The upper respiratory tract is frequently infected with viral pathogens. Elimination of normal flora by antibiotics can make the disease better or worse. Therefore, although culture and isolation is complicated by an abundant commensal population, it is very important to make a diagnosis. Purulent discharge is not pathognomonic for bacterial infection. Antibiotics are probably not indicated in the majority of upper respiratory tract infections in any species.
Infections of the lower respiratory tract are relatively common. Usually the bacteria concerned are aerobes and approximately two thirds are G-. Except in the case of aspiration pneumonia, pure infections are common. Therefore, culture and sensitivity testing is usually successful and valuable.
Cattle and sheep live outdoors at grass in NZ which means that they avoid most of the respiratory diseases caused by intensive husbandry systems overseas (pigs and chickens are not so lucky). In cattle, these are generally lumped together as bovine respiratory disease complex. Extensive use of antibiotics overseas has resulting in a high prevalence of resistance: this is not the case in NZ. Because these infections often occur as outbreaks in a herd, cost is a major consideration in the choice of drug. Transtracheal washings (or post mortem samples) followed by smear culture and sensitivity may be necessary to find the cheapest effective drug. Remember milk and meat residues!
Antibiotics are not a substitute for good husbandry.
| animal | disease | bacteria | first choice | second choice |
| cattle & sheep | pneumonia / BRD | Pasteurella ± others | penicillin< | oxytetracycline |
| horse | pneumonia | Streps | penicillin | |
| foal | pneumonia | Rhodococcus equii, Strep zooepidemicus | erythromycin & rifampicin | azithromycin |
| horse | strangles | Strep. equii | penicillin | co-trimazine |
| dog & cat | pneumonia | Pseudomonas, E. coli, Klebsiella | gentamicin | enrofloxacin |
| Streps & Staphs | ampicillin | erythromycin | ||
| unknown< | co-amoxyclav | co-trimazine | ||
| pigs | enzootic pneumonia | Mycoplasma | tylosin | oxytetracycline |
| pleuropneumonia | Actinobacillus | penicillin | oxytetracycline |
