Epizootiology of Ostertagia ostertagi in cow-calf production systems in the American Midwest.

The most common gastrointestinal nematodes found in cattle in the Midwest are Ostertagia ostertagi and Cooperia oncophora. Other parasites include Haemonchus placei, Bunostomum phlebotomum and Nematodirus helvetianus. Parasite numbers are generally low in this region, as indicated by fecal egg counts and tracer calf worm recoveries, and the numbers of parasites decrease as one travels farther north. This decrease in parasite numbers also corresponds to a similar reduction in the prevalence of clinical disease. The dynamics of fecal egg shedding are similar throughout the Midwest. Cow fecal egg counts begin to increase just prior to calving in the spring, continue to rise, reaching a peak in July and August, and return to low numbers (2 or less eggs per gram of feces (epg)) in October. Calves born in the spring (March-May) show increasing numbers of eggs in their feces throughout the grazing season, with peak recoveries in October and November, after which the numbers decline as the calves develop an immunological response. Tracer calf worm recoveries demonstrate pasture contamination for the period grazed. These recoveries show adult O. ostertagi increasing throughout the grazing season then falling to low levels over the winter. Larval inhibition of O. ostertagi, as shown by recovery of inhibited fourth stage larvae (L4) occurs throughout the year, with increasing numbers of larvae recovered in the fall. The production robbing effects of these parasites has been demonstrated by the use of a controlled strategic deworming program. Weaning weight advantages of 14 to more than 20 kg have been reported in this region of the country when compared with an untreated group.2+ !%"

Stromberg BE ，Corwin RM 《VETERINARY PARASITOLOGY》

Epidemiology of Ostertagia ostertagi in cow-calf herds in the southeastern USA.

Snyder DE 《VETERINARY PARASITOLOGY》

Epidemiological observations on gastrointestinal nematode infections in grazing cow-calf pairs in Belgium.

The epidemiology of gastrointestinal helminth infections in beef cows and calves on pasture was studied in Belgium during the 1990 and 1992 grazing seasons. Weight gain, faecal egg counts, generic differentiation of infective larvae, serum pepsinogen levels, herbage larval counts and worm burdens of tracer calves were used as parameters. In Study 1 two groups of ten cows with their spring-born calves grazing on separate pastures (A and B) were monitored during the 1990 grazing season. Ostertagia ostertagi was the predominant species shed by cows and calves. Cows on Pasture A had significantly higher egg counts at turn-out than the B cows, creating a high pasture contamination in the autumn, evidenced by high Ostertagia worm burdens in the Pasture A tracer calves. Calves of both groups showed low egg counts (mean < 60 eggs g-1 faeces, EPG) throughout the grazing season. In Study 2 nine cow-calf pairs were monitored during the 1992 grazing season. The calves were born in winter or spring. Faecal egg counts of the cows remained low throughout the trial period. During the grazing season high egg counts were observed in the calves (mean up to 778 EPG). Cooperia oncophora was the predominant species in the calves. In the cows O. ostertagi, Oesophagostomum, C. oncophora and Trichostrongylus axei were present. It is suggested that, in the first study, the cows were the major source of pasture contamination, while in the second study the winter-born calves, being older and having a higher herbage intake resulting in a higher infection level, were largely responsible for the high Cooperia pasture infection level at housing.

Agneessens J ，Dorny P ，Hollanders W ，Claerebout E ，Vercruysse J ... -  《VETERINARY PARASITOLOGY》

Observations on nematode parasitism in cow-calf production systems in southcentral/southwestern USA.

Miller JE 《VETERINARY PARASITOLOGY》

Monthly fluctuations of worm burdens and hypobiosis of gastrointestinal nematodes of calves in extensive management systems in the Pyrenees (Spain).

Almería S ，Llorente MM ，Uriarte J 《VETERINARY PARASITOLOGY》