Experimental Eimeria bovis infection in calves: a histopathological study.

Eight male holstein calves, four to six weeks of age, were infected with 100,000 sporulated oocysts of a culture containing Eimeria bovis. The calves were injected with steroids on days 13, 14 and 15 and killed on days 16, 18, 19, 20, 21, 22, 24 and 26 postinfection. The lesions caused by experimental E. bovis infection in the small and large intestines are characterized by a diphtheritic typhilitis and colitis. Severe lesions were also seen in the last metre of the ileum in a calf killed 19 days after infection. Most of the damage of the intestinal mucosa is caused by the sexual stages. There is destruction and loss of epithelial cells with subsequent exposure of lamina propria and formation of diphtheritic membranes.     

Long-term effect of toltrazuril on growth performances of dairy heifers and beef calves exposed to natural Eimeria zuernii and Eimeria bovis infections

The long-term effects of a toltrazuril treatment against natural Eimeria bovis and/or Eimeria zuernii infections were investigated in comparison with diclazuril and untreated controls on two dairy (Italian Friesian breed) and two beef (Chianina breed) farms. At each trial site, 30 calves were allocated into three groups of 10 calves each: T (treated with toltrazuril), D (treated with diclazuril) and C (left untreated). For 40 weeks post-treatment, the calves were weighed and examined clinically and parasitologically. The oocyst counts as well as the number of scour days were significantly lower in the T group than in the D and C groups. Final bodyweights and body condition scores of the T group exceeded those of groups C and D. The results confirmed that toltrazuril was highly efficacious, safe and provided productive benefits in dairy and beef calves.     

Efficacy of tulathromycin in the treatment of bovine respiratory disease associated with induced Mycoplasma bovis infections in young dairy calves

The efficacy of tulathromycin in the treatment of bovine respiratory disease (BRD) due to Mycoplasma bovis was determined following experimental infection. Two highly pathogenic strains of M. bovis (with minimum inhibitory concentration values for tulathromycin of 1 and >64 microg/ml) were inoculated into 145 calves. Four days after inoculation, calves with clinical BRD were treated subcutaneously with saline or tulathromycin (2.5 mg/kg). Compared with saline, BRD-related withdrawals, peak rectal temperatures, and lung lesion scores were significantly lower for tulathromycin-treated calves (P < .01). Tulathromycin was highly effective in the treatment of BRD due to M. bovis in calves regardless of the minimum inhibitory concentration of the challenge strain (1 or >64 microg/ml).     

Efficacy of enrofloxacin against severe experimental Anaplasma marginale infections in splenectomized calves

Four Anaplasma marginale-infected splenectomized calves with greater than 25% parasitized erythrocytes received enrofloxacin at 12.5 mg/kg SC twice, 48 hours apart. Two infected splenectomized calves were designated as untreated controls. A precipitous decline in percent parasitized erythrocytes from 39.13% to less than 1% was observed over 12 days following treatment. However, a self-limiting recrudescence of A. marginale parasites was observed within 30 days after treatment. Untreated control calves became moribund and were euthanized. These data indicate that the regimen of enrofloxacin tested herein ameliorates, but does not eliminate, A. marginale infections in splenectomized calves.     

Efficacy of tilmicosin in treatment of pulmonary infections in calves.

The efficacy of tilmicosin in the treatment of respiratory infections in calves was evaluated. According to a randomised block design, 58 calves with naturally occurring respiratory infections were treated with one of the following products: a single subcutaneous injection of tilmicosin (10 mg/kg liveweight) or daily intramuscular injections of 5 mg lincomycin and 10 mg spectinomycin/kg liveweight, for a minimum of three days. Both treatment groups initially showed similar clinical signs and their initial responses to the treatments were good. However, the tilmicosin treated calves improved more rapidly. Significantly greater improvements (P less than or equal to 0.05) were observed in their demeanour and appetite during the first 10 days after treatment began, and in their respiratory condition between five and 10 days after treatment began.     

Accidental salinomycin intoxication in calves

Twenty-four 10- to 16-week-old calves in a dairy herd in Birjand, Iran, inadvertently received an excessive dose of salinomycin mixed with barley grain. There was 58% mortality within 10 d. The calves had high serum AST, LDH, and CK activities; histopathologic lesions in myocardium, liver, and kidneys; and clinical signs associated with acute and congestive heart failure.     

Efficacy of ceftiofur for treatment of experimental salmonellosis in neonatal calves

OBJECTIVE: To evaluate therapeutic efficacy of a high extralabel dose of ceftiofur for treatment of experimental salmonellosis in neonatal calves. ANIMALS: Forty-two 1- to 4-day-old Holstein bull calves. PROCEDURE: 36 calves were orally challenged with Salmonella enteritica serovar Typhimurium (6.5 x 10(8) colony-forming units). Six additional calves were retained as nonmedicated nonchallenged control calves. Four days following Salmonella challenge, surviving calves were randomly allocated to ceftiofur-treated (5 mg/kg, IM, q 24 h) or nonmedicated control groups. Calves assigned to the treated group were medicated daily for 5 days starting on day 4 after challenge. Calves were monitored for 18 days following Salmonella challenge. Outcome assessments included clinical parameters (attitude, appetite, fecal characteristics, and rectal temperature), mortality rate, and quantitative Salmonella culture of fecal samples, mesenteric lymph nodes, and cecal contents. RESULTS: Ceftiofur treatment was associated with a significant decrease in rectal temperature and diarrhea. Three of 15 medicated calves and 4 of 14 non-medicated calves died or were euthanatized between days 4 and 18. A significant decrease in fecal shedding of Salmonella organisms was observed in treated calves, compared with nonmedicated calves. Salmonella organisms were isolated from all 10 non-medicated calves at necropsy, whereas no Salmonella organisms were isolated from 5 of 12 medicated calves. CONCLUSIONS AND CLINICAL RELEVANCE: Treatment of salmonellosis in neonatal calves with a high extralabel dose of ceftiofur (5 mg/kg, IM, q 24 h) promotes animal welfare, reduces fecal shedding of Salmonella organisms, and may promote clearance of Salmonella infections when plasma ceftiofur concentrations are maintained above minimal inhibitory concentrations.     

Efficacy of oral clorsulon in the treatment of Fasciola hepatica infections in calves

Twenty calves at each of 2 Arkansas locations were inoculated with infective Fasciola hepatica metacercariae. After 56 days, the calves at each site were randomly assigned by weight to 2 treatment groups of 10 calves/group; vehicle control or clorsulon at the rate of 7 mg/kg of body weight. All treatments were given orally as a suspension. Calves were killed 6 weeks after treatment and F hepatica counts were performed for all animals. At the 2 sites, mean levels of efficacy were 96% and 91%. Adverse reactions to clorsulon or the vehicle were not observed in the calves.     

Concurrent experimentally induced infection with Eimeria bovis and coronavirus in unweaned dairy calves.

Over a period of 3 summers, 21 colostrum-fed Holstein bull calves, 1 to 3 days old, were assigned to 7 replicates, each consisting of 3 calves. Within each replicate of 3 calves, 2 were selected at random, to be given 100,000 to 146,000 sporulated coccidia oocysts (principally Eimeria bovis) orally 60 hours after arrival at the college research farm. On the thirteenth day after coccidia inoculation, 1 of the 2 calves that had been given coccidia and the third calf that had not been inoculated, were given coronavirus by intranasal and oral routes. Calves were observed daily, and consistency of feces was scored visually. Nasal swab specimens for indirect immunofluorescent antibody testing for coronavirus and fecal samples for oocyst determination were obtained approximately every third day. Of 7 calves that were given only coronavirus, 3 developed diarrhea of short duration. Of 7 calves that were given only coccidia oocysts, 6 developed diarrhea. All 7 calves inoculated initially with coccidia and subsequently with coronavirus developed diarrhea. For 5 of 7 replicates, calves that were given coccidia and coronavirus developed diarrhea first. When overall severity, measured by fecal score and by blood in the feces, was compared, calves inoculated with coccidia followed by coronavirus were more severely affected (P less than 0.05) than were calves that were given only coronavirus. Calves that were given only coccidia oocysts appeared more severely affected than calves that were given only coronavirus, but differences were not significant.(ABSTRACT TRUNCATED AT 250 WORDS)     

Extraintestinal stages of Eimeria bovis in calves and attempts to induce relapse of clinical disease

Monoclonal antibodies to all life cycle stages of Eimeria bovis were used in an avidin-biotin immunoperoxidase test to examine extraintestinal tissues from experimentally infected calves for developmental stages of the parasite. First-generation meronts of Eimeria bovis were found in the mesenteric lymph nodes (MLNs) of three of four calves examined during the first 18 days of primary experimental infection. No extraintestinal stages were found in the MLNs of two calves examined 69 days after a primary infection or in five calves examined 6 months after a challenge infection. Tissue homogenates of liver, spleen, and MLNs from immune calves were not infectious for nonimmune recipient calves following oral or intraperitoneal inoculation indicating that infectious stages were not present in these extraintestinal tissues at the time of inoculations. Relapse of clinical coccidiosis and reoccurrence of oocyst shedding were not seen in E. bovis immune calves that were stressed by being put on a 16-week corticosteroid treatment program.     

Efficacy of tulathromycin for treatment of cattle with acute ocular Moraxella bovis infections

OBJECTIVE: To evaluate the clinical efficacy of a single injection of tulathromycin, compared with saline (0.9% NaCl) solution-treated control calves, for treatment of induced infectious bovine keratoconjunctivitis in calves. DESIGN: Clinical trial. ANIMALS: 30 Holstein bull calves ranging from 5 to 6 months old and 75 to 200 kg (165 to 440 lb) with no history of Moraxella bovis infections, no history of M bovis vaccination, and negative results for M bovis on 3 consecutive ocular bacterial cultures. PROCEDURES: Both eyes of each calf were infected with 1 X 10(10) colony-forming units of piliated M bovis for 3 consecutive days prior to the trial. On day 0, ocular lesion scores were determined for each calf and the calves were weighed and assigned to a treatment (2.5 mg/kg [1.14 mg/lb] of body weight, SC) or control group according to a stratified random allocation based on weight and lesion score. Eyes were stained with fluorescein and photographed daily to record healing. Eyes were evaluated bacteriologically for M bovis on days 0 to 6 and at 3-day intervals thereafter. RESULTS: Median time to ulcer resolution in calves treated with tulathromycin was 9.1 days. More than 50% of control calves still had ulcers at the end of the trial (21 days). Moraxella sp was isolated less often from the eyes of treated calves than from the control calves. By day 10, the treated calves had lower ocular lesion scores than control calves. CONCLUSIONS AND CLINICAL RELEVANCE: A single dose of tulathromycin (SC) was an effective treatment of calves with experimentally induced infectious bovine keratoconjunctivitis. The long serum half-life of tulathromycin, along with the results of this trial, suggests that tulathromycin may be a rational choice as a single-injection treatment for infectious bovine keratoconjunctivitis.     

Epidemiological study of risk factors for Mycoplasma bovis infections in fattening calves

To establish the role of Mycoplasma bovis as an agent of respiratory disease in fattening calves, an epidemiologic study was undertaken. A recently validated commercially available ELISA was used to diagnose M. bovis infection by seroconversion in paired sera obtained for each animal at entry in the fattening herd and at follow-up seven weeks later. Management data as well as relevant clinical and epidemiological variables were prospectively recorded. The overall seroconversion rate observed among the 415 calves in 23 fattening herds on 13 farms was 54.7%. Significant risk factors for seroconversion were the mixing of fattening herds of different age groups (risk ratio RR 1.70, 95% confidence interval (CI) 1.48 to 1.96), and the presence of at least one seropositive animal in the fattening herd (RR: 2.02; CI: 1.69 to 2.40). The proportion of clinical episodes of respiratory disease attributable to M. bovis infection was 50.3%. The average weight gain during the observation period was reduced by 7.6% in seroconverting calves and these animals had about 2 times more antibiotics prescribed by a veterinarian than calves remaining negative for M. bovis throughout follow-up (RR 1.83). Maternal antibodies against M. bovis were detected in 39% of newborn calves born from seronegative cows and had a half-life of 20 days, potentially limiting the usefulness of vaccines against M. bovis in this age group.     

Treatment of Moraxella bovis infections in calves using a long-acting oxytetracycline formulation

George, L.W. & Smith J.A. Treatment of Moraxella bovis infections in calves using a long-acting oxytetracycline formulation. J. vet. Pharmacol. Therap. 8, 55–61.
Studies were undertaken to determine the effectiveness of an oxytetracycline HCl formulation for the prophylaxis and treatment of chronic Moraxella bovis ocular infections in calves. Two separate experiments were performed. For the first, calves were separated into two groups and the eyes were infected with M. bovis. The eyes of these calves were observed and cultured for 37 consecutive days. On the 37th and 40th day, each of the five calves were treated intramuscularly with the drug (20 mg/kg of body weight). The other five calves (second group) remained untreated as controls. The cultures from the five treated calves were negative after the first antibiotic administration and remained so for 14 days. M. bovis was isolated from each eye of the control calves at least once during that time. None of the antibiotic-treated calves was completely resistant when reinfected with M. bovis. For the second experiment, calves were given a prophylactic administration of the formulation and were then infected with M. bovis 48 ( n = 4 calves) or 72 ( n = 4 calves) h later. These treatments resulted in a lower incidence of keratoconjunctivitis and a decreased duration of bacterial shedding, as compared to controls ( n = 8 calves), but did not completely prevent the occurrence of disease or the establishment of ocular infections.
Lisle W. George, Department of Medicine, School of Veterinary Medicine, University of California, Davis, CA 95616, U.S.A.     

Influence of experimental Eimeria zuernii infection on clinical blood chemistry in calves

Coccidiosis, often caused by Eimeria zuernii infection, is an important diarrhoeal disease in calves [Fitzgerald, P.R., 1980. The economic impact of coccidiosis in domestic animals. Adv. Vet. Sci. Comp. Med. 24, 121-143]. Infection trials were performed to investigate the effects of experimental E. zuernii coccidiosis on clinical blood chemistry in calves. Three groups of calves were formed: group 1 (n=14) served as uninfected control group, group 2 (n=11) was infected with 150,000 sporulated E. zuernii oocysts per calf, and group 3 (n=16) was infected with 250,000 sporulated E. zuernii oocysts per calf. Measurements throughout the prepatent and the patent period revealed a marked influence of E. zuernii infection on the following parameters: total protein, albumin, urea, bilirubin, creatine kinase, free fatty acid concentration, and cholesterol. Aberrances in these were most pronounced in group 3. No significant and/or distinct changes after infection could be detected in blood glucose concentration. E. zuernii infection impairs intestinal function and induces catabolic metabolism in affected calves. Bilirubin, urea and cholesterol concentration, and creatine kinase activity were particularly affected indicating catabolism of protein and lipids.