Trichostrongylus colubriformis infection damages intestine brush board cells and could negatively impact postabsorptive parameters of Santa Ines lambs

This study aimed to evaluate histological, digestive and postabsorptive physiological parameters in Santa Ines lambs infected with Trichostrongylus colubriformis and fed different levels of phosphorus. Therefore, eighteen Santa Ines, castrated male, six-month old, healthy lambs (initial body weight 22.4 ± 2.7 kg) were distributed in one of four treatments arranged in a 2 × 2 split-plot arrangement: Sufficient dietary P level and uninfected (SPui; n = 4), Sufficient dietary P level and infected (SPi; n = 5), Deficient dietary P level and uninfected (DPui; n = 4), Deficient dietary P level and infected (DPi; n = 5). Infected lambs received, orally, a single pulse dose of 40.000 T. colubriformis infective larval stage (L3). Animals were fed Tifton 85 hay (Cynodon ssp.; 60%), and cassava meal and maize gluten meal (40%). Measurement of nutrient apparent digestibility and nitrogen metabolism were performed in individual metabolic stalls. To achieve the trial results, it was measured methane emissions in respiratory chambers, urine purine derivatives, ruminal short-chain fatty acids (SCFA), histological cuts of duodenal mucosal tissues and passage rates fluxes, analyzed by external (Yb, Cr, and Co) and internal (iNDF) markers. Statistical procedures were performed in R studio. The fixed main effects of treatment and the interactions were tested by ANOVA, and means compared by Duncan's test at 5% significance. Apparent digestibility was not affected by treatments, however, nitrogen retained decreased (P < 0.01) and urinary nitrogen losses increased (P < 0.01) in infected animals. Small intestine digesta content, empty segment weight, and length were higher in infected animals (P < 0.05). Passage rate was not majorly affected by infection or dietary P levels. Methane emissions, SCFA concentrations, and purine derivative excretion were also not affected by treatments. Regarding the histology, the vilosity weight (P < 0.05), and crypt depth (P < 0.01) decreased in infected animals. In conclusion, T. colubriformis infection can damage intestinal mucosa and affect nitrogen metabolism, but did not affect the digesta transit, and nutrient digestibility. The P dietary levels did not promote any modification in GIT physiological parameters tested in this study.

Efferent intestinal lymph protein responses in nematode-resistant, -resilient and -susceptible lambs under challenge with Trichostrongylus colubriformis

The mechanisms underlying resistance to challenge by gastrointestinal nematode parasites in sheep are complex. Using DIGE, we profiled ovine lymph proteins in lambs with host resistance (R), resilience (Ri) or susceptibility (S) to a daily trickle challenge with the nematode Trichostrongylus colubriformis. Efferent intestinal lymph was collected prior to infection (day 1) and on days 5 and 10 post-infection. Eight proteins identified by LC-MS/MS, showed differences relating to host genotype. Of these, Serpin A3-3 and Serpin A3-7 have not been reported previously in the lymph proteome. Three acute phase proteins showed significant differences relating to interactions between breeding line and parasite challenge, including complement C3β, C3α and haptoglobin (Hp) β. In the R lambs C3α was significantly up regulated (P<0.05) on day 10, while in the Ri lambs Hp β was significantly down regulated (P<0.05). In the S lambs, levels of C3β were up regulated and levels of Hp β down regulated (both P<0.05) on day 10. Hence we demonstrate that acute phase inflammation proteins contribute to differences in the innate immune response of sheep to challenge by T. colubriformis. The findings may lead to the development of new approaches to combat nematode infestations in sheep production systems.

BIOLOGICAL SIGNIFICANCE

Breeding lines of sheep with resistance (R), resilience (Ri) or susceptibility (S) to nematode infections provide an experimental model to examine the biological mechanisms underlying the ability of some sheep to expel worms and remain healthy without the use of an anthelmintic. Using proteomics we identified differences in the expression of acute phase lymph proteins in the R, Ri and S lambs. The results will assist the development of alternative control strategies to manage nematode infections in livestock.

Gastrointestinal nematode challenge induces some conserved gene expression changes in the gut mucosa of genetically resistant sheep

Sheep have a varying ability to resist infection with gastrointestinal nematodes. This ability is due in part to genetic differences that exist between individuals. In order to define these differences we have used real-time PCR to quantify gene expression responses in the gut mucosal surface of genetically resistant and susceptible sheep, following a nematode challenge. Expression profiles were determined in response to two different nematode species, Haemonchus contortus and Trichostrongylus colubriformis, and in divergent sheep originating from two different genetic backgrounds. Results show that the response generated differs between resistant and susceptible animals and is further impacted by the origin of the sheep and nematode species used for challenge. However, some conserved features of a response mounted by a resistant or a susceptible animal were identified. Genes found to be more abundantly expressed in resistant animals include markers of an early inflammatory response, several Toll-like receptors (TLR2, 4, 9) and free radical producing genes (DUOX1 and NOS2A). Conversely, genes differentiating susceptible animals indicate a prolonged response and development of a chronic inflammatory state, characterised by elevated expression of members of the NF-kappabeta signalling pathway (IKBKB and NFKBIA) together with delayed expression of regulatory markers such as IL2RA (CD25), IL10 and TGFbeta2. While multiple nematode response pathways were identified, the identification of conserved aspects of the response which associate with resistance provides evidence that alternative nematode control strategies, such as breeding for resistant animals, may be feasible.

Intestinal, hepatic, splanchnic and hindquarter amino acid and metabolite partitioning during an established Trichostrongylus colubriformis infection in the small intestine of lambs fed fresh Sulla (Hedysarum coronarium)

Increased partitioning of amino acids (AA) from skeletal muscle to the intestine and immune system during parasitic infection may be the cause of poor growth in parasitised animals. The effect of an established Trichostrongylus colubriformis infection (6000 L3 T. colubriformis larvae for 6 d (n 5) or kept as parasite-free controls (n 6)) on AA fluxes across the mesenteric-drained viscera, portal-drained viscera (PDV), liver, total splanchnic tissues (TSP) and hindquarters were determined in lambs fed fresh Sulla (Hedysarum coronarium; 800 g DM/d) 48 d post-infection. The lambs were infused with rho-aminohippuric acid (PAH; 723 mg/h) into the mesenteric vein for 8 h to measure TSP plasma flow. Concurrently, indocyanine green (ICG; 14.6 mg/h) was infused into the abdominal aorta to measure plasma flow across the hindquarters. Blood was continuously collected from the mesenteric, portal and hepatic veins, vena cava and the mesenteric artery and plasma harvested. PAH, ICG, AA, metabolite and insulin concentrations were measured. Intestinal worm burdens on day 48 post-infection were higher in the infected lambs (P 0.10). There was a 28 % reduction in the release of AA from the PDV of infected lambs (P < 0.05). The uptakes of most AA were similar in the liver; however, there was increased uptake (P < 0.10) of AA by the TSP of infected lambs. Despite this reduction in AA availability at the liver, there was no effect of parasitic infection on AA uptake across the hindquarters (P < 0.05).

Whole-body valine and cysteine kinetics and tissue fractional protein synthesis rates in lambs fed Sulla (Hedysarum coronarium) and infected or not infected with adult Trichostrongylus colubriformis

Poor growth during parasitic infection may be due to a redistribution of amino acids away from skeletal muscle protein synthesis to the intestinal site of infection. The effect of a Trichostrongylus colubriformis infection on whole-body amino acid kinetics and tissue fractional protein synthesis rates were determined in lambs fed fresh Sulla (Hedysarum coronarium; 800 g DM/d). Lambs were dosed with 6000 L3 Trichostrongylus colubriformis larvae daily for 6 d (n 6) or kept as parasite-free controls (n 6). On day 45 post-infection, the lambs received an intravenous injection of 2H2O and infusions (8 h) of [35S]sulphate to measure the size of the whole-body water and sulphate pools, respectively. On day 48, the lambs were continuously infused for 8 h with [3,4-3H]valine into the jugular vein as well as with [1-13C]valine and [35S]cysteine into the abomasum. After the 8 h infusions, the lambs were killed and tissue samples collected from the duodenum, ileum, mesenteric lymph nodes, liver, spleen, thymus, muscle and skin. Feed intake (769 v. 689 (sd 47) g DM/d) was not affected by infection, whereas liveweight gains (50 v. -50 (sd 70) g/d) were lower and intestinal worm burdens (240 v. 18,000 (sd 7000) worms) higher in the infected lambs. Parasitic infection increased the fractional protein synthesis rates in the small intestine, mesenteric lymph nodes and liver but did not affect skin and skeletal muscle fractional protein synthesis rates during the established parasitic infection.

Influence of the route of administration on efficacy and tissue distribution of ivermectin in goat

The tissue concentration and efficacy of ivermectin after per os and subcutaneous administration were compared in goats experimentally infected with Trichostrongylus colubriformis (ivermectin-susceptible strain, INRA). Infected goats (n = 24) were treated per os (n = 9) or subcutaneously (n = 9) with ivermectin, 0.2 mg/kg, or kept as not treated controls. The faecal egg counts and small intestine worm counts were determined. Ivermectin concentration was measured in the plasma, gastrointestinal tract, lung, skin or hair, liver and adipose tissues at 0, 2, 7 and 17 days post-treatment. The efficacy of ivermectin against T. colubriformis infection in goat was 98.7 and 99.9% for subcutaneous and oral administration, respectively. Ivermectin concentration declined with time and only residual concentration was measured at 17 days post-treatment in plasma and gastrointestinal tract. Ivermectin concentration was higher after subcutaneous compared to per os injection in most of the tissue examined. In skin, hair and subcutaneous adipose tissue ivermectin persisted at significant concentrations 17 days post-treatment for both routes of administration. In our experimental conditions, ivermectin provides similar efficacy against T. colubriformis after subcutaneous or per os administration in goat. However, the lower ivermectin levels in tissues after per os administration suggest that the lasting of efficacy may be shortened after per os compared to subcutaneous administration especially in animals with poor body condition in pasture where re-infection occurs quickly after anthelmintic treatment.

Interleukin-6 expression in gut of parasite challenged sheep

Following challenge with Trichosirongylus colubrifonizis, increased numbers of T-cells and immunoglobulin responses are seen in the intestine of sheep immunised by repeated infection with live worms. IL-6 mRNA expression in the small intestine from T. colubriformis-immunised and naive sheep was determined by in situ hybridisation, whereas CD4(+), IgA(+), IgG(+) cells in the gut were evaluated by immunohistochemistry. There was constitutive expression of IL-6 mRNA by cells in the naive gut, and the number of these cells was increased by parasite challenge. There were corresponding increases in numbers of CD4(+) and TCR gamma/delta(+) T-cells and IgG(+) B-cells. Our data are consistent with a role for IL-6, perhaps produced by CD4(+) and/or TCR gamma/delta(+) T-cells or B-cells, in B-cell terminal differentiation. Infiltration of B-cells, particularly IgG(+) B-cells, may reflect parasite immunity in the host.

Subclinical infection with the nematode Trichostrongylus colubriformis increases gastrointestinal tract leucine metabolism and reduces availability of leucine for other tissues

Gastrointestinal (GI) tract leucine metabolism was measured in 6- to 9-mo-old lambs subjected to trickle infection with Trichostrongylus colubriformis larvae and in separate animals that were not infected. Animals prepared with a jejunal catheter and with indwelling catheters into the aorta and the portal- (PDV) and mesenteric- (MDV) drained viscera were infused simultaneously with [1-13C] and [5,5,5-2H3] leucine to determine GI tract sequestration of leucine from arterial and luminal amino acid pools by tracer and tracee arteriovenous concentration differences. Leucine oxidative losses and net fluxes were also determined across the GI tract. Infection had no detectable effect on whole-body leucine flux, but it increased total GI tract leucine sequestration by 24% (P<.05) and GI tract oxidative losses of leucine by 22 to 41% (P<.01). Net PDV fluxes of leucine were decreased by 20 to 32% during the infection. The infection did not alter either the proportion of precursor leucine used by GI tract metabolism that was derived from the arterial leucine pool (.84 to .88) or the proportional sequestration of digesta-derived leucine during "first pass" absorptive metabolism (.12 to .18). These findings help to elucidate the metabolic basis for the reduced growth rates and nitrogen retention observed when animals are subjected to subclinical nematode infection.

Trichostrongylus colubriformis infection in rabbits: persistence of the distal adaptive response to parasitism after anthelmintic treatment

Mucosal changes associated with anthelmintic treatment in Trichostrongylus colubriformis-infected rabbits were assessed along the entire length of the small intestine. The following groups, each of five rabbits, were compared: infected (group I); infected and treated on day 21 with fenbendazole (group IT); uninfected but given fenbendazole on day 21 (group C, controls). All animals were killed on day 28. In the proximal part of the small intestine of group I rabbits, the worms were associated with shortening of the villi and a significant depletion in alkaline phosphatase activity, which differed significantly from the findings in groups C and IT. In the same region, no difference was found between groups C and IT. In the distal small intestine, hypertrophy of villi and crypts (an adaptive response to the infection), coupled with an increase in enzymic activity, were present in both groups I and IT, in contrast to group C. These results suggest that a complete mucosal restoration occurred within 7 days of anthelmintic treatment in the parasitized part of the intestine. In contrast, the adaptive response observed beyond the main site of parasitism was not abolished by treatment. The functional significance of these findings is discussed in relation to the compensatory growth commonly observed after anthelmintic treatment in ruminants.

The influence of a heavy infection with sensitive and resistant strains of Ostertagia circumcincta and with Trichostrongylus colubriformis on the pharmacokinetics of febantel in lambs

Plasma concentrations of febantel and its major metabolites, fenbendazole, oxfendazole and fenbendazole sulphone, were determined after oral administration of 7.5 mg/kg febantel in lambs before and 28 days after infection with 100,000 L3 larvae of a benzimidazole (BZ)-sensitive or BZ-resistant strain of Ostertagia circumcincta or with 75,000 L3 larvae of a BZ-sensitive Trichostrongylus colubriformis strain. The febantel concentrations were always low, and in only a few samples were higher than the limit of detection. A mean decrease in the area under the curve (AUC) for the three metabolites of 10.2%, 16.4% and 4.9% in lambs infected, respectively, with BZ-sensitive O. circumcincta, BZ-resistant O. circumcincta and T. colubriformis was observed. The Cmax for all the metabolites was higher in the BZ-sensitive O. circumcincta group than in the naive sheep, while the Tmax occurred earlier. The Cmax and the Tmax values for all the metabolites were lower in the BZ-resistant O. circumcincta group than in their own naive controls. In the T. colubriformis group the Cmax values of the metabolites were lower and the Tmax occurred much later.

Influence of subclinical nematodosis on the kinetic disposition of fenbendazole in buffaloes

The disposition kinetics of fenbendazole was studied in buffaloes subclinically infected with gastrointestinal nematodes. There was significantly reduced uptake of the drug in infected animals compared to uninfected controls. The pH of the duodenal liquor was highly alkaline compared to the acidic pH in uninfected animals. The egg count in the faeces never became zero though the numbers were reduced to a great extent compared to pre-treatment values. The influence of the host's physiology on the reduced bioavailability of fenbendazole is discussed.

The effect of reduced feed intake on the efficacy of oxfendazole against benzimidazole resistant Haemonchus contortus and Trichostrongylus colubriformis in sheep

Within 12 h of reducing the daily intake of a 50:50 lucerne and wheaten hay ration from 800 to 400 g, there was an increase in digesta marker concentration indicating a reduction in the flow rate of digesta fluid and particulates through the abomasum of sheep. The efficacy of the recommended dose of oxfendazole (OFZ) was then tested against benzimidazole resistant Trichostrongylus colubriformis and Haemonchus contortus in sheep whose feed intake was halved 36 h before and after drug treatment. In animals fed the reduced ration there was a 60% reduction of T. colubriformis and 94% reduction of H. contortus compared with a 19% and 60% reduction respectively on the higher feed intake. It is therefore suggested that greater anthelmintic efficacy can be achieved in sheep by temporary feed reduction.

The influence of Ostertagia circumcincta and Trichostrongylus colubriformis infections on the pharmacokinetics of febantel in lambs

Plasma concentrations of febantel and its major metabolites fenbendazole, oxfendazole and oxfendazole sulphone were determined after oral administration of 7.5 mg/kg febantel in lambs before and 28 days after infection with 50,000 L3 larvae of Ostertagia circumcincta or Trichostrongylus colubriformis. The febantel concentrations were always very low and only in a few samples higher than the detection limit. The mean decrease in AUC for the three metabolites for the infected sheep in comparison to the parasite naïve sheep was 13.9% +/- 4.1% (mean +/- SEM) and 23.7% +/- 5.3% in the O. circumcincta infected and the T. colubriformis infected lambs respectively. This reduction was only significant for the T. colubriformis infected group. In order to determine a more complete pharmacokinetic profile, febantel was injected intravenously at a dose of 2.5 mg/kg in a further study.

Comparative kinetic disposition of oxfendazole in sheep and goats before and during infection with Haemonchus contortus and Trichostrongylus colubriformis

The kinetic disposition of [14C]-oxfendazole (OFZ) and its metabolites, fenbendazole (FBZ) and fenbendazole sulphone (FBZ.SO2), in plasma and abomasal fluid were determined in Merino sheep and Angora goats before and during infection with Trichostrongylus colubriformis and Haemonchus contortus. The systemic availability (area under the plasma curve, AUC) of OFZ was significantly lower in goats (13.5 micrograms.h/ml) than in sheep (22.2 micrograms.h/ml) and was reduced with infection in goats (5.6 micrograms.h/ml) and sheep (15.1 micrograms.h/ml). The elimination of plasma [14C] was faster in goats than in sheep. The responses observed for [14C] were a reflection of the behaviour of OFZ. The concentration of OFZ and metabolites in abomasal fluid were similar in both species in the absence or presence of infection. However, as the mean flow rate of abomasal fluid was slower in goats (240 ml/h) than in sheep (488 ml/h), only 7% of the dose passed the pylorus in abomasal fluid of goats compared with 14% in sheep. The presence of gastrointestinal nematodes generally increased abomasal fluid flow rate but neither species nor infection had any effect on the rate or extent of [14C] excretion in urine or faeces. It is suggested that goats possess a faster hepatic metabolism than sheep resulting in more rapid elimination of OFZ.

Nitrogen transactions along the digestive tract of lambs concurrently infected with Trichostrongylus colubriformis and Ostertagia circumcincta

Twelve lambs, paired on the basis of live weight, were cannulated in the abomasum, in the proximal jejunum approximately 4 m distal to the pylorus and in the terminal ileum. Six were infected with 3000 Trichostrongylus colubriformis and 3000 Ostertagia circumcincta larvae each day for 18 weeks and the remainder were pair-fed to individual infected lambs. All animals were offered ryegrass (Lolium perenne)-white clover (Trifolium repens) pasture, cut daily. Dry matter (DM) intake, live weight, faecal egg concentration, plasma pepsinogen and plasma protein concentrations were measured weekly. During weeks 7 and 17 after commencement of infection, the flow of digesta along the gastrointestinal tract was measured together with enteric plasma loss and true digestion and absorption of 125I-labelled albumin in the small intestine. DM intake was depressed by parasitism, being 1331, (SE 70), 423 (SE 32) and 529 (SE 52) g/d during weeks 3, 7 and 17 respectively. The flow of nitrogen at the proximal jejunum and in faeces was increased by parasitism during week 7 and at the abomasum and ileum during week 17. Plasma protein-N loss (g/d) into the gastrointestinal tract was 0.68 (SE 0.091) and 1.97 (SE 0.139) during week 7, and 0.85 (SE 0.158) and 1.96 (SE 0.396) during week 17, in control and infected sheep respectively. True digestion and absorption of albumin in the proximal small intestine, the site of infection, was very low (mean 0.08) and was not affected by parasitism. Between the abomasum and terminal ileum absorption of albumin was high (mean 0.87) and again was not affected by parasitism. It was calculated that of the total increase in endogenous protein passing from the ileum tract as a result of infection, plasma protein comprised only a small percentage (10-36%). The major proportion of digestion and absorption of protein occurred in the distal small intestine beyond the site of infection and was not affected by infection.

Demonstration of a range of inflammatory mediators released in trichostrongylosis of sheep

The levels of inflammatory mediators in the intestinal contents of sheep immunized with Trichostrongylus colubriformis larvae increased in the first 6 days after challenge. These mediators were histamine, leukotriene C4, 6-keto-prostaglandin F1 alpha (from prostacyclin) and thromboxane B2. Leukotriene C4 was released in the greatest quantities. Leukotriene B4 was present but its concentration remained unchanged after challenge. The presence of these particular mediators in the intestinal contents after challenge is consistent with antigen-induced mediator release from the mucosal mast cells found in immune sheep undergoing challenge infection. This is the first sequential analysis of mediator release in sheep that also demonstrates the release of prostacyclin and thromboxane into the intestine during expulsion of a nematode infection.

The effects of a concurrent infection of Trichostrongylus colubriformis and Ostertagia circumcincta on calcium, phosphorus and magnesium transactions along the digestive tract of lambs

Twelve lambs, paired on the basis of live weight, were cannulated in the abomasum, proximal jejunum and terminal ileum. Six were infected with 3000 T. colubriformis and 3000 O. circumcincta larvae per day for 18 weeks. The other six lambs were pair-fed to the infected lambs. All animals were offered fresh ryegrass and white clover pasture, cut daily. Dry matter intake, live weight and plasma Ca, P and Mg concentrations were measured throughout the experiment. During weeks 7 and 17 post-infection, digesta flow along the gastrointestinal tract of infected and control animals was measured. Parasitism depressed dry matter intake by 60 per cent and was associated with a reduction in retention of Ca, P and Mg in both infected and control animals. During weeks 7 and 17, parasitism increased the flow of Ca past the proximal jejunum and, during week 17, the flow of P past the terminal ileum. Increased endogenous Ca and P losses, together with a net reduction in absorption of Ca and P, were associated with depressed plasma Ca and P concentrations. These findings, together with evidence of reduced addition of P to anterior regions of the tract, indicate induced Ca and P deficiency. There was evidence for compensatory absorption of Ca and P in the large intestine and distal small intestine, respectively. Magnesium metabolism was apparently not affected by parasitism.

Effect of prolonged subclinical infection with Trichostrongylus colubriformis on the performance and nitrogen metabolism of growing lambs

Ten 5-month-old lambs, reared free of parasites and prepared with abomasal and ileal cannulas, were paired and given rations of pelleted dried grass by means of continuous feeders. From 7 months of age one of each pair was dosed daily with 2500 Trichostrongylus colubriformis larvae for 34 weeks. An untreated animal served as a pair-fed control to each infected lamb. During 5 experimental periods (pre-infection, and Weeks 6-8, 12-14, 18-20 and 29-34 of dosing) measurements were made of the amounts of N leaving the small intestine, the digestibility of 35[S]-labelled microbial protein in the small intestine, and the amounts of plasma protein leaking into the digestive tract. The infection caused a growth check (P less than 0.05) from Week 6 to approximately Week 13 of dosing. This resulted from inappetence, but also from a disruption in the N digestion and metabolism of the lambs. There was a marked eosinophilia at this time. Measurements of ileal flow rates during Weeks 6 and 12 indicated that significantly more N flowed to the terminal ileum of infected lambs during this period (Week 6, 3.1 g N day-1 P less than 0.05; Week 12, 5.0 g N day-1 P less than 0.001). Plasma N leakage into the intestine during Weeks 8 and 14 was higher in infected lambs (1.2 g N day-1 P less than 0.01 and 0.9 g N day-1 P less than 0.05, respectively) but the digestibility of 35[S]-labelled microbial protein was depressed below that of the controls during the later part of this period, i.e. during Week 13. Continued larval challenge beyond this point caused a less severe nutritional penalty. Voluntary feed intake increased and the animals started to gain weight. The amount of extra N flowing to the terminal ileum of infected lambs was less at Week 18 of dosing (3.5 g N day-1 P less than 0.01) than it had been at Week 12. Similarly, extra plasma N leakage into the tract of infected lambs was less during Week 20 (0.26 g N day-1) than during Week 14. There was however, still a detectable reduction in the coefficient of digestibility of 35S microbial protein in infected lambs during Week 19. By Weeks 29-34 the only detectable difference between the infected and control lambs was in their eosinophil counts.

The effect of daily challenge with Trichostrongylus colubriformis larvae on the nutrition and performance of immunologically-resistant sheep

Immunological resistance to Trichostrongylus colubriformis was developed in sheep by challenging them with 2500 larvae per day for 34 weeks. They were then rested for 24 weeks before being re-challenged with the same dose rate of the same larvae for 10 weeks. Nutritional, haematological and parasitological parameters were measured during the first 8 weeks of re-challenge infection. There were no faecal worm eggs excreted during the re-challenge infection. There was a small but significant increase in plasma-N leakage from Days 4 to 9 of dosing but this then declined to initial levels. There was no other detectable nutritional disturbance associated with re-infection. Re-challenge caused a rapid development of eosinophilia which peaked during Week 6 before declining to levels of the control animals by Week 8. Sheep resistant to T. colubriformis appear to be able to re-activate their immunological mechanisms when re-challenged with the parasite with little associated nutritional penalty.

Calcium and phosphorus absorption in lambs exposed to Trichostrongylus colubriformis

Ten lambs (29 +/- 1.2 kg) reared parasite-free and prepared with rumen, duodenal and ileal cannulae were paired and one of each pair was given a daily oral dose of 2500 Trichostrongylus colubriformis larvae for 14 weeks. Untreated animals received the amount of ration consumed by their infected pair-mates the previous day. During weeks 6 and 12 of infection, all lambs underwent a 7 day calcium (Ca) and phosphorus (P) balance. During weeks 7 and 13, duodenal and ileal samples were collected to determine the amounts of Ca and P entering and leaving the small intestine. The infection caused varying degrees of feed refusal in all infected animals. As a result, the data on Ca and P in excreta and the amounts of Ca and P entering and leaving the small intestine were regressed against dry matter (DM) intake for each group at each period. There were no between-period differences in these relationships. Calcium absorption and retention were unaffected by the stress of infection. Infection affected several aspects of P metabolism. Blood P concentrations were markedly reduced. Absorption of P from the small intestine was greater (P less than 0.01) in control lambs (at 1 kg DM intake 6.6 g per day) than in infected animals (2.2 g P per day), but there was a greater (P less than 0.05) duodenal flow rate of P in control lambs which suggested much higher rates of salivary secretion of P than in infected animals. Phosphorus flow rates at the ileum were greater (P less than 0.01) in infected lambs, despite the lower duodenal flow rates, which indicated a major abnormality (P less than 0.01) in small intestine absorption of P in infected animals; this may have contributed to the growth check experienced by these lambs.

Effect of phosphorus intake on growth rate, food intake and quality of the skeleton of growing lambs infected with the intestinal nematode Trichostrongylus vitrinus

The performance of growing lambs dosed daily for 12 weeks with 2500 Trichostrongylus vitrinus larvae (I) or given no larvae (control, C) was compared at two levels of phosphorus intake; 2.75 gP/kg dry matter (normal, NP) and 1.88 pgP/kg dry matter (low, LP). Both low phosphorus and T vitrinus infection reduced dry matter intake and growth rate and the combined effect of low phosphorus and infection were additive. Plasma hypophosphataemia (less than 60 mg per litre) occurred in groups CLP, ILP and INP from week 3, the values gradually returning to normal levels in INP lambs by the end of the trial. T vitrinus infection did not depress plasma phosphorus concentration below that seen in the low phosphorus controls. Both low phosphorus intake and T vitrinus infection reduced the density and mineralisation of bone, the most severely affected bones occurring in groups ILP lambs. T vitrinus infection reduced the content and concentration of phosphorus in the rumen and the effect was greater at the lower intake of phosphorus. Infection also reduced the proportion of phosphorus in the rumen liquid phase. The number of T vitrinus recovered from the intestine was higher and villous atrophy more extensive in lambs from group ILP. It is suggested that development of 'resistance' may be delayed on a low phosphorus intake.

Pharmacokinetic behaviour and anthelmintic efficacy of 1-n-butyl carbamoyl oxfendazole given by intramuscular injection

Oxfendazole (OFZ) was chemically modified to 1-n-butyl carbamoyl OFZ (C4-OFZ) in an attempt to improve the solubility of OFZ and enable it to be administered by injection. After intramuscular injection to sheep and cattle, C4-OFZ was metabolised to OFZ which resulted in higher plasma OFZ concentrations that persisted for a considerably longer period than those observed following administration of OFZ orally. The anthelmintic efficacy of injected C4-OFZ was tested, in sheep, against strains of Trichostrongylus colubriformis, Haemonchus contortus and Ostertagia circumcincta, which were highly resistant to benzimidazoles. In all cases, the C4-OFZ treatment showed a significant improvement in efficacy over the conventional oral OFZ drench.

Absorption and secretion of calcium and phosphorus in the alimentary tract of lambs infected with daily doses of Trichostrongylus colubriformis or Ostertagia circumcincta larvae

The flows of endogenous and exogenous calcium and phosphorus in the digesta at the abomasum, ileum and in the faeces were measured in growing lambs infected daily with 3000 T. colubriformis larvae (TC), 5000 O. circumcincta larvae or no larvae. The lambs were given 0.70 or 1.0 kg per day of a pelleted diet and the flow rates were measured by reference to soluble and particulate radioactive markers. The fraction of Ca and P in digesta of endogenous origin was measured by the method of isotope dilution involving a single intravenous dose of 45Ca or 32P. Ostertagia circumcincta infection was without effect on the absorption and secretion of Ca and P in the digestive tract, other than producing a small but significant increase in the endogenous faecal Ca excretion. There was, however, a striking increase in the flow of digesta at the abomasum, the DM and Na content of which was consistent with an increased secretion from the mucus-type cells in the abomasal mucosa. The extra digesta was absorbed in the small intestine. Trichostrongylus colubriformis infections reduced the absorption of exogenous P by about 30 per cent and increased losses of endogenous P due to the action of worms on the mucosa of the small intestine. The net effect of this was to induce a P deficiency in TC lambs, leading to a reduced flow of salivary P and a reduction in the plasma concentrations of P. The effect of TC on Ca metabolism was limited to an increase in endogenous faecal excretion.

Effects of concurrent subclinical infections by coccidia (Eimeria christenseni) and intestinal nematodes (Trichostrongylus colubriformis) on apparent nutrient digestibilities and balances, serum copper and zinc, and bone mineralization in the pigmy goat

Subclinical infections by the intestinal nematode Trichostrongylus colubriformis were established in 7 pigmy goats by inoculating each with 4,000 infective larvae 5 days/week for 18 weeks. At the start of the 14th week, 3 of the goats were orally inoculated daily with 10,000 sporulated oocytes of the coccidium Eimeria christenseni for 6 days, producing subclinical infections. During selected weeks, the goats were placed in metabolism cages to monitor feed consumption and collect orts, feces, and urine. Samples of rib, vertebra, and tibia were removed at time of death, on day 126. The superimposition of the coccidial infections on the nematode infections did not affect apparent ash, nitrogen, organic matter, or dry matter digestibilities; balances of nitrogen or phosphorus; serum copper or zinc concentrations; liveweights or feed conversion efficiencies. Mean calcium balances remained positive, although they were reduced during the first week of the superimposed coccidial infections. The mineralization of the matrix of the tibia and 4th lumbar vertebra was less in the goats with the superimposed coccidial infections than in those infected only with nematodes. Presence of the superimposed infections was associated with a decrease in the mean moisture and lipid contents of the tibia.

Chronic infection with Trichostrongylus vitrinus in sheep. Some effects on food utilisation, skeletal growth and certain serum constituents

The effect on food utilisation and skeletal growth of daily infection for 90 days with 2500 Trichostrongylus vitrinus larvae was investigated. Controls were killed initially or fed ad libitum. Food intake, digestibility of dry matter and nitrogen and content of body fat, protein, water and minerals were determined, and selected bones examined chemically and histologically. Serum constituents were determined weekly. Digestibility of food dry matter and nitrogen were reduced during weeks 3 and 5 after initial infection but subsequently recovered. Deposition of fat, protein, calcium and phosphorus in the body was reduced by 36, 58, 67 and 78 per cent respectively. Gross efficiency of utilisation of metabolisable energy was reduced by 36 per cent. Bone changes were associated with a reduction in osteoblastic activity. Hypoalbuminaemia, hyperglobulinaemia and hypophosphataemia were present in infected sheep. There were no significant changes in serum calcium or urea concentrations. It is concluded that the effects of continuous intakes of T vitrinus and T colubriformis larvae on host metabolism are essentially the same.

Flow and protein composition of intestinal lymph in sheep infected with the enteric nematode, Trichostrongylus colubriformis

A study of immunoglobulin and albumin concentrations and the flow of intestinal lymph was made in sheep during infection with the parasitic nematode, Trichostrongylus colubriformis. Observations were made on uninfected worm-free sheep, on worm-free sheep undergoing primary infection and on immune sheep undergoing challenge infection. The flow of intestinal lymph and the concentrations of IgG1, IgG2 and IgM in intestinal lymph and IgG2 and IgM in blood plasma remained relatively constant during both primary and challenge infection. The concentration of IgA in intestinal lymph and blood plasma increased as early as day 6 of primary infection and maximum values were observed at day 34. By day 34 of primary infection the concentration of IgG1 in blood plasma was significantly greater than that found in worm-free controls. Plasma IgG1 concentrations in resistant sheep were also significantly greater than those observed in worm-free controls. Challenge infection in immune sheep did not raise the concentration of IgA in intestinal lymph and blood or IgG1 in blood. An indirect haemagglutination test was used to detect antibodies to T. colubriformis. Primary infection did not increase anti-worm antibody titres in either intestinal lymph or serum. Significant antibody titres were present in serum and lymph from immune sheep and were rapidly increased by challenge infection. Most antibody activity in serum was associated with IgM, whereas that in intestinal lymph was associated with IgA. These observations indicate the occurrence of a local antibody response to T. colubriformis in the intestine of immune sheep.

Immune responses of sheep to the parasitic nematode Trichostrongylus colubriformis: infections in Thiry-Vella loops

Some aspects of the local immune response to nematode infection were examined by introducing fourth-stage Trichostrongylus colubriformis larvae into Thiry-Vella loops in worm-free and T. colubriformis-resistant sheep. Approximately 15% of the larvae introduced into the worm-free sheep survived and matured into adult worms, whereas less than 1% survival in resistant sheep. The amount of IgG1, IgG2, IgM and albumin discharged from loops in worm-free but not resistant sheep all increased following infection with larvae. Secretions from resistant sheep contained approximately three times as much IgA as secretions from the worm-free group and, in addition, their plasma IgG1 level was significantly higher. Antibodies against T. columbriformis were found in both plasma and intestinal secretions, the highest titres being found in the resistant sheep. During worm expulsion from loops in the resistant sheep neither immunoglobulin levels nor antibody titres in the secretions increased significantly.

Parasitism (Trichostrongylus colubriformis and Eimeria ninakohlyakimovae) in sheep: relationship between wool fiber diameter changes and feed conversion efficiency

Twenty-five lambs, 5 months of age, were used to compare the infection pressure of Trichostrongylus colubriformis with that of Eimeria ninakohlyakimovae. Effects of the parasitic infection pressure were assayed by determining body weight gains, feed conversion efficiencies, and wool fiber diameter changes (reflecting changes in protein metabolism) in lambs fed a good ration and those given a marginal diet (dehydrated alfalfa pellets). Significant differences in weight grains or feed conversion efficiencies of nematode- or coccidia-infected lambs and noninfected controls were not found, but significant differences due to the parasites' effect on wool fiber diameters and in lamb response to different feeds were found. Protein uptake or assimilation, or both, were apparently affected by a combination of infection with E ninakohlyakimovae and a marginal diet.