Dynamics of pasture contamination by gastrointestinal nematodes of cattle under extensive management systems: proposal for strategic control.

An epidemiological study of gastrointestinal nematode parasitism in beef cattle in mountainous areas of Spain was performed. The dynamics of contamination with gastrointestinal nematode larvae of Pyrenean pastures was studied over four years at five areas at different altitudes (900 m to 2100 m), grazed by animals according to traditional systems of beef cattle in mountainous areas. Grass samples were taken every two weeks and larval differentiation was performed. Worm egg counts of grazing animals were assessed in cows, heifers and calves. A consistent seasonal pattern of infective larvae on pasture through the study was observed. In hay meadows, located below 1000 m, infective larvae were found from the end of October until June of the following year. At higher altitudes (1200-2100 m), a bimodal pattern of pasture larvae contamination was observed with increases in late spring (March-June) and in late autumn (September-November). Ostertagia spp., Cooperia spp., Trichostrongylus spp., Oesophagostomum spp., and Nematodirus spp. were found, with Ostertagia spp. being the most frequently found, followed by Cooperia spp. The highest increase of larval contamination in autumn coincided with the grazing of animals in hay meadows. This elevated autumn larval population had a very important epidemiological role because these larvae remained as overwintered larvae until the following grazing season, starting the cycle of contamination of the animals.     

Effectiveness of grazing management in controlling gastrointestinal nematodes in weaner lambs on pasture in Denmark.

A dose and move to clean pasture strategy for nematode control in weaner sheep was compared to a move only strategy. Sixteen ewes with twin lambs (2-3 weeks old) were turned out on infected pasture on 4 May 1999. On 1 July, the lambs were allocated to four groups of eight and weaned on to clean pasture. Two groups (DM1+2) were treated with anthelmintics, while the other two (M1+2) were not treated. Each group was allocated to a separate paddock and set stocked until 27 September when all the animals were slaughtered to perform worm counts.Moving the weaned lambs to clean pasture reduced the faecal egg counts to less than one third within 4 weeks while the treatment reduced it to zero for 4 weeks. Faecal egg counts of the dose and move groups remained significantly lower for 6 weeks (P<0.0001) after moving to the clean pasture. After this period the differences were not significant as the dose and move groups started shedding eggs in faeces. The pasture infectivity was lower in the paddocks grazed by groups (DM1+2). The weight gains and the serum albumin levels were comparable in all four groups. O. circumcinta and Trichostrongylus vitrinus were the major species recovered. The total worm counts were significantly lower in (DM1+2) compared to M1+2, particularly the mean counts in the small intestines (T. vitrinus) (P<0.01). It was concluded that weaning lambs at the beginning of July and moving them before the expected mid-summer rise in herbage infection to a clean pasture will prevent parasitic gastroenteritis and achieve good production whether the move is accompanied by anthelmintic treatment or not. The effects will be subject to prevailing nematode species, local climatic conditions and length of the grazing season.     

Seasonal changes in pasture populations of infective larvae of gastrointestinal nematodes of cattle in eastern Nigeria

The seasonal changes in the populations of trichostrongylid infective larvae (L3) on herbage and in soil samples collected from pastures grazed by beef cattle were studied at Nsukka, eastern Nigeria, from April 1980 to July 1981. Large numbers of L3 were recovered from all samples collected during the rainy season (April to October). The rainy season herbage infestation was characterised by three clearly defined peaks. The first, which followed an 'early rains' (April) rise, occurred in the second half of May while the larger second and third peaks occurred in late July and October respectively. It is suggested that each of these peaks represented a distinct wave of infestation by a separate generation consisting of the three trichostrongylids concerned, namely Cooperia, Haemonchus and Trichostrongylus species. Although there was a sharp fall in pasture infestation following the onset of the dry season, appreciable numbers of L3 were still present on herbage in early December. The implications of these findings have been discussed in relation to the choice of effective strategic anthelmintic programmes for the prophylaxis and control of bovine parasitic gastroenteritis in the Nsukka area.     

The effect of first season chemoprophylaxis in calves on second season pasture contamination and acquired resistance and resilience to gastrointestinal nematodes

Two groups of second grazing season cattle, which had been treated with an ivermectin-sustained-release bolus (ISRB) in their first grazing season, were monitored during consecutive years (1995 and 1996) on the same second grazing season pasture. In the preceding year (1994), this pasture had been grazed by yearlings that had not received chemoprophylaxis in their first grazing season. The objectives of the study were, firstly, to investigate whether the chemoprophylactic-treated yearlings were less resistant to gastrointestinal nematodes upon subsequent exposure, and hence excreted more strongyle eggs compared to the control yearlings; secondly, whether an increased susceptibility of the previously treated animals resulted in a yearly increase of the pasture infestation on the second grazing season pasture; and finally, whether this affected the second year weight gain of the animals. In 1996, the yearlings that had been chemoprophylactic-treated in 1995 excreted higher numbers of nematode eggs, compared to the previously ‘untreated' yearlings. In addition, the proportion of Cooperia larvae was markedly higher in the faecal cultures from the chemoprophylactic treated-animals, suggesting a negative effect of preventive treatment with an ISRB on the acquired resistance of the animals. However, there was no evidence that the slightly higher egg output in the previously treated yearlings had an effect on the larval contamination of the second grazing season pasture. A significant yearly decrease in the second season average daily weight gains was observed, but it could not be inferred from the results of the parasitological parameters that the differences in second year growth were caused by different levels of resilience between chemoprophylactic-treated and -untreated animals. As the study covered three consecutive second grazing seasons, an effect of differences between years (e.g. in weather conditions or grass growth) on the results cannot be excluded.     

Use of a mixed sericea lespedeza and grass pasture system for control of gastrointestinal nematodes in lambs and kids

Because of a high prevalence of anthelmintic resistance and consumer demand for chemical free meat products, management tools to minimize the need for deworming are needed. The objective was to examine the effectiveness of grazing sericea lespedeza (SL) in a mixed grass or a pure forage system for control of gastrointestinal nematodes (GIN); in other words pasture systems included grass, grass plus SL, or SL alone (Experiments 2 and 3). Selective use of copper oxide wire particles (COWP) based on the FAMACHA(?) system was used to aid in GIN control. In Experiment 1, lambs co-grazed bermudagrass (BG; n=21) or SL in a mixed grass pasture (SLM; n=22) with dams for 14 days. In Experiment 2, lambs grazed BG (n=14), SLM (n=13), or pure SL (SLP; n=13) pastures for 56 days. In Experiment 3, doe kids grazed BG (n=12), SLM (n=13), or SLP (n=13) for 84 days. Animals were fed a 16% crude protein supplement based on NRC requirements and estimated forage quality of pastures, so that 454, 389, and 200 g/lamb (Experiment 2), or 454, 300, and 150 g of supplement/goat (Experiment 3) was fed to BG, SLM, and SLP, respectively. Animals were dewormed with COWP if FAMACHA(?) was >3. Coprocultures were conducted to identify GIN genus. In Experiment 1, FEC were reduced in lambs grazing SLM compared with BG pastures. In Experiment 2, FEC were reduced in SLP compared with BG lambs on all days, and reduced in SLM compared with BG lambs on day 56. Initially, Haemonchus contortus was the predominant nematode, but the population shifted to other species in the SL groups by the end of the study. The mean number of dewormings/lamb was 0.71, 0.20, and 0.21±0.13 for BG, SLM, and SLP groups, respectively. In goats in Experiment 3, Trichostrongylus spp. was the predominant nematode in May and June and H. contortus in July. There was little meaningful effect of forage treatments on GIN infection in kids. Because H. contortus was not the predominant nematode in kids, the integrated approaches used may not have been effective in controlling GIN. Grazing SL was effective for GIN control in lambs in early summer, but the effect was delayed in lambs grazing a mixed SL/grass pasture unless lambs initially grazed with dams. An integrated approach used that included SL grazing and COWP for deworming was effective in lambs.     

Trypanosomiasis control in Boran cattle in Kenya: A comparison between chemoprophylaxis and a parasite detection and intravenous treatment method using isometamidium chloride

Summary Two methods of trypanosome control in Boran cattle kept under very high trypanosomiasis risk were compared: the traditional intramuscular isometamidium chloride prophylaxis with a parasite detection and intravenous isometamidium chloride treatment method. The results were related to a control group under diminazene aceturate treatment. Isometamidium chloride at 0.25 mg/kg as routinely used by the ranch was of little benefit by either method, with breakthrough infections occurring as early as one week after treatment. When isometamidium chloride at 1 mg/kg was used, the curative intravenous method appeared to be superior to the intramuscular prophylaxis with regard to cost of drugs and to a 31% higher weight gain over a 30 week period. Weekly infection rates in the intravenous group decreased over time, despite an increasing trypanosomiasis challenge, with a mean interval of 6.4 weeks between treatments as compared with 4.3 weeks in a diminazene aceturate control group. It was concluded that isometamidium chloride given intravenously had not only a very good therapeutic but also a considerable prophylactic effect of not less than four weeks.

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Resumen Se compararon dos métodos para el tratamiento de la tripanosomiasis en ganado Borán, en un área de alto riesgo: El tratamiento profiláctico convencional con Samorín vía intramuscular (IM), contra un método de detección del parásito y la inyección intravenosa (IV) de Samorín. Los resultados se compararon con aquellos de un grupo tratado curativamente con Berenil. Samorín en dosis de 0.25 mg/kg como se emplea de rutina en las ganaderías, fue de poco beneficio via IM e IV, con recaídas una semana después del tratamiento. Sin embargo, cuando se utilizó Samorín en dosis de 1 mg/kg, el método curativo IV fue superior a la profilaxis IM, con relación al costo de la droga y a una ganacia de peso de 31% durante un período de 30 semanas. La tasa de infecciones semanales en el grupo inoculado vía IV, disminuyó con el tiempo, a pesar del aumento de la descarga infectiva con tripanosomas, con una media de intervalo de 6.4 semanas entre tratamientos, comparado con 4.3 semanas en el grupo tratado con Berenil. Los hallazgos permiten la conclusión, de que el Samorín aplicado vía IV, tiene efecto profiláctico y curativo, no menor de cuatro semanas.

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Résumé Deux méthodes de lutte contre les trypanosomoses chez le bétail Boran soumis à un risque trypanosomien très élevé ont fait l'objet d'une étude comparative: la prophylaxie classique avec le Samorin en intramusculaire avec recherche préalable du parasite, puis par voie intraveineuse. Les résultats ont été rapprochés de ceux du lot-témoin soumis à un traitement curatif au Bérénil. Le Samorin à la dose de 0.25 mg/kg couramment employée au ranch a donné peu de résultats quelle que soit la méthode utilisée, avec des résurgences de l'infection parfois une semaine après le traitement. Avec l'emploi d'une dose de 1 mg/kg, la méthode curative par voie intraveineuse semblait plus efficace que la prophylaxie par voie intramusculaire, si l'on se réfère au co?t des médicaments et à un gain de poids supérieur de 31% sur une période de 30 semaines. Les taux hebdomadaires d'infection dans le groupe traité par voie intraveineuse ont diminué avec le temps, en dépit d'une pression glossinaire accrue, avec un intervalle moyen de 6,4 semaines entre les traitements à comparer avec 4,3 semaines dans le groupe témoin traité au Bérénil. Les résultats permettent de conclure que le Samorin par voie intraveineuse possède, non seulement un très bon effet thérapeutique mais également une action prophylactique très importante dont la durée est au moins de 4 semaines.

     

The survival of nematodes and cestodes of sheep in the pasture during the winter in eastern Norway

Using 21 worm-free lambs in paddocks on old sheep pastures on 4 farms near Oslo, it was found that Nematodirus spp., Ostertagia spp. and Moniezia spp. were the only helminths which could survive the winter in the pasture in great numbers. A few Teladorsagia davtiani, Chabertia ovina, Trichuris ovis, Cooperia onchophora and Skrjabinema ovis survived the winter. Trichostrongylus axei, T. vitrinus and Oesophagostomum venulosnm showed a negligible ability to survive the winter in the pasture. The following species were never found to survive: Haemonchus contortus, Trichostrongylus colubriformis, Bunostomum trigonocephalum, Cooperia curticei and Strongyloides papillosus.     

Dynamics of infestation of cattle and pasture by gastrointestinal nematodes in an Atlantic temperate environment

The objective of the present study was to determine the dynamics of infestation of cattle and pasture by gastrointestinal nematodes in a mild humid environment in northwestern Spain. For this, infestation of pasture by free-living stages (L3), dynamics of faecal egg output, blood pepsinogen levels and worm burden in slaughtered animals were quantified. The results showed a high degree of annual variability, which was dependent on weather conditions. The seasons were clearly defined in the study area, with mild humid winters and relatively dry summers registered throughout the years of the study. Infestation of pasture by larvae varied from year to year, peaking during August in the first year, between August and December in the second year, and during October in the third year. The annual variation was mainly due to weather conditions, particularly the amount of rain in summer. The patterns of faecal egg output were similar in the first and third grazing seasons, with maximum levels observed in May/June; however, in the second year, the peak was reached in October. Blood pepsinogen levels increased from pasture turnout (March/April) until the end of the grazing season (November/December), reaching maximum values from August/September onwards. The nematode parasite species identified at necropsy were Ostertagia osteragi, O. lyrata, Cooperia oncophora, C. macmasteri, C. punctata and Trichuris ovis, with O. ostertagi and C. oncophora predominating. In faecal cultures, the following genera were also identified: Haemonchus, Trichostrongylus, Nematodirus, Bunostomum, Oesophagostomum and Strongyloides. There was a significant correlation (r=0.97, P<0.01) between worm burden (Ostertagia spp.) and pasture infestation (Ostertagia L3) 3 weeks prior to slaughter of the calves, and also between blood pepsinogen levels and pasture infestation by Ostertagia L3 (r=0.33, P<0.02). Correlations between worm burden and faecal egg output and between blood pepsinogen level and faecal egg output were not significant. The results obtained in the present study confirm that there is annual variability in the time-course of nematodosis in cattle, and demonstrate the importance of weather, particularly summer rainfall, in an Atlantic temperate environment.     

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.     

Anthelmintic resistance on goat farms in Georgia: efficacy of anthelmintics against gastrointestinal nematodes in two selected goat herds

Gastrointestinal nematode (GIN) parasitism is a major constraint to production of goats in the southeastern United States. The conventional method of control used by producers in this region is frequent use of anthelmintics during the warm season. Overuse of anthelmintics has led to an increase in the incidence of anthelmintic resistance in many parts of the world, but data on prevalence of anthelmintic resistance in GIN of goats in the southeastern United States are very limited. To address this issue, anthelmintic efficacy was determined in goat herds at the Fort Valley State University, Agricultural Research Station (FVSU-ARS) and the University of Georgia, College of Veterinary Medicine (UGA-CVM) using fecal egg count reduction (FECR) tests and DrenchRite((R)) larval development assays (LDA). At FVSU-ARS, 2-year-old Spanish goat does were randomly allocated to one of nine different treatment groups (n = 10): albendazole (ABZ; 20mg/kg body weight (BW)), fenbendazole (FBZ; 20mg/kg BW), ivermectin (IVM; 0.4 mg/kg BW), doramectin (DRM; 0.4 mg/kg BW), moxidectin (MOX; 0.4 mg/kg BW), levamisole (LEV; 12 mg/kg BW), morantel tartrate (MOR; 10mg/kg BW), a combination of IVM (0.4 mg/kg BW) and ABZ (20 mg/kg BW), and untreated controls. At UGA-CVM, goats were randomly allocated to one of five different treatment groups (n = 8): ABZ (20 mg/kg BW), IVM (0.4 mg/kg BW), MOX (0.4 mg/kg BW), LEV (12 mg/kg BW), and untreated controls. All drugs in both experiments were administered orally. Anthelmintic efficacy was calculated by comparing 14-day post-treatment FEC of treated and control animals, and percent reductions were interpreted using the World Association for the Advancement of Veterinary Parasitology guidelines for resistance. For the LDA, nematode eggs were isolated from pooled fecal samples of untreated control goats in each herd and used to perform DrenchRite((R)) assays. In the FVSU-ARS herd, MOX, LEV, the combination of IVM and ABZ, IVM, DRM, ABZ, MOR, and FBZ reduced FEC by 100, 91, 88, 78, 76, 62, 48, and 10%, respectively. In the UGA-CVM herd, MOX, LEV, ABZ and IVM, reduced FEC by 100, 94, 87, and 0%, respectively. In both herds moxidectin was the only drug tested that was fully effective. Results of the LDA were in agreement with results of the FECR tests for both herds. These data demonstrate the presence of GINs resistant to all three major anthelmintic classes in both goat herds.     

Bulk milk ELISA and the diagnosis of parasite infections in dairy herds: a review

The bulk milk enzyme-linked immune sorbent assay (ELISA) is a rapid and inexpensive method of assessing herd exposure to pathogens that is increasingly being used for the diagnosis of parasite infections in dairy herds. In this paper, with the dairy herd health veterinarian in mind, we review the principles of the assay and the recent literature on the potential role of bulk milk ELISA for the diagnosis of ostertagiosis, fasciolosis, parasitic bronchitis due to cattle lung worm and neosporosis. It is generally accepted that assay results reflect exposure to the parasite rather than the presence of active infection. Bulk milk ELISA can be a useful tool for the veterinary practitioner as a component of a herd health monitoring programme or in the context of a herd health investigation. It can also play a role in regional or national surveillance programmes. However, the results need to be interpreted within the context of the herd-specific health management, the milk production pattern and the parasite life cycle.     

Development and survival of free-living stages of gastrointestinal nematodes of sheep and goats on pasture in the Nigerian derived savanna

Four grass plots were sequentially contaminated with goat faeces containing known numbers of unembryonated eggs of predominantly Haemonchus contortus and Trichostrongylus spp. between October 1982 and April 1983. Four other plots were similarly contaminated with sheep faeces between February and May 1987. An additional plot was repeatedly contaminated with sheep faeces from February to April 1987. Populations of free-living stages in faeces and of infective larvae (L₃) in the herbage were subsequently monitored until the end of April and June of 1983 and 1987 respectively. During February and May 1987 two control cultures of sheep faeces were incubated in the laboratory at 25°C–30°C and at a constant temperature of 50°C and the free-living development was also monitored. L₃ developed very readily in the faeces cultured at 25°C–30°C and in those spread on a grass plot in October, at the end of the wet season, but developed less on the plot contaminated in May at the start of the wet season. Worm eggs in faeces deposited on plots during the hot dry season (December to April) or incubated at 50°C died and disintegrated after 24–48 h exposure to the high environmental temperatures. The results indicate that it is unlikely that gastrointestinal nematodes of sheep and goats can develop or survive on open pasture during the dry season in the Nigerian derived savanna zone.     

Management and control of gastrointestinal nematodes in communal goat farms in Zimbabwe

Goats are an important source of livelihood especially in smallholder communities. Infections with gastrointestinal nematodes (GIN) remain the most prevalent parasitic diseases affecting small ruminants. The study was conducted to assess management, the level of knowledge and control of gastrointestinal nematodes. Surveys were conducted in Chipinge, Shurugwi, Binga, Tsholotsho and Matobo districts, representing the five natural/agro-ecological regions (NR) in Zimbabwe. Data was collected in 135 households using a pre-tested semi-structured questionnaire. Results indicated that goats were ranked the most important livestock species, with high flock sizes in NR IV and V. Partitioning of roles was such that the adult males were involved in decision-making while females and children were involved in day-to-day management of animals. Farmers showed low levels of input use, with natural pasture (98.4%) being the main feed source and indigenous breeds (73.2%) being kept. Farmers ranked food and financial benefits as the main reasons for keeping goats. Gastrointestinal nematodes ranked the highest as the most common disease, with majority of farmers (57%) not controlling or treating animals and 63% of farmers not having knowledge on the spread of GIN. Access to veterinary services, anthelmintic class used and breeds used by the farmers had the highest effects on parasitic infections in households. Farmer education is required for capacitation of farmer in terms of disease prevention and control so as to improve goat production.     

Bermudagrass management in the Southern Piedmont USA. V: Gastrointestinal parasite control in cattle

Parasite-free pastures would improve cattle health and performance, resulting in possible economic return to producers. Our objective was to determine the effect of a single series of anthelmintic treatment of steers prior to stocking on Coastal bermudagrass pastures, during five consecutive summers, on the parasite burden in cattle. The site for this experiment had been conventionally cropped for several decades, with no exposure to cattle, and would be expected to be relatively free of nematode larvae. The experimental design was a randomized complete block (landscape features) with a split plot arrangement of treatments where main plots were pasture fertilization treatments (mineral, clover plus mineral, and broiler litter) and split plots were low and high forage mass. Anthelmintic treatment included pour-on ivermectin on day -21, albendazole on day -7, and injectable ivermectin 48 h prior to stocking of pastures, with the cattle remaining in drylot during the 48-h period prior to being placed on the experimental paddocks. All steers received only one series of treatments during any given year. Yearling Angus steers (Bos taurus) were managed in a put-and-take grazing system with three "tester" steers assigned to each paddock and "grazer" steers added or removed at 28-day intervals. From 1994 to 1998, steers grazed the paddocks for a 140-day period from mid May until early October each year. Fecal samples for worm egg counts were obtained on day 0 and at 28-day intervals, thereafter. On all sampling days after day 0, samples were obtained only from tester animals. Over the 5-year period, the mean eggs per gram of feces (epg) gradually increased from 0 (following treatment) to a mean of 2.2 (range from 0.7 to 3.0) by the end of the grazing season (the last sampling date) in October. Although the epg were not zero, they were below threshold levels that would allow development of a parasite burden in cattle. In traditional management systems, cattle graze parasite-contaminated pastures; therefore, parasites negatively impact growth and productivity throughout the entire grazing period. Periodic anthelmintic treatments simply give a temporary reprieve from those parasitic infections. Conceptually, using the current grazing system, it should be possible to maintain these pastures in a parasite-free status indefinitely; however, from a drug resistance perspective, it would be most applicable in sod-based rotation systems where cattle graze from two to five years before land is returned to row-crops. By removing the effect of parasites, cattle can grow without the physiological constraints that gastrointestinal parasites place on appetite, digestion, nutrient utilization, and general well being.     

Efficacy of a morantel sustained-release bolus for the control of gastrointestinal nematodes in Florida dairy heifers

The effectiveness of a morantel sustained-release bolus (MSRB) in controlling gastrointestinal nematode infections was determined in 70 Holstein heifer calves with no prior grazing experience. Calves were allotted to 2 treatment groups and were maintained in Florida during the grazing season on divided pastures of equal area. One MSRB was administered to each calf in 1 group at the time of turnout onto spring pasture, whereas calves in the other group remained as nonmedicated controls. By the end of the grazing season, treatment resulted in significantly (P less than 0.05) lower worm burdens and significantly improved weight gains. The MSRB-treated calves were able to reach breeding weight 2 to 4 weeks earlier than did nonmedicated calves.     

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.     

A 3-year field evaluation of pasture rotation and supplementary feeding to control parasite infection in first-season grazing cattle: dynamics of pasture infectivity

A 3-year grazing trial (2002-2004) was conducted on a commercial beef cattle farm in south-central Sweden to assess different methods of parasite control. This paper focuses on the dynamics of the free-living larval stages, whereas data on performance and within-host parasitological variables are presented in a complementary paper. Each year in May, 4 groups of 10 first-season grazing (FSG) steers were turned out on to separate 2ha paddocks and subjected to the following strategies: (1) spring turn-out on to pasture which had been grazed the previous year by second-season grazing (SSG) steers (paddock RT), followed by a move to aftermath (paddock AM) after 10 weeks (mid-July), (2) supplementary feeding with concentrate and hay for 4 weeks following turn-out (paddock FD), set stocked, (3) untreated control (paddock UT), set stocked and (4) anthelmintic treated control (paddock DO), set stocked. All paddocks were assigned a new set of FSG cattle each year whereas the treatments remained the same. Pasture infectivity were monitored partly by two tracer calves that grazed each paddock along with the FSG calves for 3 weeks after turn-out and prior to housing, partly by analysis of herbage samples for infective larvae (L3) that were collected from each paddock at monthly intervals between April and October. The predominant genera found were Cooperia and Ostertagia. Tracers grazing paddock RT overall harboured less worms, and in particular less Ostertagia spp., and tracers grazing paddock AM in mid-July harboured insignificant numbers of nematodes compared to tracers on the FD and UT paddocks. Although total worm counts varied between groups, smaller numbers were generally observed early in the grazing-season (May), compared to close to housing (September) when inhibited early L4 larvae were almost exclusively found. Results observed from herbage samples showed high numbers of L3 in spring before the time of turn-out, compared to around housing. In conclusion, the rotation control strategy showed promising results and provided a turn-out pasture that was 'nematode safe' to FSG cattle the following spring, whereas the feeding strategy failed as applied in this experiment.