non-treated control group (group C). Group E showed significantly lower faecal egg count in August and September. On four occasions in July and September, the herbage larval counts were significantly lower on the plot with the fungal-treated group than those recorded on the control plot. The average abomasal larval and adult worm counts were significantly reduced in August in group E and the average total worm count in the abomasum of group E was reduced by 87% in August compared to the non-treated group C. In October, the difference in average abomasal worm counts between group E and C was insignificant. Due to weight loss at the end of the grazing season, the control group showed a significantly lower average weight increase.

Two groups of 12 calves were given either a single infection dose of 30,000 Taenia saginata eggs (group A) or trickle infected with 12 × 2500 T saginata eggs (group B). The calves were killed 16, 22 or 54 weeks after infection and the numbers of viable and dead parasites were counted by slicing selected organs and muscles of half of the carcases. The total numbers of cysts and the numbers of viable cysts were higher in group A than in group B. Within the two groups there were no significant differences between the numbers of cysts at the three dates of slaughter. Comparable results were obtained by using an ELISA and a dot blot procedure for the detection of antibody in the serum of the infected calves; an initial increase in response during the first 10 weeks after infection was generally followed by a gradual decline. When using a monoclonal antibody-based ELISA for the detection of circulating antigens, the sera from all the 14 animals which had no viable cysts or only dead cysts at slaughter did not react with the monoclonal antibodies. Calves 122 and 123, which harboured two and 122 viable cysts, respectively, reacted positively during the late phase of the infection to the antigen-detecting ELISA . However, several other animals which harboured between two and 41 viable cysts at slaughter did not react.