Agricultural policy and sustainable livestock development.

Future agricultural and rural development is, to a large extent, influenced by the projected food needs of 2.5 billion people expected to swell the world population by 2020. This increase will require more food in general and, in view of recent experience in East Asia, more animal products. To achieve this increase will require judicious use of resources, and trade, especially in those countries where natural resources are insufficient to support food production. Achieving food sufficiency in a sustainable manner is a major challenge for farmers, agro-industries, researchers and governments. The latter play an important role as many of the farmers' choices are, to a large extent, directed by government or supra-government, often through macro- and micro-economic policy. In many countries the economic, environmental, trade and agricultural policies have not been conducive to an agricultural development that is risk-free with respect to the environment, animal welfare or public health. The recent decline of government support in agriculture forced farmers in Western countries to think about more risk adverse agricultural practices and more efficient production systems. On the other hand, many countries in Eastern Europe and the former Soviet Union, as well as other developing countries, are still going through a painful process of adjustment to new market conditions. International banks and development agencies have a mandate to help developing countries, but are somewhat restricted both by needing to work directly with governments and by their perceived dogmatic approach to development. Changing policies do, now and in the future, also affect the development of animal disease control programmes, including the control of parasitic diseases. On the one hand there is an increasing interest in risk-free control practices, and on the other hand a demand for greater regulatory control over the production process. As parasitic diseases of animals are closely linked to the environment (i.e. grazing and waste management) and public health (i.e. parasitic zoonoses), the new interest in sustainable agriculture provides a challenge for those concerned with the control and prevention of animal parasitism.

Dynamics of Lymnaea natalensis populations in the Zaria area (Nigeria) and the relation to Fasciola gigantica infections.

Observations on the seasonal changes in the Lymnaea natalensis population and the infection rate of these snails with Fasciola gigantica during 1972-1976 are reported. The data were obtained from snails in three different locations near Zaria in Northern Nigeria. One of the survey sites dried out during the drought of 1972-1974 and had to be abandoned. The snail population showed seasonal variations with the lowest number of snails at the very end of the dry season. Many juvenile snails developed at the end of the wet season and beginning of the dry season, and the population reached its climax at the middle of the dry season. Fasciola infections in the snails occurred throughout the year, but the majority of the infections appeared to be acquired during the end of the wet season resulting in a high infection rate (up to 25%) in the beginning of the dry season. There was evidence of accelerated growth and gigantism in the infested snails. The occurrence of Fasciola infections in snails appears to depend on the presence (or absence) of livestock in snail infected areas during the rainy season. The infection developing in the rainy-season generation of snails is of major importance in the dissemination of fascioliasis in livestock as metacercarial shedding more or less coincides with the river-valley grazing of cattle.

Evaluation of abomasal enzyme and hormone levels in the diagnosis of ostertagiasis.

Pathophysiological changes in the ruminant abomasum caused by Ostertagia infections include changes in the activity and concentration of gastrointestinal enzymes and hormones. Under certain circumstances, increases in concentration also occur in the bloodstream and, as such, are detectable. Determination of serum pepsinogen levels is useful in evaluating the risk or presence of ostertagiasis Type I in a herd. It seems less reliable when used to diagnose (pre) ostertagiasis in individual animals. Measurement of the concentration of other zymogens is not useful. The variations in methodology to determine pepsinogen levels (e.g. biochemical and immunological measurements) are discussed. Serum gastrin levels are, generally, increased in animals with ostertagiasis. At present, gastrin is mainly determined by RIA assays using human gastrin antibodies, but few baseline data are available on normal levels in ruminants. The use of gastrin determination as a diagnostic tool in Ostertagia-infected ruminants is limited.

Sense or nonsense? Traditional methods of animal parasitic disease control.

In recent years, there has been a resurgence of interest in traditional health-care practices in the western as well as in the developing world. In animal health, this has led to further interest in ethnoveterinary research and development, a relatively new field of study that covers traditional practices, ethnobotany and application of animal care practices embedded in local tradition. This development has practical applications for animal parasite control, whether related to epidemiology, diagnostics and therapy, or to comprehensive disease control methods leading to integrated pest/disease management. Examples are provided of traditional practices in diagnostics, herd-, grazing- and pasture-management as well as of manipulation and treatment. Many of these applications indicate a basic understanding of disease, especially epidemiology, by farmers and herders, although not always explained, or explainable, in rational western ways. Although abuse and quackery exist, the application of traditional practices seems to make sense in areas without adequate veterinary services. Moreover, acknowledgement of the value of traditional knowledge empowers local herders/farmers to try to solve their herds' disease problems in a cost-effective way. Traditional practices often make sense, albeit with some regulation to ascertain safety and to prevent abuse.

Control of trichostrongylid pasture infestation in spring by the periparturient anthelmintic treatment of housed ewes prior to or at the time of turn out.

Ewes, housed in late November and lambing in late February and March, were divided into three groups of eight, six and eight animals, and received a single treatment with ivermectin (approximately 200 micrograms kg-1) in late February (Group I), on 15 April (Group II), or on 1 May (Group III), respectively. The egg output of the ewes and, subsequently, of eight lambs (Group IV) was measured at 2-weekly intervals by counting and identifying the larvae after culture. Group I showed a small rise in larva output in March, with counts less than 100 larvae per gram of faeces (l.p.g.) whereas the other groups showed considerable increase with counts greater than 500 l.p.g. Treatment of Groups II and III just before turn out in April and May reduced the output to zero for at least 6 wk. The lambs did not show any evidence of trichostrongylid infection until the middle of July. The major parasite identified was Haemonchus contortus. The results of this trial demonstrate that 1) ivermectin treatment in February reduced but did not completely eliminate a spring rise in egg output and 2) treatment in mid-April eliminated further egg output. Ewes treated and turned out in mid-April or later were not a significant cause of pasture contamination in spring or early summer.

The trichostrongylid egg output during spring in feedlot cattle.

Larval cultures prepared from faeces collected at two-week intervals from feeder cattle originating from Michigan, Oklahoma and Kentucky, and kept in a feedlot in Michigan, were examined during the winter and spring of 1979. The animals received anthelmintic treatment shortly after entering the feedlot. The larval output, consisting mainly of Ostertagia larvae, was less than 20 larvae per g, but did show a seasonal increase during spring in the cattle originating from Kentucky and Michigan. This "spring rise" was not observed in the animals originating from Oklahoma which is thought to be related to a difference in transmission pattern of Ostertagia in the southwest as compared to the eastern and midwestern parts of the U.S.A.

The effect of pre-exposure to Fasciola hepatica or Schistosoma mansoni on challenge infection with Fasciola hepatica.

Two groups of 12 and 6 rats were inoculated with Fasciola hepatica and Schistosoma mansoni, respectively. The Schistosoma-inoculated group, as well as 6 Fasciola-inoculated rats and 6 uninfected rats were challenged 8 weeks later with F. hepatica. A control group of 6 rats was left unexposed. Eight weeks after the challenge exposure all rats were necropsied and subjected to post-mortem examination. The number of Fasciola recovered after challenge was lower in both groups of rats primarily infected with F. hepatica or S. mansoni. F. hepatica-induced pathological changes were observed in all infected rats, but were pronounced in the group which was first exposed at the time of challenge of the primarily infected groups. No Schistosoma eggs or adults were detected in Schistosoma-inoculated rats. The results demonstrated that rats primarily infected with F. hepatica acquired resistance against a challenge exposure to the homologous parasite. Also S. mansoni, even without patency, can provide partial protection against F. hepatica infection.

In vitro maintenance of Eperythrozoon suis.

In vitro maintenance of Eperythrozoon suis was attempted using a Petri dish erythrocyte culture system. In preliminary experiments, the optimal conditions for maintaining E. suis attachment to erythrocytes during incubation were anticoagulation with heparin or citrate solution, incubation with 5 or 10% CO2 at 37 degrees C, and incubation with reduced or non-reduced Eagle's minimum essential medium. Using heparin, a CO2 incubator and reduced Eagle's medium (rEM), E. suis metabolic activity was evaluated by measuring glucose consumption, and lactate and pyruvate production. Glucose consumption and lactate production were measurable while pyruvate production was not detected. Erythrocyte integrity was improved by the addition of inosine although no effect was observed on maintenance of E. suis attachment to erythrocytes or the rate of glucose consumption. To determine whether the glucose consumption observed in culture was due to E. suis glycolytic activity or enhanced erythrocyte glycolytic activity, the effect of E. suis killing by EDTA addition to medium was evaluated using rEM containing inosine (rEMI). Glucose consumption decreased proportionally with the decline in the percentage of parasitized erythrocytes induced by EDTA, indicating that glucose consumption was due to E. suis. In a subsequent experiment, the effect of different types of serum (pig or fetal calf serum) and different gaseous environments (5% CO2 incubator or candle jar) were evaluated using rEMI. Glucose consumption by E. suis was significantly increased by the addition of fetal calf serum; however, no difference in the maintenance of E. suis attachment to erythrocytes and in E. suis glycolytic activity was observed between a 5% CO2 incubator and a candle jar. Finally, the effect of medium refreshment (rEMI containing fetal calf serum) was evaluated. Maintenance of E. suis parasitism on erythrocytes and E. suis glycolytic activity were significantly improved by frequent medium refreshment. The maintenance system developed enabled successful metabolic radiolabeling of E. suis for protein/antigen analysis.

Borrelia anserina in chickens previously exposed to Borrelia theileri.

Exposure of 10-week-old White Leghorn chickens to sheep blood containing Borrelia theileri neither resulted in infection nor conferred protection against B. anserina.

A survey of helminth parasites in backyard flocks in Michigan by litter examination.

The prevalence of parasitic infections in backyard flocks was surveyed using litter samples from 74 pens located on 12 farms in central lower Michigan. Eight species of birds were represented. Two methods of litter examination (a sucrose flotation technique and a multiple washing/ZnCl2 flotation) were compared; the sucrose flotation technique was found to be more useful and was used in the survey. The following parasites eggs/oocysts were observed; ascarid-type eggs (in 34 pens from nine farms), Capillaria eggs (in 30 pens from nine farms), Strongyloides eggs (in nine pens from five farms), Syngamus eggs (in five pens from four farms), and coccidial oocysts (in 40 pens from 10 farms). Contamination of litter with ascarid-type eggs, Capillaria eggs, and coccidial oocysts was commonly found, irrespective of bird species. The contamination level in pens with more than one bird species was lower than in pens with a single species. The relatively high contamination rate may be an indication of the risk of parasitic disease in birds that are not raised under controlled conditions in confinement.

The haemoglobin types of northern Nigerian sheep.

The haemoglobin type of 515 sheep from various areas in northern Nigeria was determined. The gene-frequency of the Hb-B type was 1.00 in Uda and Balamy sheep and 0.998 in Yankassas.

Eastern Europe and the former Union of Soviet Socialist Republics: animal health systems in transition.

The economic transition in Eastern Europe and the former Union of Soviet Socialist Republics (USSR) during the last decade has profoundly changed the agricultural sector and the well-being of people in rural areas. Farm ownership changed; selected farm assets, including livestock, were transferred to farm workers or others, and the social and service structures of rural society are in a state of uncertainty. The transition has, in general, led to the deterioration of rural services. Animal health services have also deteriorated. This decline is associated with the contraction of the livestock inventory, the fragmentation of farms, higher transaction costs for service providers, and the overall decline of the rural economy which has, so far, lowered the demand for animal health services. There are considerable differences in the way that these countries are coping with the economic transition and its aftermath. Among the determining factors in the former USSR are, as follows: the speed of recovery from the legacies of large State-controlled farming and a centrally planned animal health system, the efforts made to address poverty reduction, the choice on whether to become a Member of the World Trade Organization and the requirements of such membership, the ability to provide low-cost services to a fragmented and unskilled livestock production sector. In Eastern Europe, the requirements for joining the European Union (EU) are an additional and important determining factor. In the short term, the choice of a veterinary system to serve the livestock sector may differ from country to country, depending on the legacies of the past, the status of reforms and the proximity of Western markets. Lower-income countries with an oversupply of veterinarians may support labour-intensive, low-cost systems which focus on food security and public health. The better-endowed EU accession countries may focus rather on improved disease surveillance, production enhancement, quality assurance and increased food safety. Such choices may also determine the investment made by these countries in upgrading their State system, laboratories and veterinary education facilities.

Anthelmintic activity of ivermectin in pigs naturally infected with Ascaris and Trichuris.

The anthelmintic efficacy of ivermectin administered by subcutaneous (SC) injection or orally via the drinking water was investigated in feeder pigs naturally infected with Ascaris suum and Trichuris suis. Group 1 pigs (n = 5) were given drinking water as a placebo, group 2 pigs (n = 5) were given ivermectin by SC injection (300 micrograms/kg of body weight), and group 3 pigs (n = 5) were given ivermectin in water also at a dosage rate of 300 micrograms/kg of body weight. At necropsy 11 days later, the mean worm counts in group 1 pigs were 4 for Ascaris and 50.2 for Trichuris. All adult and juvenile ascarids were removed from the intestine in groups 2 and 3 pigs. Compared with the number of Trichuris in group 1 pigs, the number of Trichuris was reduced by 91.2% and 78.1%, respectively, for the orally and SC treated pigs.

Comparative blood characteristics of ranched and free-ranging American bison (Bison bison).

Blood samples were obtained from 20 bison (Bison bison) from a ranch in northern lower Michigan, as well as from 20 free-ranging bison of the same sex and similar age from the Badlands National Park in South Dakota. Hematologic and serum biochemical values were determined. The values were comparable in both groups, except for those for BUN, aspartate transaminase, and phosphorus, which were significantly (P less than 0.001) higher in the ranched bison than in the free-ranging bison. These differences were attributed to nutritional effects. Impact of age on blood characteristics was assessed in the ranched bison only by comparing values from calves weighing less than 185 kg with those from bison weighing more than 185 kg. Calves had significantly (P less than 0.001) higher values for phosphorus and RBC counts and lower total protein values than adults. Adult bison had higher eosinophil and neutrophil counts with lower numbers of lymphocytes, suggestive of a stress leukogram, whereas calves had the typical bovine neutrophil:lymphocyte ratio.

Radiologic evaluation of the liver and gastrointestinal tract in rats infected with Taenia taeniaeformis.

In rats infected with the cestode Taenia taeniaeformis, hepatomegaly results from development of parasitic cysts in the liver. Diffuse nodular mucosal hyperplasia in the glandular region (corpus and antrum) of the stomach, and gross thickening of the intestinal mucosa also result. Between postinfection days (PID) 21 and 84, radiologic observations were made after oral administration of a barium sulfate suspension in T taeniaeformis-infected rats and in age/sex-matched controls. There was radiographic evidence of hepatic enlargement at PID 21. Enlargement of the gastric folds was first observed along the greater curvature of the stomach at PID 35. Fimbriation of small intestinal mucosal surfaces resulted from thickening of the intestinal villi and was observed in the duodenum at PID 21. Intestinal motility was assessed, and contractions were counted, using image intensification fluoroscopy, then were recorded on videotape. There were no significant differences between control and infected rats for gastric emptying time, intestinal transit time, and number of intestinal contractions per minute. Barium contrast radiography clearly indicated large gastric folds, thickening of the small intestinal villi, and hepatic enlargement, and was useful for assessing gastrointestinal motility.

Schistosomiasis and nutritional myopathy in a Brazilian tapir (Tapirus terrestris).

Gross lesions suggestive of severe hepatoenteropathy and myopathy were noted in a 4.5-yr-old Brazilian tapir (Tapirus terrestris) from a zoo in Michigan (USA). The major microscopic lesions were granulomatous hepatitis and hemorrhagic enteritis associated with non-operculated eggs compatible with those of the Schistosomatidae (Digenea). Skeletal muscle and tongue contained foci of severe acute myodegeneration and necrosis. The hepatic vitamin E value of 1.3 ppm dry weight was considered critically low.

Prevalence of Fascioloides magna in cattle and deer in Michigan.

A survey among 1.12 million cattle slaughtered in 357 packing plants in Michigan during 1977 to 1981 was conducted to determine the prevalence of liver fluke infection. The condemnation rate of liver fluke-infected livers was 0.41, 3.7, and 13.9% in the southern, northern-lower, and upper regions of Michigan, respectively. The same trend in infection rates was observed in white-tailed deer that had been examined in diagnostic laboratories in the state. A serologic survey among 50 randomly selected dairy farms detected Fascioloides antibody-carrying cattle in 3 farms. The data on prevalence in slaughter cattle were slightly biased, because many slaughter cattle originated from other states in which F magna may be less common.

Cerebrospinal nematodiasis in a goat herd.

During the fall of 1985, 4 Angora goats, from a herd of 40, were examined on a farm in central Michigan. Affected goats were alert but had neurologic deficits consistent with upper and lower moto neuron involvement. Eosinophilic pleocytosis in a cerebrospinal fluid sample from one goat was consistent with cerebrospinal nematodiasis. Parelaphostrongylosis was confirmed in 3 goats by identification of Parelaphostrongylosis tenuis larvae in spinal cord sections. Ivermectin may have influenced the herd's susceptibility to new parasitic infections. Control of parelaphostrongylosis probably is best achieved by removal of susceptible animals from treed swamps coinhabited by white-tailed deer from late summer until after the first killing frost.

Parasitic disease of the bovine nervous system.

Parasitic disease of the nervous system of cattle is mainly caused by migrating nematodes, expanding cestode cysts, or by rickettsiae and protozoa in the central nervous system. Common parasitic causes of neurologic diseases in cattle in the United States are Hypoderma larvae, toxins produced by Dermacentor ticks, and metabolic changes associated with intestinal coccidiosis.