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 untreat ed (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.     

An abattoir survey of gastrointestinal nematode infections in cattle in the central highlands of Kenya

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%), Trichostrongylus 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.     

Seasonal availability of gastrointestinal nematode larvae to cattle on pasture in the central highlands of Kenya

The type and level of infective strongylid nematode larvae on pasture were monitored fortnightly from July 1995 to June 1996 in the central highlands of Kenya. The number of larvae on pasture was moderate, reaching > 1,200 kg(-1) dry matter of grass during the period of, and soon after, the rains, and remained low in the dry seasons. The number of larvae on pasture was directly related to the rain-fall pattern which was found to be the most important factor for the development of eggs and free-living stages. Haemonchus was the predominant genus, followed in decreasing order by Trichostrongylus, Cooperia, Oesophagostomum and Bunostomum. The mean total adult worm burdens of tracer calves released at monthly intervals were related to the levels of herbage larvae and there was a positive correlation between faecal worm egg counts and worm burdens (r = 0.58) during the study period. These results indicate that a reduction in the contamination of pasture with nematode eggs before the rains could result in pastures carrying fewer larvae and thus form the basis of effective worm control programmes for cattle.     

Development and survival of infective larvae of gastrointestinal nematodes of cattle on pasture in central Kenya

On a series of pasture plots, 2 kg pats of bovine faeces containing known numbers of strongylid (Haemonchus, Cooperia, Oesophagostomum and Trichostrongylus) eggs were deposited at intervals of 4 weeks from July 1995 to June 1996. The plots were sampled every 2 weeks after contamination and infective larvae were identified and counted. Larvae of all the genera developed throughout the year, but the pats exposed during the rainy season yielded more abundant larvae on the herbage. Irrespective of the season of deposition of the pats, larvae were found in larger numbers from 2 to 6 weeks after deposition and generally declined to below detectable levels within 12 to 16 weeks of contamination. The comparatively short survival times noted in this experiment may present opportunities for manipulation of the population dynamics of the gastrointestinal nematodes in the tropical environment of Kenya.     

Fecundity of gastrointestinal trichostrongylid nematodes of sheep in the field

Twenty-two Dorset Rambouillet lambs were moved to contaminated pasture on Apr 1, 1987. At regular intervals thereafter, pairs of lambs were withdrawn and euthanatized. Gastrointestinal parasites in the abomasum, small intestine, cecum, and large intestine were removed and counted. The last pair of lambs was euthanatized 8 months after original placement on the contaminated pasture. Fecal samples were taken at 3- to 4-week intervals throughout the grazing season and the fecal egg counts were used to estimate parasite fecundity (output of eggs per female parasite per day). The principal parasite genera found included Haemonchus spp, Trichostrongylus spp, and Nematodirus spp. In each of the genera examined, parasite fecundity remained the same irrespective of the intensity or duration of infection. Estimated average fecundities (eggs/female/day) were as follows: Haemonchus contortus, 6,582; Trichostrongylus spp, 262; Nematodirus spp, 40; and Oesophagostomum venulosum, 11,098.     

Epidemiologic approach to the control of sheep nematodes

Epidemiologic approaches to parasite control, with reduced reliance on the use of anthelmintics, were studied in 6 groups of weaned lambs and 4 groups of suckling lambs grazing fertilized pastures. Strategies tested included prophylactic treatments in the spring, provision of safe pastures, treat-and-move strategies, and winter (prelambing) treatment of ewes. Suppressive treatment with a non-benzimidazole drug was used as a production yardstick against which the epidemiologic approaches were judged. Suppressive treatment with a benzimidazole drug was used to determine the drug resistance status of the flock. The success of each strategy was evaluated by measurements of body weight, wool growth, fecal egg counts, pasture larval counts, and total worm burdens. Prophylactic treatments in the spring were just as effective as suppressive treatments throughout the entire grazing season and resulted in significant (P less than 0.001) increases in weight gain. Effective parasite control also was obtained by moving ewes and lambs to safe pastures (low infectivity) in May, and resulted in significant (P less than 0.001) increases in weight gain. A treat-and-move strategy led to significant (P less than 0.001) increases in weight gain until September, but then a loss of weight in October, suggesting the need for a double treat-and-move strategy in the case of late-marketed lambs. The value of winter (prelambing) treatments for ewes also was demonstrated. Suppressive treatments with a benzimidazole drug confirmed the presence of benzimidazole-resistant nematodes.     

Strategic use of anthelmintics for parasitic nematodes in cattle and sheep

Treatment regimes for the control of parasitic nematodes in cattle and sheep are reviewed. The advantages and disadvantages of each strategy are outlined and the veterinarian's judgement of the management and economic constraints involved when recommending a particular system to a client is emphasised.     

Anthelmintic activity of ivermectin against immature gastrointestinal nematodes of sheep

Twenty-four lambs of mixed breeding with mixed experimental infections of Haemonchus contortus, Ostertagia circumcincta, Trichostrongylus axei, and T colubriformis were allotted to 4 groups. One group (control) was given the vehicle propylene glycol, and the others were given 100, 200, or 300 micrograms of ivermectin/kg of body weight by mouth. Twelve days after treatment, the sheep were necropsied. The compound was greater than 99% effective against immature stages of 4 nematode species at all dosages, except at the 100 micrograms/kg dosage, where efficacy was 96% against H contortus.     

Survey for drug-resistant gastrointestinal nematodes in 13 commercial sheep flocks.

The prevalence of drug-resistant ovine parasites in the United States has not been widely reported. Thirteen flocks, typical of commercial sheep production units, were selected for survey. Four anthelmintics (fenbendazole, ivermectin, pyrantel pamoate, and levamisole) were tested for their ability to reduce herd mean pretreatment fecal egg count. If a properly dosed and administered drug failed to reduce herd mean pretreatment fecal egg count by 80%, it was considered ineffective in that flock, and the presence of parasites resistant to that drug was inferred. Fenbendazole administration changed pretreatment fecal egg counts by +9% to -100%. On the basis of the aforementioned definition, drug resistance existed in 6 of 13 flocks. Posttreatment larval culture indicated that Haemonchus contortus survived administration of fenbendazole. Levamisole, pyrantel pamoate, and ivermectin reduced pretreatment fecal egg count by -83% to -100%; resistance to these products was not evident in the flocks surveyed.     

Avermectin-resistance in gastrointestinal nematodes of Boer goats and Dorper sheep in Switzerland

Anthelmintic resistance in gastrointestinal nematodes among small ruminants is widespread in South Africa and Dorper sheep and Boer goats have been imported into Switzerland from this country on a number of occasions. Therefore, this study aimed to investigate the occurrence of avermectin (AVM) resistant gastrointestinal nematodes (GIN) in these breeds in Switzerland. A total of 24 Boer goat farms and 12 Dorper sheep farms participated in the study. According to the faecal egg count reduction test (FECRT) AVM-resistant GIN populations were confirmed in 7 of the 24 Boer goat farms and suspected in a further 8 farms. Likewise AVM-resistance was confirmed in 2 of 12 Dorper sheep farms and suspected in a further 6 farms. Haemonchus contortus and Trichostrongylus spp. were the dominant resistant species according to larval cultures. In the farms with detected AVM-resistance the animals were additionally treated with levamisole after natural reinfection. With the exception of one farm with a 'close-to cutoff-result' the FECRT gave no indication for resistance against levamisole. The results indicate that AVM-resistance is widespread in Swiss small ruminant farms keeping Boer goats and Dorper sheep. The common tradition of grazing animals from different farms on prealpine and alpine pastures could favour the spread of resistant populations within the country.     

Epidemiology of gastrointestinal nematodes of sheep and goats in Haryana, India

Epidemiological studies on some gastrointestinal nematodes of sheep and goats in Karnal, Ambala and Rohtak districts of Haryana (India) revealed that Haemonchus contortus and Trichostrongylus spp. were responsible for parasitic gastroenteritis in these hosts. The adult parasites persisted in the host throughout the year and there was no indication of hypobiosis. The maintenance of the parasite population depended on a continuous cycle of infection between the host and the pasture. The agroclimatic conditions of the districts revealed that, in general, favourable weather conditions for the development and survival of the free-living stages of the parasites existed all year round.     

Future technologies for control of nematodes of sheep

New approaches to nematode control in sheep are urgently needed as anthelmintic drench resistance becomes ever more widespread among worm populations. Here we briefly describe and assess a number of new technologies which will become increasingly important in anti-nematode control programmes in the future. These include vaccines, immunomodulants, strategic grazing practices, the use of biological agents to destroy nematode larvae, biological anthelmintics and targeted silencing of genes regulating nematode development.     

The anthelmintic efficacy of netobimin against naturally acquired gastrointestinal nematodes in sheep

The broad-spectrum anthelmintic efficacy of netobimin (SCH 32481, Schering Corporation) was evaluated using 30 cross-bred spring lambs with naturally acquired infections of gastrointestinal nematodes. Three groups of 10 animals each were allotted into either control (given a tap water drench as a placebo) or 7.5 and 20 mg kg-1 dosage groups (given the netobimin as an oral drench). Seven to fourteen days post-treatment, animals were necropsied and nematodes recovered by standard techniques. Examination of fecal samples taken on dates of necropsy showed median egg production was reduced in treated animals (61.98% with 7.5 mg kg-1 and 100% with 20 mg kg-1). The compound was highly effective in removal of adult nematodes representing a number of genera and species of trichostrongyloids at the 7.5 and 20 mg kg-1 dose levels (shown, respectively, below). These included Ostertagia spp., with O. circumcincta, O. trifurcata, O. ostertagi and Teladorsagia davtiani (96.20%; 100%), Trichostrongylus spp., with T. axei, T. vitrinus and T. colubriformis (100%; 98.72%), Nematodirus spp., with N. spathiger, N. filicollis and N. battus (100% both levels) and Haemonchus contortus (100% both levels). High efficacies against other species of nematodes (at both dose levels) were not statistically significant (Cooperia spp., Chabertia ovina and Oesophagostomum venulosum). At 20 mg kg-1, netobimin significantly reduced populations of early and late fourth stage larvae of Ostertagia spp. by 100%. The overall efficacy (all life stages included) was 90.16% at 7.5 mg kg-1 and 98.77% at 20 mg kg-1 dose levels. No adverse reactions or signs of toxicosis were observed.     

Comparative efficacy of pyrethrum marc with albendazole against sheep gastrointestinal nematodes

The efficacies of pyrethrum marc and of albendazole against experimental sheep gastrointestinal nematode infection were compared. Sheep were infected orally with 10000 larvae (Haemonchus spp. (60.1%), Oesophagostomum spp. (13.9%), Trichostrongylus spp. (13.2%), Cooperia spp. (8.3%), Nematodirus spp. (3.5%), Strongyloides spp. (0.8%) and Ostertagia spp. (0.2%)). Faecal egg count reduction in albendazole-treated sheep was 100% by day 4 following treatment, compared to 37.03%, 31.3%, 38.9% and 51.8% on days 4, 6, 8 and 10 in pyrethrum marc-treated sheep. These reductions were statistically significant on days 8 and 10 post-treatment (p<0.05). The potential for using pyrethrins for helminth treatment is discussed.     

Update on the prevalence of anthelmintic resistance in gastrointestinal nematodes of sheep in New Zealand

Abstract

Extract

Recently, a comparison was made between the prevalence of anthelmintic resistance, determined using faecal egg count reduction tests (FECRT), on randomly selected sheep farms in a systematic national survey (Waghorn et al. 2006 Waghorn, TS, Leathwick, DM, Rhodes, AP, Lawrence, KE, Jackson, R, Pomroy, WE, West, DM and Moffat, JR. 2006. Prevalence of anthelmintic resistance on sheep farms in New Zealand. New Zealand Veterinary Journal, 54: 271–277. [Taylor & Francis Online], [Web of Science ®] , [Google Scholar]) and that derived from similar case material submitted to a veterinary pathology laboratory on a more ad-hoc basis (McKenna 2008 McKenna, PB. 2008. An examination of the relative reliability of laboratory case submissions in determining the prevalence of anthelmintic resistance in sheep nematodes in New Zealand and the possible influence of test analysis methodology on such data. New Zealand Veterinary Journal, 56: 55–59. [Taylor & Francis Online], [Web of Science ®] , [Google Scholar]). The results of that comparison showed that while there were some differences between them, there were considerable similarities in the prevalence figures obtained from either source. Those similarities, which were particularly evident in terms of the overall pattern of involvement of the various worm genera and the types of anthelmintic concerned, led to the conclusion that FECRT case submissions to veterinary laboratories may offer a useful source of information regarding changes in the prevalence of anthelminticresistant sheep nematodes in New Zealand (McKenna 2008 McKenna, PB. 2008. An examination of the relative reliability of laboratory case submissions in determining the prevalence of anthelmintic resistance in sheep nematodes in New Zealand and the possible influence of test analysis methodology on such data. New Zealand Veterinary Journal, 56: 55–59. [Taylor & Francis Online], [Web of Science ®] , [Google Scholar]). Accordingly, the present study was undertaken to make further use of this material, to try to ascertain what, if any, such changes may have taken place over the last few years.     

Economic values for resistance to gastrointestinal helminths in meat sheep in Kenya

Economic values for resistance to gastrointestinal (GI) helminths in meat sheep were estimated based on previously published genetic and phenotypic parameters in a selection index objectively optimizing gains on yearling weight (YW). A two‐trait index of YW and faecal egg count (FEC) were considered when accounting only for tangible roles of sheep production using individual records for index calculation (scheme 1) or including individual, sire, dam and male paternal half‐sib information (scheme 2). Schemes 3 and 4 were similar to schemes 1 and 2, respectively, but accounted for both tangible and intangible roles of sheep production. Economic values within each scheme were estimated for five breeding objectives as follows: (i) index response in YW equals response from single trait selection, (ii) index response in YW is maximum, (iii) the level of FEC was held constant, (iv) A predetermined response of ?0.22 (×1000) eggs per gram was assumed and (v) Monetary value of response in FEC is minimum. All estimated economic values were negative, and were Kenya Shillings (KSh) ?34.90 (US$?0.50), 0.00, ?92.20 (US$?1.32), ?153.31 (US$?2.19) and ?47.90 (US$?0.68), respectively, for options 1–5 in scheme 1. In all schemes the breeding options ranked 4, 3, 5 and 1 in descending order; however, options 1 and 5 exchanged positions in schemes 2 and 4. Economic values were responsive to changes in heritability of FEC and genetic correlation between the two traits. The magnitude of the economic values reflects the importance of including resistance to GI helminths in the breeding objectives for meat sheep in different production systems.