Topically applied ivermectin and Cooperia infections in cattle

Extract

I have read with some interest a recent report in this journal⁽¹⁾ that topically applied ivermectin (Ivomec Pour-On, MSD Agvet NZ Ltd) was found to be largely ineffective against Cooperiu infection in cattle.     

Ineffikacy of ivermectin against Cooperia spp. infection in cattle

Ivermectin, either as an injectable or topical formulation, is used widely to control parasites in New Zealand cattle. These formulations have been well documented as having high efficacy against the major nematode species which infect tattle^(1)(2)(3)(4), although the efficacy against adult Cooperia oncophora is reported to be 95%⁽⁵⁾. This is considered to be one of the doselimiting species. There have been two reports of lower than expected efficacy of the topical formulation against Cooperia spp. in cattle. In a slaughter trial, Bisset et al. ⁽⁶⁾ found that ivermectin applied topically at the recommended dose rate of 500 𝛍g/kg failed to achieve a statistically significant reduction in the burden of Cooperia spp. worms compared with untreated calves. The geometric mean of adult Cooperia spp. worms present in the treated calves was 5788 compared with 7524 present in the untreated calves. This reduced efficacy was not attributed to acquired anthelmintic resistance because ivermectin had not been used on the farm previously. In Australia, Eagleson and Allertonc⁽⁷⁾ found in controlled field trials that ivermectin applied topically at 500 𝛍g/kg ranged in efficiency in reducing faecal egg counts from 80.7% to 100% ; four out of 13 trials achieving less than 90% and a further four were in the range of 90–95% reduction. Larvae obtained from the faeces of ivermectin-treated cattle on days 11–14 after treatment were predominantly Cooperia spp.     

First report of seroprevalence of Toxoplasma gondii and Neospora caninum in dairy sheep from Humid Pampa, Argentina

The aim of this study was to describe the occurrence of antibodies to Toxoplasma gondii and Neospora caninum in dairy sheep from the Humid Pampa region, Argentina. Blood samples from 704 dairy sheep belonging to six flocks were collected. Using a cut off titer of 1:50, an indirect fluorescence antibody test was used. Antibodies to T. gondii or N. caninum were detected in 17.3 % (n?=?122) and 3 % (n?=?21), respectively. All the flocks had at least one seropositive animal to T. gondii but two of them had no seropositive sheep to N. caninum. Fifty-two of 122 (42.6 %) positive samples to T. gondii had antibody titers higher than 1:400. There was a significantly higher proportion of T. gondii seropositive animals in females and older sheep (p?<?0.05). Ten of 21 (52.3 %) positive samples to N. caninum had antibody titers higher than 1:400. This is the first report of seroprevalence of T. gondii and N. caninum in dairy sheep from Humid Pampa, Argentina. Further research is required for a better understanding of the role of toxoplasmosis and neosporosis in dairy sheep in Argentina.     

Confirmation of resistance to ivermectin by Cooperia curticei in sheep

AIM: To investigate the occurrence of resistance to a full dose of oral ivermectin by Cooperia curticei in sheep.

METHODS: Twelve lambs on a sheep and cattle property in the North Island of New Zealand were randomly allocated to one of two equal-sized groups. One group was treated orally with a single dose of ivermectin at the manufacturer's recommended dose rate of 0.2 mg/kg, while the other remained as an untreated control. Worm counts were carried out post mortem on the abomasa and small intestines of all animals in both groups 7 days after treatment.

RESULTS: While treatment with ivermectin reduced the numbers of all other worm genera to almost zero, those of Ostertagia (= Telodorsagia) circumcincta and C. curticei were reduced by only 37% and 19%, respectively.

CONCLUSIONS: These results provide clear evidence of resistance to ivermectin by O. circumcincta and C. curticei. They also appear to represent the first record of macrocylic lactone (ML) resistance in C. curticei in sheep in New Zealand or elsewhere.     

Confirmation of resistance to ivermectin by Cooperia curticei in sheep

AIM: To investigate the occurrence of resistance to a full dose of oral ivermectin by Cooperia curticei in sheep. METHODS: Twelve lambs on a sheep and cattle property in the North Island of New Zealand were randomly allocated to one of two equal-sized groups. One group was treated orally with a single dose of ivermectin at the manufacturer's recommended dose rate of 0.2 mg/kg, while the other remained as an untreated control. Worm counts were carried out post mortem on the abomasa and small intestines of all animals in both groups 7 days after treatment. RESULTS: While treatment with ivermectin reduced the numbers of all other worm genera to almost zero, those of Ostertagia(= Telodorsagia) circumcincta and C. curticei were reduced by only 37% and 19%, respectively. CONCLUSIONS: These results provide clear evidence of resistance to ivermectin by O. circumcincta and C. curticei. They also appear to represent the first record of macrocylic lactone (ML) resistance in C. curticei in sheep in New Zealand or elsewhere.     

Evaluation of the persistent efficacy of doramectin and ivermectin injectable against Ostertagia ostertagi and Cooperia oncophora in cattle

The persistent efficacy of doramectin and ivermectin injectable against moderate and high infection levels of Ostertagia ostertagi and Cooperia oncophora were evaluated in cattle. Calves were allocated to six groups of six animals. On Day 0 animals of Groups I1/I2 and D1/D2 were treated with 0.2mg/kg ivermectin and doramectin injectable, respectively. Animals of the C1, I1 and D1 groups received a daily (moderate) infection of 1000 L3 of O. ostertagi and 1000 L3 of C. oncophora, and animals of the C2, I2 and D2 groups received a daily (high) infection of 10,000 L3 of each species. The animals were infected for 21 days with both species, the infections with C. oncophora and O. ostertagi started from Days 8 and 15 post treatment, respectively. Animals were necropsied on Day 40. The calculation of the persistent activity of ivermectin and doramectin was based on the efficacy against the different developmental and adult stages of both parasites. The present study confirmed that infection levels may influence the duration of persistent efficacy of an anthelmintic. Doramectin had at the moderate infection level a persistent efficacy of at least 35 days against O. ostertagi and at least 28 days against C. oncophora; at the high infection dose persistent efficacy was somewhat shorter i.e. up to 33 days and approximately 28 days, respectively. The duration of persistent efficacy of ivermectin against O. ostertagi at the moderate infection level was between 14 and 25 days, at the high dose level up to 25 days. Persistent efficacy of ivermectin against C. oncophora could, at both infection doses, not be measured, with the present experimental design.     

Efficacy of ivermectin against Cooperia curticei infection in sheep

Lambs were inoculated with a single dose of Cooperia curticei. Subcutaneous administration of ivermectin at a dosage of 200 micrograms/kg of body weight resulted in 61.1% and 90.4% anthelmintic efficacy, when measured at 7 and 14 days after treatment, respectively. In the treatment groups, parasites that remained were located more distally in the small intestine than those in the lambs in the control groups.     

Immunity to parasitic bronchitis of yearling cattle treated with ivermectin during their first grazing season

A group of 12 winter-born calves was divided into two groups of six. During the following summer one group grazed on pasture infected with Dictyocaulus viviparus, and was treated with ivermectin injections at three, eight and 13 weeks after turn out. The other group remained housed. Both groups were housed during the winter and then together with a group of younger calves were challenged with a trickle infection of D viviparus larvae at the rate of 25 third stage larvae/kg bodyweight for one month and then slaughtered. The group which had been exposed to previous infection was least affected by parasitic bronchitis and on the basis of serological titres and worm burdens had developed resistance to the challenge infection. The other older group was also more resistant than the younger calves.     

Control of parasitic bronchitis and gastroenteritis in grazing cattle by strategic prophylaxis with ivermectin

In May 1985 four groups of 10 calves, aged between four and five months, were turned out on to separate, permanent pastures of equal area which had been seeded during the previous few days with larvae of Dictyocaulus viviparus. One group acted as a control, the second was vaccinated with lungworm vaccine before turnout and treated with thiabendazole three, eight and 13 weeks after turnout, while the third and fourth groups were given ivermectin three times (three, eight and 13 weeks after turnout) and twice (three and eight weeks after turnout), respectively. A severe outbreak of parasitic bronchitis resulted in the death of three control calves within five weeks of turnout and parasitic bronchitis and gastroenteritis affected the second group of calves after approximately four months at pasture. The calves given ivermectin excreted no lungworm larvae and remained free of clinical parasitism throughout the trial.     

Fragmentation Status of Tall-Tussock Grassland Relicts in the Flooding Pampa,Argentina

Since European settlement vast areas of the tall tussock grassland dominated by Paspalum quadrifarium Lam. and Paspalum exaltatum J. Presl (“pajonal” grassland) in the Flooding Pampa of Argentina were converted to croplands and short grasslands. With the use of Landsat satellite images, we analyzed current (1998–2000) cover and spatial integrity of the pajonal community, and compared it with a vegetation map made 50 yr ago (1956–1960). Six categories of land cover were adopted: crops, sown pastures, short grassland, pajonal, wetlands, and anthropogenic areas. With the use of metrics from FRAGSTATS, landscape pattern and composition were analyzed at two scales: 1) regionally, by comparing two edaphic domain areas with relatively low and high restrictions for agriculture (low-restriction domain [LRD] and high-restriction domain [HRD], respectively); and 2) at landscape scale, by comparing ten 22 500-ha randomly selected areas (landscapes) within each edaphic domain. Current relative cover of pajonal grassland (2 173 600 ha) was 32.5%, and similar values were obtained within each edaphic domain. However, the number of pajonal patches was higher and their mean patch size, the Euclidean nearest-neighbor distance among patches (degree of isolation), and their border regularity were lower in the LRD than in the HRD. At landscape scale, the mean size of pajonal patches diminished with the percent of agricultural land within both edaphic domains. The isolation among pajonal patches increased with percent of agricultural land in the HRD, whereas no relationship between the isolation of pajonal patches and percent of agriculture was found in the LRD. As suggested by comparison with past vegetation, current pajonal status mostly results from replacement of pajonal grassland by short grassland types, cultivated pastures, and annual crops (52% and 44% of previously occupied areas in LRD and HRD, respectively), but some expansion of pajonal grassland was also observed (10% and 4% of previously unoccupied areas in LRD and HRD, respectively).     

Resistance to benzimidazole and macrocyclic lactone anthelmintics in cattle nematodes in Argentina

In April 2003, persistent scouring and ill-thrift that was reported in calves form an intensive beef rearing operation in central Argentina despite treatments with benzimidazole and ivermectin. In order to conduct a controlled faecal egg count reduction test on this herd, 40 calves 5-8-months-old were selected on the basis that they had a nematode eggs per gram (epg) of faeces count greater than 150. Animals were divided into four groups (1-4) of 10 calves. Calves of groups 1-3 were treated, respectively, with subcutaneous injection of ivermectin (200 mcg/kg), ricobendazole (4 mg/kg) and levamisole (7.5 mg/kg), while calves of group 4 remained as untreated controls. The egg count reductions carried out 10 days later were lower than 15% in calves treated with ivermectin and ricobendazole, but 100% in animals receiving levamisole. Pooled post-treatment faecal cultures showed larval percentages of 92 and 95 for Haemonchus and 8 and 5 for Cooperia in the faeces of calves treated with ivermectin and ricobendazole, respectively. This is the first reported case of Haemonchus parasiting cattle showing simultaneous resistance to avermectins and benzimidazole type anthelmintics.     

Isolation of oxfendazole resistant Cooperia oncophora in cattle

A field strain of Cooperia oncophora resistant to oxfendazole was isolated from a commercial cattle rearing property in Waikato, New Zealand. Resistance to oxfendazole was assessed by means of a faecal egg count depression test and an in vitro egg hatch test. This is the first documented case of anthelmintic resistance in Cooperia spp. and the first report of anthelmintic resistance in cattle in New Zealand.     

Three treatments with ivermectin in year-long control of gastrointestinal nematode parasites of weaner-yearling beef cattle

Four groups of 17 crossbred beef weaners were used in an experiment which extended from 14 November 1985 to 8 October 1986 (328 days). All groups began grazing on separate, contaminated pastures at a stocking rate of 5.3 cattle ha-1 and the different treatments were: Group 1, ivermectin (IVM) injectable X 1 (200 micrograms kg-1) on 14 November only, with provision for individual salvage treatment; Group 2, IVM X 3 on 14 November, 4 February and 2 July; Group 3, IVM X 2 on 14 November and 2 July; Group 4, fenbendazole (FBZ) paste X 2 (5 mg kg-1) on 14 November and 2 July. Pairs of parasite-free tracer calves were grazed on all group pastures for 1 month at the beginning of the experiment (13 November-12 December and in spring (1 April-1 May). Yearling cattle from each group were randomly selected and removed from pasture during spring (n = 2 per group, 3 April) and at the end of the experiment (n = 3 per group, 8 October) for slaughter analysis of worm population characteristics and observation of gross pathology in the abomasum and intestinal tract. At monthly intervals, all cattle were weighed and fecal egg counts, pasture larval counts and plasma pepsinogen values were determined. The results of this investigation demonstrated that three IVM treatments of weaner-yearling beef cattle during year-long grazing, were more effective than a single IVM treatment or two treatments with IVM or FBZ in the enhancement of productivity and protection from the effects of infection with nematode parasites.     

Prevalence of clinical endometritis and its impact on reproductive performance in grazing dairy cattle in Argentina

The objective of this study was to evaluate the prevalence of clinical endometritis and its impact on reproductive performance in grazing dairy cattle in Argentina to compare data with previous reports from herds kept in confinement housing systems. A total of 243 Holstein dairy cows from three commercial dairy farms in Buenos Aires Province (Argentina) were examined for the signs of clinical endometritis 18-38 days postpartum (dpp) by external inspection and manual vaginal examination. Vaginal discharge was scored into the categories VDS 0 (transparent, clear mucus), VDS 1 (mucupurulent discharge), VDS 2 (purulent discharge) and VDS 3 (purulent discharge with fetid odour). Cows diagnosed with VDS 1 to VDS 3 were regarded as affected with clinical endometritis and cows with VDS 0 as free of clinical endometritis. All cows were re-examined 14 days later following the same examination protocol. Prevalence of clinical endometritis 18-38 dpp was 35% and decreased to 18% at re-examination. Cows with no palpable ovarian structures or periparturient disorders were at higher risk for clinical endometritis. Hazard for pregnancy was significantly lower in cows with purulent or fetid odour discharge compared with reference cows with no discharge (HR=0.49; p=0.01), resulting in a lower proportion of cows pregnant by 360 dpp (66% vs 78%). Furthermore, the number of services per pregnancy was higher for cows with clinical endometritis than for cows without clinical endometritis (4.4 vs 3.1; p=0.04). Cows with clinical endometritis were 1.6 times as likely to be culled as cows with no signs of clinical endometritis. In conclusion, the prevalence and the impact of clinical endometritis in a pasture-based, extensive dairy production system in Argentina were similar to previously published data from dairy farms with confinement production systems.