Accuracy of the FAMACHA system for on-farm use by sheep and goat producers in the southeastern United States

FAMACHA is a practical on-farm system designed to provide small ruminant producers a tool for improving their management of Haemonchus contortus infections. Although this system has become very popular and widely accepted by small ruminant producers in many regions of the southern United States, there is very limited data reported on the effectiveness of the FAMACHA system when performed by farmers. The objective of this study was to evaluate the accuracy of the FAMACHA system for on-farm use by small ruminant producers during the summer season. Small ruminant producers from Georgia, Louisiana, Florida, and Puerto Rico were trained to use the FAMACHA system by veterinarians and scientists experienced with this method. FAMACHA scores were assigned at least every 2 weeks by producers to weaned and mature sheep (n=552) and goats (n=676) of various breeds and ages between April and September 2004. At intervals that varied among farms from 2 to 8 weeks, researchers determined body condition scores (BCS; 1=thin and 5=fat) and collected blood and feces from a group of animals selected randomly to determine packed cell volume (PCV) and fecal egg counts (FEC). Two separate anemia thresholds were evaluated; these were defined by either FAMACHA score (>or=3 versus >or=4) or PCV (<or=19 versus <or=15%). The correlation between FAMACHA scores and PCV or FEC was high for both sheep and goats (P<0.001). Specificity was maximized when FAMACHA scores of 4 and 5 were considered anemic, but sensitivity was low. Sensitivity for detecting anemic animals was 50% for sheep and 89% for goats when eye score values of >or=3 were considered anemic and PCV cutoff was <or=15%. The percentage of false negatives (anemic animals not identified by FAMACHA evaluation) was less than 5% in sheep and less than 1% in goats when FAMACHA scores>or=3 were considered anemic and PCV cutoff was <or=15%. In both sheep and goats, predictive value of a negative was greater than 90% for all anemia and eye score categories. These data indicate that the FAMACHA method used by producers is a valuable tool for identifying anemic sheep and goats in the southern United States and Puerto Rico.

[Physiopathological mechanisms of abomasal Trichostrongylidae infections in small ruminants]

Abomasal Trichostrongylidae infections are still today an important cause of scarce performances in small ruminants, mainly when bred in extensive systems. Although morpho-biology, symptomatology, prophylaxis and therapy of these infections are well known, other, such as physiopathology, are less investigated. The aim of the present note is to review the more important physiopathogenetic mechanisms of abomasal Trichostrongylidae infections, with special emphasis to Haemonchus spp. and Teladorsagia spp. The parasitic anorexia due to the action of gastrin, the defects of digestion due to hypocloridia, the scarce intestinal absorption and anaemia caused by H. contortus are discussed. Furthermore, the effects of hypersensitivity sometimes caused by these abomasal nematodes are examined. A better knowledge of physiopathological mechanisms can represent an important factor to understand the relationships between host and parasite, useful to set up new diagnostic techniques or new therapeutic and prophylactic protocols for sanitary education and control plans of these important and widespread parasitic infections.

Accuracy of an anaemia scoring chart applied on goats in sub-humid Kenya and its potential for control of Haemonchus contortus infections

We tested the practical application of an anaemia scoring chart (the FAMACHA chart) as a method for controlling Haemonchus contortus in goats kept under smallholder conditions in a sub-humid area of Central Kenya. The objectives were: (1) to test the accuracy of the FAMACHA chart in identifying anaemic goats (PCV< or =18); (2) to quantify the proportion of goats left untreated at farm level when using the chart. On each of two farms, Small East African goats of various ages were allocated to two treatment groups; a FAMACHA group (F1 (n=34) and F2 (n=31) on farms 1 and 2, respectively) and a control group (C1 (n=34) and C2 (n=30)). In F1 and F2 goats with a FAMACHA score of 3, 4 or 5 were treated with anthelmintic after scoring. In C1 and C2 goats were treated every 4 weeks from 15 February to 20 July. Every 2 weeks all goats were scored with the FAMACHA chart and weighed. Furthermore, faecal samples were collected for faecal egg counts (FEC) and blood samples were collected for packed cell volume (PCV) determination. H. contortus was found to be the predominant nematode on both farms. The mean FECs were higher on farm 1 compared to farm 2, while in contrast the mean PCV levels were lowest on farm 2. The latter was most likely due to the presence of Fasciola spp., flea and tick infections on farm 2. The accuracy of the chart was evaluated by using PCV as the gold standard for anaemia (PCV< or =18%). The mean percentage of false-negative scorings per sampling was 0.7% on farm 1 and 1.6% on farm 2, while the mean percentage of false-positive scorings was 9.7% and 21.4%, respectively. It is most likely that the accuracy of the chart was negatively affected by the concurrent parasite infections on farm 2. The mean proportion of untreated goats per sampling was 89% and 77% on farm 1 and farm 2. It was concluded that the FAMACHA chart can be a valuable tool for decision-making in control of H. contortus in goats kept under smallholder conditions, without morbidity or mortality unacceptable to the farmer. The application may further reduce the risk of development of anthelmintic resistance by increasing refugia. However, caution should be taken under conditions where other anaemia-causing parasites are present (e.g. Fasciola spp. and ecto-parasites), since this possibly decreases the accuracy of the FAMACHA chart.

Haemonchus contortus and Trichostrongylus colubriformis in pen-trials with Javanese thin tail sheep and Kacang cross Etawah goats

Weight gain costs due to infection were higher in sheep than goats, 28 and 17.5%, respectively, for Trichostrongylus colubriformis and 48.7 and 32.2%, respectively, for Haemonchus contortus. The extent of bodyweight cost attributed to anorexia in sheep infected with H. contortus was higher (13.5 g/day) than in sheep infected with T. colubriformis (2.3 g/day). On the other hand, bodyweight cost due to the other pathogenic effects in sheep infected with T. colubriformis were higher (35.6 g/day) compared to sheep infected with H. contortus (10.9 g/day). A strong relationship between faecal egg count and worm count (r=0.79, P=0.006) was shown only in sheep infected with T. colubriformis. About half of the infected sheep and goats had low or zero faecal egg counts throughout the study. In about 40% the egg count rose initially but became low by weeks 10-16, whereas in about 10% counts increased progressively throughout the period of observation and these animals also had the highest numbers of worms at slaughter. Packed cell volume was reduced in sheep and goats infected with H. contortus but serum protein and haemoglobin levels were unaffected. Sheep infected with T. colubriformis had a higher level of eosinophilia after 8 weeks (18.4%) than sheep infected with H. contortus (11.4%), whereas this pattern was reversed in goats and levels were also lower (4.1 and 8.9%, respectively). There was no apparent relationship between eosinophilia and resistance to infection with H. contortus or T. colubriformis.

[A new control method for Haemonchus contortus: FAMACHA]

FAMACHA is a method that has been developed against Haemonchus contortus which causes anemia in sheep and goats especially in tropical and subtropical areas. The basic principle of the method is the detection of the color changes in the mucous membrane of the eye that is caused by anemia. According to the FAMACHA Anemia Guide, (FAG), the mucous membranes of the eyes of animals are inspected for color differences at two or three week intervals. The criteria are used for treating the animals. Thus FAG provides practical diagnosis and treatment of animals that are actually affected by H. contortus. Avoiding unnecessary treatment prevents the formation of drug resistance. The method is effective only if it is used with an effective Trichostrongylidae control program. The FAMACHA method can be tested in Turkey where H. contortus is a problem; especially in mild and rainy areas. Furthermore, the method maybe modified for other parasites causing anemia.

Haemonchus contortus egg excretion and female length reduction in sheep previously infected with Oestrus ovis (Diptera: Oestridae) larvae

Mixed parasitic infection of animals is a common phenomenon in nature. The existence of one species often positively or negatively influences the survival of the other. Our experimental study was started with the objectives to demonstrate the interaction of Haemonchus contortus and Oestrus ovis in relation to cellular and humoral immune responses in sheep. Twenty-two sheep of Tarasconnais breed (France) were divided into four groups (O, OH, H and C) of five or six animals. Group O and OH received 5 weekly consecutive inoculations with O. ovis L1 larvae (total = 82 L1) in the first phase of the experiment between days 0 and 28. On the second phase, groups OH and H received 5000 L3 of H. contortus on day 48 while group C served as our control throughout the experimental period. Parasitological, haematological, serological and histopathological examinations were made according to standard procedures and all animals were slaughtered at day 95. There was no significant variation in the number and degree of development of O. ovis larvae between the two infected groups. Furthermore, in tissues examined in the upper respiratory tract (nasal septum, turbinate, ethmoide and sinus), group O and OH has responded similarly on the basis of cellular inflammatory responses (blood and tissue eosinophils, mast cells and globule leucocytes (GL)) and serum antibody responses against the nasal bots. This may indicate that the presence of H. contortus in the abomasa of group OH had no marked influence over the development of O. ovis larvae in the upper respiratory tract. On the other hand, we have observed a significantly lower H. contortus female worm length, fecal egg count (FEC) and in utero egg count in animals harbouring the nasal bot (OH) than in the mono-infected group (H). This was significantly associated with higher blood eosinophilia, higher packed cell volume (PCV) and increased number of tissue eosinophils and globule leucocytes. We conclude that, the establishment of O. ovis larvae in the upper respiratory tract has initiated higher inflammatory cellular activity in group OH there by influencing the development and fecundity of H. contortus in the abomasum.

The modulatory influence of Trypanosoma brucei on challenge infection with Haemonchus contortus in Nigerian West African Dwarf goats segregated into weak and strong responders to the nematode

Although Nigerian West African Dwarf (WAD) goats are relatively resistant to infection with Haemonchus contortus and are also trypanotolerant, natural outbreaks of both infections are known to occur. Despite their relative resistance to H. contortus WAD goats nevertheless show variability in response phenotype and it was of interest to examine the effect of this variability on the outcome of concurrent trypanosome infection. Trypanosoma brucei infections were established in goats that were initially classified as good or poor responders to H. contortus. Thirty-nine goats were exposed to an escalating infection with H. contortus, and on the basis of their mean faecal egg counts (FEC) were allocated to high FEC (poor responders, 18 goats with the highest FEC) or low FEC (good responders, 18 goats with the lowest FEC) classes. Nine uninfected naive control goats were included to provide reference baseline values. Retrospective analysis of parasitological and pathological parameters after allocation into high/low FEC classes showed that FECs differed significantly, in both classes packed cell volume (PCV) values fell relative to naive controls, neither class lost weight and both generated marked IgG responses. All goats received anthelmintic on day 61, half of each group was infected with 50 million trypanosomes and on day 67, excepting the controls, all goats were challenged with 3000 L3 of H. contortus. Trypanosome parasitaemia was generally low, and marginally, but not significantly, higher in the low compared with high FEC class, peaking 12-16 days after exposure in both groups and then falling to below microscopically detectable levels (although still detectable by sub-inoculation into mice) by week 3. At autopsy (days 109/110), worm burdens were significantly higher in the trypanosome-infected goats from the high FEC class, relative to all other groups. Trypanosome infected goats showed a tendency (although not significant) towards higher FEC and, irrespective of their FEC class, had lower PCV values although body weight did not vary significantly. All goats challenged with H. contortus had higher antibody levels than naive controls, but neither trypanosome infection nor FEC class affected the magnitude of responses. These results confirm that WAD goats comprise a range of response phenotypes to initial H. contortus infection and that trypanotolerance is a key trait of this breed. Although immunity to nematode infection develops even in poor responders, these animals harbour higher nematode burdens during concurrent infection with T. brucei.

[Use of FAMACHA Scoring System as a diagnostic aid for the registration of distinguishing marks in the breeding program for lambs exposed to an experimental Haemonchus contortus infection]

The control of gastro-intestinal nematodes in sheep has almost entirely been based on the use of anthelmintics and pasture management. Therefore anthelmintic resistance escalated in the past. One way of reducing this problem may be the limitation of anthelmintic treatment to those animals with clinical symptoms only. The FAMACHA Eye-colour-chart is based on the principle knowledge that the colour of mucous membranes are correlated with the anaemiae situation of an animal. To monitor anaemic animals they are identified and classified in a 1 to 5-color scale based on the colour of the conjunctiva, and anaemic animals can be selectively treated. It helps to reduce treatments and therefore the development of drug resistance. The objective of this study was to estimate the correlation between FAMACHA-scores, haematocrit values, faecal egg counts, plasma albumin level and worm burden following an experimental infection with Haemonchus contortus in lambs. The estimated correlations have been low. This proofs the limits of the FAMACHA system under a situation of low parasite pressure.

The FAMACHA system for managing haemonchosis in sheep and goats by clinically identifying individual animals for treatment

Escalating anthelmintic resistance has made it essential to develop alternative ways of worm management for reducing selection for worm resistance, and one of the most promising approaches is to treat only those animals unable to cope with worm challenge, thus favouring unselected worms originating from untreated animals. Only clinical evaluation of anaemia (FAMACHA system) and the body condition score are regarded as being of practical value or having potential, respectively, for repeatedly examining flocks or herds and identifying individuals for treatment. Only the FAMACHA system has been tested well enough for use under practical farming conditions. However, further investigation is needed on its effect on animal production, and methods to reduce labour. Trials over several seasons showed that most sheep under severe Haemonchus contortus challenge required no, or only one treatment over a full summer season. A small minority (usually < 5%) needed more than two treatments. Most sheep could cope without regular treatment. With sufficient training, clinical evaluation of anaemia was found reliable for practical use. The overwhelming majority of trainees (some poorly literate) were able to implement the FAMACHA system successfully. The dynamics of haemonchosis in a flock can easily be monitored. Farmers, farm workers and veterinarians all rated the system very highly (> 80%) and treatment costs dropped by approximately 58%. The heritability of FAMACHA values obtained by clinical evaluation was high at 0.55 +/- 0.17% in a Merino stud with +/- 550 young rams and ewes which were the progeny of 21 sires. The FAMACHA system may not be as applicable to goats as to sheep, but further work is necessary. The main benefits of the system are the reduction in treatments, its use for discriminating between animals of varying ability to cope with infection (thus allowing genetic selection), and its lowering of selection pressure on H. contortus for anthelmintic resistance.

Testing for clinical anaemia caused by Haemonchus spp. in goats farmed under resource-poor conditions in South Africa using an eye colour chart developed for sheep

A novel clinical assay for the assessment and subsequent treatment of Haemonchus infection in sheep to slow down the development of anthelmintic resistance--the FAMACHA system--has been developed, tested and validated in South Africa. The system is based on a colour chart with five colour categories depicting varying degrees of anaemia that are compared with the colour of the mucous membranes of the eyes of sheep. The animal is then scored from severely anaemic (pale) through anaemic to non-anaemic (red) and those animals considered in danger of succumbing to the effects of haemonchosis are treated. This method was tested in goats farmed under resource-poor conditions in South Africa. Analyses in goats performed during the summers of 1998/1999 and 1999/2000 show a test sensitivity of 76 and 85%, respectively, meaning that the system may be used to identify correctly 76-85% of those animals in need of treatment with an anthelmintic. However, the test specificity remains low at 52-55%. This means that a large proportion of those animals that would not require treatment would in fact be treated. However, when the use of the FAMACHA system is compared with conventional dosing practices where all the animals are treated, using the FAMACHA system would result in a large proportion of the animals being left untreated. The untreated animals are then able to deposit the eggs of anthelmintic-susceptible worms on the pasture, while the treated ones should pass very few ova, given an effective anthelmintic. This maintains a reservoir of susceptible larvae in refugia, and should slow down the development of anthelmintic resistance. The validation of the FAMACHA system for goats for use by resource-poor farmers, which this paper describes, may have wide application in the tropics and subtropics of sub-Saharan Africa and elsewhere.

Interaction between Trypanosoma evansi and Haemonchus contortus infection in goats

An experimental study on interaction between Trypanosoma evansi and Haemonchus contortus infections was conducted in 42 male Barbari goats of 6-9 months age. Parasitological observations like prepatent period, faecal egg count, worm burden and mortality were made in animals infected with H. contortus followed 1 week later with T. evansi and vice versa. These parameters were also examined in animals with single infection with each of these parasites. It was revealed that T. evansi infection in goats lowered the normal resistance to H. contortus. The prepatent period was markedly reduced to 16-18 days in cases where T. evansi preceded H. contortus as compared to 21-25 and 21-23 days in single H. contortus and in a H. contortus preceding T. evansi infection, respectively. The rate of L(3) establishment was significantly enhanced in infection where T. evansi preceded H. contortus. A higher rate of mortality and more pronounced pathological effects were observed in combined infections than in single ones.

The interaction of Trypanosoma congolense and Haemonchus contortus in Djallonké sheep

The interaction between Trypanosoma congolense and Haemonchus contortus was studied in 5 groups of 8 Djallonké sheep. Two groups received a single infection with either H. contortus or T. congolense, and 2 groups were infected with T. congolense followed by H. contortus (TH) or vice versa (HT). One group was kept as uninfected controls. Mortality due to infection was observed only in the dual infection groups. In the TH group, the effects were more acute whereas in the HT group they were more chronic. No significant differences in weight gain could be demonstrated between infected and control groups. Djallonké sheep are able to withstand a single infection with either T. congolense or H. contortus, which confirms their trypanotolerant nature and provides preliminary indication of resistance against helminth infections. However, when exposed to successive infections with both parasites, some of the animals lose this tolerance.

Cortisol as an indicator of severity of parasitic infections of Haemonchus contortus in lambs (Ovis aries)

Two experiments were conducted with lambs to examine the effects of experimental infections of Haemonchus contortus on circulating cortisol levels. In both experiments, naive lambs were divided into three groups based on inoculum doses of 0 (control), 2000 (low dose) and 20,000 (high dose) infective larvae. In experiment 1, the lambs were sampled once daily from day 1 post-inoculation (p.i.) until day 39 p.i. Lambs from the high-dose group had significantly higher sustained levels of cortisol throughout the course of the infection than either the low-dose group or control lambs. In experiment 2, blood was sampled at 30-min intervals for 4 hr on day 21 p.i. The high-dose group also had highest cortisol levels. The consequences of chronic stress and the resultant elevated cortisol concentrations potentially could compromise animal health and animal well-being.

Reduced egg counts in mixed infections with Oestrus ovis and Haemonchus contortus: influence of eosinophils?

In all, 2 groups of lambs were infected either with Oestrus ovis first-instar larvae or with 10,000 third-stage larvae (L3) of Haemonchus contortus. Another group of lambs was infected with both parasites. Fecal nematode egg counts, plasma pepsinogen concentrations, specific O. ovis enzyme-linked immunosorbent assay (ELISA) antibodies, and blood eosinophil counts were monitored and compared to with the values recorded for a control group of uninfected lambs. There was no significant difference between the burden of H. contortus found in mixed and single infections. However, the nematode egg production was significantly depressed in mixed infections. O. ovis affects the population of H. contortus at least by decreasing the parasite egg output. This effect may be mediated through the increase in eosinophil production stimulated by the presence of O. ovis.

Interaction between Ostertagia circumcincta and Haemonchus contortus infection in young lambs

Twenty-one-week-old, worm-free, pen-reared lambs were infected with either 6000 O. circumcincta L3 per week, or 3000 H. contortus L3 per week, or both (9000 L3 per week). Egg counts were monitored throughout the experiment, and worm burdens and larval establishment rates of both worm species were estimated after 4, 7, 10 and 13 weeks of infection. After 10-13 weeks of infection with H. contortus only, establishment of O. circumcincta was lower than in previously uninfected controls, demonstrating that a high level of immunity to H. contortus affords some cross-protection against O. circumcincta. Total H. contortus worm burdens and egg counts (about 2000 worms and 3000 e.p.g., respectively) in sheep infected with both worm species were less than half those observed in sheep infected with H. contortus alone (about 5000 worms and 10,000 e.p.g., respectively). Cross-protection between the two species was observed, but was probably less important than the reduction in H. contortus establishment that was caused by O. circumcincta disrupting abomasal physiology.

Comparison of the effects on milk production of concurrent infection with Haemonchus contortus and Trichostrongylus colubriformis in high- and low-producing dairy goats

The impact of nematode parasitism of the digestive tract on milk output and milk quality was examined in dairy goats. In addition, the consequences of worm infection were compared in goats with different lactation performance (ie, with initial high or low milk production). Forty-eight goats in the second month of lactation were allotted equally to 2 groups. The first group was given 5,000 Haemonchus contortus and 20,000 Trichostrongylus colubriformis larvae. The 24 additional goats remained free of parasites. Parasitologic, serologic, and milk data were collected every 2 weeks for 5 months, and body condition of the goats was scored throughout the study. Results of strongyle egg count in feces, increase in pepsinogen values, and reduction in RBC count, PCV, and serum inorganic phosphate concentration indicated subclinical infection. This subclinical parasitism induced a decrease in body condition scoring and led to persistent decrease in milk yield, ranging from 2.5 to 10% reduction from control values. Changes in fat and protein contents were not detected. In contrast, the consequences of infection were more severe in the 6 goats with the highest milk production at the start of the study. Decrease in milk output ranged between 13.0 to 25.1%, and was associated with decrease in fat content. Comparison of the response to parasitism in the 6 goats with the highest lactation performance and the 6 goats with the lowest performance indicated differences between both subgroups. According to parasitologic and pathologic data, high-producer goats had less resistance and/or resilience to infection associated with more severe consequences on milk production.

The interaction of Trypanosoma congolense and Haemonchus contortus infections in trypanotolerant N'Dama cattle

The interactions between Trypanosoma congolense and Haemonchus contortus infections were studied in N'Dama calves. A total of 38 N'Dama bulls was divided into four groups and each group infected either with H. contortus 1 week after infection with T. congolense or with T. congolense 4 weeks after infection with H. contortus, or with either infection singly. Parasitological (faecal egg counts, parasitaemia), haematological (packed cell volume, white blood cell counts, albumin) and clinical parameters (body weight change, mortality rate) were compared among the various groups. The results showed a reduced prepatent period and a markedly increased pathogenicity of H. contortus infections in animals with a concurrent T. congolense infection. The most harmful combination was a H. contortus infection 1 week after the T. congolense infection which resulted in a progressive and severe anaemia, accompanied by hypoalbuminaemia, increased weight loss and high mortality. The anaemia induced by dual infections showed a low responsiveness to chemotherapy and in several cases supportive treatment did not help recovery. The results also showed that animals with a concurrent T. congolense and H. contortus infection ran a higher risk of succumbing during the infection, and also during 10 weeks following treatment. Although infections with T. congolense alone produced no clinical signs, they were found to significantly reduce the ability of infected animals to mount a normal response to a subsequent H. contortus infection. It was concluded that the increased H. contortus egg excretion observed in animals infected with both parasites might significantly increase the risk of nematode infections and that the reduced prepatent period might necessitate more frequent anthelmintic treatments. These interactions should, therefore, be considered wherever attempts are made to control these two diseases.

Infection of goats with Haemonchus contortus and Trichostrongylus colubriformis: histopathology and pH changes

Two groups of goats were experimentally infected with Haemonchus contortus and Trichostrongylus colubriformis, and killed at various days after infection (DAI). The percentage of worms that established in the abomasum and the small intestine was low. At necropsy, abomasums from infected goats had thickened walls and oedematous folds. At 7 DAI there was an initial infiltration of eosinophils and some neutrophils which tend to increase with age of infection. The mean pH of the abomasum in goats infected with H. contortus was 5.43 (range 5.3-5.7), while that of the control goats was 3.30 (range 2.8-3.7).

Selection of ivermectin-resistant Trichostrongylus colubriformis in lambs

A mixed population of Haemonchus contortus, Teladorsagia circumcincta and Trichostrongylus colubriformis was passed for four generations through lambs. In successive passages and on Day 6 (D6), lambs were dosed subcutaneously with ivermectin at 100, 200, 250 and 225 micrograms kg-1 body weight, respectively. No larvae of H. contortus were recovered after the first passage and following the third drug exposure only T. colubriformis was present. Larvae of the selected strain of T. colubriformis developed to third stage, sheathed larvae in vitro in concentrations of ivermectin that inhibited development of larvae from the original strain of T. colubriformis. A definitive control test was then run with 45 lambs, to compare this selected strain to the original strain. The treatments were 150 micrograms kg-1 subcutaneous (SC) D6, 200 micrograms kg-1 SC D6, 200 micrograms kg-1 intraruminal (IR) D6 and 200 micrograms kg-1 SC D21; all treatments were compared to non-treated controls, selected or original strain as applicable. The D6 IR and D6 SC 150 micrograms kg-1 treatments were greater than 99% effective in both strains, although the D6 SC 200 micrograms kg-1 treatment was 85 and 48% effective in the original and selected strain, respectively. The D21 200 micrograms kg-1 was only 58% effective against the selected strain. There was significant (P less than 0.001) differences between the original and selected strains of T. colubriformis for both fecal egg output and worm counts. The exposure of four generations of immature T. colubriformis to ivermectin selected for partial resistance.

Infection with Ostertagia ostertagi in goats and calves

In order to determine the usefulness of the goat as a model host for Ostertagia ostertagi, a series of experiments was conducted in which young goats and calves were experimentally infected with L3 of calf-source and goat-source isolates. The goat-source isolate was derived from a continuous passage of the bovine parasite in goats. Patent infections resulted in 73 out of 86 inoculated goats (85%). The largest number of patent infections was observed when inoculation consisted of a single dose of goat-source larvae. Percent establishment of infection was generally low in goats inoculated with either larval source. Time taken to achieve patency in goats was frequently within the range normal for cattle infections, but was often extended (21-67 days). With the exception of the generally higher level of establishment of goat- or calf-source isolates in calves and the low frequency of the vulval flap in adult female worms established in goats, little difference was observed in percent establishment or worm population characteristics of the two isolates in goats as based on source of larval inoculum, inoculation course, and age of host at inoculation. Prolonged passage of infection in goats did not result in stabilized isolate more adapted to the goat or less adapted to calves. Fecal egg counts were generally minimal or negative in goats during the first 30 days of infection, but were often increased and not substantially lower than counts in calf infections after 60 or 90 days. Low level egg counts in goats were observed to persist for up to 17 months. During the spring of 2 years, goat kids grazed on a cattle pasture acquired O. ostertagi infections which included adult worms, but a larger number of early L4. The latter were presumed to be inhibited in development just as such inhibition occurs in cattle during spring.

Parasites as stressors: plasma cortisol responses of goats infected with the stomach worm Haemonchus contortus to exogenous corticotropin (ACTH)

Ten male, juvenile pigmy goats of similar age and weight were allocated randomly to two groups. Goats in one group were each inoculated with 20,000 infective larvae of Haemonchus contortus. The other group served as uninfected controls. Goats were housed together, and precautions were taken to avoid the creation of differential, between group, stressogenic circumstances. Body weights, nematode egg production, hematocrits, and clinical signs were monitored over a 61-day period following inoculation of larvae. On Days 59 and 61, adrenal response tests (ART) were conducted by measuring the levels of plasma cortisol before and 2 h after administration of porcine ACTH at the rate of 0.35 I.U. kg-1 body weight on Day 59 and 2.2 I.U. kg-1 on Day 61. Although the infections did not reduce body weights, they were 'heavy' on the basis of egg production, and led to significant reductions in packed erythrocyte volumes. There was no significant difference between the groups of goats in the responses to ART, indicating that the infections did not produce sufficient stress to reduce the ability of the adrenal cortex to respond to exogenous ACTH.

Pathologic changes in lambs with Ostertagia circumcincta infections associated with decreased infectivity of Haemonchus contortus

Two experiments were done to examine the severity and type of abomasal lesions induced by moderate infections of Ostertagia circumcincta in young lambs and to examine the differences in pathologic changes in lambs with monospecific and combined infections of O circumcincta and Haemonchus contortus. Observations included descriptions of gross and microscopic changes in the abomasums, as well as quantitative analysis of the thickness of the mucosa, numbers of mucus-containing cells, and inflammatory cell accumulations. Seemingly, the changes in the abomasal mucosa of lambs inoculated with O circumcincta were mild and included dilated glands, focal accumulations of lymphocytes, and significant (P less than 0.05) numerical increases of mucus-containing cells, eosinophils, and globule leukocytes, and increase of mucosal thickness when compared with those in noninoculated controls. These differences were less pronounced in lambs given anthelmintic treatment to remove O circumcincta. When H contortus infections were superimposed upon O circumcincta infection, the changes were essentially the same as those described for O circumcincta plus a small, but significant (P less than 0.05), numerical increase of globule leukocytes. Abomasal mucosa of lambs inoculated only with H contortus was more roughened and hyperemic than that of lambs with combined infections, but contained few dilated glands and globule leukocytes. Our conclusions were that moderate infection with O circumcincta did not cause severe or permanent damage to the abomasal mucosa and that such infection decreased the severity of the gross lesions produced by H contortus.