Strategic use of anthelmintics for parasitic nematodes in cattle and sheep

Treatment regimes for the control of parasitic nematodes in cattle and sheep are reviewed. The advantages and disadvantages of each strategy are outlined and the veterinarian's judgement of the management and economic constraints involved when recommending a particular system to a client is emphasised.     

Strategic use of anthelmintics to prevent parasitic gastroenteritis in cow-calf herds in California

On the basis of the hypothesis that the peak numbers of infective nematode third-stage larvae (L3) on herbage in winter months results from fall contamination of pastures, 2 methods to reduce fall contamination were tested. In trial 1, morantal sustained-release boluses were administered to 15 fall-calving cows on Sept 7, 1982. Fifteen untreated cows (controls) were placed on separate pastures. Numbers of L3 on herbage during the winter and spring were assessed by use of worm-free tracer calves. In trial 2, 19 cattle due to calve in the fall were administered 200 micrograms of invermectin/kg of body weight, SC, on Sept 2, 1983. Also, 17 cattle similarly were given a placebo injection and served as control animals. Treated cattle were placed on the pasture used by control cattle in trial 1 and control cattle on the pasture used by treated cattle in trial 1. Worm-free tracer calves were again used to assess numbers of L3 on herbage. In trial 1, tracer calves grazing the control animal pasture from January 14 to 28 acquired 37 times as many nematodes as did those grazing the treated animal pasture. In trial 2, the greatest difference observed was a 10-fold increase of nematodes in calves grazing control animal pastures, compared with worm numbers in tracer calves grazing the treated animal pasture.     

Gastrointestinal parasites of working donkeys of Ethiopia

The general prevalence and population composition of gastrointestinal and pulmonary helminths of working donkeys were studied. For the purpose 2935 working donkeys were coprologically examined for nematode and cestode, and 215 donkeys for trematode infections. Seven donkeys that died due to various health problems or were euthanased on a welfare ground were necropsied and the parasites were recovered and identified to the species level. The study was conducted during the periods 1996-1999. Coprological examination revealed 99% strongyle, 80% Fasciola, 51% Parascaris, 30% Gastrodiscus, 11% Strongyloides westeri, 8% cestodes and 2% Oxyuris equi infection prevalence. Over 55% of donkeys had more than 1000 eggs per gram of faeces (epg). Forty two different species of parasites consisting of 33 nematodes, 3 trematodes, 3 cestodes and 3 arthropod larvae were identified from postmortem examined donkeys. Among the nematodes 17 species of Cyathostominae and 7 species of Strongylinae were identified. Other parasites identified include, Habronema muscae, Draschia megastoma, Trichostrongylus axei, Strongyloides westeri, Anoplocephala perfoliata, Anoplocephala magna, Anoplocephaloides (Paranoplocephala) mamillana, Parascaris equorum, Fasciola hepatica, Fasciola gigantica, Gastrodiscus aegyptiacus, Dictyocaulus arnfieldi, Oxyuris equi, Probstmayria vivipara, Gasterophilus intestinalis, Gasterophilus nasalis, Rhinoestrus uzbekistanicus and Setaria equina. This study revealed that working donkeys in Ethiopia are infected with a range of helminths and arthropod larvae, which are representatives of the important pathogenic parasites found in equids worldwide.     

Clinical dental findings in 203 working donkeys in Mexico

Clinical dental examinations of 203 unsedated working donkeys in tropical and temperate climatic areas in Mexico revealed a high prevalence (62%) of dental disease with sharp enamel points present in 98% of the animals. More significant dental disorders (diastemata, 4%; overgrown teeth, 18%; worn teeth, 16%; missing teeth, 0.5%; displaced teeth, 1.5%; fractured teeth, 2%) with welfare implications that required immediate treatment were also present in 18% of donkeys.The high prevalence of buccal ulcers (14.3%) and calluses (13.3%) present in this population was believed to be due to the high prevalence of sharp enamel points in conjunction with the use of tight nose bands and head collars. Dental disease was significantly associated with age groups, but not with body condition score or to the climatic area where the donkeys lived. As part of more general examinations, 81% of donkeys that had faecal egg counts performed, had parasite burdens which mainly showed a moderate level of infection. This study concluded that dental disease is a welfare concern in working donkeys in Mexico.     

Sustainable use of anthelmintics in grazing animals

It is suggested that the major factor in avoiding the development of anthelmintic resistance is the percentage of worms that do not encounter the anthelmintics (worms in refugia). This in turn is determined by the numbers of larvae on pasture, the percentage of animals treated and whether any stages in the host can avoid the action of anthelmintic. To maintain anthelmintic efficacy the percentage of worms in refugia must be sufficiently large. In cattle, this should involve treating only first-year animals and using a different pasture each year for calves. For sheep, only animals that have to be treated should be dosed with anthelmintic and clean grazing strategies that involve the use of anthelmintics should be avoided. For horses, reliance should be placed on the removal of faeces from pasture and only treating when the animals' condition requires it. Without a change in anthelmintic use there is the likelihood of increasing numbers of cases for which no anthelmintic is effective and animal welfare may be compromised.     

Gasterophilosis: a major cause of rectal prolapse in working donkeys in Ethiopia

A retrospective study was conducted to investigate the cause of rectal prolapse in working donkeys in Ethiopia. Analysis of data on rectal prolapse cases obtained from the Donkey Health and Welfare Project clinic at the School of Veterinary Medicine, Addis Ababa University, from 1995 to 2004 revealed that 83.6% (n = 177) of the cases were associated with Gasterophilus nasalis. The rest 10.7% and 5.7% were associated with work-related (overloading) cause and diarrhoea, respectively. The mean and median numbers of G. nasalis recovered from the rectum of infected donkeys were 66 and 64, respectively, with a range of 2–195. Over 100 G. nasalis larvae were recovered from the rectum of 22% of the donkeys. Circular demarcated ulcer-like and deep circumferential pits or ring-like mucosal lesions were found at the larval attachment sites. G. nasalis infection and the associated rectal prolapse were observed year round. However, the intensity of rectal larval infection and incidence of rectal prolapse were significantly higher during the rainy season (P < 0.01). Age and sex of the donkeys had no significant effect on the intensity of rectal larval infection and incidence of rectal prolapse (P > 0.05).     

Risk factors for strap-related lesions in working donkeys at the World Heritage Site of Petra in Jordan

A risk analysis was undertaken in an attempt to improve improvised rump straps on donkeys carrying tourists at the World Heritage Site at Petra, Jordan. Tail-base lesions were identified in 63 of the 86 donkeys. Observations and questionnaires were used to collect data relating to the straps, donkey health and human attitudes. The worse lesions were associated with padded rather than unpadded straps, if tightly fitted. Padding could be a cause of, or a response to lesions, but results suggest that it did not effectively aid healing. Significantly worse lesions occurred with unclean than with clean straps and, contrary to many recommendations, cotton straps were associated with worse lesions than were synthetic straps. Since this was an exploratory study, findings should be considered to generate (not to test) hypotheses and any resulting interventions will require monitoring. Further possible risks are discussed, referring to medical and veterinary literature and applied expertise in working equines.     

Mucosal surface area and fermentation activity in the hind gut of hydrated and chronically dehydrated working donkeys

The effects of mild chronic dehydration on fermentation rate and mucosal surface area in the cecum, dorsa and ventral colon, and descending colon of the hindgut were investigated in South African donkeys (n = 11) in agricultural work. Dehydration representing a 6% drop in BW (n = 6) was associated with increased fermentation activity in the cecum (252 +/- 22.9 vs. 161 +/- 13.5 micromol/g of DM.h(-1), P < 0.01) and enhanced fluid retention in the ventral colon (0.81 +/- 0.026 vs. 0.73 +/- 0.034 mL/g gut, P < 0.05). Fermentation activity in the next segment of the hindgut, the ventral colon, of dehydrated donkeys was also greater numerically (92.5 +/- 22.60 vs. 77.9 +/- 10.40 micromol/g of DM.h(-1)), but this difference was not significant. Total mucosal and crypt surface area per unit volume of gut (Sv, microm2/microm3) was greater in dehydrated donkeys for the cecum (253 +/- 23.0 vs. 161 +/- 13.5, P < 0.01), the ventral colon (286 +/- 6.2 vs. 171 +/- 9.8, P < 0.01), the dorsal colon (276 +/- 18.2 vs. 256 +/- 11.0, P < 0.05), and the descending colon (260 +/- 20.3 vs. 191 +/- 15.2, P < 0.05). Enhanced fermentation activity and enhanced mucosal absorptive or secretory capacity within the hindgut during chronic dehydration was associated with an observed maintenance of appetite. These adaptations in the hindgut are valuable physiological attributes for working donkeys in semi-arid regions where they are frequently exposed to chronic dehydration.