Effects of three anthelmintic treatment regimes against Fasciola and nematodes on the performance of ewes and lambs on pasture in the highlands of Kenya.

The efficacy of strategic anthelmintic control of liver flukes (Fasciola) and gastrointestinal (GI) nematodes on the performance of ewes and lambs on pasture was assessed on a farm in the highlands of Kenya. In May 1999, 45 Corriedale ewes, aged between 2 and 3 years, were ear-tagged, weighed and allocated randomly to three equal treatment groups based on body weight. Faecal samples taken at this time revealed low levels of strongyle-type eggs per gram of faeces (EPG) and the presence of liver fluke eggs in only a few of the animals. All the animals were then set stocked for 12 months on separate paddocks in an area endemic for both Fasciola and GI nematodes. The ewes in group 1 were given a combined anthelmintic treatment against Fasciola and GI nematodes during the periods recommended for the control of Fasciola in the area (February, June and October). The ewes in group 2 were given the combined treatments 3 weeks after the onset of both the short and long rainy seasons (November and April, respectively). Those in group 3 were given separate treatments for Fasciola (February, June and October) and nematodes (3 weeks after the onset of the rainy seasons). The anthelmintic treatment against Fasciola consisted of triclabendazole at 10 mg per kg body weight, and that against nematodes was levamisole at 10 mg per kg body weight. The nematode EPG for the ewes in group 1 were higher than in groups 2 and 3 during both rainy seasons. The nematode EPG did not differ significantly between groups 2 and 3. The prevalence of Fasciola eggs (number of ewes shedding eggs in a group) in the ewes in groups I and 3 remained very low throughout the study period compared to those in group 2. The highest birth weights and the weight gains of lambs were recorded for the group of ewes given separate anthelmintic treatments for Fasciola and nematodes (group 3). The results of this trial indicated that, in an area like Nyandarua District, where liver flukes and GI nematodes are important constraints to sheep production, the best practice is to give separate treatments for the two groups of parasites at the recommended times.

Strategic control of gastrointestinal nematodes of sheep in the highlands of central Kenya.

The effectiveness of anthelmintic treatments given 3 weeks after the onset of rains to control gastrointestinal nematodes in sheep in the highlands of central Kenya was investigated. The study was carried out on a farm situated approximately 85 km north west of Nairobi in Nyandarua District of central Kenya. In May 1999, 35 Corriedale ram lambs aged between 8 and 10 months were eartagged, weighed and given albendazole at 3.8 mg/kg body mass. The animals were then allocated to three treatment groups. Three weeks after onset of both the short and long rains' season in November 1999 and April 2000 respectively, lambs in groups 1 and 2 were dewormed. Lambs in group 1 were given closantel at 10 mg/kg body mass in November and closantel plus albendazole at 3.8 mg/kg body mass in April. Lambs in group 2 were given albendazole at 3.8 mg/kg body mass on both occasions, while lambs in group 3 were maintained as the untreated controls. Nematode eggs per gram of faeces (epg) for lambs in the control group were significantly higher (P < 0.05) than in the treated groups beginning from November, when the strategic treatments started. The levels of epg did not differ significantly between the two treated groups. Body mass for the treated groups was significantly higher (P< 0.05) than for the control group from January 2000 until the experiment was terminated. The rainfall received in the study area in 2000 during the long rain season was inadequate and only occurred for a short period. The amount of herbage on pastures was therefore not adequate and all the study animals started losing mass from June 2000 until the experiment was terminated. The cumulative mass gain and amount of wool produced by the treated lambs during the study period did not differ significantly. There was therefore no difference in using either of the two drugs. It is concluded that, strategic anthelmintic treatments of sheep at the start of the wet season in the highlands of central Kenya is effective in controlling gastrointestinal nematodes. To prevent high levels of re-infection during the season of the long rains (April to June), it is recommended that, during this season, a second treatment be given 5-6 weeks after the first one or at the start of the dry season.

Resistance to benzimidazoles and levamisole in nematode parasites of sheep in Nyandarua District of Kenya.

The occurrence of anthelmintic resistance on 25 sheep farms in the Nyandarua District of Kenya was investigated, using the faecal egg count reduction test (FECRT), the egg hatch assay (EHA) and a larval development assay (LDA). In the FECRT, resistance to both benzimidazoles (BZs) and levamisole (LEV) was detected on four farms, resistance to LEV only on three farms and to BZs, only on two farms. Haemonchus contortus was the predominant nematode species in both pre-treatment and post-treatment faecal cultures. Out of the six farms where BZ resistance was detected in the FECRT, only isolates from one farm had an LD50 value higher than 0.5 microM thiabendazole (TBZ) (0.1 microgram TBZ/ml) in the EHA indicating resistance. Isolates from three other farms, where susceptibility to BZs was detected and four with suspected BZ resistance in the FECRT, had LD50 values higher than 0.5 microM TBZ in the EHA. The LD50 values for TBZ in the LDA for four of the six isolates with BZ resistance in the FECRT were higher than 0.5 microM (0.59-2.07) TBZ. There were disagreements in ascribing resistance for various farms, between methods of calculating and interpreting the faecal egg count reduction percentages (FECR%) based on the arithmetic mean, and those where the geometric mean eggs per gram (EPG) of faeces are used. Inclusion of pre-treatment EPG or control group EPG in the calculation of FECR% resulted in similar variations.

The strategic use of closantel and albendazole in controlling naturally acquired gastrointestinal nematodes of sheep in the Kenya highlands.

The strategic use of closantel, a narrow-spectrum salicylanilide anthelmintic against bloodsucking helminths, and of albendazole, a broad-spectrum benzimidazole anthelmintic, in the control of gastrointestinal nematodes of sheep was investigated on a farm in Nyandarua District in the highlands of Kenya. Thirty Corriedale female lambs aged between 9 and 12 months were assigned to three treatment groups of 10 lambs each. The three groups were set stocked on separate paddocks for 12 months. Lambs in group 1 (strategic treatment group) were treated with closantel and albendazole at the beginning and towards the end of the long rains (April and June, respectively) and towards the end of the short rains. (December). During the intervening dry season, the lambs were treated with albendazole. Lambs in group 2 (suppressive treatment group) were kept 'worm free' by regular deworming with albendazole at 3-weekly intervals for 12 months. The third group of lambs remained untreated (control group). Gastrointestinal nematode infections and pasture infectivity were well controlled in the case of the strategic treatment group. This resulted in higher weight gains, wool production, packed cell volume, and serum albumin and protein concentrations compared with the untreated control lambs. These parameters were comparable between the strategic treatment and the suppressive treatment groups of lambs. It was concluded that worm control strategies based on the epidemiology of the parasites and the sustained anthelmintic action of closantel in combination with broad-spectrum anthelmintics can provide effective control of gastrointestinal nematodes of sheep in the study area.