Haemonchus contortus and Trichostrongylus colubriformis in pen-trials with Javanese thin tail sheep and Kacang cross Etawah goats

Weight gain costs due to infection were higher in sheep than goats, 28 and 17.5%, respectively, for Trichostrongylus colubriformis and 48.7 and 32.2%, respectively, for Haemonchus contortus. The extent of bodyweight cost attributed to anorexia in sheep infected with H. contortus was higher (13.5 g/day) than in sheep infected with T. colubriformis (2.3 g/day). On the other hand, bodyweight cost due to the other pathogenic effects in sheep infected with T. colubriformis were higher (35.6 g/day) compared to sheep infected with H. contortus (10.9 g/day). A strong relationship between faecal egg count and worm count (r=0.79, P=0.006) was shown only in sheep infected with T. colubriformis. About half of the infected sheep and goats had low or zero faecal egg counts throughout the study. In about 40% the egg count rose initially but became low by weeks 10-16, whereas in about 10% counts increased progressively throughout the period of observation and these animals also had the highest numbers of worms at slaughter. Packed cell volume was reduced in sheep and goats infected with H. contortus but serum protein and haemoglobin levels were unaffected. Sheep infected with T. colubriformis had a higher level of eosinophilia after 8 weeks (18.4%) than sheep infected with H. contortus (11.4%), whereas this pattern was reversed in goats and levels were also lower (4.1 and 8.9%, respectively). There was no apparent relationship between eosinophilia and resistance to infection with H. contortus or T. colubriformis.     

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.     

The efficacy of a controlled-release albendazole capsule in suppressing nematode burdens in sheep

An experiment was undertaken between July and November 1985 in East Gippsland, Victoria, to determine the efficacy of an intra-ruminal controlled-release albendazole capsule against naturally acquired worm burdens and larval challenge in Merino hoggets. Two groups of 20 sheep, one group untreated, the other dosed with a capsule were grazed together; 5 sheep from each group were slaughtered for total worm counts 30 and 101 d after capsules were administered. Serum anthelmintic concentrations, faecal egg counts and body weights were monitored. Most capsules were exhausted within 91 d of administration. During the estimated 80 d for which they remained active the capsules were highly effective against the benzimidazole-susceptible worm populations. Faecal egg counts were reduced to zero and total worm populations were reduced by over 97% 30 d after administration. By 101 d egg counts were increasing and worm counts indicated that sheep were becoming reinfected. Sheep treated with the capsules grew faster than those not treated.     

Resistance to thiabendazole, fenbendazole and levamisole in Haemonchus and Trichostrongylus species in sheep on a Kenyan farm

Resistance to thiabendazole (TBZ), fenbendazole (FBZ) and levamisole (LVM) in naturally acquired gastrointestinal nematode parasites in sheep was investigated on a farm where anthelmintic resistance was suspected. This was measured by both the in vitro egg hatch assay, and reductions in faecal egg and worm counts in treated animals. In the egg hatch assay, nematode eggs were incubated in various concentrations of either TBZ or LVM. The level of resistance was expressed as the drug concentration inhibiting 50% of the eggs from hatching (LC50). The nematode population had LC50 values of 0.26 microgram ml-1 TBZ and 3.12 micrograms ml-1 LVM. In the faecal egg and worm count reduction test, naturally infected sheep were treated with either TBZ (88 mg kg-1), FBZ (10 mg kg-1) or LVM (15 mg kg-1). Faecal egg and total worm counts from these sheep were then compared with counts from untreated sheep. TBZ, FBZ and LVM failed to reduce the faecal egg counts and total worm counts by more than 90%. Based on the identification of larvae from faecal cultures, the most predominant nematode species in the resistant population were Haemonchus (62%) and Trichostrongylus (28%). TBZ reduced faecal egg counts for both species by less than 90%. FBZ and LVM also reduced Haemonchus spp. eggs by less than 90%. Other nematode species numbers did not satisfy criteria for the determination of efficacy.     

The influence of age on the variation among sheep in susceptibility to natural nematode infection

A longitudinal study of faecal nematode egg counts was made in naturally infected Scottish Blackface sheep over two grazing seasons to 75 weeks of age. Although egg counts were lower in the second grazing season the variation among animals was greater. Egg counts were repeatable from 3 months of age. The repeatability of faecal egg counts within and between grazing seasons was about 0.3. Animals with lower than average egg counts in the first grazing season tended to have lower than average egg counts in the second grazing season. Therefore lambs with relatively low faecal egg counts after 3 months of age are likely to retain their advantage in the following year.     

Epidemiology of parasitic gastrointestinal nematode infections of ruminants on smallholder farms in central Kenya

In order to establish the infection pattern with gastrointestinal nematodes in ruminants in the central Kenya highlands, a study was carried out in 58 smallholder farms. The study involved monthly faecal examinations from sheep, goats and cattle and pasture sampling from eight communal grazing areas. Each month, six Dorper worm-free tracer lambs were introduced and four locally grazed cross-bred sheep were purchased for parasite recovery. The mean faecal egg counts (FEC) for cattle were low throughout the study period, whereas those for sheep and goats showed a seasonal pattern with high levels of infection occurring during the two main rainy seasons, especially in March, April and October. There were significant differences in egg counts over time and among farms. Haemonchus contortus was the most prevalent nematode in the tracer lambs whereas the previously exposed locally grazed sheep had significantly lower numbers of H contortus but significantly higher numbers of Trichostrongylus species The highest levels of infection in the tracer lambs occurred in November 1995 and January, May and June 1996. Based on this study, it is now possible to explore the possibility of using strategic treatments for the control of parasitic gastroenteritis in this area of Kenya.     

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 influence of relative resistance and urea-supplementation on deliberate infection with Teladorsagia circumcincta during winter

The consequences for lambs of infection over the winter with Teladorsagia circumcincta were quantified by deliberate, trickle infection of selected animals at 7 months of age. Infected and control uninfected animals were each allocated into four groups, relatively resistant animals on a normal diet, relatively resistant animals on an isocaloric diet supplemented with urea, and relatively susceptible animals on the same two diets. Resistance and susceptibility was assessed by faecal egg counts following natural infection during the summer preceding the deliberate infection. During the deliberate infection egg counts remained low and most parasites recovered at necropsy were inhibited larvae. Nonetheless, infection reduced weight gain, decreased albumin and fructosamine concentrations and provoked a noticeable pepsinogen and eosinophil response. As most larvae were inhibited these responses may have been largely a consequence of immuno-inflammatory responses in the host rather than the direct action of parasites themselves. Relatively resistant animals on the supplemented diet allowed fewer larvae to establish and had higher fructosamine concentrations, higher albumin concentrations and decreased pepsinogen responses. Therefore, a combination of relatively resistant sheep and nutritional supplementation appears most efficient at controlling infection.     

The dynamics, prevalence and impact of nematode infections in organically raised sheep in Sweden

A three-year survey (1997-99) was carried out on organically reared sheep flocks throughout Sweden. The aim was to determine the prevalence and intensity of nematode infections and to establish relationships between sheep management practices and parasite infections. Faecal samples from ewes and lambs were collected from 152 organic flocks around lambing-time and during the grazing-period for analysis. Results were compared with the different management practices that farmers use to prevent parasitism in their flocks. A high proportion of the flocks was infected with nematodes. The most prevalent species were Haemonchus contortus, Teladorsagia circumeincta, Trichostrongylus axei. T. colubriformis and Chabertia ovina and infections progressively increased during summer in lambs grazing on permanent pastures. Severity of parasitic infection in lambs was highly dependent on egg output from the ewes. H. contortus was found in 37% of the flocks, even at latitudes approximating the Polar Circle. Nematodirus battus was recorded for the first time in Sweden during the course of this study. Lambs turned out onto permanent pasture showed higher nematode faecal egg counts (epg) than lambs that had grazed on pastures, which had not carried sheep the previous year. This beneficial effect of lambs grazing non-infected pastures persisted if the ewes were treated with an anthelmintic before turn-out and if the lambs were kept on pastures of low infectivity after weaning. In lambs, the prevalence and the magnitude of their egg counts were higher during autumn in flocks where lambs were slaughtered after 8 months of age, compared with flocks where all lambs were slaughtered before this age. These results will be used in providing advice to farmers of ways to modify their flock management in order to minimise the use of anthelmintics, but at the same time efficiently produce prime lambs.     

Overberg research projects. X. Faecal egg counts in the interpretation of nematode worm burdens in sheep

Worm egg counts were compared with nematode worm burdens from data collected from greater than 400 sheep killed in experiments on the epidemiology of nematode parasites in the Overberg, in the winter rainfall area of the southern Cape Province. Data were analysed in several ways but no method could be found to accurately estimate the number of nematodes present from the faecal egg count in respect of individual sheep. However, the mean natural log egg count (epg) can roughly predict the mean natural log nematode count in groups of sheep.     

Biological control of field infections of nematode parasites of young sheep with Duddingtonia flagrans and effects of spore intake on efficacy

A field study was undertaken to determine the effects of feeding Duddingtonia flagrans to young Merino sheep on pasture. A total of 60 mixed sex lambs 4-5 months old were divided into six even groups on the basis of liveweight. On Monday to Friday, each week for 6 months, three groups were offered barley grains on which D. flagrans had been cultured while the other three groups remained untreated. Every 4 weeks liveweights were recorded and faecal samples collected for nematode egg count estimation. Feeding D. flagrans reduced faecal egg counts and tended to improve liveweight gains, but considerable differences were observed between groups within treatment. These differences are thought to result from variations between the groups in consumption of the treated barley with the "best" consumers showing the greater effects of treatment.     

A survey on anthelmintic resistance in nematode parasites of sheep in Lusaka,Zambia

While surveys in Southern Africa indicate anthelmintic resistance of gastrointestinal nematodes to be common in small ruminants in South Africa, Kenya and Zimbabwe there have been no reports of resistance in Zambia. The objective of this study was to determine whether anthelmintic resistance occurs in Zambia, and to obtain information on nematode control practices in the country. During the rainy season six commercial sheep farms were selected in and around Lusaka and Chisamba. Worm control practices were gauged by means of a questionnaire, and the Faecal Egg Count Reduction Test was performed for assessing anthelmintic efficacy of albendazole, levamisole and ivermectin. On all farms anthelmintic treatment was the only approach used to control nematode infections. Frequency of treatment varied from twice a year to every 6 weeks and drugs of different anthelmintic groups were alternated within the same year. There was a wide range in faecal egg counts of individual sheep before treatment, with some individual counts of up to 87000. Larval identification showed that Haemonchus was almost the only genus recovered from the faecal cultures before and after treatment. Albendazole resistance was found on five of the six farms. On each of the four farms where ivermectin gave less than 95% reduction in egg counts, there was resistance to albendazole as well. Levamisole showed an efficacy of 95% or higher on all six farms.     

The effect of dietary protein levels before turnout on subsequent faecal nematode egg output of grazing sheep in the Joannina region of Greece

The effect of dietary protein levels before turnout on the subsequent faecal egg output of gastrointestinal nematodes was examined in two genotypes of grazing sheep, with or without anthelmintic treatment. Lambs were given a low protein (LP) or a high protein (HP) diet for three months (December to March) until grazing started. Half of the animals in each diet group were given anthelmintic treatment (AT) in March and June. The four groups (LP-AT, LP-NT, HP-AT and HP-NT) each consisted of pure-bred Butsiko and cross-bred Butsiko/Karamaniko lambs and grazed separate plots that were initially parasitologically and nutritionally similar. Faecal egg counts were recorded monthly until the experiment ended in July. Mean faecal counts for strongyle-type eggs were higher in the LP-NT group than all the other groups and higher in the LP than the HP groups indicating that faecal egg counts during grazing were influenced by levels of dietary protein before turnout. This effect was intensified in the absence of anthelmintic treatment. No genotype differences were detected.     

Epidemiology of nematode parasites of sheep around Jimma,southwestern Ethiopia

An investigation was made into the epidemiology of nematode infections of sheep in two districts of Jimma zone, southwestern Ethiopia. We used two approaches—long-term monitoring of identified sheep for nematode infection and abattoir or market survey for analysis. In the first monitoring regime, we used 80 lambs [40 sheep (20 per sex) from each district (Dedo and Yebu)] averaging 4–5 months of age. Faecal egg counts (FEC), packed cell volume (PCV) and body weight changes were monitored over a period of 1 year. Additionally, faecal samples were collected (on a weekly basis) from sheep brought to abattoir/market for 1 year to monitor faecal egg counts. The nematode parasite burden, as judged by FEC and PCV, was generally low indicating that the climatic conditions are not conducive to the development and survival of nematode eggs and the free-living stages; hence, little transmission occurred. In the experimental flocks, the highest FEC and lower PCV were recorded during the long rainy season (June to September) with peak in August and September. Faecal samples collected from abattoir/market also followed the same trend. Results from experimental sheep indicated that location had a significant (P < 0.01) effect on FEC, PCV and average daily body weight gain. The FEC and PCV for sheep in Yebu (mid-altitude) district were 126 ± 3.33 and 30.6 ± 0.26, whereas the values for Dedo (highland) were 93 ± 4.35 and 32.0 ± 0.21, respectively. The results indicate that the highland areas are comparatively less favourable to the survival and development of nematodes. Female lambs had lower FEC and higher PCV compared to male lambs (P < 0.05). The overall nematode parasite challenge in the area, however, is low. We, therefore, recommend rotational grazing management combined with monitoring parasite load and selective treatment to reduce productivity loses and pasture contamination.     

A model for study of lungworm (Dictyocaulus sp.) and gastrointestinal nematode infection in young red deer (Cervus elaphus)

A model of sub-clinical parasitism in young red deer, using concurrent trickle infections of lungworm (Dictyocaulus sp.) and mixed gastro-intestinal (GI) nematodes of deer-origin was evaluated. 20 parasite-free deer calves were artificially reared indoors from 4 days of age. A further five calves were naturally reared on pasture with their dams, treated with anthelmintic and brought indoors at 3-4 months. At 4-4.5 months of age they were individually housed and allocated to five groups (n=5). Groups were dosed 3 x per week, for 9 weeks with 0, 100 and 500, 200 and 1000 (2 groups), 400 and 2000 infective larvae of lungworm and mixed GI nematodes, respectively, cultured from deer faeces. Liveweight and voluntary feed intake measurements and faecal and blood samples were taken weekly. In the fourth week following cessation of trickle infection, deer were euthanased and lung and GI nematodes recovered. Both lungworm and GI nematode infections became patent at Week 4 of infection. Maximum group arithmetic mean faecal egg counts were 100-190 epg. Maximum group arithmetic mean faecal lungworm larval counts were 58-123 lpg. Group arithmetic mean nematode counts at slaughter ranged from 439-806 for GI nematodes and 31-73 for lungworm, respectively. Despite low nematode counts, reduced liveweight gain, voluntary feed intake and serum albumin concentration, elevated serum pepsinogen, gastrin and globulin concentrations and elevated peripheral eosinophil counts and slight haemoconcentration, but no clinical signs, were observed. The reduction in liveweight gain was related to the reduction in voluntary feed intake (r2=0.83; p<0.088). Naturally-reared deer had similar liveweight gains, voluntary feed intake and nematode counts to artificially-reared deer. Thus, methods of infection to produce concurrent sub-clinical lungworm and GI nematode burdens for study of sub-clinical parasitism in young deer have been defined.     

Role of host and environment in mediating reduced gastrointestinal nematode infections in sheep due to intensive rotational grazing

We have previously reported marked reductions in faecal worm egg counts (WECs) and drenching frequency in sheep on an intensive rotational grazing system (IRG) in a cool temperate environment with summer-dominant rainfall. These experiments were designed to determine the role of the host and environmental factors in mediating this. The role of host factors was investigated by administering a fixed larval challenge in each of the 4 seasons of the year to groups of 20 young sheep on three different management systems, including IRG. This comprised a mixed larval challenge containing infective larvae of Haemonchus contortus and Trichostrongylus colubriformis 7 days after short-acting anthelmintic treatment. A range of measurements was then made up to day 35 post-challenge. The role of environmental factors was determined by assessing pasture infectivity in four seasons using faecal worm egg counts (WECs) and pooled faecal culture of worm-free tracer sheep. The management systems were high input (HI) with high fertiliser inputs high stocking rate and relatively long grazing periods; typical New England management system (TYP) with moderate fertiliser inputs and stocking rate and relatively long grazing periods and; Intensive rotational grazing (IRG) with moderate fertiliser inputs and stocking rate but very short (mean 5 days) grazing periods and long (mean 103 days) rest periods. IRG sheep had higher mean WEC at 28 and 35 days after fixed larval challenge than HI and TYP sheep in spring (IRG: 9500 ± 1000; HI: 4000 ± 1000; TYP: 7200 ± 1000 eggs/g, P<0.01) and summer (IRG: 8400 ± 750; HI: 5300 ± 800; TYP: 4400 ± 700 eggs/g; P<0.001) and also had lower live weights during these seasons. There was no difference in WEC after the autumn challenge (IRG: 5100 ± 450 HI: 4500 ± 450; TYP: 4200 ± 450 eggs/g; P ≈ 0.36) but IRG had lower WEC than TYP following the winter challenge (IRG: 2900 ± 400; HI: 2300 ± 400; TYP: 4300 ± 400 eggs/g, P<0.01). The tracer sheep (used to determine pasture infectivity) on IRG had significantly lower WECs during winter, spring and summer than those under the other management systems. Faecal culture and larval differentiation revealed that faeces from tracers on IRG contained significantly lower proportions of H. contortus and significantly higher proportions of Trichostrongylus spp. and Teladorsagia circumcincta than faeces from tracers on the HI and TYP treatments. Thus, when IRG was most efficacious for worm control, during spring and summer when short graze and long rest periods were maintained, sheep on this system exhibited greater susceptibility to larval challenge while tracer sheep indicated lower pasture infectivity. This demonstrates that the effects of IRG on WEC are mediated by reduced larval challenge rather than increased host resistance to infection.     

Haemonchus spp. in sheep farmed under resource-poor conditions in South Africa--effect on haematocrit,conjunctival mucous membrane colour and body condition

A longitudinal study was conducted on the differential faecal egg counts, haematocrits and body condition scores of sheep belonging to resource-poor farmers at Rust de Winter, Gauteng province, and Kraaipan, North West Province, South Africa. The animals were scored for level of anaemia using the FAMACHA method, an assay for the clinical evaluation of anaemia caused by Haemonchus spp. Periods of higher Haemonchus egg counts occurred from October to March for sheep at Rust de Winter and from September/October to February or April for sheep at Kraaipan. Lower haematocrit values were registered during these periods as was a higher incidence of anaemic conjunctival mucous membrane colour scores compared to the period April to September. No clear relationship between the faecal egg counts and the body condition scores was evident. Although wider application of the FAMACHA system in sheep raised by resource-poor farmers should be investigated, the present study indicates that this method may certainly prove to be a valuable worm control strategy for such livestock owners.     

Egg output of Ostertagia circumcincta in sheep given single infections of varying size

The faecal egg counts of groups of sheep given 5 000, 20 000 or 40 000 infective larvae of Ostertagia circumcincta reached a peak at about 28 days after infection; the height of the peak varying directly with the number of larvae given. At 35 days the ratios of total worm burdens and the total eggs in all females amongst the groups were similar. Between 35 and 70 days post infection the faecal egg counts fell to a low level which was roughly the same regardless of the number of larvae administered. At 70 days the two groups of lambs given the two higher doses of larvae had similar worm burdens, but those given 5 000 larvae harboured about half as many. At this time the total eggs in all females was approximately the same in each group. Whatever factor, in addition to worm numbers, which may have limited egg output appeared to be ineffective until some time after the peak egg count was reached.     

Clinical pathology of experimental Schistosoma curassoni infections in sheep and goats

The clinical pathology of Schistosoma curassoni infection in sheep and goats was studied for 22 weeks following experimental infection with 7000 and 4000 cercariae, respectively. Excretion of eggs began at week 7 after infection: in goats the numbers increased to 30 to 50 eggs per gram faeces (epg) at weeks 8 to 18, followed by a reduction. In a pregnant goat, epg values increased markedly before and after parturition. The mean faecal egg counts in sheep were lower than in goats, increasing to a maximum level of 30 epg at weeks 16 and 17 after infection. Infected sheep maintained growth rates roughly comparable with controls, whereas infected goats failed to gain as much weight as the controls. Infected goats and sheep produced eosinophil counts of about 3 x 10(3) mm-3, five and eight weeks after infection, respectively. Sheep developed a progressive anaemia from week 11 after infection, in goats blood values remained within normal limits. Differences in serum protein concentration were observed between infected and uninfected goats about nine weeks after infection, but not in sheep. Increased total protein values, hyperglobulinaemia and lowered albumin to globulin ratios were features of infected goats. Serum glutamate oxaloacetate transaminase, glutamate pyruvate transaminase, gamma-glutamyl transferase, total lactate dehydrogenase and bilirubin were not significantly changed. The mean recovery in sheep was 608 worms, in goats 428 worms, but the total tissue egg counts were higher in the latter. Of the total eggs deposited in the goats 92 per cent were found in the liver with 51.5 per cent in the ovine liver. The histopathological changes were studied.     

The anthelmintic efficacy of the plant, Albizia anthelmintica, against the nematode parasites Haemonchus contortus of sheep and Heligmosomoides polygyrus of mice

Albizia anthelmintica Brong., belongs to the plant family Mimosaceae. The plant is widely used in East Africa by poor smallholder farmers and pastoralists to treat their livestock against internal parasites. The anthelmintic effects of water extracts from the bark of A. anthelmintica, obtained from three different geographic areas in Kenya and using different methods of preparation, were tested at different doses in sheep and mice infected with the nematode parasites Haemonchus contortus and Heligmosomoides polygyrus, respectively. Lambs were infected with 3000 infective larvae of H. contortus and treated with the plant preparations 28 days later, while mice were infected with 200 infective larvae of H. polygyrus and treated 18 days later. Proximate analysis established high levels of crude proteins in A. anthelmintica bark. Two sheep out of the 45 treated with the plant preparations suffered from transient bloat, which was relieved by dosing with a surfactant. Significant reductions in faecal egg counts were observed in lambs treated with A. anthelmintica in two of the three experiments undertaken, but the efficacy levels achieved were well below the 70% reduction required. Similar values of packed red cell volume and live weight gain were observed for treated and control lambs. There was no overall significant effect of treatment with A. anthelmintica on faecal egg and total worm counts in mice. A dose rate of 1000 mg/kg bodyweight of A. anthelmintica preparation resulted in death of all mice. The results show that A. anthelmintica at the doses and preparations used is not efficacious against H. contortus in sheep or against H. polygyrus in mice.