Seasonal changes of gastrointestinal nematode burden in sheep under an intensive grazing system

A study was conducted of the monthly fluctuations of worm burdens and arrested development of gastrointestinal (GI) nematodes in sheep from a commercial farm of the Ebro valley (Spain). Twenty-four previously helminth-free female lambs (permanent lambs) grazed together with a flock of 500 resident ewes for 12 months following a three lambing/2-year reproductive management system. Two helminth-free lambs (tracer lambs) were added to the flock each month and allowed to graze for 4 weeks. Measurements were made of the population of infective larvae on the pasture, and of levels of serum pepsinogen and faecal worm eggs in ewes and lambs. Additionally, post-mortem worm counts from two tracer and two permanent lambs were used to establish the level of infection at monthly intervals. Three generations of parasites were identified in the experiment. The generation derived from eggs deposited the previous autumn gave rise to the first infection of the animals in January and May. This infection had low consequences for the animals, but it signified the initiation of infection and the resumption of the annual cycle of pasture contamination. The second generation, appearing between June and July, was the year's most important source of infection and gave rise to an outbreak of parasitism in permanent lambs. This was indicated by an increase in levels of serum pepsinogen, the appearance of diarrhoea, and an important decrease in lamb growth rates. The third wave of infection, occurring in October and November, there was less impact than the previous one with respect to the level of infection, but it was the origin of the future over-wintering population. Teladorsagia circumcincta was the predominant species, followed by Haemonchus contortus and Trichostrongylus colubriformis. The highest numbers of worm recovered from both the tracer and permanent lambs were observed in July, with average numbers of 7900 and 19,200, respectively.The inhibition phenomenon was more evident in permanent than in tracer lambs, and mainly affected H. contortus as evidenced by populations exhibiting arrested larvae values of over 70% in January and February.Results obtained in this study confirm the epidemiological importance of the over-wintering L(3) generation as the initial source of the animal's infection and the origin of the annual resumption of pasture contamination cycles.     

Efficacy of eprinomectin pour-on against gastrointestinal nematode infections in sheep

Two field trials were conducted in two farms (farms A and B) in southern Italy, to assess the efficacy of eprinomectin applied topically at the dose rate of 500 micro g/kg to sheep with naturally occurring infections of gastrointestinal nematodes (GIN). The nematode population determined by necropsy consisted of Teladorsagia circumcincta, Haemonchus contortus, Trichostrongylus vitrinus, T. capricola, Nematodirus sp., and Chabertia ovina in sheep from farm A, and of T. circumcincta, T. vitrinus, T. capricola, T. colubriformis, and C. ovina in sheep from farm B. In each farm, 42 female sheep were assigned to a eprinomectin treated group (E-group) and a control untreated group (C-group) of 21 animals each. On farm A, the percentage reductions in strongyle faecal egg counts from E-group compared to C-group were 99.1% on day 10; 97.4% on day 30; and 67.0% on day 60. On farm B, on the same days, they were 95.4, 84.9, and 69.4%, respectively. In the course of the two trials, eprinomectin was well tolerated by all the animals with no adverse reactions following the topical treatment.     

Intensive rotational grazing assists control of gastrointestinal nematodosis of sheep in a cool temperate environment with summer-dominant rainfall

While rotational grazing methods have an accepted role in the management of gastrointestinal nematodosis (GIN) of small ruminants in humid tropical regions, their efficacy and application in cool temperate regions is more controversial. This study evaluated GIN over 2 years in three classes of fine wool Merino sheep (lambs, hoggets and ewes) under three different sheep management systems in a cool tableland environment near Armidale NSW Australia (950m altitude, 30 degrees 31'S, 151 degrees 39'E). The management systems were High input (HI) with high fertiliser inputs, a target of 100% sown pasture, high stocking rate (13.4 dry sheep equivalents/ha) and relatively long grazing periods; Typical (TYP) New England management system with moderate fertiliser inputs and stocking rate (9.3DSE/ha) and relatively long grazing periods; and Intensive rotational grazing (IRG) with moderate fertiliser inputs and stocking rate (8.8DSE/ha) but very short (mean 5 days) grazing periods and long (mean 103 days) rest periods. Twenty sheep of each class in each management treatment were sampled monthly for faecal worm egg counts (WEC, followed by larval differentiation), and body weights with a blood sample taken for haematology every second month. The proportion of sheep with WEC above zero did not differ between management systems but the magnitude of WEC did, with sheep under IRG displaying lower mean WEC than those on the other treatments (IRG: 326, HI: 594, TYP: 536, eggs/g P<0.0001). This was despite a significantly longer mean interval between anthelmintic treatments (IRG: 144 days, HI: 77 days, TYP: 78 days, P<0.0001). The IRG management system also influenced the composition of the infections with sheep on this treatment having a significantly lower proportion of Haemonchus contortus in their faecal cultures (IRG: 59.7%, HI: 79.4%, TYP: 80.9%, P<0.05) and a significantly higher proportion of Trichostrongylus spp. Sheep on the IRG treatment also had a significantly higher haematocrit (HCT) than those on the other management systems. Despite the lower WEC and higher HCT, sheep under IRG also had significantly lower bodyweights and fleece weights overall, although this was only evident in sheep raised to adulthood prior to the experiment, not those raised during the 2-year experimental period. The results demonstrate that IRG systems with short grazing periods and long rest periods between grazing events can assist with control of GIN in cool temperate climates where H. contortus is the dominant parasite.     

Effect of a single injection of doramectin on gastrointestinal nematode infections of sheep grazing on alpine pastures.]

The persistent effect of doramectin injectable against gastrointestinal nematodes was investigated in a controlled field study with 70 sheep kept on alpine pastures in Switzerland. After grazing on home pastures for four weeks 50 lambs and 20 ewes were allocated to two equal groups according to age and body weight. At turnout to alpine pasture in June doramectin (0.3 mg/kg) was administered by intramuscular injection to 25 lambs and 10 ewes (Group D), whereas control sheep (Group K) remained untreated. Animals of both groups were kept on separate pastures (altitude: 1100 m) and were rotated between three paddocks during a total grazing period of 13 weeks. After doramectin treatment faecal examinations of Group D sheep showed a marked reduction of the trichostrongyle egg output which remained close to zero for eight weeks. During this period serum pepsinogen levels did not indicate the presence of a substantial immature worm burden in the abomasal mucosa. In the last five weeks of the alpine grazing period the trichostrongyle egg counts increased markedly in the lambs of Group D. Lambs of the control group developed moderate-to-high Haemonchus-infections, and eight animals of this group had to be treated with anthelmintics. Lambs of Group D had gained significantly (P < 0.05) more weight eight weeks after turnout whereas the mean bodyweight stagnated during the last five weeks of the grazing period. The results indicate, that the single administration of 0.3 mg/kg doramectin to lambs and ewes provided good protection against severe infections with gastrointestinal nematodes for a period of approximately eight weeks.     

Climate and the epidemiology of gastrointestinal nematode infections of sheep in Europe

The free-living stages of gastrointestinal nematode parasites of sheep are strongly affected by climate. Thus, extreme heat and cold are detrimental to development and survival, while, within tolerable limits, increasing temperatures generally accelerate development but increase mortality. Moisture is needed for development and translation of larvae from faeces to pasture, and so rainfall is a limiting factor for transmission. Together, these factors underpin seasonal patterns of infection in sheep, as well as geographic variation in the epidemiology and relative importance of different species within Europe. Local knowledge and experience enable treatment to be targeted appropriately to prevent dangerous levels of infection. This traditional know-how can be supplemented by predictive epidemiological models, built on thorough understanding of the influence of climate on larval availability. However, management also has a dominant role in determining patterns of infection, and is itself influenced by climate. Current geographic variation in nematode epidemiology across Europe, and knowledge of systems from outside Europe, can provide only limited perspectives on the likely effects of climate change on disease in future. This is because disease arises from complex interaction between host and parasite factors, and the implementation of optimal control strategies to meet new challenges will be slowed by the inertia of current systems. Approaches to nematode control must therefore take account not only of parasite biology, but also the forces that shape sheep farming systems and management decisions.     

Resistance of Santa Ines, Suffolk and Ile de France sheep to naturally acquired gastrointestinal nematode infections

A study was conducted to assess the breed resistance against nematode infections in Santa Ines, Ile de France and Suffolk male lambs over a 9-month period in S?o Paulo state, Brazil. Lambs were born during the winter (year 2000) and were weaned at 2 months of age. The animals were then housed and treated with anthelmintics to eliminate natural infections by gastrointestinal nematodes. In late October 2000, lambs were placed in a paddock, where they stayed until August of the following year. Fecal and blood samples were taken from each animal every 2 weeks. On the same day, a pasture sample was collected to determine the number of infective larvae on the herbage. To prevent deaths, individual treatment with anthelmintics was provided to lambs with fecal egg counts (FEC) higher than 4000 eggs per gram (EPG) or with a packed cell volume (PCV) lower than 21%. In August 2001, all animals were slaughtered and the worms present in samples of the gastrointestinal contents were identified and counted. Most of the Suffolk and Ile de France sheep received three to six anthelmintic treatments over a period of 7 months, while most of the Santa Ines were not treated. Reductions in PCV and plasma protein values associated with high FEC and worm burdens were recorded, particularly, in Suffolk and Ile de France lambs. Haemonchus contortus and Oesophagostomum columbianum burdens and number of nodular lesions caused in the large intestine by O. columbianum larvae were significantly lower in Santa Ines sheep. All three breeds showed similar Trichostrongylus colubriformis worm burdens. The relative resistance of Santa Ines young male sheep was superior to that of Suffolk and Ile de France sheep.     

Resilience of second year grazing cattle to parasitic gastroenteritis following negligible to moderate exposure to gastrointestinal nematode infections in their first year

The influence of gastrointestinal nematode infections on performance of four groups of female Holstein Friesian calves was monitored until the end of the second grazing season (SGS). In the first year three groups were grazed and one group (G4) was permanently housed. General and grazing management during the first grazing season (FGS) was arranged such that G1 acquired moderate infections, G2 low infections and G3 very low infections with gastrointestinal nematodes. These infections were monitored through faecal egg counts, differentiation of faecal larval cultures, pasture larval counts, serum pepsinogen values, ELISA with a recombinant Cooperia oncophora protein, weight gain, tracer worm counts and sentinel worm counts. In 1998 all four groups were grazed together as one herd from 23 April to 26 October and infections were monitored with the same techniques with the exception of sentinel calves.In the FGS weight gain was higher in G4 than in the other groups and higher in G3 (28. 6kg) than in G1. Weight gain of G2 was intermediate to G1 and G3 but did not significantly differ from either group. In the SGS weight gain in G4 was far less than in any other group and the mean weight at the end of the experiment was 41.9, 38.6 and 50.9kg lower than G3, G1 and G2, respectively. Though no significant differences were observed between G1, G2 and G3 at the end of the experiment it was obvious that the weight gain advantage of G3 over G1 at the end of the FGS had disappeared.Parasitological and serological findings in the SGS indicated that G3 and G4 had build up less immunity during the FGS compared to G1 and G2.The conclusion of the experiment is that resilience to parasitic gastroenteritis in the SGS depends on the level of exposure to nematodes in the FGS. However, problems with poor weight gain only will be expected when exposure is very low in the FGS and high in the SGS.     

Epidemiology and seasonal dynamics of gastrointestinal nematode infections of sheep in a semi-arid region of eastern Ethiopia

A study on the epidemiology and seasonal dynamics of gastrointestinal nematode infections of sheep was carried out in a semi-arid region of eastern Ethiopia for 2.5 years (May 2003 to September 2005). The experimental flock comprised a total of 60 Black Head Ogaden sheep, consisting of four equal groups of young male and female and old male and female sheep. These grazed on communal pastures together with a larger university flock, as well as with animals owned by neighbouring small-holder farmers. A new experimental flock was established each year of the study. Parasitological data (EPG, faecal culture L3, PCV and FAMACHA estimates) and animal performance (weight change) were recorded each month on all experimental animals. In addition, four tracer lambs were assigned each month to the flock to determine the seasonal patterns of infective larvae acquired from pasture. Results showed distinct seasonal patterns associated with the bi-modal annual rainfall. High levels of infection occurred during the short and long rain seasons with peaks occurring in May and September of each year. Haemonchus contortus was the most prevalent parasite, followed by Trichostrongylus spp., with a number of other nematode species being occasionally recorded. H. contortus showed and increased propensity to undergo arrested development during the dry seasons. Correlations between EPG and PCV, EPG and FAMACHA eye scores, and PCV and FAMACHA eye scores were all highly significant (P<0.001). However, there was no significant association between the EPG and LW of the study animals during each study year. This information will provide a basis for developing epidemiologically based control strategies for gastrointestinal nematode parasites that are appropriate for flocks owned by small-holder farmers of semi-arid areas of eastern Ethiopia.     

Relationship of nematode cholinesterase activity and nematode burdens to the development of resistance to trichostrongyle infections in sheep

The changes in nematode cholinesterase (ChE) activities were examined in relation to the development of resistance in (1) a flock of young grazing sheep, (2) grazing and penned sheep treated with dexamethasone and (3) penned sheep receiving a single mixed infection. Nematodes from grazing sheep with high faecal egg counts (FECs) had higher ChE activities than those from sheep with low FECs. Female nematodes tended to have higher ChE activities than males, and ChE activities in both tended to decline with increasing age of the sheep. The decline in female Trichostrongylus colubriformis ChE activity was associated with a decline in both worm length and in utero egg count. No decline in nematode ChE activity was observed when grazing sheep were treated with dexamethasone. ChE activity of T. colubriformis established in immunosuppressed penned sheep declined 10-20 fold 8 weeks after cessation of treatment. Nematode burdens in the small intestine and abomasum of grazing sheep were significantly correlated, and in individual species they were also correlated with ChE activities. The development of resistance in sheep and the elimination of adult nematode burdens is discussed in relation to gastrointestinal mucosal globule leucocyte numbers, mucus antiparasite activity and the impairment of nematode metabolic function.     

Serum pepsinogen levels to monitor gastrointestinal nematode infections in cattle revisited

The serum pepsinogen level is widely accepted as a useful parameter for monitoring gastrointestinal nematode infections in first-season grazing calves. However, several aspects, with possible implications for its practicality and the way to use the pepsinogen test, have received little attention to date. The objectives of this study were to evaluate (1) the reproducibility of a pepsinogen assay; (2) the required sample size for a reliable diagnosis and (3) the compliance to and effect of advice based on pepsinogen levels determined in year one on the nematode infection levels in the next generation of calves. Despite a high repeatability of the pepsinogen assay within the reference lab, the reproducibility between different labs was poor. There was more variation in pepsinogen levels between herds than between animals within a herd, suggesting that it is most useful to make a herd level diagnosis. Sample size calculation indicated that sampling seven animals sufficed to obtain a reliable indication of calf groups of up to 40 animals. Eighty-two herds were followed-up over two consecutive years and 39 (48%) had followed the advice that was formulated based on pepsinogen levels. Thirty-nine percent of the herds were advised to reduce the intensity of chemoprophylaxis. Samples from animals of those herds showed a higher pepsinogen level in the second year, but none of them had a mean pepsinogen level that is considered excessive. It is concluded that pepsinogen determination at housing from a limited number of animals can contribute to the design of the anthelmintic control strategy in the next year and a more targeted use of anthelmintics. However, more efforts are needed to harmonize the assay between veterinary diagnostic labs.     

Impact of eprinomectin on grazing behaviour and performance in dairy cattle with sub-clinical gastrointestinal nematode infections under continuous stocking management

Forty spring-calving cows and heifers (20 of each) were allowed to acquire infection with gastrointestinal (GI) nematodes naturally during grazing. The control group (10 cows and 10 heifers) were compared with 20 similar animals treated with eprinomectin in order to evaluate the effect of GI nematodes on grazing behaviour, milk production, body condition score and live weight. The animals were paired according to parity and milk yield during the week prior to treatment, then within replicate pair randomly allocated to a different treatment group. The grazing area was sub-divided into 20 replicated paddocks of equivalent size and topography. Grazing pairs of either control or treated animals were randomly assigned to each paddock over the duration of the study (one pair per paddock). Grazing behaviour was recorded for both groups over a 10-day period commencing 4 days after treatment with eprinomectin. Milk yield was recorded daily and milk quality was recorded weekly. Live weight and body condition score were recorded on the day of allocation, the day of initial treatment and thereafter at weekly intervals until the end of the 4-week trial. Faecal samples were collected from each animal prior to, and after, allocation and submitted for counts of nematode eggs. Additional faecal samples were taken at the end of the study for culture and nematode identification. Individual faecal samples were also analysed for residual digestibility. Pasture samples for nematode larval counts were taken at the same time as faecal sampling. The parasitological results showed low levels of faecal nematode egg output throughout the study, with the heifers having higher counts than the cows. Faecal culture yielded species of Ostertagia, Cooperia, and Trichostrongylus. Pasture larval levels were very low throughout with no value exceeding 68 larvae/kg dry matter (DM) of herbage. There were significant (P < 0.05) effects of treatment on grazing time, eating time, total bites, total grazing jaw movements (TGJM), idling time and mean meal duration. Treated cows and heifers grazed for 47 and 50 min longer per day, respectively, than controls (P = 0.016). Mean meal duration was extended as a result of anthelmintic treatment by 11 and 38 min, in cows and heifers, respectively (P = 0.012). There were no significant (P > 0.05) treatment effects on ruminating time or residual faecal digestibility, but idling time was significantly reduced in both treated cows and heifers, by 50 and 110 min, respectively (P = 0.010). In the treated cattle, there was an increase in solids-corrected milk yield compared with the control cattle, which was significant (P < 0.05) in weeks 2 and 3 after treatment. The response was particularly marked in heifers, where the difference in yield between treated and controls was up to 2.35 kg/day. The differences in live weight gain and condition score over 28 days post-treatment were significant (P < 0.05) in both cows and heifers, in favour of the treated animals.     

Failure of Duddingtonia flagrans to reduce gastrointestinal nematode infections in dairy ewes

A field study was conducted on three Swiss farms to investigate the efficacy of Duddingtonia flagrans against naturally acquired infections of gastrointestinal nematodes in adult dairy sheep. On each farm the ewes were divided into two equal groups. One group received Duddingtonia during a period of 4 months at a daily dose rate of 10(6) chlamydospores per kilogram body weight, the second group acted as controls. At an overall moderate infection level in all farms D. flagrans did not have a significant effect on the observed parasitological parameters with the exception of a significantly reduced herbage infectivity in one farm. In contrast, the results from faecal cultures indicated a mean suppression of larval development during the fungus-feeding period between 82, 89 and 93% on the three farms, respectively. The discrepancy observed between the fungus efficacy in coprocultures and on pasture, which was also observed in several other studies deserves further research.     

The relative resistance to gastrointestinal nematode infection of three British sheep breeds

The relative resistance of Manx Loaghtan, Shetland and Southdown sheep to naturally acquired gastrointestinal nematode infection was assessed over a ten week period. Thirty shearling ewes, ten from each of the three breeds, were co-grazed on an infective pasture. The animals were initially treated with an anthelmintic to minimise previous nematode infection, and faecal samples were collected from individual animals every two weeks. Southdown sheep had significantly higher faecal egg counts (FEC) than Shetland by week 6, and than Manx Loaghtan by week 10. After ten weeks there was an 86-fold difference in FEC between Shetland and Southdown sheep, and a 14-fold difference between Manx Loaghtan and Southdown sheep. These preliminary results suggest that primitive Shetland and Manx Loaghtan sheep may have greater resistance to gastrointestinal parasites, a trait that could be of value to the UK livestock industry.     

The effectiveness of the new morantel sustained-release trilaminate bolus against gastrointestinal nematode infections in cattle in their first grazing period

The efficacy of a recently developed Morantel-Sustained-Release-Trilaminate-Bolus (Paratect Flex Bolus [PFB]-Pfizer Inc.) against gastrointestinal nematode infections in cattle was assessed by monitoring faecal egg counts (EpG), herbage larval counts, serum pepsinogen levels and liveweight gains in first season calves. In two field trials (1987 and 1988), a PFB-Bolus was administered to two different groups of animals (1987: 15 calves; 1988:13 calves) at turnout (29 May 1987; 26 May 1988), control groups were included. In 1988, 13 calves received for comparison an Oxfendazole-Release-Bolus (Systamex Intervall Bolus [OXF]-Coopers Inc.). All groups were grazed on adjacent but separately fenced pastures throughout the season, until housing (27 October 1987; 15 October 1988). When compared with controls, the PFB-groups showed significantly lower EpG values and consequently, lower herbage larval counts throughout the season in both trials. From day 30 after turnout, the PFB-group had significantly lower serum pepsinogen levels, which reflects the low degree of abomasal damage in these animals. When compared to controls, the PFB-treated animals showed significantly higher weight performances. The mean weight-gain benefit of PFB-treated animals was +12.5 kg (p less than 0.05) and +21.1 kg (p less than 0.005) in 1987 and 1988, resp. No difference occurred between PFB-treated and OXF-treated calves, the latter outperformed the control animals by +21.6 kg (p less than 0.005).     

Effects of non-genetic factors on responses to gastro-intestinal nematode infections in Ethiopian sheep

The effects of non-genetic factors on responses to gastrointestinal nematode infections were examined in artificially infected indigenous Horro and Menz lambs in the central highlands of Ethiopia. The experiment involved lambs of two sexes, infection and monitoring regimens (3 levels), dam parity (4 levels) and birth types (2 levels). A total of 152 weaner lambs (103 Menz and 49 Horro) were used. Endoparasite challenge involved three infection periods (primary, secondary and tertiary) each separated by an anthelmintic treatment. Data were collected on faecal egg counts (FEC), packed cell volume (PCV), worm count, and weight gain. Female lambs were found to harbor lower numbers of T. colubriformis counts and had lower (p < 0.01) FEC in tertiary infection compared to males. Younger animals were more susceptible to the nematode infections than older animals as measured by all the parameters studied (p < 0.01). Twins had higher FEC in both secondary and tertiary infections compared to singles. Lambs born to dams of first parity had higher PCV and lower FEC values during the tertiary infection compared to other parities. These results would be used as basic information in designing a more rational control strategy and should also help to advise on better management care for less resistant sheep.     

Efficacy of ivermectin against induced gastrointestinal nematode infections in goats

The efficacy of ivermectin (0.08 per cent w/v oral solution) at different dose levels was evaluated against induced infections of adult Haemonchus contortus (21 days old) and Trichostrongylus colubriformis (21 days old) and fourth stage larvae of Oesophagostomum columbianum (17 days old), Ostertagia circumcincta (five days old) and Strongyloides papillosus (five days old). Twenty-five Boergoats (mutton goats) were randomly allocated by bodyweight within each sex to an untreated control group and four ivermectin treatment groups; ivermectin was administered at either 25, 50, 100 or 200 micrograms/kg orally, once. The goats were killed and processed for worm recovery 25 to 27 days after treatment. At 25 micrograms/kg the efficacy of ivermectin varied from 43 per cent for adult T colubriformis to more than 99 per cent for fourth larval stage O columbianum. Ivermectin at 50 micrograms/kg or higher was 99 per cent or more effective against all induced parasite infections with the exception of ivermectin at 50 micrograms/kg against S papillosus (97 per cent). For all parasites there was a statistically significant (P less than 0.05) difference between the control group and the pooled treated groups. No adverse reactions to ivermectin treatment were observed in the goats.