Appetite, digestive efficiency, feed utilization and carcass evaluation of housed calves naturally infected with gastrointestinal nematodes

The progress of two groups of 10 calves, which had previously been exposed to trichostrongyle infections by grazing infected pastures, was monitored from housing in October to slaughter the following April. Each of the animals of one group had received a morantel sustained release bolus, the other control group remained untreated. The high faecal egg counts and serum pepsinogen concentrations, together with the clinical signs of ostertagiosis observed in the controls in October, persisted during the first month of housing but improved thereafter. From late November onwards, no difference in feed intake and digestive efficiency was observed between the groups. The control calves exhibited a significantly greater feed conversion efficiency over the period February-April, (7.5 vs. 12.3 kg feed kg-1 liveweight gain, P less than 0.001). This reduced the liveweight advantage of the MSRB group over the controls at housing to 25 kg.     

Effects of the fenbendazole SR bolus on Trichostrongylus infections in young calves during two consecutive grazing periods

A two-year study was conducted in northern Germany to investigate the effects of the fenbendazole slow release (SR) bolus on trichostrongyle infections in cattle. Two groups of dairy replacement calves were either given a bolus at their first turncut on pasture or treated with fenbendazole suspension twice in mid-summer and at housing. Bolus-treated and control animals were set stocked on separate pastures during their first grazing season (26 weeks) and grazed together during the second year (24 weeks). During the first season the bolus prevented substantially the output of strongyle eggs for more than four months resulting in a lower infection risk in late summer and autumn as compared to the control group. The plasma pepsinogen concentrations remained low in the bolus-treated cattle during their first grazing period but rose in the controls soon after turnout which indicated increasing trichostrongyle-caused damages of the abomasal mucosa. During the following housing period and the second grazing season the bolus-treated animals showed higher egg counts than the controls. No clinical sign of parasitic gastroenteritis and no patent lungworm infections were observed during the study. The bolus-treated cattle performed better than the control animals during both grazing seasons although the control group had compensated temporarily the group difference in weight gains during the housing period. In conclusion, the use of the fenbendazole SR bolus may impair the development of immunity to trichostrongyle infections to some extent but, under the present conditions, this does not seem of clinical or economic importance.     

Observations on parasitic gastroenteritis and parasitic bronchitis in calves over two grazing seasons

Two outbreaks of parasitic gastroenteritis were observed in a group of 10 first-season grazing calves, one in mid-July and one in mid-September. In both cases emergency anthelmintic treatment was needed to prevent further damage. Severe clinical signs were observed together with high faecal egg counts and high serum pepsinogen and gastrin concentrations. Low total protein and albumin concentrations were also observed, especially during the second outbreak. The ostertagia antibody levels followed a similar pattern to the serum pepsinogen and gastrin concentrations. At the end of the housing period a mild type II ostertagiasis was observed. In the second grazing season the heifers did not show any signs of parasitic gastroenteritis, but there was a serious outbreak of husk which required treatment.     

Effect of a single injection of doramectin on gastrointestinal nematode infections of sheep grazing on alpine pastures.]

The persistent effect of doramectin injectable against gastrointestinal nematodes was investigated in a controlled field study with 70 sheep kept on alpine pastures in Switzerland. After grazing on home pastures for four weeks 50 lambs and 20 ewes were allocated to two equal groups according to age and body weight. At turnout to alpine pasture in June doramectin (0.3 mg/kg) was administered by intramuscular injection to 25 lambs and 10 ewes (Group D), whereas control sheep (Group K) remained untreated. Animals of both groups were kept on separate pastures (altitude: 1100 m) and were rotated between three paddocks during a total grazing period of 13 weeks. After doramectin treatment faecal examinations of Group D sheep showed a marked reduction of the trichostrongyle egg output which remained close to zero for eight weeks. During this period serum pepsinogen levels did not indicate the presence of a substantial immature worm burden in the abomasal mucosa. In the last five weeks of the alpine grazing period the trichostrongyle egg counts increased markedly in the lambs of Group D. Lambs of the control group developed moderate-to-high Haemonchus-infections, and eight animals of this group had to be treated with anthelmintics. Lambs of Group D had gained significantly (P < 0.05) more weight eight weeks after turnout whereas the mean bodyweight stagnated during the last five weeks of the grazing period. The results indicate, that the single administration of 0.3 mg/kg doramectin to lambs and ewes provided good protection against severe infections with gastrointestinal nematodes for a period of approximately eight weeks.     

The effect of rotational grazing for periods of one or two weeks on the build‐up of lungworm and gastrointestinal nematode infections in calves

Summary

An experiment was carried out with three groups of grazing calves and one housed control group to study the effect of rotational grazing for periods of 1 and 2 weeks on the build up of lungworm and gastro‐intestinal nematode infections respectively. The experiment demonstrated that rotational grazing for periods of I week on six plots prevented the build‐up of heavy lungworm infections. A buildup of heavier lungworm infections was observed in a group that was rotationally grazed for periods of 2 weeks on three plots and a group which remained on one plot throughout the grazing season; there was no difference between these two groups. In all three situations, there was an adequate development of immunity against D. viviparus, as measured by worm recovery after challenge infection at the end of the experiment in comparison with worm recovery of the similarly challenged control group. Neither rotational grazing scheme protected the calves against gastrointestinal helminthiasis, because tracer calves, which grazed for 4 days only in August or October, acquired infections which would have resulted in severe illness or even death if necropsy had been postponed for a week.     

Feed intake of grazing calves exposed to trichostrongyle infection and treated with the morantel sustained release bolus

Herbage intake was measured in two groups of 20 first-year grazing cattle. The animals in one group each received a morantel sustained release bolus at turnout to control nematode parasitism and the animals in the other group remained untreated. The latter group showed a mean peak faecal egg count of 655 eggs per gram (e.p.g.) in October associated with high serum pepsinogen concentration and clinical signs of ostertagiasis, compared with a peak of 119 e.p.g. in the treated group which remained in good health. In September the daily voluntary feed intake of the untreated animals was significantly depressed (94 g kg-1 body weight vs. 77 g kg-1 P less than 0.001), but no difference in digestive efficiency was recorded between the two groups. This difference in feed intake was associated with a 47 kg mean live weight advantage of the treated animals at housing.     

Immunity of ivermectin treated cattle to challenge from helminth parasites in the following season

Two groups of yearling cattle which had been treated with ivermectin either three and eight, or three, eight and 13 weeks after turn out to trichostrongyle contaminated pasture in their first grazing season were exposed in the following season to natural challenge with helminth parasites. To assess their immunity to this challenge each group shared a pasture with parasite naive first season calves. No anthelmintic treatments were administered at any time during the year. Throughout the grazing period the yearlings showed normal respiratory rates, negative faecal lungworm larval counts, and, relative to the calves, low faecal trichostrongyle egg counts. All the first season calves developed patent lungworm infections and on one occasion the mean respiratory rates of each group of calves were significantly greater than those of the yearling cattle. At the end of the grazing period, from early May until late September or October 1986, the cattle were removed from pasture and together with parasite naive controls challenged with either 10 or 22 third stage larvae of Dictyocaulus viviparus/kg bodyweight and necropsied between 18 and 23 days later. Although the experimental challenge resulted in relatively heavy lungworm infection of the naive controls, none of the yearlings and only three of the 11 calves which had been at pasture were found to be infected. However, large numbers of arrested fourth stage larvae of Ostertagia ostertagi were present in all the naturally infected yearlings and calves.     

Dictyocaulus viviparus in calves: effect of rotational grazing on the development of infections.

A study was made of the possibility of reducing lungworm infections in young grazing calves by rotational grazing for weekly periods on six paddocks. For this purpose three groups of four calves each were grazed on separate pastures in 1989, whereas a fourth group served as a permanently housed control group. Two groups of calves were infected experimentally with six doses of 10 larvae of Dictyocaulus viviparus during the first 3 weeks on pasture. In the third group, low natural infections with overwintered larvae occurred. One of the experimentally infected groups was rotationally grazed for weekly periods on six small plots while both other groups were set-stocked. Faecal larval counts and worm counts in tracer calves demonstrated lower lungworm infections in the rotationally grazed group than in both set-stocked groups. However, the numbers of worms found after challenge infection and subsequent necropsy were relatively high in the rotationally grazed group, indicating that development of immunity was less than in both other groups. Owing to the dry weather conditions in the summer of 1989, no serious clinical signs of husk developed in any of the three groups. These dry conditions, however, did not prevent the build-up of heavy pasture infectivity with gastrointestinal nematodes resulting in heavy worm burdens and serious clinical signs in tracer calves grazing for 4 days in August and September-October, respectively. This implies that rotational grazing did not have a clear effect on build-up of gastrointestinal nematode infections.     

Effect of strategic treatments with invermectin on parasitism of set-stocked calves exposed to natural trichostrongyle infection in Lithuania

The effect of strategic treatments with ivermectin in first-season calves exposed to trichostrongyle nematodes on naturally contaminated pasture was studied. Twenty first season heifer calves were divided into 2 groups, according to live weight, and on 22nd May each group was turned out onto a 1 hectare pasture. Group A (Plot A) was treated with ivermectin at weeks 3, 8 and 13 after turn out, while group B (Plot B) served as an untreated control group. The study showed that control calves exhibited increase in trichostrongyle egg counts in August, while treated calves were excreting low numbers of trichostrongyle eggs. Pasture larval counts on Plot B (control animals) were low during the first part of the grazing season, followed by a steep rise towards the end of July. In contrast, the numbers of infective larvae recovered from Plot A remained low throughout the season. Both groups showed comparable weight gains from May up to the middle of July. However, from then on, Group B (controls) had lower weight gains than ivermectin treated Group A. From the end of July onwards, most untreated calves (Group B) showed clinical signs of parasitic gastroenteritis. It can be concluded that the strategical ivermectin treatments were successful, and faecal egg counts, pepsinogen levels and herbage larval counts clearly demonstrated that this was accomplished through suppression of pasture contamination with nematode eggs and subsequent reduction of pasture infectivity.     

Bovine ostertagiasis: a changing epidemiological pattern?

An unusual epidemiological pattern in bovine ostertagiasis is described in which clinical ostertagiasis occurred in calves grazed on a silage aftermath from late July. The calves were treated with the anthelmintic levamisole prior to grazing the aftermath and the latter had not been grazed since the previous autumn. Analysis of the herbage larval counts suggests that delayed emergence of overwintered Ostertagia ostertagi L3 from the soil was the most likely source of the infection.     

Grazing‐induced changes in muscle microRNA‐206 and ‐208b expression in association with myogenic gene expression in cattle

To investigate the roles of microRNAs (miRNAs) in muscle type conversion, the effects of 4 months of grazing on the expression levels of miRNAs and mRNAs associated with skeletal muscle development were analyzed by quantitative RT‐PCR using the Biceps femoris muscle of Japanese Shorthorn cattle. After 4 months of grazing, the expression of muscle fiber type‐associated miR‐208b was higher in the grazed cattle than in the housed. In concordance with the pattern in miR‐208b expression, the expression of MyoD, a myogenic regulatory factor associated with the shifting of muscle property to the fast type, was lower in the grazed cattle after 4 months of grazing than in the housed cattle. In addition, the expression of MyHC‐2x (a fast type) was higher in the housed cattle than in the grazed, after 4 months of grazing. During the grazing period, miR‐206 expression decreased in the housed cattle, whereas expression in the grazed cattle did not change, but rather remained higher than that of the housed cattle even at 3 months after the grazing ended. These miRNAs including miR‐206 persisting with muscles of grazed cattle may be associated with regulation of muscle gene expression during skeletal muscle adaptation to grazing.     

Anthelmintics and control

Anthelmintic control of Ostertagia ostertagi in cattle presents some special problems because the arrested larval stage (hypobiotic EL4) tolerates all of the older anthelmintics. The only anthelmintics on the North American market that are effective against this stage as well as the adult and developing stages are ivermectin and fenbendazole. In addition to these, the newer broad-spectrum benzimidazoles and probenzimidazoles, albendazole, febantel, netobimin and oxfendazole, are effective and available in other countries. These anthelmintics can be used for prophylaxis of Type II ostertagiasis. The older anthelmintics, levamisole, morantel tartrate, thiabendazole, coumaphos, haloxon and phenothiazine, are effective against the adults and to some extent the developing stages of O. ostertagi so that they can be used to treat Type I ostertagiasis. They can also be used to prevent incoming larvae from establishing if they are administered continuously over a long period of time. This is possible with long term in-feed administration or by the use of the morantel slow release bolus. In cooler temperature regions, where cattle are housed over the winter, this bolus is given at turnout to remove any parasites in the animals and to kill incoming larvae for 60-90 days. This can prevent the build up of significant infective larvae on pasture so that very few arrested L4 larvae accumulate in the summer/autumn, effectively preventing Type II ostertagiasis from occurring later. The use of ivermectin and the newer benzimidazoles in intermittent or slow release devices should prove highly effective in the control of Type I and II ostertagiasis, as well as of subclinical ostertagiasis. To achieve maximum economic benefit, the use of anthelmintics should be based on sound epidemiological considerations, so that stock are not rapidly reinfected after treatment.     

Antibody responses to natural Dictyocaulus viviparus exposure in first year grazing cattle using vaccination or different kinds of anthelmintic treatment.

In two field trials vaccination or different anthelmintic treatments against Dictyocaulus viviparus infections were used in 6 groups of first year grazing cattle. The antibody response to lungworm infections was determined using an ELISA. Cattle treated once or repeatedly at long intervals with levamisole developed clinical signs of dictyocaulosis. The detection of anti-D. viviparus antibodies at the end of the grazing season confirmed that these anthelmintic treatments were not able to prevent lungworm infections. Cattle that received strategically administered treatments with ivermectin remained clinically healthy. These cattle were seronegative until the end of the trial which proved the efficacy of the strategic control. Cattle that received an intraruminal slow release bolus did not develop clinical disease. However one animal shed lungworm larvae and the herd became seropositive at the end of the grazing season indicating a history of infection. The serological examination of a cattle herd at the end of the grazing season is able to demonstrate a history of lungworm infections and to determine the efficacy of anthelmintic control measures.     

Control of Ostertagia ostertagi infections in Australia

The control of Ostertagia ostertagi infections in Australia is aimed specifically at young cattle in their first and second year of grazing after weaning. Mature breeding stock are not routinely treated. The recommended strategy is preventive, using an integrated approach of timed anthelmintic treatments in relation to the epidemiology of ostertagiasis in different environments. Best results are obtained when treatments, given at weaning and 6 months later, are combined with a move to 'safe' pastures which have not been grazed by cattle for the previous 6 months. Good results are also obtained in the winter rainfall regions when set-stocked cattle are treated before and during autumn to prevent contamination of pastures at this time. More complicated grazing management, involving the spelling of pastures during autumn and winter, combined with anthelmintic treatments, is needed in some summer rainfall regions where weather conditions are especially favourable for the development and survival of the free-living stages of O. ostertagi.     

A Study on the Effects of Tactical Drenchings with a Benzimidazole against Ostertagiasis in Calves

In the present study tactical fenbendazole treatments against ostertagiasis in calves were given at short intervals towards the end of the grazing season. This prevented clinical disease and had moderate effects on parasitic loads in animals that stayed on the same pasture throughout the season. The feasibility of tactical treatments is discussed in relation to various strategical control measures.     

Immunity of calves treated with an oxfendazole pulse release bolus to challenge with Dictyocaulus viviparus

Two experiments were performed to study the effect of an oxfendazole pulse release intraruminal device (OPRB) on the development of lungworm infection and immunity in calves. Infections were monitored in OPRB-treated and control calves by faecal and pastural larval counts. Levels of immunity of grazing groups and helminth-free housed groups were compared by challenge infection. Even though signs of parasitic bronchitis were seen only in control animals, sufficient immunity had developed in OPRB-treated calves to prevent disease after a substantial challenge infection. However, the degree of immunity was less than in untreated grazing control groups and there were indications that it was related to initial infection levels. These results imply that the OPRB may successfully control parasitic bronchitis, provided that pasture larval infections are sufficient to allow the development of immunity.     

Trichostrongyle larval populations on herbage from grazed and ungrazed cattle pastures in south west Scotland

In the course of studies on the control of bovine parasitic gastroenteritis in south west Scotland using a morantel sustained release bolus the populations of trichostrongyle infective larvae on herbage were monitored over a two-year period. From the results of the herbage analysis and the worm burdens in parasite naive tracer calves introduced at the end of 18 months, it was clear that considerable numbers of infective larvae of Ostertagia ostertagi and Cooperia oncophora survived for at least 18 months on pastures not grazed at all. The results suggest that in south west Scotland after one, or even two, seasons with no further contamination of grazing, permanent cattle pastures cannot be assumed to be helminthologically 'safe' and that this should be taken into consideration when determining prophylactic strategies.     

Resilience of second year grazing cattle to parasitic gastroenteritis following negligible to moderate exposure to gastrointestinal nematode infections in their first year

The influence of gastrointestinal nematode infections on performance of four groups of female Holstein Friesian calves was monitored until the end of the second grazing season (SGS). In the first year three groups were grazed and one group (G4) was permanently housed. General and grazing management during the first grazing season (FGS) was arranged such that G1 acquired moderate infections, G2 low infections and G3 very low infections with gastrointestinal nematodes. These infections were monitored through faecal egg counts, differentiation of faecal larval cultures, pasture larval counts, serum pepsinogen values, ELISA with a recombinant Cooperia oncophora protein, weight gain, tracer worm counts and sentinel worm counts. In 1998 all four groups were grazed together as one herd from 23 April to 26 October and infections were monitored with the same techniques with the exception of sentinel calves.In the FGS weight gain was higher in G4 than in the other groups and higher in G3 (28. 6kg) than in G1. Weight gain of G2 was intermediate to G1 and G3 but did not significantly differ from either group. In the SGS weight gain in G4 was far less than in any other group and the mean weight at the end of the experiment was 41.9, 38.6 and 50.9kg lower than G3, G1 and G2, respectively. Though no significant differences were observed between G1, G2 and G3 at the end of the experiment it was obvious that the weight gain advantage of G3 over G1 at the end of the FGS had disappeared.Parasitological and serological findings in the SGS indicated that G3 and G4 had build up less immunity during the FGS compared to G1 and G2.The conclusion of the experiment is that resilience to parasitic gastroenteritis in the SGS depends on the level of exposure to nematodes in the FGS. However, problems with poor weight gain only will be expected when exposure is very low in the FGS and high in the SGS.     

Production, parasitological and carcase evaluation studies in steers exposed to trichostrongyle infection and treated with a morantel bolus or fenbendazole in two consecutive grazing seasons

Friesian steers were exposed to natural trichostrongyle infection and left untreated (controls) or treated with either a morantel sustained release bolus or fenbendazole at two week intervals (clean) in each of two consecutive grazing seasons. In the second grazing season the mean liveweight gains of the clean, morantel treated and control groups of cattle over 152 days were 105, 131 and 109 kg respectively (morantel treated greater than clean, control P less than 0.02). The cattle were slaughtered following an indoor fattening period. The dressed carcase weight, killing out percentage and related carcase measurements were superior in the treated groups. Eighty per cent of the clean and morantel treated cattle graded satisfactorily and qualified for subsidy payment whereas less than 30 per cent of the control cattle were successful. Rib joint analyses showed significantly lower total weight, eye muscle weight and area together with a higher bone content in control cattle.     

Effect of nematophagous fungus Duddingtonia flagrans and energy supplementation on the epidemiology of naturally infected kids

Gastrointestinal (GI) nematode infection is a major constraint for grazing livestock production. The increasing prevalence and severity of anthelmintic-resistant nematodes in many parts of the world has led to a search for non-chemical control options. Under experimental conditions, the nematophagous fungus Duddingtonia flagrans is emerging as an alternative to chemotherapy for the control of GI nematode infection in biological production systems. Also, recent information points to the role of energy nutrition to increase the immune response against GI nematode infection. In this study the effect of D. flagrans and energy supplementation on the epidemiology of GI nematode infections is explored on grazing kids. Four groups of 10, 4-month old goats were turned out on infected pasture in the early spring and allocated to four separate paddocks where they were rotationally grazed for 16 weeks. One of these groups (F) received 0.5 x 10(6) D. flagrans spores/kg BW/d. Another group (S) was supplemented with 100 g barley grain per day. A third group (F+S) received both nematophagous fungi and barley supplement treatments simultaneously while the fourth group (C) was used as a non-treated control. Both nematophagous fungi and barley supplement had a significant effect (P<0.01) on reducing pasture infectivity, faecal egg excretion and worm burdens at slaughter that was particularly evident for Trichostrongylus colubriformis. The combination of both treatments showed a synergistic effect on the control of gastrointestinal nematode infections. At slaughter, the average total post-mortem worm count of the F+S group was reduced by 65% compared with the non-treated control. The results herein show that D. flagrans can act as an efficient biological control agent against kid GI nematode infections on pasture, which could further improve carcass characteristics. While small amounts of energy supplement can also reduce kid infection, the effect of D. flagrans as a biological control agent appeared clearly enhanced both in magnitude and duration by energy supplementation. This has clear implications for grazing animals and provides an efficient method for the practical control of parasitic nematodes in biological production systems.