Population evolution of the free-living stage of goat gastrointestinal nematodes on herbage under tropical conditions in Guadeloupe (French West Indies)

Criollo goats limit their grass intake in the early morning suggesting a prophylactic self-medication behaviour in a heterogeneous vegetation

The present study compared the feeding behaviour of goats in the early morning (EM = 7:00-8:30 a.m.) and late morning (LM = 9:30-11:00 a.m.) in response to their natural gastrointestinal nematode (GIN) infection status. Twelve female adult goats (37 ± 7.7 kg live weight (LW); 5 ± 1 years) with browsing experience in the tropical deciduous forest were divided into two groups (n = 6): INF group, with natural GIN infection, and non-infected (NI) group, dewormed with moxidectin (0.4 mg/kg LW subcutaneous). Feeding behaviour (dry matter intake (DMI)) of two resource types (grasses vs. shrubs + herbs) was estimated by direct observation for 4 weeks on two grazing moments (EM vs. LM). Environmental temperature and relative humidity at pasture level were measured twice weekly. The GIN egg counts and goats' LW were measured on days 0, 14 and 28. Temperature (mean ± standard deviation) at EM (26.2 ± 1.5 °C) was lower than at LM (38.7 ± 1 °C; P < 0.01). Humidity was higher on the EM (85.1 ± 2.6%) compared to LM (60.4 ± 5.6%; P < 0.01). Irrespective of the infection status, goats consumed similar amounts of grass and shrubs + herbs during EM (P > 0.05). On the other hand, the experimental groups consumed more grass than shrubs + herbs during LM (P < 0.05). The latter suggested prophylactic behaviours strategies to (a) avoid GIN infective larvae, (b) balance the protein:energy ratio of the diet and (c) avoid saturation of detoxification pathways for the secondary compounds consumed from shrubs + herbs. The constant consumption of shrubs + herbs during the study may have reduced the GIN egg count of the INF group.

Goats worm burden variability also results from non-homogeneous larval intake

For small ruminants, Gastrointestinal Nematodes (GINs) are responsible for severe economic losses and they are also an animal welfare problem. GIN use their host to reproduce and disperse eggs on the pasture, from where they can re-infect another animal. The high density of hosts on the pasture and the extreme tolerance of GIN to environmental constraints make GIN eradication almost impossible. In addition, significant resistance to anthelmintic treatment requires sustainable and integrated management to maintain the health and financial well-being of livestock farming. In this context, models of the complex interactions between host, GIN and environment can help us to design long term optimal management strategies. To build such models, quantitative information is needed but are generally very challenging to collect. In this article, we focus on the number of ingested larvae per animal, which we propose to characterise by using a simulation framework based on the estimation of the spatial distribution of the host over time. Our framework allows us to show that worm burden individual variation is not only explained by the host’s genetics, as is often the case, but is also a result of the grazing spatial process.

The Pathophysiology, Ecology and Epidemiology of Haemonchus contortus Infection in Small Ruminants

The parasitic nematode Haemonchus contortus occurs commonly in small ruminants, and it is an especially significant threat to the health and production of sheep and goats in tropical and warm temperate zones. The main signs of disease (haemonchosis) relate to its blood-feeding activity, leading to anaemia, weakness and frequently to deaths, unless treatment is provided. Due to the high biotic potential, large burdens of H. contortus may develop rapidly when environmental conditions favour the free-living stages, and deaths may occur with little prior warning. More chronic forms of haemonchosis, resulting in reduced animal production and eventually deaths, occur with smaller persistent infections, especially in situations of prolonged, poor nutrition. The global distribution of the main haemonchosis-endemic zones is consistent with the critical requirements of the egg and larval stages of H. contortus for moisture and moderate to relatively warm temperatures, but the seasonal propensity for hypobiosis (inhibition of the fourth-stage larvae within the host) largely explains the common, though sporadic, outbreaks of haemonchosis in arid and colder environments. The wide climatic distribution may also reflect the adaptation of local isolates to less favourable ecological conditions, while an apparent increase in the prevalence of outbreaks in environments not previously considered endemic for haemonchosis - especially cold, temperate zones - may be attributable to climatic changes. Although the risk of haemonchosis varies considerably on a local level, even where H. contortus is endemic, the extensive range of ecological investigations provides a sound basis for predictions of the relative geographical and seasonal risk in relation to climatic conditions.

Feasibility of a "leader-follower" grazing system instead of specialised paddocks with regard to integrated gastrointestinal control in small ruminant farming

In the humid tropics, small ruminant farmers have to deal with gastrointestinal parasitic nematodes (GIN), among which anthelmintic resistant (AR) populations are rapidly spreading. Although targeted selective treatments (TSTs) are being increasingly used in breeding stock, suppressive drenchings remain the rule in younger animals, for safety and ease of implementation. Until now, the weaned animals are grazed on dedicated plots, making the selection and spread of AR parasites inevitable. Given that GINs disseminate through pastures, we compared the usual grazing system (control) to a "leader-follower" grazing system (LF) for managing the entire GIN population at the farm scale. There were no significant differences between treatments for the dam reproductive parameters and level of GIN infection nor for the pre-weaning death rate of the kids. The 70-day weight of the litter was significantly lower for LF than for control goats (9.71 vs. 11.64 kg, P < 0.05). Although they were more infested with GIN (1860 vs. 966 epg, P < 0.05), the LF weaned animals grew faster (53.4 vs. 40.8 g day(-1), P < 0.05) and their death rate was lower (4.0 vs. 7.7 %, P < 0.05). The overall animal output was estimated to 1010 [911; 1086] vs. 966 [885; 1046] kg LW ha(-1) year(-1), for LF and control grazing systems, respectively. Additionally, the LF grazing system would make the stocking rate easier to manage. Therefore, it is to be recommended as a complement of TSTs in sustainable small ruminant farming.

Effects of stocking rates on gastrointestinal nematode infection levels in a goat/cattle rotational stocking system

Gastrointestinal nematodes (GIN) are increasingly resistant to anthelmintic drugs worldwide, so integrated control methods are more and more needed for the sustainability of small ruminant farming. Such methods rely on knowledge in epidemiology, physiology, and genetics. Ecological studies have highlighted the effect of host density on parasite populations, and in the humid tropics, rotational grazing systems were designed according to the survival of GIN free-living stages. This study aimed to assess the effects of mixed stocking and host stocking rate on host GIN infection level. Four groups of 15-17 Creole male kids were raised on irrigated pasture from weaning (about 3 months) until the age of 7 months, at four partial stocking rates (pSR): 100% (control), 75% (G75), 50% (G50), and 25% (G25) of the total stocking rate of the pasture. The last three groups were associated with weaned Creole heifers to obtain the same overall stocking rate as the control. Animals grazed in a 'leader' goat and 'follower' cattle design: the G25, G50, and G75 paddocks were split into six plots; each plot was grazed by goats for 1 week and by heifers the following week. The pasture then rested for 4 weeks before the animals were returned for a new grazing sequence. Five control plots were grazed rotationally for 1 week, and rested for 4 weeks. This design was repeated three times a year for a total of 10 repetitions. Average faecal egg counts (FEC) decreased according to a power function of the pSR: FEC=1829pSR(3.7). The observed death rate decreased significantly with the pSR (27.6%, 16.4%, 11.9%, and 12.2%). The kids grew faster in G25 (51 g d(-1)) than in G50 (43 g d(-1)) and G75 or control (32 g d(-1), p<0.05). Heifers were not significantly infected with GIN and grew normally (about 0.48 kg d(-1)). Reducing the pSR by associating a non-host species in a rotational stocking system may be a very promising component of integrated GIN control, at least for the humid tropics.

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.

Effects of sheep and cattle alternate grazing on sheep parasitism and production

Production of sheep (nursing ewes) grazing alternately with cattle (growing weaned heifers) was compared to the production of sheep or cattle grazing alone (controls). Pasture production and sheep parasitism were also monitored. The herbage allowance was higher for the control heifers than for the alternate heifers, but the leaf to green material ratio (LGMR) was lower, and no difference on heifer growth was revealed (443 vs. 431g.d(-1), P = 0.54). The LGMR was higher for the alternate sheep (+3 points) than for the control sheep, except during the dry season, when the herbage density was lower. The effects of parasitism on the packed cell volume of alternate ewes and lambs were lower than those of control ewes and lambs. However, the infection of sheep by Cooperia sp. (better adapted to cattle) was significantly higher for the alternate sheep than for the controls, and some indication of cattle infection by Haemonchus contortus was suggested. The 70-day lamb weight was higher in the alternate grazing system than in the control (+0.76,+1.11 and+0.61kg for the dry, intermediate and rainy seasons, respectively), and the average 70-day lamb production per ewe exposed was 21.42kg in the alternate grazing system vs. 18.59kg in the control (P = 0.003).

Evaluation of targeted drenching using Famacha© method in Creole goat: Reduction of anthelmintic use, and effects on kid production and pasture contamination

Haemonchus infection was monitored for 2 years (six kidding periods) in a Creole goat flock grazing under oceanic-tropical climate. Two hundred and thirty individual does were involved from late pregnancy to weaning. Anaemia diagnoses using Famacha method and packed cell volume (PCV) were compared. The best agreement (Kappa=0.33) was found if anaemia was declared when PCV values fell to 16 or below and Famacha score was 4 or 5. Drenching policy according to Famacha method was compared to systematic drenching policy. Using the Famacha method allowed a dramatic decrease in anthelmintic use during the periparturient period (0.57 individual dose instead of three doses for the control). The proportion of the nematode population on the pasture not derived from previously-treated goats (in refugia) was estimated to about 79% (65-90%) of the pasture contamination derived from the Famacha group. On the average, goats which needed to be drenched produced less than the control or undrenched goats (kid average daily gain was decreased by about 15%). The repeatability of the need for drenching individual does was estimated to 0.41. The older goats or the goats in poorer body condition at kidding needed more drenching than the younger animals and the animals in good body condition. Consequently the Famacha method may be used as an additional tool for the culling management.

Substitution of benzimidazole-resistant nematodes for susceptible nematodes in grazing lambs

Multi-drug-resistant gastrointestinal nematode parasite populations are becoming more and more prevalent. Since anthelmintic treatments are of limited effectiveness, one solution could be to replace the anthelmintic-resistant population by a susceptible population, in order to re-establish the possibility of drug-based anthelmintic control. We investigated this substitution strategy in 4 paddocks of 0·7 ha, each of which was seeded with a benzimidazole-resistantTeladorsagia circumcinctapopulation. The proportion of benzimidazole-resistant worms in these paddocks ranged from 20% to 89%. A 2-step replacement was performed: first, the paddocks were not grazed for 6 months (from December to July), and then the grass was cut to eliminate any residual infective larvae, before contaminating each of the paddocks with 10 seeder lambs experimentally infected with a benzimidazole-susceptible strain ofT. circumcincta(from July to November). At the end of the experiment, all the populations on the 4 paddocks were phenotypically benzimidazole-susceptible, but genotyping indicated that 2 populations harboured 1% and 3% resistant worms respectively. This study demonstrates that nematode replacement is feasible in temperate areas, using semi-intensive stock management, even when the initial levels of benzimidazole-resistance are very high. Further research should next assess replacing the whole community to cope with the species diversity observed under field conditions.

Eradication of targeted species of internal parasites

Eradication can be defined as the permanent reduction to zero of the incidence of infection caused by a specific agent as a result of deliberate efforts. Eradication strategies must be designed to increase access to and utilization of veterinary and animal health support services beyond that normally achieved by routine services. Consequently, before undertaking an eradication program, proponents must be certain that they can be sure of a commitment of resources sufficient to complete the project. A helminth eradication campaign would require the application of anthelmintics to all hosts at a level aimed at killing heterozygote resistant individuals. This strategy runs counter to the prevailing opinion that resistance to chemicals will always occur and control schemes should accept some production loss by letting a proportion of parasites escape selection (in refugia) and thereby increase the useful life of the chemical. Under certain circumstances, environmental constraints may make some species of parasitic nematodes vulnerable to an eradication program. Anthelmintics have been used to exploit these constraints in past control programs and have lead to local eradication of several species of gastro-intestinal parasitic nematodes. Also, there are at present eradication programs for nematode parasites of human that are based on anthelmintic treatment. However, the suppressive pesticide treatment required to bring about the virtual elimination of species is a high-risk strategy and should only be undertaken if eradication is an achievable goal. It is also important to plan an exit strategy if eradication fails.

Managing parasiticide resistance

Resistance to antiparasitic drugs is all too common in parasites of veterinary interest. The fact that resistance has arisen in so many different species of parasite and hosts against so many different drugs and in so many geographic areas suggests that the resistances may have common features. Such features may be useful in generating ideas for resistance management. Although describing the nature and presence of resistance remains an important objective, there is now a pressing need to develop improved methods of detection of resistance and to devise schemes for integrated parasite management (IPM). Multidisciplinary teams of researchers and extension workers are exploring new ways to deal with the problem of resistance.

Epidemiology of gastro-intestinal nematodes of sheep in wet tropical conditions in Malaysia

A study on the seasonal variations in the population structure of Haemonchus contortus and Trichostronglyus colubriformis was conducted for a period of 12 months in a typical large scale sheep farm on improved pasture in Peninsular Malaysia which has a wet tropical climate. Successive groups of helminth-free tracer lambs were grazed for 4 weeks together with naturally infected sheep and were necropised for worm counts 2 weeks after their removal from the pasture. The monthly populations of H. contortus fluctuated slightly except in May and August during which more worms were found in the tracer animals. The numbers of T. colubriformis were comparatively high from October to December 1992 and again in March 1993, low during April and June 1992. Small numbers of hypobiotic larvae of H. contortus were detected in the tracer animals. Development and survival of infective larvae of H. contortus and T. colubriformis on pasture were investigated by spreading faeces containing eggs on grass plots in October 1993, February and May 1994. Development of the eggs to the infective larvae occurred within one week and their survival times were 7 weeks in the 3 experiments. The potential for control by rotational grazing is discussed.

Herbage density of third-stage larvae of goat strongyles during the dry season in Guadeloupe

The objective of this study was to determine the main sources of variation in herbage densities of infective third stage larvae of goat strongyles during the marked dry season of 1994 in Guadeloupe (FWI). Herbage samples were collected for L3 density (LD) determination by an accurate method, 4 times at 4-week intervals in 58 paddocks of 21 farms spread out in five regions of the archipel of Guadeloupe. At the same time, FEC of each grazing animal and fecal culture for parasite genus determination according to sex and age were carried out. Stocking rate, dry matter content of soil, and daily climatic data were also recorded. An index of egg development in larvae (IEDL) was calculated as the ratio of LD to the eggs deposed during the 4th, 3rd, and 2nd weeks before sampling. Medians of LD in herbage were 3397, 1853, 1410, and 324 L3/kg DM for all parasites, Haemonchus, Trichostrongylus, and Oesophagostomum, respectively. Date of sampling, region, and irrigation practice in the northern windward region were the main sources of variation in LD and in frequency of each parasite. LD decreased as the dryness lasted, but it remained important (500 L3/kg DM) despite the drought. LD in windward regions were higher than in other regions. The region, the farm, and the paddock were the main sources of variation of IEDL. LD of each parasites were inversely correlated to global radiation recorded 1 to 3 weeks before herbage sampling, but no relation was found with rainfall data. Trichostrongylus frequency in L3 population increased as the dryness lasted. A dryness axis was extracted from environmental variables (climatic data, dry matter of soil, duration of dryness) by a multiple factorial procedure. LD and Haemonchus frequency in L3 population were inversely correlated to dryness axis (p < 0.01). In contrast, Trichostrongylus frequency was positively correlated to the dryness component.

Comparison of methods for counting third stage larvae of gastrointestinal nematodes of small ruminants in tropical pastures

The accuracy and the precision of a simple and reliable technique for the extraction and the counting of third stage larvae densities of gastro-intestinal strongyles of ruminants from pasture samples are assessed in tropical conditions, i.e. for pangola pastures and for the genera of Haemonchus and Trichostrongylus. To separate the larvae from herbage samples, water washings obtained by a centrifuge spin-dryer were put to sediment in disposable plastic bags. The extraction and counting of larvae from sediments were achieved by exhaustion of sediments with repeated sucrose/water interface procedures. The recovery rate of third stage infective larvae (L3) added to the sediment was 79.1% (+/- 9.49%). The accuracy, estimated as recovery rate of L3 added to herbage samples, was 76.5 (+/- 11.31%). The recovery by the sedimentation method was 3.5 times higher than that of a filtering method through a 20 microns sieve. The detection limit was estimated to be 130 L3 kg-1 dry matter. Precision, estimated as the residual standard deviation of duplicate assays, was 1857 L3 kg-1 dry matter (mean 9164 L3 kg-1 dry matter). Results obtained in routine epidemiological surveys of gastro-intestinal strongylosis of small ruminants in West Africa and in the West Indies demonstrated the usefulness of the technique.

Rotational grazing for control of gastrointestinal nematodes of goats in a wet tropical environment

A preliminary experiment involving contamination of pasture plots with eggs of Haemonchus contortus, Trichostronglyus colubriformis and Oesophagostomum columbianum every month for a year established that in the tropical environment of the Pacific island of Tongatapu, hatching and development of all species was rapid and continuous, with a short survival on pasture (3-7 weeks) of the resulting infective larvae. These results indicated that a rotational grazing system consisting of ten paddocks grazed in sequence for 3.5 days at a time may permit a reduction in the frequency of anthelmintic treatment of goats. In comparison with an adjacent set-stocked flock which required treatment on three occasions during the year when mean flock egg counts exceeded 2000 eggs per gram (EPG), rotationally grazed goats generally maintained mean egg counts of less than 1000 EPG. Anthelmintic treatment was only given to rotationally grazed goats individually as they kidded, and there were indications that even this precaution was unnecessary. Because of the expense of frequent anthelmintic treatment and the resulting selection of strains of anthelmintic-resistant nematodes, rotational grazing of small ruminants through fencing, tethering or herding deserves further investigation as a nematode control option in wet tropical environments.

Faecal water content and egg survival of goat gastro-intestinal strongyles under dry tropical conditions in Guadeloupe

Faeces from naturally infected goats were deposited on a natural grassland during the dry season in Guadeloupe (French West Indies) at different times throughout the day. The grass was either 7 or 20-30 cm tall. After a period of between several hours and 7 days, the number of viable strongyle eggs and the faecal water content were measured. Faecal temperature was recorded continuously. Faecal temperature was greater than 40 degrees-45 degrees C at midday and dehydration was rapid between 8 a.m. and 2 p.m. Egg mortality was greater on short than on tall grass and higher in morning than in evening deposits. Minimal faecal water content during the first 36 h explained the 74%, 55% and 38% mortality rate for eggs of Oesophagostomum columbianum (OC), Haemonchus contortus (HC) and Trichostrongylus colubriformis (TC), respectively. In all, 5%-22% of the eggs of the latter species remained viable in a state of anhydrobiosis after 7 days on the ground. A delay of only 2 days between goat departure and irrigation would be sufficient to ensure that greater than 95% of O. columbianum and H. contortus eggs and 70% of T. colubriformis eggs are destroyed.

Pasture populations of cattle nematode larvae in Guadeloupe (French West Indies)

The development of numbers of third-stage (L3) larvae of gastrointestinal nematodes after pat (faeces) deposition by heifers is described, using a mathematical model, for seven experiments carried out in Guadeloupe (French West Indies). A dramatic rise in L3 population size occurred on herbage near pats, 17-25 days after pat deposition. There was no clear relationship between climatic data and L3 population dynamics. However, 5 successive days of rainfall induced the resumption of larval migration in two experiments. Changing the unit of expression of L3 population size (100 L3 m-2 vs 1000 L3 per kg DM) did not alter estimates of the model parameters. The evolution of L3 population of Haemonchus and Cooperia were similar.