Control Of Gastrointestinal Nematode Infections Research Articles

The first report of multidrug resistance in gastrointestinal nematodes in goat population in Poland

BackgroundProphylactic anthelmintic treatment with one of three basic classes of anthelmintics (benzimidazoles, macrocyclic lactones and imidazothiazoles) is still the mainstay of control of gastrointestinal nematode infections in small ruminants worldwide. As a consequence, anthelmintic resistance is a serious threat to small ruminant health and production. While the resistance to one class of anthelmintics has already been reported in most of countries, the newly-emerging problem is the resistance to two or even all of classes referred to as multidrug resistance. This study aimed to evidence the presence of multidrug resistance of gastrointestinal nematodes in goats in Poland.ResultsThe combination of one in vivo method (fecal egg count reduction test) and two in vitro methods (egg hatch test and larval development test) performed in two goat herds in the southern Poland showed the presence of gastrointestinal nematodes resistant to fenbendazole and ivermectin in both herds. Moreover, in one herd it revealed the development of resistance to the last effective anthelmintic, levamisole, in response to one-year intensive use. Haemonchus contortus was the most prevalent gastrointestinal nematode in samples in which resistance to benzimidazoles and ivermectin was found, whereas Trichostrongylus colubriformis predominated when resistance to levamisole was observed.ConclusionThis study shows for the first time that multidrug resistance of gastrointestinal nematodes to three basic classes of anthelmintics is already present in goat population in Poland. Moreover, it may indicate that different species or genera of gastrointestinal nematodes are responsible for the resistance to specific anthelmintics.

Assessment of targeted selective treatment criteria to control subclinical gastrointestinal nematode infections on sheep farms

Control of sheep gastrointestinal nematode (GIN) infections mostly relies on the use of anthelmintics. Refugia-based control strategies as targeted selective treatments (TST) can delay anthelmintic resistance development, but the optimal decision criteria for selecting individuals to be treated in subclinical infection scenarios remain unclear. The present study aimed to evaluate the suitability of body condition score (BCS) and faecal egg counts (FEC) as treatment indicators and to determine their optimized threshold values for treatment in TST by determining the relationships of BCS, FEC and anthelmintic treatment with several productive parameters in pre-mating and pre-partum periods at an individual level. Deworming in pre-mating period increased BCS gain, but its magnitude was directly associated with strongyle FEC before treatment. Deworming also increased fertility in ewes with BCS < 2.75 and the proportion of lambing ewes that got pregnant during the first ovulation cycle. Nevertheless, treatment did not yield productive benefits in ewes with higher BCS values. On the other hand, deworming in the pre-partum lowered lamb peri-partum mortality and increased lamb weight at birth and the growth of lambs during lactation, especially in lambs born from ewes with strongyle FEC > 400 epg before treatment. These results showed that FEC and especially BCS can be potential decision criteria for the implementation of TST in these types of scenarios. The TST scheme derived from the present results on the control of GIN infections should include anthelmintic treatment of ewes with BCS lower than ≈ 3 approximately five weeks before mating and lambing. In the pre-lambing period, treatment may be unnecessary if flock mean strongyle FEC is lower than ≈ 200 epg, as the proportion of ewes with individual FEC > 400 epg would be very low. The results suggest that implementation of this TST scheme would provide benefits, such as the improvement of productivity, a rational management of parasites in refugia, and preservation of future efficacy of anthelmintics, in comparison to traditional deworming schemes.

Nematodes Resistance on Anthelmintics Group of Benzimidazole in Ruminants

One factor that inhibits the increase in ruminant productivity is nematode infection. It’s cause a decrease in feed intake, weight gain, milk production, disease, death, and expensive medical expenses The control of gastrointestinal nematode infections in livestock, over the past decades is primarily based on the preventive or curative use of chemotherapeutics and generally uses broad-spectrum anthelmintic such as benzimidazole, probenzimidazole, imidazothiazole, macrolide and ivermectin. The widespread use of several antelmintic groups now causes an increase in the incidence of gastrointestinal nematodes resistance against anthelmintics. Anthelmintics derived from various types of plants are expected to replace the benzimidazole so that it can reduce the level of resistance of the gastrointestinal nematodes in ruminants. However, for the future there is still a lot of research needed to further improve the ability of natural medicinal drugs to cope with gastrointestinal nematode infections in ruminants. Keywords : benzimidazole, nematode,resistance, ruminants

Economic viability of anthelmintic treatment in naturally infected beef cattle under different nutritional strategies after weaning

The aim of the present study was to evaluate the effects of treatment with different anthelmintic compounds on the productivity of naturally infected calves and the economic viability of these treatments within extensive breeding systems employing different nutritional strategies after weaning. For this purpose, 4 farms with 42-60 calves naturally infected with gastrointestinal nematodes were selected. The calves were distributed into 6 groups (7-10 animals each) per farm and treated with ivermectin 1%, ivermectin 3.15%, eprinomectin 5%, levamisole 7.5%, albendazole 15%, and control group (no treatment). These animals were evaluated over an experimental period of 150days. Levamisole 7.5% presented the best capacity for the reduction of eggs per gram (EPG) of feces in all herds evaluated, followed by albendazole 15% and eprinomectin 5%. Parasite resistance to multiple drugs was found in all herds, especially those of Cooperia, Haemonchus, Oesophagostomum, and Trichostrongylus. For farm 1, differences in weight gain and EPG reduction percentages led to a difference of US$285.06 between the levamisole and ivermectin 3.15% groups. Similar findings were noted for the levamisole and ivermectin 1% groups of farm 3, with a difference of US$399.37 because of the final weight gain in these groups. For farms 2 and 4, the ivermectin 3.15% and control groups, respectively, were the most profitable; these unexpected results were possibly influenced by variables not measured during the experimental period. This study suggested that anthelmintic treatments should always precede an efficacy test, once they are demonstrated to be most profitable under adequate breeding conditions, to ensure adequate control of gastrointestinal nematode infection.

Molecular analysis of benzimidazole-resistance associated SNPs in Haemonchus contortus populations of Uruguay.

Haemonchus contortus is one of the most important parasite nematodes of small ruminants around the world and causes great economic losses in livestock production. Control of gastrointestinal nematode infections, like haemonchosis, relies mainly on anthelmintic drugs, but its excessive and inappropriate use has caused serious drug resistance issues in many countries, including Uruguay, where sheep production occupies an important place in the country's economy. Benzimidazole (BZ) anthelmintics have been used for decades to treat sheep against H. contortus infection and resistance to this anthelmintic group has been widely described. Molecularly, BZ resistance in H. contortus has been correlated with single nucleotide polymorphisms (SNPs) of the β-tubulin isotype 1 gene at codon 200 and 167 (both TTC to TAC, F167Y and F200Y) and at codon 198 (GAA to GCA, E198A).The aim of this work was to explore the presence of these tubulin SNPs in H. contortus adult worms recovered from sheep abomasa from a slaughterhouse in Uruguay. The mean resistant allelic frequencies at positions F167Y and F200Y were 20.25 and 47.45%, respectively, for worms recovered from naturally infected sheep slaughtered in 2013, while those that were slaughtered in 2014 presented only F200Y SNP with a frequency of 86.89%. Also H. contortus Kirby adult worms (anthelmintic- susceptible McMaster isolate), recovered from artificially infected sheep, were analyzed as reference for comparative purposes This analysis showed susceptible genotype at 167 and 198 position, and a low level of the resistance allele at the 200 position (3.66%). This is the first study for the presence of SNPs in the isotype-1 β-tubulin gene of H. contortus populations in Uruguay, which is consistent with the previous epidemiological studies carried out through the method of fecal egg count reduction test (FECRT), thus confirming the serious resistance levels to BZ anthelmintics also in this country.

Anti-parasitic benefit of nematophagous fungi and Haemonchus contortus vaccine in small ruminants

As anthelmintic resistance continues to escalate, the need for alternative parasite control methods in small ruminant has increased. Copper oxide wire particles and sericea lespedeza are commercially available in the United States. Several other novel control methods, such as feeding nematophagous fungal chlamydospores, and vaccination against Haemonchus contortus, hold great promise for control of gastrointestinal nematode infections in small ruminants. The Haemonchus contortus vaccine is licensed for use in sheep in Australia, but is not yet available in the United States. Experiments conducted around the world have demonstrated the excellent nematode controlling advantages of feeding Duddingtonia flagrans chlamydospores to grazing livestock. A commercially available product is expected to be available in the near future.

Monepantel induces hepatic cytochromes p450 in sheep in vitro and in vivo

Monepantel (MOP), a new amino-acetonitrile anthelmintic for the treatment and control of gastrointestinal nematode infections and associated diseases in sheep, is approved and marketed as oral solution under the trade name Zolvix® (Novartis Animal Health Inc., Switzerland). The effect of MOP on hepatic cytochromes P450 (CYP) has been investigated in sheep. In an in vivo experiment, castrated rams (9-months old) were treated with the recommended therapeutic dose of MOP. Non-treated animals represented the controls. After 24h, the animals were stunned and exsanguinated. Microsomal fractions and total RNA were prepared from liver homogenates. The activities towards alkyloxyresorufins, 7-methoxy-4-trifluoromethylcoumarin and midazolam were assayed and mRNAs of individual CYP isoforms were quantified. In an in vitro procedure, primary cultures of ovine hepatocytes were incubated with or without MOP (10μM) for 24h and then expression levels of individual CYP isoforms were analyzed. Results showed that MOP significantly increased all CYP-related activities and CYP3A24 mRNA in sheep. The induction effect of MOP on CYP3A was similar or even higher than those of dexamethasone and rifampicin, well-known CYP3A inducers. As CYP3A enzymes belongs to the most important biotransformation enzymes, their induction may have serious pharmacological and/or toxicological consequences. These facts should be taken into account when other drugs together with or after MOP (Zolvix®) are administered to sheep.

A Review of the Epidemiology and Control of Gastrointestinal Nematode Infections of Small Ruminants

Small ruminants are the host to different species of gastrointestinal nematodes and their epidemiology depends on the aspects of host–parasite relationship and the prevailing agro-climatic conditions. Haemonchus, Trichostrongylus, Bunostomum are highly prevalent in small ruminants of warmer climates, whereas Teladorsagia (Ostertagia), Nematodirus and Cooperia are responsible for severe diseases in small ruminants of temperate areas. This is, because of the fact that the free-living stages of these parasites are strongly affected by moisture conditions of the soil and the climate. Thus, extreme heat and cold are detrimental to development and survival, while, within tolerable limits, increasing temperature generally accelerates the development. Although nematodes of small ruminants are ubiquitous in all agro-climatic zones, their presence does not necessarily result in diseases. Various categories of anthelmintics decrease the level of infection and reduce the egg output of these parasites, whereas grazing management lowers the level of larval exposure to host. Usually the treatment regimes of gastrointestinal nematodes are based on extrapolation of epidemiological studies carried out elsewhere, although the control strategies designed for one geo-climatic region and farming system may not necessarily be appropriate for all agro-ecological zones and farming systems. This paper reviews the current epidemiology, control of gastrointestinal nematode infections of small ruminants and the current alternatives to conventional anthelmintics to control gastrointestinal nematode infections with an emphasis on the inevitable rise of anthelmintic resistance and the suggestions that need to be considered for the future integrated control of these nematode infections in small ruminants.

A review of the epidemiology and control of gastrointestinal nematode infections in cattle in Zimbabwe

In this review, the main gastrointestinal nematodes infecting cattle in Zimbabwe and the epidemiological factors influencing their occurrence are reviewed and discussed. Nineteen gastrointestinal nematode species that belong to seven families have been found to occur in cattle in Zimbabwe. The main genera reported to date are Cooperia, Haemonchus, Trichostrongylus and Oesophagostomum and the dominant species are Cooperia pectinata, Cooperia punctata, Haemonchus placei and Trichostrongylus axei. The mixed infection by several species from the genera is the cause of parasitic gastroenteritis in cattle in Zimbabwe. Production and husbandry practices, season, host age and environment are considered to be the main factors that influence gastrointestinal nematode infection in cattle. The geographical distribution of the gastrointestinal nematodes is also reviewed in relation to the climatic conditions of the country. Various control options are discussed and how they are applicable to the Zimbabwean situation. Based on reports and existing data on the epidemiological features of the gastrointestinal nematode infection in cattle, practical control measures are critically reviewed and recommendations are made for a national control programme.

Pharmaceutical treatments of gastrointestinal nematode infections of sheep—Future of anthelmintic drugs

Various interacting factors have been identified to explain why health plans for nematode parasite control, based on conventional epidemiological knowledge and involving pharmaceutical treatments of their sheep hosts have become unsustainable. Of these, the emergence of anthelmintic resistance has had a major impact on the economics of sheep farming, necessitating fundamental managemental changes. This review focusses on the use of anthelmintic drugs for the control of gastrointestinal nematode infections in sheep, emphasising the need to develop sustainable strategies in the face of inevitable parasite evolution in response to exposure to anthelmintic drugs and other noxious stimuli, or favourable opportunities resulting from changing animal management and climatic factors.

Effect of nematophagous fungusDuddingtonia flagransand energy supplementation on the epidemiology of naturally infected kids

Gastrointestinal (GI) nematode infection is a major constraint for grazing livestock production. The increasing prevalence and severity of anthelmintic-resistant nematodes in many parts of the world has led to a search for non-chemical control options. Under experimental conditions, the nematophagous fungus Duddingtonia flagrans is emerging as an alternative to chemotherapy for the control of GI nematode infection in biological production systems. Also, recent information points to the role of energy nutrition to increase the immune response against GI nematode infection. In this study the effect of D. flagrans and energy supplementation on the epidemiology of GI nematode infections is explored on grazing kids. Four groups of 10, 4-month old goats were turned out on infected pasture in the early spring and allocated to four separate paddocks where they were rotationally grazed for 16 weeks. One of these groups (F) received 0.5 x 10(6) D. flagrans spores/kg BW/d. Another group (S) was supplemented with 100 g barley grain per day. A third group (F+S) received both nematophagous fungi and barley supplement treatments simultaneously while the fourth group (C) was used as a non-treated control. Both nematophagous fungi and barley supplement had a significant effect (P<0.01) on reducing pasture infectivity, faecal egg excretion and worm burdens at slaughter that was particularly evident for Trichostrongylus colubriformis. The combination of both treatments showed a synergistic effect on the control of gastrointestinal nematode infections. At slaughter, the average total post-mortem worm count of the F+S group was reduced by 65% compared with the non-treated control. The results herein show that D. flagrans can act as an efficient biological control agent against kid GI nematode infections on pasture, which could further improve carcass characteristics. While small amounts of energy supplement can also reduce kid infection, the effect of D. flagrans as a biological control agent appeared clearly enhanced both in magnitude and duration by energy supplementation. This has clear implications for grazing animals and provides an efficient method for the practical control of parasitic nematodes in biological production systems.

Exploiting the effect of dietary supplementation of small ruminants on resilience and resistance against gastrointestinal nematodes

This paper focuses on targeted nutritional supplementation as a means to reduce the requirement for chemotherapeutic control of gastrointestinal nematode infection of small ruminants and considers the limitations to practical application. Supplementary feeding, particularly with additional dietary protein, can assist resilience to infection during times when metabolic resources are being directed towards dealing with the pathophysiological effects of infection and away from production of meat, milk and fibre. Substantial experimental evidence from studies of both sheep and goats supports this hypothesis particularly in relation to young lambs and kids after weaning and in ewes around parturition. In addition, nutritional supplementation frequently increases resistance to infection, as indicated by decreased faecal worm egg counts and worm burdens. As a result, supplementation has the potential to reduce the requirement for anthelmintic treatment. Practical application of this knowledge can, however, be quite complex in many small ruminant production systems. In general, strategic supplementation should target those times when nutrient requirements are greatest and provide those nutrients which are deficient whether protein, energy, minerals or trace elements. Complexity arises when we consider that nutrient requirements will differ between localities for different species and breed of host, at different stages of growth and reproduction, with differing seasonal availability of forage, with different species of nematodes and different levels of established infections and exposure to infective stages. As a starting point, the provision of nutrients to optimize rumen function and animal performance in the particular production system should assist in maintaining resilience to nematode infection. Provision of nutrients in excess of this requirement, if economically feasible, may yield further benefits in some situations and reduce the need for alternative control measures for gastrointestinal nematode parasites.

Effect of strategic deworming of village cattle in Uganda with moxidectin pour-on on faecal egg count and pasture larval counts : short communication

Strategic application of moxidectin pour-on (Cydectin) was evaluated in Uganda for its effect on pasture larval counts and gastrointestinal nematode faecal egg counts in village cattle kept under tethering (semi-intensive) grazing management. The strategic deworming schedule involved treating cattle twice at an interval of 2 months, at the end of the 1st wet season and during the 2nd wet season. Two groups of 30 cattle, each consisting of a treated and a control group, were examined for nematode infections every 4 weeks from June 1999 to January 2000. The treated group had significantly lower mean faecal egg counts than the untreated groups (t-value = 2.47, P < 0.05). Generally, the pasture larval counts on treated farms were lower than on untreated ones, but not significantly so (t-value = 2.22, P = 0.068). Pasture larval counts with different nematode species on treated farms were lower than on untreated ones, but the differences were not significant for Haemonchus spp. (t-value = 1.68, P = 0.145), Oesophagostomum spp. (t-value = 1.87, P = 0.111), Trichostrongylus spp. (t-value = 1.93, P = 0.102), Dictyocaulus spp. (t-value = -0.74, P = 0.485) and Cooperia spp. (t-value = -1.00, P = 0.356). Treated farms did, however, have significantly lower pasture larval counts of Bunostomum spp. (t-value = 4.64, P < 0.05). This study has revealed that the application of moxidectin pour-on on cattle has an effect on faecal egg count and pasture contamination under the tethering grazing system. Moxidectin pour-on and the strategic deworming schedule evaluated here could be used for the control of gastrointestinal nematode infections in cattle by small-scale farmers who practise tethering or semi-intensive grazing management in Uganda and other tropical countries, especially where there is a bimodal rainfall pattern.

Evaluation of anthelmintic properties of extracts from some plants used as livestock dewormers by pastoralist and smallholder farmers in Kenya against Heligmosomoides polygyrus infections in mice

Parasitic nematodes are among the most common and economically important infectious diseases of grazing livestock, especially in small ruminants in the tropics and subtropics in Kenya the control of gastrointestinal nematode infections in sheep and goats is usually made with synthetic anthelmintics but substantial levels of anthelmintic resistance have been recorded. A number of medicinal plants, that may provide possible alternatives, and are used by pastoralists and smallholder farmers in Kenya as deworming agents for their livestock and equines, namely Aframomum sanguineum, Dodonea angustifolia, Hildebrandtia sepalosa, Myrsine africana, Rapanea melanophloeos from Kenya, and Azadirachta indica from Kenya and Malaysia, together with the chemicals embelin and santonin that occur in some of these plants, were evaluated against Heligmosomoides polygyrus in mice. Commercial anthelmintics, namely ivermectin, pyrantel and piperazine, were also investigated, both to validate the mouse model system and to assess efficacy of these drugs against H. polygyrus. Pyrantel and ivermectin were highly effective in reducing the numbers of H. polygyrus worms as well as eggs in faeces of the mice, but piperazine had a lower activity. Application of santonin and M. africana significantly reduced the number of total worm counts (TWC) but not faecal egg counts (FEC). The use of embelin, R. melanophloeos and A. indica reduced FEC but not TWC. In all cases, however, reductions were well below the a priori level of 70% required for biological significance. A. sanguineum, D. angustifolia and H. sepalosa had no effect on either TWC or FEC. In conclusion, none of the plant preparations had any biologically significant anthelmintic effect in this monogastric host–parasite model system.

Nutritional influences on the expression of genotypic resistance to gastrointestinal nematode infection in sheep

This paper reviews experiments investigating the responses of resistant and susceptible genotypes of sheep to gastrointestinal nematode infection under differential nutrition. Using faecal egg count as a measure of host resistance, differences between genotypes appeared to be greatest under conditions of low nutrient availability and under such conditions both resistant and susceptible genotypes generally responded to supplemental protein by reducing faecal egg count. However, when nutritional conditions were moderate to good, responses to additional protein tended to be observed only in susceptible genotypes. In general, host genetic resistance was associated with reliable reductions in faecal egg count of moderate to large magnitude, while nutritional intervention was less reliable at reducing faecal egg count, and induced reductions of smaller magnitude. The situation was very different when examining host resilience to infection, as determined by sheep productivity in the face of infection. Increased host resistance was rarely associated with improved growth or production during the period of infection. In contrast, nutritional supplementation reliably increased host productivity irrespective of infection status and prevailing nutritional conditions. A general model of the relationship between nutrient availability and host resistance and resilience in resistant and susceptible genotypes is postulated. Taken together, the studies reviewed in this paper suggest that selection for host resistance and strategic nutritional intervention have complementary roles in the integrated control of gastrointestinal nematode infection in sheep. The former will contribute primarily to the epidemiology of the disease by reliably reducing faecal egg output over a wide range of conditions, reducing host challenge and the number of treatment interventions required. The latter will reliably boost host resilience to infection, with lesser effects on resistance, and the economic rationale for use will require accounting for the full spectrum of production and disease responses.

The intensity and duration of primary Heligmosomoides polygyrus infection in TO mice modify acquired immunity to secondary challenge

The effect of dose and duration of immunizing infections of Heligmosomoides polygyrus on protection against homologous challenge was studied in female TO mice. Primary infections were terminated at various levels with pyrantel embonate (adult infections) or ivermectin (larval infections) and mice were then challenged with 500 infective larvae (L3). The level of protection to secondary challenge positively correlated with the intensity of the primary immunizing infection but truncation of larval infection produced significantly better protection than termination of the adult nematode infection. The duration of the primary larval infection (1-6 days) positively correlated with the level of protection to secondary challenge, antibody responses and the proportion of circulating eosinophils. Histological changes in the gastrointestinal tract, peripheral leucocytic changes and antibody responses of the mice to H. polygyrus adult somatic antigens indicate both a cellular and humoral basis of host immunity to secondary challenge. Although the TO mice are slow responders in that they harbour chronic infections, immunization by intramucosal killing of the larval stage produced strong protection against secondary challenge infection. The presence of dead immunogenic larval stages within the intestinal wall may well be an important factor, since it exposes the host to stage specific antigens at an appropriate location. The implications of the findings for the control of gastrointestinal nematode infections are also discussed.

The intensity and duration of primary Heligmosomoides polygyrus infection in TO mice modify acquired immunity to secondary challenge

AbstractThe effect of dose and duration of immunizing infections of Heligmosomoides polygyrus on protection against homologous challenge was studied in female TO mice. Primary infections were terminated at various levels with pyrantel embonate (adult infections) or ivermectin (larval infections) and mice were then challenged with 500 infective larvae (L3). The level of protection to secondary challenge positively correlated with the intensity of the primary immunizing infection but truncation of larval infection produced significantly better protection than termination of the adult nematode infection. The duration of the primary larval infection (1–6 days) positively correlated with the level of protection to secondary challenge, antibody responses and the proportion of circulating eosinophils. Histological changes in the gastrointestinal tract, peripheral leucocytic changes and antibody responses of the mice to H. polygyrus adult somatic antigens indicate both a cellular and humoral basis of host immunity to secondary challenge. Although the TO mice are slow responders in that they harbour chronic infections, immunization by intramucosal killing of the larval stage produced strong protection against secondary challenge infection. The presence of dead immunogenic larval stages within the intestinal wall may well be an important factor, since it exposes the host to stage specific antigens at an appropriate location. The implications of the findings for the control of gastrointestinal nematode infections are also discussed.

The effectiveness of doramectin pour-on in the control of gastrointestinal nematode infections in cow–calf herds

Two field studies were conducted in the USA to determine the efficacy of a single strategically-timed dose of doramectin pour-on in the control of gastrointestinal nematodosis in beef cow–calf herds and the resultant effects on calf productivity. One study was carried out between May and October 1996 in a spring-calving herd at a site located in Idaho (ID) and the other between January and July 1997 in a fall-calving herd at a site located in Mississippi (MS). In each study, cow–calf pairs were randomly allotted by sex of calf to pastures and one of two treatment groups (doramectin pour-on at the recommended dose rate of 500 μg/kg body weight or untreated control). There were four pasture replicates per treatment at each site. Each pasture contained 12 cow–calf pairs at the ID site and 15 cow–calf pairs at the MS site. Treatment was administered to cows and calves on 21 May 1996 (ID) or 23 January 1997 (MS). Following treatment, cow–calf pairs were assigned to their designated pastures where they remained until the calves were weaned 140 (ID) or 168 (MS) days later. Cow and calf fecal egg counts and calf body weights were recorded on treatment day and then at monthly intervals until study termination. Doramectin treatment reduced nematode egg output in cows and calves over the entire grazing season compared to untreated controls and resulted in calf weight gain improvements of 9.8 kg ( p=0.295) at the ID site and 17.4 kg ( p=0.0002) at the MS site.

The effectiveness of a single dose of doramectin pour-on in the control of gastrointestinal nematodes in yearling stocker cattle

Three field studies were conducted to determine the efficacy of a single dose of doramectin pour-on in the control of gastrointestinal nematode infections in yearling stocker calves on pasture. These 140-day studies were carried out between October 1995 and March 1996 in Tennessee (TN), between January and June 1997 in Louisiana (LA), and between May and September 1997 in Wisconsin (WI). Calves with patent nematode infections were equally allocated to treatments (doramectin pour-on, at 500 μg/kg body weight or untreated control) and pastures as randomized complete-block designs (LA and TN studies) or completely at random (WI study). There were six pasture replicates per treatment at each site, with each pasture replicate accommodating six calves at the TN site (36 calves per treatment), five calves at the LA site (30 calves per treatment), and seven calves at the WI site (42 calves per treatment). Fecal samples for nematode egg counts were collected on Day 0, and at 28-day intervals thereafter. Body weights were recorded on Day 0 and at 28-day intervals until study termination. Nematode egg output of the doramectin-treated groups was reduced over the entire grazing period compared to those in the untreated control groups, resulting in average daily weight-gain advantages of 0.055 kg ( p ≤ 0.05) for the TN study, 0.208 kg ( p ≤ 0.05) for the LA study, and 0.116 kg ( p ≤ 0.05) for the WI study.

Effect of molasses-urea-block (MUB) on dry matter intake, growth, reproductive performance and control of gastrointestinal nematode infection of grazing Menz ram lambs

The effect of urea-molasses feed-supplement blocks (MUB) on feed utilisation and the inclusion of anthelmintic medication into the blocks at strategic times to control nematode parasites was studied in lambs grazed on low quality tropical pasture. 120 Menz ram lambs of 5–7 months of age were divided into six groups for methods of treatment against internal parasites and urea molasses supplementation. The benzimidazole anthelmintic fenbendazole was administered at the rate of 10 mg kg −1 liveweight as a drench or via medicated MUB. Animals grazed in two lots during the day and had access to grass hay in night pens ad libitum. Groups 1–3 comprised a non-supplemented (NOSUP) lot that only grazed while groups 4–6 consumed, in addition, an average of 80 g per head per day of molasses-urea-block (SUPP) supplement. The MUB supplement was provided daily for nine months but medicated MUB was used only for strategic prophylactic treatment against nematodes. SUPP animals had higher daily DM intakes (568 ±11 versus 532 ± 11 g DM per head per day, P < 0.05), the advantage being greatest in the wet season when there was also a concomitant increase in herbage digestibility ( P < 0.001). SUPP animals were 4kg heavier (25.7 ± 0.5 versus 21.7 ± 0.5 kg, P < 0.05) and had deposited more body reserves as judged by condition score (3.2 ± 0.1 versus 2.4 ± 0.1) after 6 months. The level of infection with endoparasites was lower in the dry than in the wet season. Medicated MUB was as efficient in treating against endoparasites as drenching. Similarly, the MUB supplement mitigated the effect of endoparasitism. Anthelmintic treatment did not improve testicular size or semen quality ( P> 0.05). Testicular growth increased faster during the first 3 months to highest values of 26.9 ± 0.3 and 25.3 ± 0.3 cm, respectively in SUPP and NOSUP animals ( P < 0.001) at 6 months. Semen quality improved with age and was better in SUPP than NOSUP males ( P < 0.05– P < 0.001). It is concluded that MUB supplementation is a suitable method for supplementing the nutrition of grazing sheep in Ethiopia, and that MUB feeding can help alleviate the effect of endoparasitism.