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.

Levels of serum IgE in response to gastrointestinal nematodes in cattle.

Serum IgE concentration has been considered a valuable measurement in parasitic infections, yet little has been reported regarding cattle. This study examines the association of IgE levels of nematode-naïve Holstein steer calves and the level of gastrointestinal parasitism acquired by grazing irrigated pasture for 30 days. Total IgE levels were determined by enzyme-linked immunosorbent assay (ELISA) specific for bovine IgE on serum collected both before and after exposure to parasite-infected pastures. Following necropsy, parasite loads were determined by direct count from the contents of the abomasum, small intestine, cecum and large intestine; species of Ostertagia and Cooperia being the most common helminths found. Significant increases of IgE in the serum of calves with light infestations were seen, whereas calves with moderate to heavy infestations showed only mild IgE increases. With increased parasite burden, the frequency of increased IgE levels was reduced. Additionally, there appeared to be a seasonal correlation relating the level of serum IgE detected to the number of worms counted and to the course of parasite development.

Seasonal prevalence of gastrointestinal nematodes of beef calves grazed on irrigated pastures in the lower Sacramento Valley of California.

Two worm-free calves were allowed to graze on irrigated pasture with a naturally infected herd for each of 34 one-month periods from November 1979 to August 1982. After each grazing period, the calves were transferred to a cement-floored pen for 3 weeks and then were euthanatized and necropsied. Ostertagia ostertagi and Cooperia oncophora were the most prevalent species of nematodes recovered. Adults and larvae of Ostertagia spp and Cooperia spp were most numerous in winter and spring and least numerous during summer. The proportions of Ostertagia spp that were inhibited as fourth-stage larvae increased in late fall, peaked from March through April, and then decreased to low values during summer. The maximal inhibition in 1980, 1981, and 1982 was 72, 65, and 62%, respectively. The number of larval Cooperia spp was highest in winter months and, except for one grazing period when 55% of the Cooperia spp were larvae, the total numbers represented less than 15% of the nematode population during all grazing periods. Other nematodes encountered were Trichostrongylus axei, Haemonchus spp, O lyrata, and O occidentalis in the abomasum; C surnabata, C punctata, Nematodirus helvetianus, T colubriformis, and Bunostomum phlebotomum in the small intestine; and Oesophagostomum venulosum and Trichuris ovis in the large intestine.

Importance of diagnostic aspects in ostertagism.

Diagnostic methods which reveal only the presence or absence of Ostertagia in grazing animals are of little importance since all will acquire some degree of infection when grazed in the temperate regions of the world. Ostertagia infections may be (1) light--no disease or performance losses occur; (2) moderate--disease may or may not be overtly visible but performance losses occur or (3) heavy--disease is overt with or without death loss. The differentiation of these levels of infection is a quantitative matter insofar as the number of parasites correlates with the degree of pathology and is much less certain than is the presence or absence of infection. Historically, the quantitative parasite egg count in feces (eggs per gram (e.p.g.)), combined with the usual subjective and objective information obtained in clinical examinations has been the procedure used to obtain a quantitative estimate of the level of infection. More recently, the use of plasma pepsinogen levels as an indication of gastric pathology has been adopted by some laboratories. Neither of these methods have met with the desired level of accuracy, but they do have considerable value when their limitations are recognized. In the present era of emphasis on epidemiologically based control programs we are faced with yet another aspect of diagnosis, namely that of a quantitative estimate of numbers of infective stages (L3) on herbage. Methods to assess the number of L3 on forage are not satisfactory for routine clinical use. This paper evaluates the primary objectives of diagnosis as applied to the herd and flock. It briefly evaluates current methodology insofar as the diagnosis of parasitic gastroenteritis is concerned. The use of e.p.g. counts in clinical practice is discussed. Examples applicable to herds of weaner and stocker cattle are presented.

Anthelmintic treatment of pastured dairy cattle in California.

The relationship of anthelmintic treatment for subclinical gastrointestinal nematode parasitism with resultant milk production was studied on 3 California dairies where animals were maintained on a pasture-based nutritional program. All of the animals that started lactating (freshened) during a 12-month period participated in trials in which coumaphos was given as a feed top dressing to animals averaging 30 days into lactation. All of the animals that freshened during the subsequent 12-month period from 2 of the same 3 dairies participated in trials in which thiabendazole was administered at or within 2 weeks before freshening. Anthelmintic administration during 2 consecutive lactation cycles under the conditions of the present study resulted in no consistent reproducible significant changes in milk production.

Seasonal occurrence of infective nematode larvae in California Sierra foothill pastures grazed by cattle.

Worm-free Holstein tracer calves were used to assess the seasonal variation in number and course of development of nematode parasites of cattle on an irrigated pasture located in the California Sierra foothills. The most common genera of nematodes found in the abomasum and small intestine were Ostertagia and Cooperia, respectively. The infective Ostertagia larvae on herbage were most numerous in early spring and lowest in summer months. Arrested development of Ostertagia occurred in mid-to-late spring. The percentage of the population of Ostertagia found to be arrested larvae was constant (73% to 95%) over 4 years, even though the total number of nematodes in the genus was markedly different. Levels of infection with Ostertagia and Cooperia were found to correlate with pasture contamination occurring in the preceding fall and concurrent winter months. In the cecum and large intestine, Oesophagostomum venulosum was found to be the most common nematode. It is suggested that this species may replace Os radiatum as the cattle nodular worm in regions where climate is similar to that of the southwestern coast of North America. Evidence of seasonal hypobiotic development of Oe venulosum was found. Other genera of nematodes observed in tracer calves were Trichostrongylus, Haemonchus, Bunostomum, Trichuris, and Dictyocaulus.

A potential diagnostic reagent for bovine cysticercosis.

A fraction of larval Taenia hydatigena cyst fluid was shown to have high sensitivity and specificity in the enzyme-linked immunosorbent assay (ELISA) for the detection of bovine antibodies to the heterologous parasite Taenia saginata. This antigenically active lipoprotein fraction was isolated by ultracentrifugal density flotation using either ammonium sulfate (specific gravity = 1.231 g per ml) or NaCl/KBr (specific gravity = 1.225 g per ml), followed by ion-exchange chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) indicated that this fraction was composed of high molecular weight (65,000 to 77,000 Mr) and low molecular weight (9,500 to 16,000 Mr) proteins. Electrophoresis under non-denaturing conditions in either acrylamide (5%) or agarose (1%) resulted in 1 major diffuse band staining for both protein and lipid. The high and low molecular weight proteins observed on SDS-PAGE under reducing conditions could not be resolved by gel filtration chromatography and emerged as a single lipoprotein peak. This T. hydatigena cyst fluid fraction appears promising as a diagnostic reagent in the ELISA for bovine cysticercosis.

Seasonal occurrence of infective nematode larvae in California high Sierra pastures grazed by cattle.

Worm-free Holstein calves were used to assess the seasonal variation in numbers of nematode infective larvae on herbage at 2 commercial cow-calf ranches in the Sierra Nevada mountains. Both ranches used Herefords as their basic breed. One ranch near Sattley, California, is at an elevation of approximately 1,500 m above sea level, whereas the study area on the 2nd ranch near Susanville is at an elevation of approximately 1,250 m above sea level. Worm-free tracer calves were allowed to graze for approximately 30 days and were then kept free of further nematode infection until euthanasia and necropsy approximately 30 days after removal from the pastures. At necropsy, the number, species, and stages of development of nematodes in the gastrointestinal tract were determined. The most common species of nematode in the abomasum was Ostertagia ostertagi and in the small intestine Cooperia oncophora. Infection levels decreased during early summer and were low in midsummer to early fall. In late fall and winter, infection levels began to increase, and highest infection levels were obtained during the spring. A low level of inhibited development (up to 18%) of 4th-stage O ostertagi occurred in November and December. Considerably higher levels of inhibition (up to 61%) were observed in March, April, and May. Inhibition of development in Cooperia spp was not noticed. Other nematodes seen were O lyrata, C mcmasteri, C punctata, Trichostrongylus axei, Haemonchus sp, and Nematodirus helvetianus.

Failure of brewer's yeast as a repellent to fleas on dogs.

Active and inactive brewer's yeast, when given as a dietary supplement to dogs at the rate of 14 g/day, failed to repel or kill fleas. Twenty dogs in each of 3 groups were inoculated weekly for 7 weeks with 100 unfed cat fleas (Ctenocephalides felis). One group served as a control while one group received inactive and the other active yeast during the last 5 weeks of the trial. There were no significant differences in flea counts among the 3 groups during the first 4 weeks of yeast supplemental feedings. Total flea counts during the 5th week of yeast supplementation did not differ significantly from the counts on control dogs, although there was a significant difference between counts from dogs receiving active and those receiving inactive yeast.

Anthelmintic treatment of nonpastured dairy cows in California.

Many dairy cattle are housed under drylot conditions, which generally are not considered conducive to elevated populations of gastrointestinal parasites. Thus, an examination of the potential benefits to be obtained by anthelmintic treatment of lactating cows under these circumstances was initiated. Because there were no statistically significant differences in milk production between control and treated groups, routine deworming cannot be considered economically sound under the management conditions described.

Seasonal occurence of infective nematode larvae on irrigated pasture grazed by cattle in California.

During the period extending from Dec 1, 1975, to Dec 22, 1976, 3 distinct peaks in the concentration of infective nematode larvae on pasture forage were detected by use of helminth-free tracer calves. Two of these peaks, 1 occurring in the spring and 1 in the fall, consisted mainly of Ostertagia ostertagi and Cooperia sp. It is concluded that these 2 peaks can be anticipated annually and constitute unsafe periods of grazing. The 3rd peak was comprised largely of Haemonchus placei and Cooperia sp. It is concluded that this peak occurred as the result of unusual rainfall and reduced evaporation in August. Arrested developed (24% to 30%) of O ostertagi larvae occurred only during the spring peak. This finding indicates that on irrigated pastures in California, type I ostertagiasis can be expected to occur as the result of infection during the spring and/or fall peaks, whereas type II ostertagiasis can be expected to occur in the fall as a result of infection obtained during the spring peak. Arrestment in development of Cooperia sp occurred during spring (14%) and fall (23%) peaks. Haemonchus placei larvae increased their propensity for arrestment in development from zero to 82% during the months following the peak level of infection in summer. Other nematodes encountered were Trichostrongylus axei and Nematodirus helvetianus.

Influence of plasma A esterase on anthelmintic action of haloxon in sheep.

Controlled trials were conducted to evaluate the anthelmintic action of haloxon in 2 phenotypes of lambs, 1 having an A esterase in plasma which rapidly hydrolyzes di-(2-chloroethyl)aryl phosphates and the other without this enzyme. A total of 116 lambs, 57 with and 59 without the plasma A esterase, 6 to 9 months old, harboring naturally acquired nematode infections were used in 3 trials. Haloxon was administered orally at 20, 25, and 35 mg/kg of body weight. Nematodes against which haloxon was evaluated in the abomasum were Ostertagia circumcincta and Trichostrongylus axei and in the small intestine were T vitrinus, T colubriformis, Nematodirus spathiger, and N filicollis. The anthelmintic efficiency of haloxon did not differ in the 2 phenotypes of sheep.

Acute oral median lethal dose of haloxon and coumaphos in sheep as influenced by plasma A esterase.

Determination of the acute oral medial lethal dose (LD50) of haloxon for lambs classified as to the presence or absence of plasma esterases (A esterase; EsA) rapidly hydrolyzing haloxon revealed markedly different values for the 2 phenotypes of sheep. The LD50 for EsA- lambs was 763 mg/kg of body weight with 95% confidence limits of 543 to 1,072 mg/kg. The acute oral LD50 for EsA+ lambs remains undetermined but was demonstrated to be in excess of 11,392 mg/kg. The acute oral LD50 for a closely related organophosphate (coumaphos) was not different in the 2 phenotypes of sheep.

Thiabendazole-resistant strains of Haemonchus and Ostertagia in California lambs.

Ten parasite-free experimental lambs were inoculated intraruminally with a mixed-larvae inoculum which contained approximately 5,000 Haemonchus contortus infective larvae. Five lambs were treated with thiabendazole (66 mg/kg of body weight) and 5 were untreated controls. All lambs were killed 35 days after inoculations were done, and parasites present were recovered. Reduction in numbers of recovered Haemonchus contortus (25.7%) and Ostertagia spp (26.8%) were not significant (P greater than 0.05).

Anthelmintic efficacy of oxfendazole in calves.

Oxfendazole, methyl [5-(Phenylsulfinyl)-1H-benzimidazol-2-yl]carbamate given to calves at dose level of 2.5 mg/kg as a paste, as a bolus, or as a drench resulted in excellent (97 to 100%) anthelmintic efficacy against mature Ostertagia ostertagi, Trichostrongylus axei, Cooperia oncophora, C mcmasteri, C pectinata, C punctata, Nematodirus helvetianus, Trichostrongylus longispicularis, Chabertia ovina, and Oesophagostomum radiatum. Against the early 4th stage larvage of O ostertagia and N helvetianus, these formulations had anthelmintic efficacies of 71% to 87% and 21% to 65%, respectively. As the result of differences in drug intake by individual calves, a pelleted feed additive given as top dress on chopped alfalfa hay gave an unsatisfactory mean anthelmintic response. Anthelmintic action in individual calves ranged from none to 98--100%.

Anthelmintic efficiency of oxfendazole in California lambs.

Oxfendazole, methyl 5(6)-phenylsulfinyl-2-benzimidazole carbamate, was given by oral drench (5 mg/kg) to California lambs harboring natural infections of gastrointestinal nematodes. Ninety-nine percent of adult Ostertagia circumcincta, Ostertagia trifurcata, Trichostrongylus axei, Trichostrongylus vitrinus, Trichostrongylus colubriformis, Nematodirus filicollis, and Nematodirus spathiger were removed by the anthelmintic.

Temephos collars for control of fleas on dogs and cats.

Efficacy of polyvinyl chloride collars containing temephos [0,0'-(thiodi-4,1-phenylene) 0,0,0',0'-tetramethyl bis-(phosphorothioate)] was elevaluated in dogs and cats against the cat flea (Ctenocephalides felis). Over a period of 42 weeks, collared (treated) and control dogs were experimentally infested with 100 fleas 23 times, and control and treated cats were similarly infested 20 times during a 41-week period. Flea populations on treated dogs were reduced by 80% or more for at least 36 weeks. Initially, flea reduction by 80% occurred within 1 day, but in dogs wearing the same collars for 26 weeks, this reduction occurred in 3 to 6 or more days. Only during the first 2 weeks of wearing the collars were all fleas killed on all dogs within a 6-day period after infestation. Residual efficiency was lowest on highly active dogs and greatest on inactive dogs. The residual efficiency on cats was somewhat better than on dogs. At the end of 41 weeks, collars on cats reduced the flea population by 85 to 90% within 1 to 5 days following infestation. Collars on cats, as on dogs, were 100% efficacious only during the first 2 weeks of the trial.

Insecticidal activity of propoxur- and carbaryl-impregnated flea collars against Ctenocephalides felis.

Ten dogs were fitted with 10% propoxur-(0-isopropoxyphenyl methylcarbamate) and 10 dogs were fitted with 16% carbaryl-(1-naphthyl-N-methylcarbamate) impregnated flea collars. Ten cats were fitted with carbaryl-impregnated flea collars. There were 5 control animal for each trial. Insecticidal activity against experimental infestations with the cat flea (Ctenocephalides felis) was evaluated. The propoxur collars on dogs reduced the flea populations by 90% within 2 days of infestation for at least 13 weeks. By the 16th week, the flea population was reduced 65% in 2 days and 87% in 7 days. In subsequent infestations, efficiency was less than 80% after 7 days. Carbaryl collars on dogs reduced the flea population by as much as 80% in 2 days for a period of 16 weeks. An efficiency of at least 80% at 7 days was maintaned for 17 weeks. Carbaryl collars on cats reduced the flea population within 2 days by 80% or more for a period of at least 19 weeks--the last experimental infestation.

Enzyme polymorphism in Fasciola hepatica L.: esterases.

Homogenates of individual adult Fasciola hepatica, collected from bile ducts of sheep, were subjected to isoelectric focusing in polyacrylamide flat-bed gels after which zymograms were made by enzymatic and staining reactions. Seven identifiable isozymes that hydrolyzed alpha-naphthyl acetate were found. These 7 isozymes were identified by their isoelectric points as 5.10, 5.15, 5.25, 5.40, 5.55, 5.65, and 5.75. None of these isozymes was common to all F hepatica examined. Combinations of these isozymes in individual flukes revealed 7 distinct phenotypes, the frequency of which varied between local populations, i.e., populations of flukes obtained from individual sheep of different origin. In addition to these 7 isozymes, there were weak staining bands of enzyme activity, between pH 5.8 and the cathode end of the gels, which could not be accurately identified. The method of isoelectric focusing and zymogram preparation used in the present study did not reveal cholinesterase activity, even though the presence of activity in homogenates was demonstrated by polyacrylamide disc-gel electrophoresis. Strong activity of acid phosphatase between pH 5 and 6 was found, but poor resolution prevented obtaining accurate identification of isozymes. Weak activity with poor resolution of isozymes of alkaline phosphatase was observed between pH 4.4 and 5.75.

Phenotypic differences in female Ostertagia circumcincta as demonstrated by isozymes hydrolyzing alpha-naphthyl acetate.

According to results of disc gel electrophoresis of homogenates prepared from individual female nematodes of the species Ostertagia circumcincta and subsequent staining of gel preparations, a maximum of 5 isozymes, hydrolyzing alpha-naphthyl acetate, were present. On the basis of resolution and mobility, these isozymes could be classified as 2 slow and 3 fast bands. Phenotypic differences were observed in the intensity of individual bands, as well as in the presence (or absence) of bands.