Coccidia in Hereford Calves on Summer and Winter Ranges and in Feedlots in Utah

Abstract

Field experiments were conducted to study the incidence of coccidia in young Hereford calves during two grazing and feeding seasons. Oocysts of Eimeria auburnensis, E. bovis, E. canadensis, E. cylindrica, E. ellipsoidalis, E. subspherica, and E. zurnii were identified. Eimeria zurnii appeared to be the causative agent of winter coccidiosis although E. bovis was frequently present in small numbers. The incidence of infection, as determined by periodic fecal examination, increased from zero after birth to 100 per cent approximately 2 months after weaning. The incidence rate did not always include the more pathogenic E. zurnii and E. bovis; however, there was a marked increase in the incidence of infections caused by E. zurnii and E. bovis during the fall and winter. Tranquilizers were used in one experiment, and some calves were weaned slowly in attempts to alleviate the of weaning and to prevent outbreaks of winter coccidiosis. Nevertheless, outbreaks occurred during each of the study years. The estimated loss from coccidiosis in cattle in the United States is approximately $10 million annually (Agricultural Research Service, 1954). Of the estimated $37.4 million loss in cattle attributed to internal parasitism, more than one-fourth is due to coccidiosis. The major portion of this loss probably occurs in animals of less than 1 year of age, which are in feedlots being prepared for market. A condition known as winter coccidiosis has been known to occur in commercial feedlots and on ranches of the western United States north of central Colorado, Utah, Nevada, and California for several years. The infections usually occur during the winter, when cold or sloppy weather is common, most frequently affecting calves in their first winter. The principal symptom is a diarrhea, which typically becomes bloody. In severely affected animals, tenesmus occasionally results in prolapse of the rectum. There is rapid loss of condition, lack of appetite, and sometimes convulsions. Death losses as high as 25 per cent have been observed in weanling calves in severe outbreaks. Recovery is usually slow, and frequently animals recovering from severe attacks do not grow well. The pattern of coccidial infections in Hereford calves on ranges has not been reported and little is known of the rate at which infections are acquired and the species that are involved. Stress is often suggested as a factor conReceived for publication 6 November 1961. tributing to outbreaks of winter coccidiosis. The present investigation was undertaken to secure information relative to the pattern of coccidial infections acquired on the range, the rate of build-up in the herd, and the influence of some stress factors.