Influence of dietary protein on parasite establishment and pathogenesis in Finn Dorset and Scottish Blackface lambs given a single moderate infection of Haemonchus contortus

An experiment was conducted to examine the influence of dietary protein on parasite establishment and pathogenesis of Haemonchus contortus in lambs of two breeds. Finn Dorset and Scottish Blackface. The lambs were introduced to high protein (170 g crude protein (CP) kg-1 dry matter (DM) or low protein (88 g CP kg-1 DM) diets at three months old and infected one month later with 125 larvae (kg bodyweight)-1. Blood and faecal samples were collected for analysis and bodyweights recorded weekly. The lambs were killed 20 weeks after infection. A second experiment was conducted in Blackface lambs solely to determine the influence on parasite establishment of the high and low protein diets following infection with 125 larvae kg-1. These lambs were killed five or 14 weeks after infection. Results showed that in Scottish Blackface lambs dietary protein did not significantly influence the establishment of H contortus. However, in Finn Dorset lambs dietary protein may have influenced parasite establishment since lambs on the low protein diet had a higher faecal egg output four weeks after infection and more severe clinical signs than infected lambs of the same breed on a high protein diet.     

Partial protection of lambs against Haemonchus contortus by vaccination with a fractionated preparation of the parasite

Florida Native lambs, less than 6 months of age, were successfully vaccinated against Haemonchus contortus with a high mol. wt fraction (greater than 30,000 daltons) derived from a somatic extract of H. contortus larvae (SEL) and excretions and secretions (ES) of larvae isolated during in vitro development from the infective 3rd to 4th stage. A 59% reduction in adult worm numbers was obtained in vaccinates compared to naive lambs following challenge. The protection in vaccinated lambs was similar to that seen in lambs exposed to a primary infection of H. contortus larvae which had been cleared with anthelmintic prior to the challenge infection. The unfractionated SEL/ES preparation and a low mol. wt fraction gave no significant protection against challenge infection.     

A study of some factors influencing the immunization of sheep against Haemonchus contortus using attenuated larvae

The respective roles of age of lamb, size of immunizing dose, previous exposure to infection and anthelmintic therapy on the immune response of Scottish Blackface sheep to gamma-irradiated H. contortus larvae were studied.As previously shown, young lambs immunised at 10 and 14 weeks of age failed to develop a significant resistance to subsequent challenge.In contrast, parasite-naive lambs immunised at 9 and 10 months of age with 10 000 H. contortus larvae irradiated at 60 kiloröntgens developed a highly significant immunity to subsequent challenge. This degree of immunity was not significantly altered by the administration of spaced doses of normal larvae from 10 weeks of age until the point of vaccination.Worm-free lambs vaccinated at 9 and 10 months of age failed to develop any immunity to subsequent challenge when the anthelmintic thiabendazole was administered 3 weeks after each immunizing infection.     

The effect of dietary protein on the pathogenesis of acute ovine haemonchosis

Two experiments were conducted to examine the ifluence of dietary proteins on parasite establishment and pathogenesis in Finn Dorset/Dorset Horn lambs infected with Haemonchus contortus. The lambs were introduced to high (169 g) or low (88 g crude protein (CP) kg⁻¹ dry matter (DM)) protein diets at 3 months of age and infected 1 month later with 350 larvae kg⁻¹ body weight (BW). Blood and faecal smaples were collected for analysis and body weights recorded weekly. In the first experiments some of the infected lambs were killed 6 weeks after infection and the remainder 5 weeks later. In the second experimental all the infected lambs were killed 4 weeks after infection.

The results showed that lambs on a low protein diet were less able to withstand the pathogenic effects of infection with 350 H. contortus larvae kg⁻¹ BW than lambs given the higher protein diet. Thus mortality was greater in the low protein group and adverse clinical signs, such as inappetance, weight loss and oedema were osbserved more frequently. This group also had a more severe anaemia, hypoproteinaemia and hypoalbuminnaemia than the high protein group. In contrast, faecal egg counts, total daily faecal egg output and worm burdens were similar in all groups of infected lambs, indicating that the diets did not influence parasite establishment.     

Protection of lambs with a purified metabolite of exsheathed third-stage Haemonchus contortus larvae

Helminth-free lambs (approx 4 months old) were inoculated SC with a purified metabolite of exsheathed third-stage Haemonchus contortus larvae. The metabolite was obtained from in vitro cultivation and was identified as XL3FA1. After 3 periodic XL3FA1 inoculations, lambs were challenge exposed with H contortus. Multiple vaccinations with XL3FA1 did not inhibit the development of worm populations in the lambs; however, worm egg production seemed to be inhibited.     

Trichostrongylus colubriformis and Haemonchus contortus infections in light bodyweight Merino lambs

OBJECTIVE; To show that low bodyweight is a predisposing cause of high Trichostrongylus colubriformis and Haemonchus contortus burdens and egg counts in Merino lambs. DESIGN: A comparison was made, among lambs of different bodyweights, on the effect on immunity of a primary or secondary viable infection with T colubriformis or H contortus larvae. PROCEDURE: Sixty-one Merino lambs, 1 or 6 months of age, were penned indoors and given primary, or both primary and secondary, infection of T colubriformis or H contortus. Faecal egg counts, worm counts and parasite-specific immunoglobulin concentrations were examined for their relationships with bodyweight. RESULTS: Bodyweight at the start of a primary infection was correlated with worm burden, worm fecundity and jejunal IgA antibody concentration. Merino lambs weighing less than 23 kg at the time of first exposure to T colubriformis or H contortus had impaired ability to develop protective mucosal immunity and to resist homologous challenge. CONCLUSION: If the goal is to ensure that lambs develop immunity before weaning, then every endeavour should be made to achieve the combination of critical bodyweight and exposure to moderate levels of nematode infection as soon as possible.     

Effects of the chitin synthesis inhibitor diflubenzuron on development of Ascaris suum and Haemonchus contortus

The potential of the chitin synthesis inhibitor diflubenzuron (DFB) to alter the development of the parasitic nematodes (Ascaris suum and Haemonchus contortus was investigated. DFB given orally (10 mg kg-1 per day for 30 days) to sheep inoculated with H. contortus infective larvae did not prevent the establishment of adults or affect fecal egg output. However, there was a significant (greater than 90%) decrease in the number of infective larvae recovered from fecal cultures derived from lambs harboring H. contortus adults that were treated with DFB. DFB did not affect egg hatching. Oral administration (10 mg kg-1 per day for 20 days) of DFB to swine harboring adult A. suum adults had no effect on the adult worm burden or on egg morphology, but eggs removed from worms obtained from DFB-treated swine contained less chitin than eggs removed from untreated control swine. DFB also inhibited chitin synthesis in vitro in the isolated reproductive tract of A. suum adults. These results indicate that DFB at high doses can inhibit the subsequent development of H. contortus larvae in the feces. Since H. contortus larvae lack chitin, DFB may act on these larvae by a mechanism independent of a direct effect on chitin synthesis.     

Fibrinogen-degrading proteins from Haemonchus contortus used to vaccinate sheep.

Sixteen nonsibling sheep, approximately 12 months old, that were raised in a helminth-free environment, were used for 2 protection studies 6 months apart. Sheep were vaccinated weekly for 5 weeks by IM injection of fibrinogen-degrading proteins derived from the intestinal tract of adult Haemonchus contortus. Ten days after the last vaccination, sheep were given 2,500 infective H contortus larvae by intraruminal injection. Vaccinated sheep produced specific antibodies, and were protected from the worm challenge. Significant differences in mean fecal worm egg counts for 56 days after worm challenge, in mean numbers of H contortus worms, and female fecundity ratios at necropsy were detected in vaccinated sheep, compared with those in control sheep. These data suggest that the fibrinogen-degrading proteins have a protective role in vaccination of sheep against H contortus.     

The effect of dietary protein on the pathophysiology of acute ovine haemonchosis

An experiment was conducted to examine the effect of dietary protein on the pathophysiology iof acute haemonchosis in Finn Dorset/Dorset horn lambs.

Erythrokinetic and metabolic studies using ⁵¹Cr-red cells, ⁵⁹Fe-trasferrin and ¹²⁵I-albumine and digestive efficiency and nitrogen balance measurements wer conducted between 19 and 39 days after infection. Identical radioisotopic and nutritional studies were conducted later on pair-fed control lambs.

The results demonstrated that lambs on a law protein diet (88 g crude protein (CP) kg⁻¹ dry matter (DM)) were less able to withstand the pathyphysiological consequences of infection with 350 Haemonchus contortus larvae kg⁻¹ body weight than lambs given a high protein (170 g CP kg⁻¹ DM) diet, despite similar worm budens.

Erythrokinetic studies indicated that abomasal blood loss was similar in both groups of infected lambs, and circulating red cell volumes were reduced and plasma volumes were expanded to a similar degree in both groups. The majority of infected lambs in both dietary groups responded equally well to the gastric haemorrhage by increasing the rate of red cell production and their absorption of dietary iron was greater than in the control lambs. Albumin catabolism was increased in both groups of infected lambs, particularly in those given the low protein diet.

Within each dietary group there were no differences in the digestibilities of the various proximate fractions of the experimental diets and no differences in the urinary of faecal nitrogen losses between infected lambs and their pair-fed control. However, loss of appetive was a major feature of the disease, particularly in the lambs given the low protein diet and this feature appeared to be crucial in determining the ability of the infected sheep to withstand the pathophysiological effects of the parasite.     

Investigation of Haemonchus contortus infections in sheep. Comparison of irradiated larvae and transfer factor treatment

A comparison is made between the resistance conferred to Haemonchus contortus challenge by irradiated larval treatment and transfer factor (TF) treatment in four-month-old lambs and seven-month-old lambs. As in previous investigations the irradiated larval treatment failed to confer resistance to the four-month-old lambs challenged with 10,000 third stage larvae while similar irradiated larval treatment in seven-month-old lambs reduced the worm burdens by 40 per cent compared to controls. The TF treatment produced a 34 per cent reduction in the challenge infection in the four-month-old lambs and a 45 per cent reduction in the seven-month-old lambs compared to the control lambs. It is concluded that TF activity operates independently of immune competence.     

Influence of dietary protein supply on resistance to experimental infections with Haemonchus contortus in Ile de France and Santa Ines lambs

The effect of Haemonchus contortus infection in sheep fed with a moderate and high protein content diet was evaluated in two breeds of sheep. Forty-eight Ile de France and Santa Ines lambs were maintained indoors since birth, in worm-free conditions. The lambs were allocated after weaning in four groups of six animals per breed, which were either infected or remain uninfected and given access to either a moderately or highly metabolizable protein diet. The moderately and highly metabolizable protein diets were calculated to supply 75 and 129 g metabolizable protein per kg of dry matter (MP/kg DM), respectively. The infection consisted of a trickle infection with 300 infective larvae, three times a week, for 12 weeks. Significant differences were observed for mast cell, globule leukocyte and eosinophil counts in the abomasal mucosa of the infected groups compared to the control of both breeds (P<0.05), regardless of the diet supplied. Significantly higher IgA anti-L5 antibody was detected in the infected Santa Ines groups than in the infected Ile de France groups (P<0.05). Increased metabolizable protein supply resulted in larger body weight gain and higher packed cell volumes for both breeds (P<0.05). Both breeds showed an increased ability to withstand the pathophysiological effects of H. contortus infection when given access to the highly metabolizable protein diet. However, increased metabolizable protein supply resulted in reduced worm burdens in Santa Ines lambs but not in the Ile de France lambs (P<0.05). The present results show that the increase in protein content in growing lamb diets may benefit resistance and resilience to gastrointestinal parasites but that these benefits may vary among breeds.     

Haemonchus contortus resistance to ivermectin and netobimin in Brazilian sheep.

Suffolk, Texel, Hampshire Down and Ile de France sheep from the municipalities of Porto Amazonas, Piraquara and Araucaria in the State of Paraná, and Bagé in the State of Rio Grande do Sul were brought to Sobral, State of Ceará, to be used in a cross-breeding project. On arrival they had clinical signs of nematode parasitosis, and one Suffolk female died. The animals were treated orally with ivermectin (0.2 mg kg-1) and fifteen days later with netobimin (20.0 mg kg-1). Neither drug reduced the egg counts (measured in eggs per gram, EPG) significantly, and this suggested that the nematodes in the sheep were resistant to the anthelmintics used. Haemonchus contortus was the species involved. The egg counts were reduced after oral treatment with trichlorfon (100.0 mg kg-1). Haemonchus contortus larvae obtained from these animals before trichlorfon treatment and passaged through two nematode-free sheep were used in a further experiment. Twenty 6- to 9-month-old nematode-free lambs were infected with the H. contortus larvae (10,000 per animal) and after the infection was confirmed, were randomly divided into four groups of five animals. Group I was orally treated with ivermectin at 0.2 mg kg-1, Group II with oral netobimin at 20.0 mg kg-1, Group III with oral trichlorfon at 100.0 mg kg-1 and Group IV was a non-treated control. Egg counts and faecal cultures were taken before dosing on the day of treatment and seven days later when all animals were necropsied and the nematodes were collected from the abomasa and counted.(ABSTRACT TRUNCATED AT 250 WORDS)     

Serum IgG response of Manchego lambs to infections with Haemonchus contortus and preliminary characterization of adult antigens

Manchego lambs (16-18 weeks old) were infected with 2500 infective larvae (L3) of Haemonchus contortus and challenged 2 months later with 5000 L3. The serum IgG anti-Haemonchus response was estimated by enzyme-linked immunosorbent assay (ELISA) using soluble proteins from adults and L3. Previously infected Manchego lambs failed to mount a protective immune response against challenge, at least as assessed by faecal egg counts and pre-patency periods. Primary infection did not provoke any rise in specific anti-parasite serum antibodies, whereas a weak but significant rise was observed in challenged 6.5-month-old lambs which was very similar in both infected and non-infected lambs. The serum IgG anti-parasite response was higher against larval antigens than adult soluble proteins. Preliminary characterization of adult and larval soluble proteins by electrophoresis under reducing and denaturing conditions and Western blotting showed high cross-reactivity of both extracts. Immunoblots of adult H. contortus probed with infected and challenged lambs' sera did not yield conclusive results, although some low molecular weight peptides were recognized.     

Effectiveness of copper oxide wire particles for Haemonchus contortus control in sheep

OBJECTIVE: To assess the efficacy of copper oxide wire particles (COWP) for the control of H contortus infections in grazing sheep. PROCEDURE: In experiment 1, 40 worm-free Merino hoggets (11 to 12 months of age) were divided into four equal groups and allocated to separate 0.8 ha pasture plots. Two groups then received 2.5 g COWP whereas the other two groups were untreated. From 1 week after COWP treatment all lambs received a weekly infection of 2000 H contortus larvae. At week 8, six sheep from the untreated group were then allocated to two groups and treated with either 2.5 or 5.0 g of COWP to establish therapeutic efficacy of treatment. Experiment 2 followed a similar protocol but was conducted with 40 worm-free Merino lambs (3 to 4 months of age) and no assessment of therapeutic efficacy was made. Results: In experiment 1 no significant difference in faecal worm egg counts was observed between treatments and faecal worm egg counts remained less than 3000 epg in all animals. Total worm counts were reduced by 37% by COWP treatment (P = 0.055). Both 2.5 g and 5.0 g doses of COWP at 8 weeks of infection reduced faecal worm egg counts by > 85% with the higher dose giving an earlier response to treatment. In experiment 2, faecal worm egg counts at 4 and 6 weeks were reduced by more than 90% in the COWP treated lambs and worm numbers were 54% lower after 6 weeks when all remaining untreated lambs had to be treated for haemonchosis. Mean faecal worm egg counts in the COWP lambs remained below 3500 epg and clinical disease did not develop in the majority of lambs before the end of the experiment at 10 weeks. CONCLUSION: Treatment with COWPs appears to have the potential to reduce establishment and worm fecundity of Haemonchus spp for an extended period and may offer livestock producers a supplementary means of reducing larval contamination of pasture particularly in areas where anthelmintic resistance is a problem and copper supplementation is likely to be beneficial.     

Possible relationship of levels of mucosal IgA and serum IgG to immune unresponsiveness of lambs to haemonchus contortus

Abomasal mucus IgA and serum IgG antibodies were studied in adult sheep and young lambs vaccinated with irradiated Haemonchus contortus larvae and subsequently challenged with normal larvae. In the adult sheep protection against challenge was associated with raised levels of these antibodies. Vaccination of the lambs, on the other hand, did not protect against challenge nor did it stimulate either serum IgG or mucus IgA antibodies. The latter remained at levels similar to those of both control lambs given a single challenge infection and worm-free adult sheep.     

The effect of age on the response of sheep to vaccination with irradiated trichostrongylus colubriformis larvae

Vaccination with irradiated Trichostrongylus colubriformis larvae produced a high level of immunity, as judged by faecal egg counts and worm burdens following challenge with normal larvae, in nine of ten sheep aged 10 months. In lambs aged 3 months, vaccination was less effective. Some lambs developed partial immunity, but others did not respond.Serum levels of antibodies to T. colubriformis acetylcholinesterase reflected the extent of antigenic exposure rather than the degree of immunity acquired, and there was no evidence that the unresponsiveness of the lambs was due to a deficiency in antibody production.Unresponsiveness was not associated with the numbers of circulating lymphocytes, monocytes or granulocytes, or with the numbers of mast cells, eosinophils and neutrophils at the site of infection. However, there were many globule leucocytes in the intestinal mucosa of adult sheep which were resistant to challenge infection. On the other hand, few of these cells were found in vaccinated lambs which generally gave a poor response to challenge.     

Studies on Haemonchus contortus. XII. Effect of Trichostrongylus axei in Dorper lambs on natural pasture lightly infested with H. contortus

Weaned Dorper lambs on natural pasture were predosed with 40 000 infective larvae (L3) of Trichostrongylus axei, irradiated (0,3 kGy) L3 of T. axei or closantel at 10 mg/kg either in September or November 1978 and were compared with Merino yearlings predosed with 40 000 L3 of T. axei in November 1977. The following summer (December-March) only 178,6 mm of rain fell and very few H. contortus were present on pastures. Artificial challenge with 20 000 L3 of Haemonchus contortus with the local strain from the University of Pretoria's experimental farm was given 6-7 months after predosing with T. axei. When compared with the controls, significant reductions occurred only in Group 11 (T. axei irradiated at 0,3 kGy on Day +63) (P = 0,025); Group 2 (T. axei on Day 0) (P = 0,003) and Group 4 (T. axei and closantel on Day 0) (P = 0,049). We concluded that predosing with T. axei was unsuccessful in Dorpers and Merinos artificially challenged 6-7 months later with H. contortus.     

Effect of weaning on antibody responses and nematode parasitism in Merino lambs.

Lambs weaned at eight weeks old were compared with control lambs which remained with their dams; both groups grazed the same pasture. Weaning significantly reduced the growth rate, control lambs being, on average, 6 kg heavier than weaned lambs at 15 weeks old. When contamination of pasture with larval parasites was light, both groups of lambs suffered only modest parasitic infections. When lambs were experimentally infected with 5000 Haemonchus contortus and 10,000 Trichostrongylus colubriformis larvae at eight weeks old, the mean faecal egg count for weaned lambs was twice that for controls at 12 weeks old (P less than 0.001) and weaned lambs suffered a significantly greater decline in packed cell volume than controls over the next four weeks. Antibody responses following immunisation with either ovalbumin or Brucella abortus at four and at eight weeks old, did not differ significantly between control and weaned lambs. In contrast serum antibody responses to H contortus and T colubriformis differed significantly between the two groups, with controls responding earlier and more strongly than weaned lambs. The practical significance of these findings is that up to three months old, suckled lambs, when faced with a substantial parasite challenge, have much better prospects than weaned lambs.     

Decrease in establishment of Haemonchus contortus caused by inoculation of a Taenia hydatigena larvae vesicular concentrate

The effect of Taenia hydatigena larvae vesicular concentrate (ThLVC) on the establishment of an experimental infection by Haemonchus contortus was evaluated. The lambs that received ThLVC showed a greater (P<0.05) average of blood eosinophils (BE) than the lambs that did not receive ThLVC. Lambs that were only infected with H. contortus larvae showed a fecal egg count (FEC) and an adult phase (AP) number greater (P<0.05) than lambs that received ThLVC prior to infection. No effect was observed in size and prolificacy of AP after the administration of ThLVC. The infection with H. contortus caused an increase (P<0.05) in CD4+ lymphocytes in abomasal lymph node (ALN) and the combination of ThLVC plus the infection with H. contortus caused an increase (P<0.05) in CD4+ lymphocytes in the abomasal wall (AW). In addition, a positive correlation between gamma-delta lymphocytes of ALN (r=0.73, P<0.05) with the presence of AP in the abomasum was observed. The quantity of plasma cells in ALN and AW was not affected by the administration of ThLVC nor related to the resistance observed. The results shown in this work leave no doubt that ThLVC administration prior to inoculation produces eosinophilia and partially protects against the establishment of H. contortus. However, this protection is not only attributable to the role of eosinophils, since ThLVC can function stimulating other immune response cells, such as T lymphocytes, both contributing to prevent the presence of worms.     

Effect of environmental stimuli on pre-infective and infective stages of Haemonchus contortus in the northern United States for the induction of hypobiosis

The effects of both natural and artificial conditioning of pre-infective and infective stages of Haemonchus contortus were examined in two studies with 108 crossbred lambs, using an Ohio isolate of H. contortus known to exhibit up to 100% winter hypobiosis. The intensity of hypobiosis varied from 0 to 36% in 17 lamb groups given larvae subjected to various temperature and photoperiod conditions. The results in lambs given larvae conditioned for 4-8 weeks were not significantly different from those in lambs given freshly cultured larvae. It is suggested that winter hypobiosis of H. contortus in the northern U.S.A. is an obligatory survival mechanism that occurs without the need for external stimuli to trigger the onset of hypobiosis.