Contortus Burdens Research Articles

Efficacy of a Haemonchus contortus vaccine under field conditions in young alpacas

Anthelmintic resistance to Haemonchus contortus creates increasing management challenges with small ruminants and camelids. The commercial vaccine, Barbervax®, contains H11 and H-gal-GP antigens, derived from gut mucosal membrane enzymes of H. contortus involved in digesting blood. Antibody neutralization of these antigens causes failure of H. contortus to digest blood, resulting in parasite death. H11 and H-gal-GP are considered “hidden” antigens, meaning the host immune system does not encounter these proteins under natural infection. Therefore, repeat immunization is required to maintain protective humoral responses. One previous study evaluated the safety of Barbervax® in camelids but the efficacy could not be assessed due to lack of successful infection in the controls. The objective of the current study was to evaluate clinical parameters of anemia, fecal egg counts (FECs), and humoral immune responses of healthy alpacas after immunizing with Barbervax® compared to non-vaccinated controls, all under natural environmental exposure on parasite-laden pastures. A crossover-like study was performed where twenty alpacas (298 ± 66 days of age) were assigned to be initially vaccinated with Barbervax® (n=10) or receive no treatment (n=10). Three doses of Barbervax® were administered at three-week intervals. Feces and blood were collected on Day −10, 0, 21, 43, 64, 85, 106, and 135 to evaluate FECs, packed cell volume (PCV), and antibody titers. Each group was kept on separate adjacent pastures. Tracer sheep (n=2 per study group) were introduced on Day 43 for a three-week period to ensure parasite acquisition. For the crossover-like component on Day 85, the initial non-vaccinated group was administered Barbervax® with dosing repeated on Day 106 and 135. Results indicated all initially vaccinated alpacas produced antibody titers to vaccine antigen that corresponded to lower mean FECs compared to the initially non-vaccinated group. A reduced mean FEC in the vaccinate group was observed 21 days after peak antibody titers. Similarly, when pooled vaccinate antibody titers were noted to wane on Day 106, an increase in FEC was observed at the following time point (Day 135). Conclusions from our study support the use of Barbervax® to reduce H. contortus burdens in alpacas. Furthermore, a less than 30-day lag time between antibody titer and resultant effect in FECs was observed. Additional studies assessing the ability of Barbervax® to reduce H. contortus burdens during subsequent grazing seasons would provide even greater information regarding the use of Barbervax® within alpaca herds to modulate H. contortus infections, refugia, and anthelmintic use.

Early-onset immune response to Haemonchus contortus infection in resistant Santa Ines suckling lambs compared with susceptible Ile de France

Santa Ines, an indigenous Brazilian hair sheep, in comparison with European sheep breeds (e.g., Ile de France), show greater resistance against gastrointestinal nematode (GIN) infections, mainly to Haemonchus contortus. Here we bring novel findings that address some gaps regarding the resistance traits involved in the development of the immunity of young lambs in the first few weeks of life to H. contortus infection. This study aimed to compare parasitological, humoral, and local effector cell-mediated responses, also the histopathological differences in the abomasal mucosa of Santa Ines (SI) and Ile de France (IF) suckling lambs serially infected with H. contortus. Parasitological variables, local and circulating humoral immunity, and local cellular response were evaluated in naïve Santa Ines (n = 14) and Ile de France (n = 12) lambs, randomized into four groups: infected SI (n = 8), non-infected control SI (n = 6), infected IF (n = 8) and non-infected control IF (n = 4). Lambs from infected groups were first infected at 14 days old, and multiple infections were conducted every second day, until the age of 66 days old (52 days post first infection). In comparison with infected Ile de France, infected Santa Ines lambs had lower mean eggs per gram of faeces, lower total H. contortus worm burden, lower females’ length, greater abomasal lymph node weight, greater mucosal thickness in the fundus, and also higher counts of eosinophils in the fundus, and mast cells and globule leukocytes in both fundic and pyloric mucosa of the abomasum. Intrabreed differences were observed into the infected Santa Ines group, with three of the eight lambs classified as highly resistant for displaying H. contortus burden ranging only from 1 to 42 worms. Overall, Santa Ines suckling lambs showed great resistance against H. contortus infection in comparison with Ile de France lambs, being able to mount a robust innate immune response at an early age, and before weaning.

Galectins and collectinis expression are increased in Haemonchus contortus-infected corriedale sheep.

Galectins and collectins are proteins classified in the lectin family that have the ability to recognize molecular patterns associated with pathogens. Studies on cattle have demonstrated high expression of these proteins during infection with gastrointestinal nematodes. The aim of this study was to investigate whether the level of Haemonchus contortus infection would alter the expression of galectins (Gal11 and Gal14) and collectins (SPA and CGN) in sheep. Twelve Corriedale sheep exposed to natural infection with nematodes were divided into two groups: group 1 (G1, n = 7) and group 2 (G2, n = 5), with low and high parasite burdens, respectively, based on fecal egg counts and abomasal parasite counts. The fecal egg counts and abomasal parasite counts were significantly different (p < 0.05) between the groups. Galectin and collectin gene expression was observed in all sheep abomasal samples. However, animals with lower infection levels showed lower expression of the genes Gal14, SPA and CGN (p < 0.05). Expression of lectins was associated with the abomasal H. contortus burden, thus suggesting that these proteins may have a role in controlling of this infection.

Effects of substituting finely ground sorghum for finely ground corn on feed digestion and meat quality in lambs infected with Haemonchus contortus

The objective of this study was to determine the effects of substituting different levels of finely ground sorghum (FGS) for finely ground corn (FGC) on feed digestion and meat quality in lambs infected with Haemonchus contortus. Twenty-four male Ujumqin lambs at 90±6.3 days of age were randomly assigned to receive one of four dietary treatments for 8 weeks prior to slaughter. The four diets contained 0g/kg FGS and 400g/kg FGC (CON), 100g/kg FGS and 300g/kg FGC (LFGS), 200g/kg FGS and 200g/kg FGC (MFGS), and 400g/kg FGS and 0g/kg FGC (HFGS). Before feeding, all lambs were dewormed and experimentally infected with 10,000 H. contortus third stage larvae. After a 28-day adaption to larvae infection, the feeding period was started. Fecal and blood samples were collected and lambs were weighed every 2 weeks. At the end of the feeding period, lambs were slaughtered, meat samples were collected, and the H. contortus burden in the abomasum was determined. The results demonstrated interaction effects between treatment and sampling time on fecal egg count (FEC; P<0.001) and packed cell volume (PCV; P<0.001) in lambs. The FEC decreased and the PCV increased significantly over the feeding period. As the dietary FGS content increased, the H. contortus burden in the abomasum, the abomasal mucosal surface (HBAM), and the abomasal contents (HBAC) decreased linearly (P<0.001). In addition, the ratio of HBAM to HBAC decreased numerically but not linearly (P=0.196) and the ratio of male to female H. contortus increased linearly (P=0.016). Although dry matter intake decreased linearly (P=0.001) as the dietary FGS content increased, no differences in the average daily weight gain and feed conversion ratio were observed between lambs in the FGS substitution groups and CON group. The apparent digestibility of all feed nutrients in the MFGS diet was numerically higher than those in other diets. As the dietary FGS content increased, the dressing percentage of lambs (P<0.001), total heme pigment content (P<0.001), and amount of tannins in meat increased linearly (P<0.001). Diets containing 100–400g/kg FGS did not affect total amino acids levels in meat, although levels of some individual essential amino acids increased as the FGS in diets increased. In conclusion, substitution of 100–400g/kg FGS inclusion for equal amounts of FGC in diets is not only beneficial for protection of lambs against H. contortus infection but also for improving the meat color in lambs by increasing the deposition of antioxidant tannins in the meat.

Effects of supplementation with dietary green tea polyphenols on parasite resistance and acute phase protein response to Haemonchus contortus infection in lambs

The objective of this study was to determine the effects of supplementation with dietary green tea polyphenols (GTPs) on parasite resistance and acute phase protein (APP) response to Haemonchus contortus infection in lambs. Thirty male Ujumqin lambs were randomly assigned to five treatment groups for an 8-week feeding period. Treatments included: (1) uninfected as control, (2) infected but not given GTP (INFGTP0) and (3)–(5) infected and fed 2, 4, or 6g GTP/kg feed (dry matter basis; INFGTP2, INFGTP4, and INFGTP6, respectively). Fecal and blood samples were collected to determine fecal egg count (FEC), packed cell volume (PCV), and APP concentrations. Live weight was measured once every 2 weeks. At the end of the feeding period, lambs were slaughtered to determine the adult H. contortus burden. The results demonstrated interaction effects between treatment and sampling time on the average daily gain (ADG; P=0.0005), FEC (P<0.0001), PCV (P=0.0005), and concentrations of serum amyloid A (SAA), haptoglobin (Hp), lipopolysaccharide binding protein (LBP), and α1-acid glycoprotein (α1AGP) (P<0.0001). From days 0 to 56, the ADG values for all infected lambs were lower than that of uninfected lambs, but the ADG values for all GTP-fed lambs were higher than that of INFGTP0 lambs, especially from days 28 to 42. The FECs of all GTP-fed lambs were higher than those of uninfected lambs but lower than that of INFGTP0 lambs. The PCVs of all infected lambs were lower than those of uninfected lambs, but PCV increased with increasing amounts of GTP supplementation. Furthermore, supplementation with different concentrations of GTP significantly reduced the numbers of adult H. contortus, including both males and females (P<0.0001), and the H. contortus burden in INFGTP6 lambs was reduced to uninfected levels. Overall, the SAA, Hp, LBP, and α1AGP concentrations of all infected lambs were higher than those of uninfected lambs from days 0 to 56. Two peaks in expression were observed from days 0 to 3 and at day 28, and APP concentrations of all GTP-fed lambs were lower than those of INFGTP0 lambs, except for SAA in INFGTP6 lambs. In conclusion, quantitative measurements of APP responses to H. contortus infection provide valuable diagnostic information for monitoring infection progression and treatment responses in lambs. An appropriate dose of dietary GTP supplementation can increase host resistance by reducing H. contortus burden and weight loss and suppressing blood APP expression.

Persistence of the efficacy of copper oxide wire particles against Haemonchus contortus in grazing South African goats

A study was conducted to examine the duration of anthelmintic effect of copper oxide wire particles (COWP) in grazing goats, as data for the persistence of efficacy of COWP in this host species is limited. Forty-eight indigenous male goats were infected naturally by grazing them on Haemonchus contortus-infected pasture. When the faecal egg count (FEC) in the goats was 3179±540 eggs per gram of faeces (mean±standard error), half the animals were treated with 4g COWP (day 0; mean live weight=25.5±0.8kg). Eight treated (COWP) and eight non-treated (CONTROL) goats were removed from the pasture on each of days 7, 28 and 56, maintained for 27 or 29 days in concrete pens and then humanely slaughtered for nematode recovery. Mean liver copper levels were in the high range in the goats removed from pasture at day 7 (treated: 191±19.7ppm; untreated: 120±19.7ppm; P=0.022), but had dropped to normal levels at days 28 and 56. The mean H. contortus burdens of the treated versus the non-treated goats were, respectively, 184±48 and 645±152 for the goats removed from pasture at day 7 (71% reduction; P=0.004), 207±42 and 331±156 at day 28 (37% reduction; P=0.945) and 336±89 and 225±53 at day 56 (−49% reduction; P=0.665). Weekly monitoring of FECs after treatment until slaughter indicated that the COWP-treated goats had lower FECs than the controls, the treatment main effect being significant at days 7, 28 and 56 (P<0.01). The day main effect and the treatment×day interaction were only significant for the goats removed from pasture at day 28 (P≤0.001). Packed cell volumes increased during the course of the experiment (day, P<0.001), but the treatment main effect was significant only for the goats removed from pasture at day 28 (CONTROL 28 d, 28.65±0.52%<COWP 28 d, 31.31±0.52%; P<0.001). No differences in live weight between groups were considered to be of any practical significance. The study indicated that persistence of efficacy of COWP is limited in goats, extending at most to 28 days after treatment. However, repeated COWP administration at three-month intervals may be safe, given that liver copper levels return to normal two to three months after COWP treatment.

Parasitism by Oestrus ovis: Influence of sheep breed and nematode infections

Previous studies showed that Santa Ines (SI) hair sheep were more resistant to gastrointestinal nematode infections (GIN) than Ile de France (IF) sheep. The present experiment aimed to evaluate if that reported resistance difference against GIN also occurred against Oestrus ovis infestation and also to evaluate the influence of O. ovis infestation on the gastrointestinal nematodes (GIN) infections. SI (n=12) and IF (n=12) young male lambs were weaned at 2 months of age and moved to a paddock (0.3ha) with Brachiaria decumbens grass, where they also received concentrate ration. The animals were kept together during the experimental period (September to early December 2009). Fecal and blood samples were taken from all animals every 2 weeks and body weight and nasal discharge score (oestrosis clinic signs) were recorded on the same occasion. In early December 2009, all lambs were sacrificed and O. ovis larvae and GIN were recovered, counted and identified according to the larval stage. All animals were infested by different larval instars of O. ovis without any statistical difference between breeds (P>0.05). The SI lambs had an average of 24.8 larvae, and the intensity of infection ranged between 14 and 39 larvae, while the IF lambs showed an average of 23.5 larvae with the minimum and maximum from 11 to 36 larvae, respectively. SI lambs presented the lowest nematode fecal egg counts (FECs) and the lowest mean numbers of Haemonchus contortus, Trichostrongylus colubriformis and Strongyloides papillosus, however, there was no significant differences between group means (P>0.05). Inverse relationship between numbers of O. ovis larvae and gastrointestinal nematodes was observed in both breeds. SI sheep showed a significant increase in blood eosinophils and total IgE serum levels and these variables were negatively correlated with nematode FEC. A negative correlation was observed between total IgE serum level and H. contortus burden in both breeds. In conclusion, there was no breed difference regarding O. ovis infestation and in each breed, animals with more nasal bot fly larvae tended to display smaller worm burden.

A stochastic model accommodating the FAMACHA © system for estimating worm burdens and associated risk factors in sheep naturally infected with Haemonchus contortus

A previously developed multiple regression algorithm was used as the basis of a stochastic model to simulate worm burdens in sheep naturally infected with Haemonchus contortus over five consecutive Haemonchus seasons (November to January/February) on a farm in the summer rainfall region in South Africa, although only one season is discussed. The algorithm associates haemoglobin levels with worm counts in individual animals. Variables were represented by distributions based on FAMACHA © scores and body weights of sheep, and Monte Carlo sampling was used to simulate worm burdens. Under conditions of high disease risk, defined as the sampling event during the worm season with the lowest relative mean haemoglobin level for a class of sheep, the model provided a distribution function for mean class H. contortus burdens and the probability of these occurring. A mean H. contortus burden for ewes ( n = 130 per sample) of approximately 1000 (range 51–28,768) and 2933 (range 78–44,175) for rams ( n = 120 per sample) was predicted under these conditions. At the beginning of the worm season when the risk of disease was lowest (i.e. when both classes had their highest estimated mean haemoglobin levels), a mean worm burden of 525 (range 39–4910) for ewes and 651 (range 37–17,260) for rams was predicted. Model indications were that despite being selectively drenched according to FAMACHA © evaluation, 72% of the ewes would maintain their mean worm burden below an arbitrarily selected threshold of 1000 even when risk of disease was at its highest. In contrast, far fewer rams (27%) remained below this threshold, especially towards the end of the worm season. The model was most sensitive to changes in haemoglobin value, and thus by extrapolation, the haematocrit, which is used as the gold standard for validating the FAMACHA © system. The mean class haemoglobin level at which there was a 50% probability of worm burdens being ≤1000 worms was 7.05 g/dl in ewes and 7.92 g/dl in rams.

The effect of long-term feeding of fresh and ensiled cassava (Manihot esculenta) foliage on gastrointestinal nematode infections in goats

The benefit of long-term feeding of fresh or ensiled cassava foliage on gastrointestinal parasite in goats was evaluated. Eighteen male goats (15.15 +/- 2.83 kg and between 4-6 months) were randomly allocated into three treatments supplemented with 200 g of wheat bran head(-1) day(-1). All groups were fed ad-libitum on either grass (CO), fresh cassava (CaF) or ensiled cassava foliage (CaS). At the beginning of the trial, each goat was inoculated with 3000 L3 containing approximately 50% Haemonchus contortus. Individual LWt, FEC and PCV were measured at weekly intervals for 10 weeks. At the termination of the experiment all goats were slaughtered for worm recovery and enumeration. The goats in CaF and CaS had similar weight gains while those in CO lost weight (p < 0.05) through the trial. FEC in CaF and CaS were lower (p < 0.05) than CO during the patency of parasite infections, but there was no difference between CaF and CaS goats. PCV of all groups decreased from above 30% to around 25% at the end of the trial. The compositions of established worm burdens were mainly H. contortus (19-40%) and Trichostrongylus colubriformis (55-76%). TWB did not differ among the groups, however, CaS significantly reduced H. contortus burdens, as compared to CaF and CO (p < or = 0.005). Thus, ensiled cassava foliage reduced the H. contortus population while the fresh foliage only reduced worm fecundity.

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. 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. 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. 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. 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.

Impact of condensed tannins from tropical forages on Haemonchus contortus burdens in Mongolian gerbils ( Meriones unguiculatus) and Pelibuey lambs

Two experiments were conducted to assess effects of condensed tannins (CT) from tropical forage crops on Haemonchus contortus burdens, feed intakes and body weights of experimentally infected Mongolian gerbils ( Meriones unguiculatus) and Pelibuey lambs. Forty weaned gerbils were assigned to 10 treatments with four replicates. Gerbils of treatments 2–10 were orally fed 1000 exsheathed larvae and two levels (7.5 and 15 mg/kg body weight, BW) of purified CT from Arachis pintoi, Leucaena leucocephala, Manihot esculenta or Albendazol. Nine days after oral infection, gerbils were killed and the number of larvae in the stomach was determined. There were effects on stomach larvae counts (P<0.05) with the highest average count (135 larvae) occurring in the untreated control (P<0.05) and the L 4 larvae ( i.e., developing in intestinal submucosa phase) was lowest (18, 17 and 16 larvae) for gerbils receiving extracts from L. leucocephala, A. pintoi and M. esculenta, respectively. The uninfected control, and the Albendazol-treated groups, had practically no larvae. In the second experiment, fifty-two 45-day old Pelibuey lambs were randomly assigned to nine treatments: an uninfected control, or fed either Medicago sativa and/or three tannin containing forages ( i.e., A. pintoi, Gliricidia sepium, M. esculenta), and an Albendazol-treated group. Treatments 2–9 were artificially infected with 5000 exsheathed L 3 larvae ( i.e., infective phase). Lambs were killed 36 days after infection and the number of parasites in the abomasum was quantified. In lambs on the test diets, the number of larvae were decreased (P<0.05) by up to 70% compared to the untreated control (3801 larvae). Lambs consumed from 0.5 to 4.9 g/kg BW/day of CT. In neither of the experiment was feed intake or BW adversely affected by administration of CT.

Consequences of the unusually warm and dry summer of 2003 in The Netherlands: Poor development of free living stages, normal survival of infective larvae and long survival of adult gastrointestinal nematodes of sheep

During 2003 a grazing study was performed at Utrecht University to evaluate evasive grazing and application of Duddingtonia flagrans for the control of parasitic gastroenteritis in sheep. However, the summer of 2003 (June–August) was unusually warm and dry. As a result the patterns of gastrointestinal nematode infections deviated from those observed in more average years. The proportion of eggs that developed to infective larvae was far lower than normal in July–August. On the other hand, survival of larvae that had developed before the middle of July was not affected compared to other years. In fact, severe haemonchosis was observed in (tracer) lambs grazed at the end of July on pastures that had been contaminated from 26-05 to16-06 and from 16-06 to 07-07. Moreover, tracer lambs grazing in September on some of these plots still acquired large Haemonchus contortus burdens. Over 60% of H. contortus that had established before the middle of July appeared to be able to survive until October in the virtual absence of re-infection. That may have consequences for the application of evasive grazing as a control option in that suppression of adult burdens might still be necessary, through a limited use of anthelmintics or through alternative deworming strategies.

Nematode burdens and cellular responses in the abomasal mucosa and blood of Florida Native, Rambouillet and crossbreed lambs

This experiment was carried out to compare the worm burden and cellular responses in the abomasal mucosa and blood of Florida Native and Rambouillet lambs and also in animals produced by crosses of these two breeds (generations F1 and F2). Animals were exposed to infection by gastrointestinal nematodes on three different occasions. The first infection was natural, occurring while they were suckling lambs. After weaning, they were kept indoors for 53 days and then were allowed to graze a contaminated pasture for 50 days for a second natural infection. The third infection was an artificial challenge with 6000 Haemonchus contortus infective larvae. The highest mean fecal egg counts (FEC) values were found in Rambouillet lambs followed in decreasing order by F1, F2 and Florida Native lambs. Throughout the trial, most of the high mean packed cell volumes and plasma protein levels were recorded in the F2 lambs; in contrast, most of the low values were found in the Rambouillet lambs. During the natural infection period, the highest percentages of larvae in the fecal cultures of the lambs were Haemonchus. However, high percentages of Trichostrongylus larvae were found particularly in Florida Native lambs. The mean number of blood eosinophils increased after the artificial challenge, reached a peak 21 days after infection and then declined. The highest and lowest blood eosinophil means were recorded in F2 and Florida Native lambs, respectively. The H. contortus burden was significantly higher in Rambouillet and in F1 lambs than in Florida Native and F2 lambs ( p < 0.05), while no significant differences were recorded among eosinophil, mast cell and globule leucocyte counts in the abomasal mucosa ( p > 0.05). The highest correlation coefficient recorded at the end of this study was between FEC and worm burden ( r = 0.7). These two parameters showed a moderate negative correlation with PCV, plasma protein and mast cell counts in the abomasal mucosa. The results obtained in this study indicate that crossbreeding Florida Native and Rambouillet sheep can be a rapid way to combine and improve the characteristics of these two breeds. The parasitological results were promising, however, more studies will be necessary to verify the impact of crossbreeding in other traits.

Interaction of parasitism and nutrition in goats: effects on haematological parameters, correlations, and other statistical associations

Weaned wether goats ( n = 144) approximately 6 months of age were placed in a 2 × 3 factorial experiment to test the effects and interaction of two levels of nutrition (growth + maintenance, NUT1; and twice growth + maintenance, NUT2) and three levels of Haemonchus contortus burden (0, 500, and 2000 larvae administered every 2 weeks; W0, W500, and W2000, respectively) on packed cell volume, red blood cell count, total serum protein and leukocytes. The statistical analysis revealed clear and proportionate differences among levels of infection for all variables. A significant ( P < 0.05) nutritional effect was also found associated with all the variables except leukocytes. Nutrition by worm load interactions were found for packed cell volume and leukocytes. The neutrophil/lymphocyte ratio was higher in the NUT1-infected animals, leading to the nutrition by worm load interaction for leukocyte . An analysis for the different leukocyte types revealed significant ( P < 0.05) differences among infection levels for lymphocytes, while nutrition level was found to be a significant effect for basophil count and immature white cells. Several significant correlations were observed between pairs of variables. Faecal egg output could be predicted from actual worm count in three of the four necrospy periods. The clear differences observed for blood parameters were not present in production traits, suggesting that physiological thresholds may play an important role in framing the metabolic activity of biological organisms. Total serum protein was the best indicator of these effects on production parameters.

Interaction of parasitism and nutrition and their effects on production and clinical parameters in goats

Weaned wether goats ( n = 144) approximately 6 months of age were placed in a 2 × 3 factorial design experiment for 5 months to test the main effects and interaction of two levels of nutrition (growth+maintenance, NUT1; twice growth+maintenance, NUT2) and three levels of Haemonchus contortus burden (0, 500 and 2000 larvae administered every 2 weeks: W0, W500 and W2000, respectively) on weight, feed intake, level of infection and packed cell volume (PCV). The rationale for the experimental design was based on the lack of information concerning the interaction between nutritional status and worm burden. Results indicated significant effects of worm burden levels on PCV, faecal egg contents (eggs per gram of feces (EPG)), actual worm numbers, feed intake and efficiency of feed utilization. Nutrition×worm burden interactions were also significant for PCV and EPG. However, the differences detected for PCV and actual worm numbers did not translate into large or consistent differences in body weight. Goats on NUT2, after an initial period, showed little difference in body weight, irrespective of worm burden. Within the NUT1 level, W0 kids weighed more than W500 or W2000 kids throughout the study. Although not statistically significant, this constitutes a trend towards an interaction between nutrition and worm burden. In both nutrition levels, there were no body weight differences between W500 and W2000 until the last 14 days. Feed intake was depressed in the first 3 months of the experiment for infected animals, but was subsequently followed by a compensatory reaction. Lower establishment rates, based on actual worm counts, were observed for the higher infection level, but in both infection levels establishment rates tended to decrease with time. Nutrition was found to be more important to counteract the consequences of a parasitic infection than to counteract the establishment of that same infection.

The periparturient rise in fecal egg counts in three strains of Florida native ewes and its value in predicting resistance of lambs to Haemonchus contortus

The periparturient rise in fecal egg counts in three strains of Florida Native ewes and its value in predicting resistance of lambs to Haemonchus contortus. International Journal for Parasitology 16: 185–189. Significant ( P < 0.05) differences in the magnitude of the periparturient rise in fecal egg counts (PPR) occurred in ewes of three strains of Florida Native sheep. Non-lambing ewes ( n = 12) and lactating University strain ewes ( n = 31), a strain selected over a 26-year period for parasite resistance by survival at pasture without anthelmintic treatment, had lower fecal egg counts than ewes of either Maxcy strain ( n= 17), a commercial strain treated regularly with anthelmintics, or Backlinie strain ( n = 16), a strain of Florida Native sheep that had some crossbreeding to Hampshire and Suffolk in their genotype and were regularly treated with anthelmintics. Whereas both Maxcy and Backlinie ewes showed a pronounced PPR, none occurred in non-lambing ewes ( n=12) and the slight rise in fecal egg counts observed in University ewes was not significantly different from that of the non-lambing ewes. Backlinie ewes having twin lambs ( n = 5) had a higher PPR than Backlinie ewes with single lambs ( n = 11) or Maxcy ewes with single lambs ( n = 15), but all three groups had higher PPRs than University ewes with single lambs ( n = 27). No differences occurred in fecal egg counts of non-lambing ewes regardless of strain. Six weeks after weaning fecal egg counts of all ewes were uniformly low regardless of strain or prior lactation status. Ram lambs born to these ewes showed no significant strain differences in Haemonchus contortus burdens after experimental infection, deworming with levamisole and reinfection, although University lambs ( n= 13) had lowest mean worm burdens at necropsy (2437) followed by Maxcy lambs ( n= 12, mean =3106) and Backlinie lambs ( n= 13, mean =3670). There was no significant correlation between worm burdens in these lambs and the magnitude of the PPR in their dams. Eight to 16 weeks after turn out to a common parasite-infested pasture ewe lambs ( n = 13) born to University ewes had lower fecal egg counts than similar ewe lambs ( n=8) born to Backlinie ewes. Prior to this time differences were not significant and egg counts were generally low. The magnitude of the PPR in their dams was not significantly correlated with fecal egg counts or PCVs of individual ewe lambs.

Regulation of Haemonchus contortus populations in sheep exposed to continuous infection

Groups of sheep were infected three times weekly for 15 weeks with infective larvae of Haemonchus contortus at four rates ranging from 600 to 4800 larvae per week. At 3-weekly intervals, sheep from each group were killed for total worm counts after receiving a dose of radiolabelled larvae which enabled a direct measurement of establishment of incoming larvae during the continuing infection. Peak H. contortus burdens were reached between 6 and 9 weeks of infection, and were related to infection rate. In the groups receiving 2400 and 4800 larvae per week, worm numbers then declined rapidly and by the end of the experiment were lower than those in the groups given 600 or 1200 larvae per week. Establishment of incoming larvae was not influenced by infection rate, and declined from 45% in the first 4 weeks of infection to insignificant levels during the final 6 weeks. The proportion of incoming larvae arrested in their development increased as the infection progressed. It was concluded that H. contortus numbers were regulated by development of resistance to infection and by a loss of established worms which was related to the current rate of larval intake, and to the host's previous experience of infection.

Resistance of nonlambing exotic and domestic ewes to naturally acquired gastrointestinal nematodes

No breed differences in Haemonchus contortus burdens were found when nonlacfating exotic (St. Croix and Barbados Blackbelly), domestic (Finn-Dorset × Rambouillet) and 1 2 exotic- 1 2 domestic ewes grazed fall pasture, but all ewes had significantly ( p < 0.05) lower worm burdens at necropsy than tracer lambs grazing the same pasture. Florida Native ewes grazing the same pasture showed significantly ( p < 0.05) less packed cell volume (PCV) decrease and significantly ( p < 0.05) lower fecal egg counts than the other ewe breeds but were not available for necropsy. Tracer lambs had a significantly ( p < 0.05) greater PCV decrease and significantly ( p < 0.05) higher fecal egg counts than ewes. The results of this study suggest that breed differences in the periparturient rise in fecal egg counts of exotic and domestic ewes observed in an earlier study may have been caused by breed differences in the periparturient relaxation of immunity rather than breed differences in the ability to acquire immunity to worms.

Effect of anthelmintic treatment of ewes at parturition and lambs at weaning on the build up of Haemonchus contortus populations in lambs in the Netherlands

In two groups of ewes and lambs, grazing pastures which were used respectively by calves and sheep in the previous year, infection with Haemonchus contortus was virtually prevented by a single treatment of the ewes with fenbendazole before turning out. In another group, grazing a pasture which was not grazed in the previous year, a delay of approximately eight weeks in the build up of high H contortus burdens in lambs was obtained by this treatment, compared with a group of untreated ewes grazing similar pasture. In two groups of lambs treated with fenbendazole at weaning and subsequently grazed on pastures which could be considered free or almost free of H contortus respectively, the build up of high pasture infectivity levels for H contortus also took at least six to eight weeks. It is suggested that treatment of ewes at parturition and lambs at weaning might delay the build up of high H contortus burdens in the lambs by less than the six to eight weeks observed in these experiments when such treatment is less than 100 per cent effective.

Quantitative studies of ovine haemonchosis. 2. Relationship between total worm counts of Haemonchus contortus, haemoglobin values and bodyweight

The relationships between Haemonchus contortus burdens, haemoglobin levels and bodyweight, were examined in 50 commercial Merino sheep, 9–18 months of age, in south-east Queensland where haemonchosis was endemic. Worm counts and haemoglobin levels were predictable ( P<0.001, r=0.68) from the equations log worm count = B.wtt × 0.06942 + log worm count × (−2.18896) + 12.51557. Bodyweight was not predictable from either worm counts or haemoglobin levels. Although bodyweight was represented in both equations, it was only a small and insignificant contributor. When haemoglobin levels became moderately depressed (<10.5 g%) or severly depressed (<8.0 g%), then the number of worms associated with these haemoglobin levels varied with the bodyweight of the sheep. For sheep up to 20 kg, 10.5 g% Hb was associated with 112 worms and 8 g% with 355 worms. However, 355 worms caused only moderate depression of Hb levels in sheep over 50 kg, and 1259 worms were required to cause severe depression (<8.0 g%) in sheep over 50 kg. Three sheep were found to be severely anaemic in the presence of less than 100 worms. It was postulated that additional factors of time and nutrition may have affected these sheep. The sheep were of low bodyweight, in poor condition (low fat score) and were subject to high stocking rates on long grass pastures and high rainfall in autumn. Other internal parasite species present were Nematodirus spp. and Trichostrongylus spp. However, their numbers were low (57 and 218 worms, respectively) and did not contribute to anaemia. The correlation between H. contortus and Nematodirus spp. was found to be negative but non-significant ( r = −0.26, P<0.01), while the correlation between H. contortus and Trichostrongylus spp. was positive and significant ( r = 0.38, P<0.01).