The effects on merino lambs of chronic infection with Trichostrongylus rugatus

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.

The relative contributions of T. colubriformis, T. vitrinus, T. axei and T. rugatus to sheep infected with Trichostrongylus spp. on the northern tablelands of New South Wales

This survey was designed to determine the spatial and temporal distribution and the relative contributions of Trichostrongylus colubriformis, Trichostrongylus vitrinus, Trichostrongylus axei and Trichostrongylus rugatus to sheep infected with Trichostrongylus spp. on the northern tablelands of NSW. Thirty completed larval cultures were collected from a commercial parasitology laboratory servicing the northern tablelands of NSW between June and December 2007. Cultures were selected at random from farms within the study area whenever the combined results of faecal worm egg counting and coproculture indicated >200 Trichostrongylus spp. eggs per gram and >40% Trichostrongylus spp. respectively. Selection of cultures was constrained to prevent multiple samples from a single grazing property. Larval cultures were stored at 4 degrees C and subsequently used to artificially infect GIN-free sheep which were sacrificed for the collection of gut contents at 3 weeks post-infection. Abomasal contents were examined for the presence of T. axei. From the anterior small intestine 100 adult male Trichostrongylus spp. per animal were identified to species (T. colubriformis, T. vitrinus or T. rugatus) according to spicule morphology. T. colubriformis was the most prevalent Trichostrongylus species (present in 100% of the samples) as anticipated in a summer rainfall region. T. vitrinus was present in 20% of the samples whilst T. rugatus was present in only 10% of the samples, yet when present comprised a much higher proportion of the total Trichostrongylus population than has previously been reported. In an unexpected result, T. axei was not identified in any of the samples collected. The epidemiological basis for these results and the implications for gastro-intestinal nematode control are discussed.

Observations of the sheath extension of the third stage, infective larvae of Trichostrongylus rugatus

The length of the sheath extension of third stage (L(3)), infective larvae of Trichostrongylus rugatus is reported. The total length and length of the sheath extension of L(3) recovered from the faeces of sheep originating from two localities in South Australia were measured. The total length of larvae was 615-722 microm and the length of the sheath extension was 46-56 microm (mean 51.5). The larvae of T. rugatus comprised up to 72% of the larvae recovered. Worm free sheep were infected with larvae from the two localities and L(3) were recovered following culture of faeces from these experimentally infected animals. L(3) measured 640-746 microm in total length with a sheath extension of 46-56 microm (mean 51.4). Adult nematodes recovered from gastro-intestinal tracts were identified as T. rugatus. The length of the sheath extension used in conjunction with the total length is a characteristic that enables confident differentiation of infective larvae of T. rugatus from other Trichostrongylus species infecting sheep in southern Australia and Haemonchus contortus.

Effects of challenge with trichostrongylid nematode larvae on immunologically resistant grazing yearling sheep in South Australia

Paddocks near Gawler, South Australia, were grazed by newly weaned sheep which received either no anthelmintic treatment, regular 3-weekly treatment or a single treatment in February. A decline in the faecal egg count of untreated sheep in autumn associated with the ingestion of infective larvae indicated that the sheep had developed a resistance to reinfection. At the end of the experiment, 10 sheep were experimentally infected with Trichostrongylus vitrinus larvae to demonstrate this resistance. Untreated sheep grew less wool and had lower body weights when compared with treated animals and were extremely 'daggy'. A single treatment in February did not prevent production losses or scouring.

Comparison of the effects of infection with Trichostrongylus colubriformis, T. vitrinus and T. rugatus in merino lambs

Groups of six worm-free merino lambs were infected with 100,000 larvae of T. colubriformis, T. vitrinus, T. rugatus or a mixture of the three species and were slaughtered 21 days later. Nematodes were distributed predominantly in the first 3 m of the small intestine where they caused subtotal villus atrophy. T. vitrinus caused severe erosion of the epithelium; erosion was less severe with T. colubriformis infections and mild with T. rugatus infections. Plasma concentrations of albumin declined during the experiment and were most marked in sheep infected with T. vitrinus. Plasma phosphate concentrations declined during infection with all three species, while plasma concentrations of globulin and calcium declined only in sheep infected with T. vitrinus. Food intake was reduced in all groups, but was most marked with sheep infected with T. vitrinus. T. vitrinus appeared to be more pathogenic than the other species.