Effect of strategic gastrointestinal nematode control on faecal egg count in traditional West African cattle

This paper reports on the effect of strategic anthelmintic treatments and other determinants on faecal egg counts (FEC) of Trichostrongyles in N'Dama cattle of a west African village. Initially, 527 animals from 13 private N'Dama cattle herds were monitored in a longitudinal study from October 1989 to December 1994. Each herd was stratified by age and animals were sequentially allocated to two groups with similar age distributions. One group received a single anthelmintic treatment of fenbendazole (7.5 mg/kg BW), in October 1989 (n = 250), whereas the other group remained untreated (n = 277) throughout the study. In the next rainy season (June to October), the treated animals were treated twice (in July and September). The same treatment schedule was used in the subsequent rainy seasons until December 1994. Biannual anthelmintic treatments decreased the level of FEC between 31% (late dry season) and 57% (rainy season), when compared to untreated controls. The highest levels of FEC were found during the rainy season from June to October. FEC levels decreased until 4 years of age, after which they remained on a constant low level. The variability of returns to anthelmintic treatments between herds did not seem to be influenced by FEC at the herd level. The financial evaluation of anthelmintic interventions cannot be predicted from FEC and must necessarily rely on the direct monitoring of livestock productivity parameters.     

Performance and nematode infection of ewe lambs on intensive rotational grazing with two different cultivars of <Emphasis Type="Italic">Panicum maximum</Emphasis>

The daily live weight gain (DLWG), faecal nematode egg counts (FEC), and packed cell volume (PCV) of Suffolk, Ile de France and Santa Inês ewe lambs were evaluated fortnightly for 56 days in the dry season (winter) and 64 days in the rainy season (summer) of 2001-2002. The animals were distributed in two similar groups, one located on Aruana and the other on Tanzania grass (Panicum maximum), in rotational grazing system at the Instituto de Zootecnia, in Nova Odessa city (SP), Brazil. In the dry season, 24 one-year-old ewe lambs were used, eight of each breed, and there was no difference (p > 0.05) between grasses for DLWG (100 g/day), although the Suffolk had higher values (p < 0.05) than the other breeds. In the rainy season, with 33 six-month-old ewe lambs, nine Suffolk, eight Ile de France and 16 Santa Inês, the DLWG was not affected by breed, but it was twice as great (71 g/day, p < 0.05) on Aruana as on Tanzania grass (30 g/day). The Santa Inês ewe lambs had the lowest FEC (p < 0.05) and the highest PCV (p < 0.05), confirming their higher resistance to Haemonchus contortus, the prevalent nematode in the rainy season. It was concluded that the best performance of ewe lambs on Aruana pastures in the rainy season is probably explained by their lower nematode infection owing to the better protein content of this grass (mean contents 11.2% crude protein in Aruana grass and 8.7% in Tanzania grass, p < 0.05) which may have improved the immunological system with the consequence that the highest PCV (p < 0.05) observed in those animals.     

Epidemiology of gastrointestinal nematodes in cattle on traditional, small-scale dairy and large-scale dairy farms in Iringa district, Tanzania

A longitudinal study was carried out to determine the prevalence, distribution and intensity of gastrointestinal (GI) nematodes in traditional, small-scale dairy and large-scale dairy cattle farms in Iringa district, Southern highlands of Tanzania. Coprological examination of cohorts for GI nematode eggs in faeces, tracer worm counts and pasture larval counts were performed monthly for 1 year. Results indicated that the type of management, especially the grazing habit has a significant influence on the prevalence and intensity of GI nematodes. The predominant nematodes were Cooperia spp. (51.6%), Oesophagostomum radiatum (35.7%) and Haemonchus placei (10.2%). The worm burden in tracers was mainly composed of Cooperia spp. (83%) in large-scale dairy farms, while O. radiatum was dominant (60.8%) in traditional farms. Faecal egg counts (FEC) and tracer worm counts were generally low and FEC peaked only in calves and weaners/yearlings. Adults and all age groups in small-scale dairy farms had very low FEC throughout the year. Pasture larval counts, FEC and tracer worm counts peaked towards the end of the rainy season. Based on conditions of the study area, farmers could save substantial amount of money through strategic treatments as opposed to the previous routine of treating the whole herd at least four times a year. Strategic treatments are recommended in calves and weaners only in traditional and large-scale dairy farms. Strategic treatment of adults and small-scale dairy cattle might be not necessary. Strategic treatments at the end of the rainy/early dry season (May/June) and at the end of the dry/early rainy season (November/December) are recommended in the district. An additional treatment against GI nematodes in calves during the mid rainy season (February/March) might be important.     

A survey of seasonal patterns in strongyle faecal worm egg counts of working equids of the central midlands and lowlands, Ethiopia

A study was conducted for two consecutive years (1998–1999) to determine the seasonal patterns of strongyle infection in working donkeys of Ethiopia. For the purpose 2385 donkeys from midland and lowland areas were examined for the presence of parasitic ova. A hundred percent prevalence of strongyle infection with similar seasonal pattern of strongyle faecal worm egg output was obtained in all study areas. However, seasonal variations in the number of strongyle faecal worm egg output were observed in all areas. The highest mean faecal worm egg outputs were recorded during the main rainy season (June to October) in both years in all areas. Although an increase in the mean strongyle faecal egg output was obtained in the short rainy season (March–April) followed by a drop in the short dry season (May), there was no statistically significant difference between the short rainy season and long dry season (Nov–Feb) (P > 0.05). A statistically significant difference however, was obtained between the main rainy season and short rainy season, and between the main rainy season and dry season (P < 0.05). Based on the results obtained it is suggested that the most economical and effective control of strongyles can be achieved by strategic deworming programme during the hot dry pre-main rainy season (May), when the herbage coverage is scarce and helminthologically ‘sterile’, and the arrested development of the parasites is suppose to be terminating. This could insure the greatest proportion of the existing worm population to be exposed to anthelmintic and also reduces pasture contamination and further infection in the subsequent wet season.     

In vivo anthelmintic activity of Dorycnium rectum and grape seed extract against Ostertagia (Teladorsagia) circumcincta and Trichostrongylus colubriformis in sheep

AIM: To assess the in vivo anthelmintic activity of condensed tannins (CT) in the forage species Dorycnium rectum and Medicago sativa, and in an extract from grape (Vitus vinifera) seeds (GSE), against two species of parasite, Teladorsagia (Ostertagia) circumcincta and Trichostrongylus colubriformis, at different stages of their life cycle, in sheep that were parasite-na?ve or previously exposed to nematodes. METHODS: In Trial 1, a factorial treatment structure was used to compare faecal nematode egg counts (FEC) and worm burdens in 40 weaned Romney lambs fed either the CT-containing forage D. rectum (12% dry matter; DM) or M. sativa (lucerne; 0.2% DM). Twenty na?ve and 20 previously-exposed lambs were drenched free of parasites then reinfected with known species and numbers of parasites, and housed in pens indoors on a diet of lucerne pellets and chaffed hay. Groups of lambs (n=5 lambs per group) were fed one of the forages over one of two time periods within the parasite's life cycle. Six to nine days after the last feeding of fresh forages, faecal samples were collected for FEC, and all lambs were slaughtered and worm counts conducted. In Trial 2, 12 Suffolk x Romney lambs were surgically implanted with an abomasal cannula and then housed indoors in metabolism crates. After infection with parasites, six lambs were infused continuously over a 14-day period with a commercially available CT GSE (96% DM, made up to 34 g/L in water); the remaining lambs were infused with water. During infusion, samples were collected for egg hatch and larval development assays. After infusion, samples were collected for FEC, and all lambs were slaughtered and worm counts conducted. RESULTS: In Trial 1, there was a significant (p<0.001) difference in burdens of O. circumcincta between na?ve lambs and those previously exposed to parasites, but no other differences were recorded. In Trial 2, lambs infused with GSE had significantly (p<0.05) fewer T. colubriformis at slaughter and significantly (p<0.001) fewer eggs hatched in the egg hatch assay (EHA) than for lambs infused with water. Overall, the differences attributable to GSE were small in magnitude, being an 11% drop in egg hatch, and an 18% drop in numbers of adult T. colubriformis after 14 days of continuous infusion. No other differences were recorded. CONCLUSION: The results indicate that the in vivo anthelmintic activity of these CT sources is, at best, modest and is unlikely to be of any practical value. Further, these data emphasise that in vitro activity is an unreliable indicator of in vivo efficacy for CT-containing forages and extracts.     

Does suckling offer protection to the lamb against Teladorsagia circumcincta infection?

This study tested the hypothesis that milk has a direct effect on the establishment of infection with Teladorsagia circumcincta, and provides information on the effects of suckling on resilience to infection in young lambs. Of 46 six-week-old twin-born lambs, one from each twin was allowed to continue suckling (S-) and its twin-weaned (W-) while both were concurrently infected with an average of either 0 (-0; n=7/group), 250 (-250; n=8/group) or 1000 (-1000; n=8/group) third stage infective larvae (L3) of T. circumcincta per day, providing six treatment groups. All groups grazed minimally contaminated pasture, and after 42 days were slaughtered for necropsy. Low pasture larval contamination was confirmed in W0 and S0 lambs by faecal egg counts (FEC) of less than 30 eggs per gram (EPG) and burdens of less than 140 worms. There was no difference in FEC between weaned and suckled lambs. Within infection regime, total worm burdens were 55-60% greater in the weaned compared with their suckled counterparts (P=0.05), and represented 27 and 17%, respectively, net establishment of larvae. The greater worm burdens of both groups of weaned animals, which compared with their suckled counterparts, and of those infected with 1000 compared with 250 larvae per day, were associated with shorter female adults that had fewer eggs in utero, perhaps indicating intra-worm population regulation, but highlighting the limitation of FEC in assessing nematode burdens of such young lambs. There was no effect of infection on live weight gain of either weaned or suckled groups and the possibility was raised that, in such young lambs, immune unresponsiveness may be responsible. The major benefit of continued milk consumption appears to lie more in providing nutrients for enhanced growth rather than in improving resilience of the lambs to infection.     

Grazing sericea lespedeza for control of gastrointestinal nematodes in lambs

Alternatives to chemical dewormers are needed to counter anthelmintic resistance and improve worm control in organic management systems. The objective was to examine the effectiveness of grazing sericea lespedeza (SL) compared with grass pastures for control of gastrointestinal nematodes (GIN) in lambs. In Experiment 1, Katahdin lambs grazed bermudagrass (BG; n=14), tall fescue (TF; n=7), or SL (n=19) pastures during early summer months. In Experiment 2, lambs grazed TF (n=15) or SL (n=13) pastures during late summer. Stocking rate of pastures was based on forage availability; additional lambs grazed pastures in Experiment 2, but were not sampled. Lambs were dewormed with 0.5 g COWP if FAMACHA(?) score was >3. In Experiment 1, FEC were reduced within 35 days in SL compared with BG lambs (forage by time, P=0.03). The PCV was more resilient to changes over time in SL compared with other groups of lambs (forage by time, P=0.001). In Experiment 2, FEC were lower (P=0.02) and PCV tended to be higher (P=0.09) in lambs grazing SL compared with TF forage. Incidence of deworming was similar among forage groups in both experiments. Grazing SL reduced FEC in lambs in early and late summer, despite reluctance by lambs to graze. Grazing forage and selective deworming using COWP was effective in lambs.     

Effects of genetic and environmental factors on pre-weaning and post-weaning growth in West African crossbred sheep

Effects of genetic and environmental factors on pre-weaning and post-weaning growth were studied in West African crossbred sheep. Effects of lamb genotype (7/8 Sahelian–1/8 Djallonké, 3/4 Sahelian–1/4 Djallonké and 1/2 Sahelian–1/2 Djallonké; hereafter denoted 7/8Sa, 3/4Sa and 1/2Sa, respectively), parity, type of birth, sex of lamb and year-season of lambing on birth weight, weaning weight, 8-month weight and pre- and post-weaning growth rates were determined. At birth 7/8Sa and 3/4Sa lambs were heavier (p<0.01) than 1/2Sa lambs. Lambs born to first-parity ewes were lighter (p<0.01) at birth than lambs of older ewes. At weaning and 8 months of age, lambs born to fourth-parity ewes were heavier (p<0.05) than those born to ewes of the other parities. Parity did not have any significant effects on pre-weaning growth rate. Lambs born in the rainy season of 2001 were significantly heavier at birth and at 8 months of age than those born in the dry season of 2001/02, but there was no difference between the two groups at weaning. Pre-weaning growth rate was significantly faster in lambs born in the dry season of 2001/02 but the reverse was true for post-weaning growth rate.     

The strategic use of closantel and albendazole in controlling naturally acquired gastrointestinal nematodes of sheep in the Kenya highlands

The strategic use of closantel, a narrow-spectrum salicylanilide anthelmintic against bloodsucking helminths, and of albendazole, a broad-spectrum benzimidazole anthelmintic, in the control of gastrointestinal nematodes of sheep was investigated on a farm in Nyandarua District in the highlands of Kenya. Thirty Corriedale female lambs aged between 9 and 12 months were assigned to three treatment groups of 10 lambs each. The three groups were set stocked on separate paddocks for 12 months. Lambs in group 1 (strategic treatment group) were treated with closantel and albendazole at the beginning and towards the end of the long rains (April and June, respectively) and towards the end of the short rains (December). During the intervening dry season, the lambs were treated with albendazole. Lambs in group 2 (suppressive treatment group) were kept worm free by regular deworming with albendazole at 3-weekly intervals for 12 months. The third group of lambs remained untreat ed (control group). Gastrointestinal nematode infections and pasture infectivity were well controlled in the case of the strategic treatment group. This resulted in higher weight gains, wool production, packed cell volume, and serum albumin and protein concentrations compared with the untreated control lambs. These parameters were comparable between the strategic treatment and the suppressive treatment groups of lambs. It was concluded that worm control strategies based on the epidemiology of the parasites and the sustained anthelmintic action of closantel in combination with broad-spectrum anthelmintics can provide effective control of gastrointestinal nematodes of sheep in the study area.     

Effects of management system,legume feeding and anthelmintic treatment on the performance of lambs in North Sumatra

Sixty-four lambs in North Sumatra were used in a factorial experiment comprising two systems of management (grazing and stall-feeding), four levels of legume supplementation (0, 250, 500 and 1,000 g/d Pueraria javanica) and two anthelmintic treatments (none and albendazole every four weeks). The experiment lasted five months. The mortality rate for lambs not given anthelmintic was 28%, significantly higher (P less than 0.05) than for animals given anthelmintic which had zero mortality. Anthelmintic treatment increased growth rate from only 2 g/d to 29 g/d (P less than 0.05) and reduced faecal egg count from 1,700 epg to 270 epg. When not given anthelmintic grazing lambs had a higher mortality rate (38%) than stall-fed lambs (19%) but this difference was not significant. When given anthelmintic grazing lambs has a slightly higher growth rate (32 g/d) than stall-fed lambs (26 g/d). System of management had no apparent effect on egg count. Legume supplementation reduced the egg count of lambs not given anthelmintic but had no significant effect on mortality or growth rate.     

Exploration of the epidemiological consequences of resistance to gastro-intestinal parasitism and grazing management of sheep through a mathematical model

Predicting the impacts of selection for decreased faecal egg count (FEC) (i.e. host resistance) in grazing ruminants is difficult, due to complex interactions between parasite epidemiology, management and host responses. A mathematical model including heritable between lamb variation in host-parasite interactions, Teladorsagia circumcincta epidemiology and anthelmintic drenching, was developed and used to (i) address such interactions and their impact on outcomes including FEC, live weight (LW, kg) and pasture larval contamination (PC, larvae/kg DM), and (ii) investigate how grazing management strategies, aimed at reducing host exposure to infective larvae via pasture moves at 40 day intervals, affect these outcomes. A population of 10,000 lambs was simulated and resultant FEC predictions used to assign the 1,000 lambs with the highest and lowest predicted FEC to 'susceptible' (S) and 'resistant', (R) groups, respectively. The predicted average FEC of the S group was ～8.5-fold higher than the R group across a grazing season. The R and S groups were then simulated to graze separate pastures (R(sep) and S(sep)); and repeated for 3 grazing seasons to allow predictions to diverge and stabilize. Further, different grazing strategies were superimposed on all groups. PC and average FEC were affected by whether lambs of different resistance genotype grazed together or separately, with differences increasing across grazing seasons. By the third grazing season the average PC of the R(sep) group was reduced by ～83%, and the S(sep) group was increased by ～240%, in comparison to the whole population average. Average FEC of the R(sep) group was reduced by ～40%, and the S(sep) group increased by ～46% in comparison to the R and S groups, respectively, whilst drenching had little impact on the proportional differences in FEC between groups. Predicted LW was similar for the R and R(sep) groups irrespective of anthelmintic treatment, whilst LW of the S(sep) group was reduced by ～14% compared to the S group for un-drenched lambs, and by ～4% for drenched lambs. The differing grazing strategies were predicted to have little impact on FEC or LW, with the exception of the S(sep) group which was predicted to have a 2kg increase in LW when drenched and moved to a clean pasture. Together, these results suggest that host genotype has a substantial impact on parasite epidemiology, however the benefits of anthelmintic treatment and grazing management should only be expected for susceptible animals. This supports the use of targeted selective treatment, focussing on susceptible animals.     

The effect of providing feed supplementation and anthelmintic to donkeys during late pregnancy and lactation on live weight and survival of dams and their foals in central Ethiopia

Anthelmintic treatment (A), feed supplementation (F), anthelmintic and feed supplementation (A+F) or traditional management (Control) was given to 166 pregnant female donkeys in three localities (Holetta, Debre Zeit and Adami Tulu) in Ethiopia during an on-farm study. Treatments started during the last trimester of pregnancy and continued until 6 months after parturition when the foals were weaned. The same treatments were administered to foals once they reached 1 month of age. Live weights of adults and foals were measured throughout the study along with work output of adult donkeys and survival to weaning of the foals. Faecal worm egg counts (FEC) and blood packed cell volumes (PCV) were recorded monthly. When applied alone, anthelmintic treatment (A) or feed supplementation (F) had no significant effect on live weight gain or foal survival. However, when combined, anthelmintic and feed supplementation (A+F) significantly (p<0.05) improved both live weight gain in adults and foals and foal survival. Workout was not affected by any of the treatments. Treatments A and A+F resulted in a highly significant (p<0.001) reduction in FEC in all three localities during the course of study and for at least 6 months after the last dose of anthelmintic in one of the study areas (Holetta). None of the treatments had any significant effect on PCV. Donkey owners in Ethiopia should be encouraged to adopt both anthelmintic treatment and feed supplementation if they expect tangible benefits in animal performance.     

Seasonal variation in the parasite burden and body condition of working donkeys in East Shewa and West Shewa regions of Ethiopia

A survey of donkeys arriving at markets in three localities in East and West Shewa regions of central Ethiopia was carried out during 2002. Total faecal worm egg counts and body condition scores were measured for a total of 963 donkeys over a 12-month period. Total faecal worm egg counts did not differ significantly between localities but there was significant (p < 0.001) seasonal variation within localities. Levels of helminth infection closely followed rainfall patterns, being lowest (956 eggs per gram of faeces, e.p.g.) at the end of the long dry season (February) and highest (2022 e.p.g.) in the middle of the long wet season (August). Body condition score was associated closely with level of helminth infection (Goodman-Kruskal measure of association 0.60-0.80). Seasonal variation in body condition score reflected the temporal changes in worm burden and the availability of forage. It is suggested that a body condition score of 3 or less could be used as a simple means of identifying donkeys that require therapeutic treatment with anthelmintic. It is further proposed that economically viable strategic control of helminths in donkeys could be achieved by administering a single annual dose of avermectin-based anthelmintic at the start of the long rainy season (May-June). This may allow donkeys to recover body condition when available forage is most abundant and nutritious. It is also recommended that protein-rich feed supplementation be provided during the later part of the dry season (November-January). This may help maintain body condition when forage is scarce and the helminth challenge is at its lowest.     

Brave or gullible: testing the concept that leaving susceptible parasites in refugia will slow the development of anthelmintic resistance

AIM: To test the theory that creating a reservoir of unselected worms by leaving a proportion of lambs in a flock untreated with anthelmintic, i.e. in refugia, will slow the development of anthelmintic resistance in nematode parasite populations. METHODS: Newly weaned Romney lambs (n=180) were infected with two nematode parasite species, Teladorsagia (= Ostertagia) circumcincta and Trichostrongylus colubriformis. For each species, the challenge doses contained a mixture of infective larvae from benzimidazole-resistant and -susceptible isolates calculated to yield, from the combined population, a 95% reduction in faecal nematode egg counts (FEC) following treatment with albendazole. Once the infections were patent, the lambs were divided into nine groups of 20 animals, and each group was allocated to one of three treatments. In Treatments 1, 2 and 3, 100%, 90% and 80% of animals were treated with an anthelmintic, respectively. For treatments 2 and 3, the heaviest animals remained untreated. Following treatment, each group was moved to its own previously prepared low-contamination pasture. Lambs grazed this pasture for 7 weeks before again being treated and moved to new low-contamination pastures (Shift 1 and Shift 2). The parasite populations on pasture resulting from the different treatments were subsequently sampled using tracer lambs, and worm eggs derived from these were used in both egg-hatch assays (EHA) and larval development assays (LDA), to measure albendazole-resistance status. RESULTS: Treating all animals each time the groups were moved to new low-contamination pastures resulted in higher levels of albendazole resistance (p<0.05), measured using EHA and LDA, in subsequent parasite generations than when either 10 or 20% of animals were left untreated. However, higher FEC in the tracer lambs grazed on pastures in Treatments 2 and 3, compared with Treatment 1, indicated an increased level of pasture contamination as a result of leaving some animals untreated. CONCLUSIONS: The results demonstrate that creating a reservoir of unselected parasites slows the development of anthelmintic resistance, and emphasises the risk of treating all animals prior to a shift on to low-contamination pasture. However, higher levels of pasture contamination, resulting from untreated animals, indicate the difficulty in managing both worm control and resistance.     

Helminthiasis characterization and anthelmintic efficacy for ewes and lambs raised in tropical semiarid region

In this study the helminthiasis and anthelmintic effectiveness in ewes and lambs were evaluated in a semiarid region of Brazil. Twelve sheep farms were investigated using semi-structured questionnaires and fecal egg count (FEC) reduction test was employed to analyze the profile of anthelmintic resistance. Groups of at least 10 animals with FEC ≥ 300 were selected. After 12 h of fasting, homogeneous groups of lambs or ewes were treated with albendazole, levamisole moxidectin, or oxfendazole and control groups were not treated. Feces were collected before treatments and 14 days after, and larvae genera were identified after cuprocultures in both periods. Extensive grazing was the predominant creation system, using hybrid Santa Ines animals. The separation by age was promoted in 75% of herds; however, maternity pickets there were only in three farms. The strategic treatments were performed only in 8.4% of sheep farms and 16.6% used the anthelmintic efficacy test and alternated anthelmintic classes after 1 year. The initial FEC means for lambs were significantly higher than ewe FEC averages. For lamb tests, moxidectin and levamisole showed higher efficacy (p ≤ 0.05) than benzimidazoles. For ewe tests, moxidectin and levamisole showed efficiencies >75%. Haemonchus spp. and Trichostrongylus spp. were the most frequent nematodes before treatments and the genus Haemonchus was the most prevalent after anthelmintic treatments (p < 0.05). Variations of anthelmintic susceptibility were observed for categories and herds evaluated, which emphasizes the importance of the effectiveness tests for the choice of anthelmintics for ewes and lambs.     

In silico exploration of the impact of pasture larvae contamination and anthelmintic treatment on genetic parameter estimates for parasite resistance in grazing sheep

A mathematical model was developed to investigate the impact of level of Teladorsagia circumcincta larval pasture contamination and anthelmintic treatment on genetic parameter estimates for performance and resistance to parasites in sheep. Currently great variability is seen for published correlations between performance and resistance, with estimates appearing to vary with production environment. The model accounted for host genotype and parasitism in a population of lambs, incorporating heritable between-lamb variation in host-parasite interactions, with genetic independence of input growth and immunological variables. An epidemiological module was linked to the host-parasite interaction module via food intake (FI) to create a grazing scenario. The model was run for a population of lambs growing from 2 mo of age, grazing on pasture initially contaminated with 0, 1,000, 3,000, or 5,000 larvae/kg DM, and given either no anthelmintic treatment or drenched at 30-d intervals. The mean population values for FI and empty BW (EBW) decreased with increasing levels of initial larval contamination (IL(0)), with non-drenched lambs having a greater reduction than drenched ones. For non-drenched lambs the maximum mean population values for worm burden (WB) and fecal egg count (FEC) increased and occurred earlier for increasing IL(0), with values being similar for all IL(0) at the end of the simulation. Drenching was predicted to suppress WB and FEC, and cause reduced pasture contamination. The heritability of EBW for non-drenched lambs was predicted to be initially high (0.55) and decreased over time with increasing IL(0), whereas drenched lambs remained high throughout. The heritability of WB and FEC for all lambs was initially low (～0.05) and increased with time to ～0.25, with increasing IL(0) leading to this value being reached at faster rates. The genetic correlation between EBW and FEC was initially ～-0.3. As time progressed the correlation tended towards 0, before becoming negative by the end of the simulation for non-drenched lambs, with increasing IL(0) leading to increasingly negative correlations. For drenched lambs, the correlation remained close to 0. This study highlights the impact of IL(0) and anthelmintic treatment on genetic parameters for resistance. Along with factors affecting performance penalties due to parasitism and time of reporting, the results give plausible causes for variation in genetic parameter estimates previously reported.     

Regulation of the resistance to nematode parasites of single- and twin-bearing Merino ewes through nutrition and genetic selection

Periparturient Merino ewes obtained from lines of sheep that had been selected either for increased resistance to Haemonchus contortus (R) or at random (C) were supplemented, while grazing at pasture, with either nil or 250 g/day cottonseed meal (CSM) for the 6 weeks prior to or the 6 weeks after the start of parturition. Ewes from both supplement groups had lower (mean 66% reduction) faecal egg counts (FECs) during the postpartum period and this coincided with a period of maternal body weight loss. Factors which increased the rate of maternal body weight loss, such as pregnancy and lactation status, also increased FEC. Evidence is presented that the magnitude of the periparturient rise (PPR) in FEC in grazing ewes will be greatest during periods of maternal weight loss and at these times supplementation to increase metabolisable protein (MP) supply will be most effective in increasing resistance to nematode parasites. The resistance of R ewes to nematode parasites was greater than that of C ewes throughout the experiment and was sufficiently low such that anthelmintic treatment in a commercial environment may not have been required. Irrespective of actual FEC, ewes from all treatment combinations exhibited a PPR in FEC. Reduced FEC of R ewes resulted in reduced apparent pasture larval contamination after 18 weeks of continuous grazing but supplementation was ineffective in this regard. It is suggested that integrated parasite management (IPM) programs for periparturient ewes should make use of both protein supplementation and genetic selection to increase worm resistance and reduce dependency on anthelmintics for worm control.     

The Effect of Providing Feed Supplementation and Anthelmintic to Donkeys during Late Pregnancy and Lactation on Live Weight and Survival of Dams and Their Foals in Central Ethiopia

Anthelmintic treatment (A), feed supplementation (F), anthelmintic and feed supplementation (A + F) or traditional management (Control) was given to 166 pregnant female donkeys in three localities (Holetta, Debre Zeit and Adami Tulu) in Ethiopia during an on-farm study. Treatments started during the last trimester of pregnancy and continued until 6 months after parturition when the foals were weaned. The same treatments were administered to foals once they reached 1 month of age. Live weights of adults and foals were measured throughout the study along with work output of adult donkeys and survival to weaning of the foals. Faecal worm egg counts (FEC) and blood packed cell volumes (PCV) were recorded monthly. When applied alone, anthelmintic treatment (A) or feed supplementation (F) had no significant effect on live weight gain or foal survival. However, when combined, anthelmintic and feed supplementation (A + F) significantly (p < 0.05) improved both live weight gain in adults and foals and foal survival. Workout was not affected by any of the treatments. Treatments A and A+F resulted in a highly significant (p<0.001) reduction in FEC in all three localities during the course of study and for at least 6 months after the last dose of anthelmintic in one of the study areas (Holetta). None of the treatments had any significant effect on PCV. Donkey owners in Ethiopia should be encouraged to adopt both anthelmintic treatment and feed supplementation if they expect tangible benefits in animal performance.     

Anthelmintic and nutritional effects of heather supplementation on Cashmere goats grazing perennial ryegrass-white clover pastures

To investigate anthelmintic and nutritional effects of heather supplementation in goats grazing perennial ryegrass-white clover pastures, 40 dry Cashmere goats were randomly assigned to 4 treatments in a 2 x 2 factorial arrangement: 2 grazing management treatments (supplementation with heather vs. nonsupplementation) and 2 anthelmintic treatments (treatment vs. nontreatment). Goats grazed continuously from May to September 2004. At the end of the grazing period, the number of dead goats due to gastrointestinal parasitism was 1 in the group supplemented with heather and dosed with anthelmintic, 4 in the group that received neither supplementation nor anthelmintic, and 0 in the other 2 groups. For goats that did not receive anthelmintic treatment, the percentage of heather in the diet was negatively correlated with fecal egg count in August (r = -0.59, P < 0.05) and September (r = -0.49, P < 0.1) and positively correlated (r = 0.54, P < 0.05) with BW changes during the grazing season. Therefore, the correlation coefficient between BW change and fecal egg count was negative (r = -0.62, P < 0.05). Rumen ammonia concentrations were always lower in supplemented goats (P < 0.05). However, VFA concentrations were greater in goats consuming heather (58.9 vs. 50.9 mmol/L), which suggests that ruminal fermentation was not adversely affected by consumption of tannins. Heather availability in the vegetation might represent a valuable opportunity and sustainable method to control gastrointestinal nematode infections in a goat production system based on grazing perennial ryegrass-white clover pastures.     

Seasonal Variation in the Parasite Burden and Body Condition of Working Donkeys in East Shewa and West Shewa Regions of Ethiopia

A survey of donkeys arriving at markets in three localities in East and West Shewa regions of central Ethiopia was carried out during 2002. Total faecal worm egg counts and body condition scores were measured for a total of 963 donkeys over a 12-month period. Total faecal worm egg counts did not differ significantly between localities but there was significant (p<0.001) seasonal variation within localities. Levels of helminth infection closely followed rainfall patterns, being lowest (956 eggs per gram of faeces, e.p.g.) at the end of the long dry season (February) and highest (2022 e.p.g.) in the middle of the long wet season (August). Body condition score was associated closely with level of helminth infection (Goodman-Kruskal measure of association 0.60–0.80). Seasonal variation in body condition score reflected the temporal changes in worm burden and the availability of forage. It is suggested that a body condition score of 3 or less could be used as a simple means of identifying donkeys that require therapeutic treatment with anthelmintic. It is further proposed that economically viable strategic control of helminths in donkeys could be achieved by administering a single annual dose of avermectin-based anthelmintic at the start of the long rainy season (May–June). This may allow donkeys to recover body condition when available forage is most abundant and nutritious. It is also recommended that protein-rich feed supplementation be provided during the later part of the dry season (November–January). This may help maintain body condition when forage is scarce and the helminth challenge is at its lowest.