Experimental Nematode Infection Research Articles

Effect of experimental nematode infection on serum mineral concentrations in growing lambs.

The objective of the present study was to determine the possible effect of gastrointestinal nematodes upon serum mineral concentrations of lambs. Twelve male lambs were used. Lambs were randomly assigned to 2 groups (n = 6): Group 1 infected with gastrointestinal nematodes and Group 2 as controls. Lambs of Group 1 were infected with a single dose of 15,000 L3 larvae of GI nematodes (Haemonchus, Teladorsagia, Trichostrongylus, Cooperia and Oesophagostomum-Bunostomum). Blood samples were collected from the investigated animals individually every 2 weeks. However, the differences in serum macro-minerals (Ca, Mg, P, K, and Na) among groups were not significant. Although the differences in serum macro-minerals among groups were not significant and the iron serum concentration remained unaltered, the gastrointestinal parasitism reduced significantly/substantially the serum copper levels.

Effects of the initial level of milk production and of the dietary protein intake on the course of natural nematode infection in dairy goats

The level of dietary protein is known to alter the establishment and the pathophysiology of gastrointestinal nematodes in sheep. On the other hand, high-producing dairy goats are less resistant and/or resilient than low-producing ones to experimental nematode infection. During a 2-year study, we have investigated the course of a natural nematode infection (mainly T. colubriformis) in a high-producing dairy goat flock. In year 1, 50 grazing goats divided in high (HP) or low producer (LP) were compared from April to October for parasitological and milk parameters. In year 2, the 25 HP goats were only considered and were allocated to two levels of dietary protein, high level (HPr) with a protein coverage of 125% or normal level (NPr) with a protein coverage of 106%. They were monitered as above. In year 1, HP goats showed a greater nematode egg output (1856 vs. 1000 epg) associated with higher values in T. colubriformis IgG in autumn than LP ones whereas the decrease in serum phosphate concentration was similar in both groups. In year 2, HPr goats exhibited lower egg ouput in autumn (2219 vs. 2817) vs. NPr ones. Moreover, milk yield and fat content were significantly higher in HPr vs. NPr in the 2nd part of the study. HP goats are less resistant to nematode infection in natural conditions. Resistance and resilience of HP goats may partially be improved by a protein supplementation in the diet.

Repeated infections with Haemonchus contortus and Trichostrongylus colubriformis in dairy goats: comparison of resistant and susceptible animals.

A total of 70 strongyle-free French Alpine dairy goats were exposed to a combination of sequential and challenge infections with Haemonchus contortus and Trichostrongylus colubriformis third-stage larvae. The sequential infection consisted of three inoculations at 50-day intervals, each infection being abbreviated by anthelmintic treatment at 40 days postinoculation. The challenge infection, composed of the same nematode strains, was undertaken 2 months later, when goats were at their 1st month of lactation. Fecal egg counts (FECs), packed cell volumes (PCVs), pepsinogen concentrations, inorganic phosphate concentrations, and peripheral eosinophil numbers were measured at 30-40 days after each inoculation. Goats were defined as being resistant or susceptible according to their level of nematode egg output following the first inoculation. Significant differences in FECs were recorded between the two groups throughout the further inoculations and the challenge infection. The reliability of FECs was supported by the high repeatability values found within and between infections. With regard to blood constituents, only PCVs related to H. contortus infection showed values that differed significantly between the two groups, resistant goats having higher PCVs after the first and the third inoculations than did susceptible animals. However, this difference was not detectable after the challenge infection. The milk production yield for the current lactation was significantly lower in the resistant goats. Moreover, resistant animals exhibited constantly greater body condition scores as compared with susceptible animals. These results indicate that the individual responsiveness of dairy goats to experimental nematode infection can be estimated on the basis of FECs and PCVs (for H. contortus) and is negatively related to the level of milk production of the animals.

Persistent efficacy of topical moxidectin against Dictyocaulus viviparus and Ostertagia ostertagi

The persistent activity of moxidectin topically administered at the dose rate of 0.5 mg kg −1 bodyweight was evaluated against experimental nematode infection in 30 calves randomly allocated to six groups. Five groups were treated on days −42, −35, −28, −21 and −14. The 6th group remained untreated as a control. On Day 0, the calves were infected experimentally with 1000 Dictyocaulus viviparus and 50 000 Ostertagia ostertagi larvae and killed 3 weeks later. The formulation of moxidectin showed excellent activity against both parasites up to 5 weeks (>99%). Six weeks after treatment the reduction in the number of D. viviparus was still high (>90%). No adverse reactions to moxidectin were observed in any of the animals.

Persistent efficacy of doramectin against experimental nematode infections in calves

Three studies were conducted involving cattle exposed to experimental nematode infections. These studies were designed to investigate the prophylactic activity of a single subcutaneous treatment of doramectin at 200 μg/kg −1 body weight against infections of Ostertagia ostertagi, Cooperia oncophora and Dictyocaulus viviparus. For each study, parasite-naive calves were randomly allocated to either a treated or a matched control group. One group received doramectin and the other received either no treatment or an injection of saline at 1 ml per 50 kg body weight by the subcutaneous route. Thereafter, all calves received a daily oral challenge of infective larvae of the particular parasite species on test in each study. Challenge of each pair of treatment/control groups continued for periods of 14, 21 or 28 days. An interval of 14–21 days was then allowed to permit the parasites which had established to mature, after which all animals were slaughtered and their worm burdens determined using standard techniques. Geometric mean worm burdens were calculated from the log worm counts and used to estimate percentage efficacy. Accumulated burdens of C. oncophora in doramectin-treated cattle resulting from a daily challenge infection for 14 or 21 days were reduced by 99.2% and 90.7% respectively, in comparison with those of non-treated control animals. For D. viviparus, burdens were reduced by 100% and 99.9% after a 21 or 28 day challenge, respectively. The corresponding figures for O. ostertagi were 99.9% after a 21 day challenge and 93.7% after a 28 day challenge.

Low Level Feed Administration of Morantel Tartrate in the Prophylaxis of Experimental Nematode Infections in Lambs and Calves

SUMMARY In Experiment 1 three groups of worm-free lambs were given 5 000 Trichostrongylus colubriformis larvae daily for 23 days. Two groups were medicated in the food for 28 days with either 1.0 or 1.25 mg/kg/day morantel tartrate. The third group remained unmedicated as control. Post-mortem worm counts showed a reduction of 73% ( P In Experiment 2 three groups of worm-free calves were given 1000 Ostertagia ostertagi and 50 Dictyocaulus viviparus larvae daily for 63 days. Two groups were medicated in the food for the whole period with either 1.0 or 1.5 mg/kg/day morantel tartrate. The third group remained unmedicated as control. Faecal egg counts showed a significant reduction in cumulative Ostertagia egg excretion of 67% ( P P Dictyocaulus larval excretion of 50 and 80% compared with controls for the 1.0 and 1.5 mg/kg/day dose levels respectively.