Effects of 3-methylindole production and immunity against bovine respiratory syncytial virus on development of respiratory tract disease and rate of gain of feedlot cattle

OBJECTIVE

To determine whether immunity against bovine respiratory syncytial virus (BRSV) mitigates the effects of 3-methylindole (3MI) on occurrence of bovine respiratory tract disease (BRD) and rate of gain in feedlot cattle.

ANIMALS

254 mixed-breed beef cattle.

PROCEDURE

Cattle were randomly assigned to 1 of 3 groups at the time of arrival at the feedlot. One group was vaccinated with an inactivated BRSV vaccine, another was vaccinated with a modified-live BRSV vaccine, and the third was maintained as unvaccinated control cattle. On days 0 and 28, serum BRSV antibody concentrations were measured, using serum neutralizing and ELISA techniques. Serum 3MI concentrations were measured at feedlot arrival and 3 days later. Cattle were monitored for development of BRD. At slaughter, lungs were evaluated grossly for chronic lesions.

RESULTS

Higher serum 3MI concentrations early in the feeding period were associated with lower mean daily gain. Control cattle were more likely to be treated for BRD after day 3, compared with cattle vaccinated with the modified-live BRSV vaccine. Humoral immunity against BRSV did not appear to modify the effect of 3MI on development of BRD or mean daily gain.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that abrogating the effects of 3MI and BRSV infection may improve the health and growth performance of feedlot cattle. However, in this study, immunity against BRSV did not appear to protect against the potential synergism between 3MI and BRSV infection, possibly because of the slow rates of gain of cattle included in the study or timing of sample collection.

Evaluation of the ability of orally administered aspirin to mitigate effects of 3-methylindole in feedlot cattle

OBJECTIVE

To evaluate the ability of orally administered aspirin to mitigate 3-methylindole (3MI)-induced respiratory tract disease and reduced rate of gain in feedlot cattle.

ANIMALS

244 beef cattle.

PROCEDURE

In a masked, randomized, controlled field trial, calves were untreated (controls) or received a single orally administered dose of aspirin (31.2 g) on entry into a feedlot. Serum 3MI concentrations were measured on days 0, 3, and 6. Rumen 3MI concentration was measured on day 3. Cattle were observed daily for clinical signs of respiratory tract disease. Lungs were evaluated at slaughter for gross pulmonary lesions.

RESULTS

Mean daily gain (MDG) in cattle treated with aspirin, compared with control cattle, was 0.06 kg greater in the backgrounding unit and 0.03 kg greater for the overall feeding period. Neither serum nor rumen 3MI concentrations appeared to modify this effect. Cattle treated with aspirin were more likely to be treated for respiratory tract disease. Mortality rate, gross pulmonary lesions, and serum and rumen 3MI concentrations were similar between groups. Increased rumen 3MI concentration was associated with a small difference in risk of lung fibrosis.

CONCLUSIONS AND CLINICAL RELEVANCE

Cattle given a single orally administered dose of aspirin on feedlot entry had higher MDG in the backgrounding unit and for the overall feeding period, but this finding could not be attributed to mitigation of effects of 3MI. This may have been influenced by low peak 3MI production and slow rates of gain.

Evaluation of an acriflavine disk assay for differentiating Staphylococcus aureus from other staphylococci isolated from bovine milk

OBJECTIVE

To develop an acriflavine disk assay for identification of Staphylococcus aureus and to test whether the acriflavine disk assay could be used to differentiate S aureus from other staphylococci isolated from bovine milk samples.

DESIGN

Prospective study.

SAMPLE POPULATION

882 staphylococcal isolates from bovine milk samples and 3 S intermedius isolates from dogs.

PROCEDURE

Paper disks saturated with various amounts of acriflavine were used in a growth inhibition assay to determine the amount of acriflavine that would most reliably differentiate S aureus from other staphylococci. For all isolates, hemolytic pattern, results of tube coagulase tests after 4 and 24 hours of incubation, growth on acriflavine-supplemented media, results of an acriflavine disk assay, and results of an automated identification system were determined.

RESULTS

10 micrograms of acriflavine/disk was determined to be the most appropriate concentration for use in the assay. All 112 isolates identified as S aureus by the automated identification system were resistant to this concentration of acriflavine, and only 1 of 236 isolates identified as non-S aureus staphylococci was resistant. There was substantial agreement between results of using the acriflavine disk assay as a diagnostic criterion for differntiating S aureus isolates from non-S aureus staphylococci and results of the automated identification system. Agreement between results of determining hemolytic pattern and results of other diagnostic tests was only moderate.

CLINICAL IMPLICATIONS

The acriflavine disk assay, using 10 micrograms of acriflavine/disk, was a practical, accurate method for differentiating S aureus isolates from non-S aureus staphylococci.

Effects of oral administration of a calcium-containing gel on serum calcium concentration in postparturient dairy cows

Various nutritious nutritional-supplement gels are being marketed for use in veterinary medicine. This study was designed to determine whether serum calcium, phosphorous, or magnesium concentrations were different between cows given a gel containing calcium chloride as its active ingredient (treated) and cows given inert carrier gel (control). The study revealed a significant (P < 0.01) increase in serum total calcium concentration within 5 minutes of administration of a calcium gel given to cows within 1 hour of parturition. Serum total calcium concentration had returned to baseline value by 24 hours after calcium gel administration. Serum inorganic phosphorus concentration also increased significantly (P < 0.05) after treatment. Significant changes in serum magnesium concentrations were not detected.

Hemangiosarcoma of the external naris in a cow

A tumor was removed from the nose of a 4-year-old Holstein. Hemangiosarcoma was diagnosed on histologic examination. Redevelopment of the tumor necessitated a second surgery. Routine CBC and serum biochemical analysis were normal. Clinical signs of metastasis were not reported by the owner during the next 13 months before the cow was sold for slaughter.

Sex-related susceptibility of bulls to gastrointestinal parasites

The effects of sex and anabolic implants on fecal egg counts and pasture contamination were examined in 77 naturally infected yearling bulls, steers, and heifers of mixed beef breeds grazing the same contaminated pasture in southern Ohio in the spring of 1990. Fecal egg counts were compared in seven groups of 10-14 animals each, twice before anabolic implants and twice after implants. Comparisons were made between untreated bulls, steers, and heifers, between steers with and without implants, and between heifers with and without implants. Bulls had significantly (P < 0.01) higher fecal egg counts than steers, and counts from steers were not significantly different to those from heifers. There were no significant differences between counts from implanted and control steers or heifers. The results have important practical implications both for parasite control and for bovine parasite research. There is a need to pay special attention to young bulls when designing parasite control programs, and to distribute the sexes equally between groups when doing research trials with cattle of mixed sexes. Some previous studies on worm population dynamics and anthelmintic evaluation may need to be re-examined in the light of sex differences.