Many farmers and feedlot owners have first-hand experience of the damage respiratory diseases can cause to a cattle farming enterprise. Although pneumonia is a multifactorial disease that can be caused by a multitude of viruses, infectious bovine rhinotracheitis (IBR) is frequently diagnosed in herds and feedlots. It is a member of the herpes family of viruses and certain animals in a herd can be carriers; it is eventually shed when cattle are exposed to stressful conditions.
There are several stress factors that weaken an animal’s immune system and impede its ability to fight the virus. It subsequently damages the mucous membranes in the animal’s respiratory system. To purposefully manage pneumonia caused by IBR or any other virus, a number of management practices must be assessed in order to address all the factors associated with this disease.
Effect of respiratory diseases on herds
Pathogenic organisms have no trouble harming an animal’s respiratory system if the animal’s immune system is not functioning as it should. Stressful environmental factors such as long-distance transport, mingling of cattle and substandard feed management can make cattle more susceptible to lung and respiratory tract infections.
IBR in cattle is one of many pathogenic micro-organisms that can lead to bronchopneumonia. Bronchopneumonia in cattle causes inflammation in the trachea that leads to the lungs. Pathogenic organisms such as IBR, bovine viral diarrhoea (BVD), parainfluenza virus type 3, various bacteria, mycoplasma and Chlamydophila can all lead to primary and secondary infection of the lungs and upper respiratory tract.
Whereas a virus such as IBR usually acts as the primary agent causing superficial lesions on the lungs, bacteria such as Mannheimia haemolytica, Pasteurella multocida and Histophilus somni act as the secondary agents, which will contribute to the development of full-scale pneumonia. Mycoplasma organisms are isolated in only 50% of pneumonia cases.
Negative environmental factors that induce stress in cattle play a key role in the development of pneumonia. The immune systems of carriers of IBR are weakened by stress conditions, which inhibit the various defence mechanisms of the upper regions of the animal’s respiratory system, thus allowing the virus to wreak havoc in the bovine’s lungs.
Of all the diseases found in feedlots, pneumonia is the main source of economic losses. Weight loss in animals and the cost of antibiotic treatments are but a few of the economic implications that can drastically affect a producer’s pocket.
Yet in South Africa, IBR is more frequently diagnosed in cattle than lung disease (contagious bovine pleuropneumonia), as animal health authorities have all but eradicated lung disease by culling infected animals immediately.
The clinical signs
According to renowned veterinarian and manager of the Ruminant Veterinary Association of South Africa (RuVASA), Dr Faffa Malan, it has been shown that an animal may have been ill for at least three to four days by the time the farmer detects the early clinical signs of pneumonia.
Bronchopneumonia will usually develop ten to 14 days after a stressful event. Additional cases can also be diagnosed in the herd two to three weeks after the first cases have been observed. Pneumonia can at times affect up to 50% or more of the animals in a herd.
Animals should be vaccinated timeously and livestock that have already contracted pneumonia, must be treated as soon as possible to ensure the best prognosis.
In feedlot cattle the most obvious clinical sign is usually a suppressed appetite. Although feed intake is difficult to measure, the affected animal will become more emaciated as the infection worsens. The behaviour of the animal can also change from a curious disposition to more asocial tendencies.
As full-scale pneumonia develops, other signs such as fever, lethargy, nasal discharge, watery eyes, and a high respiration rate coupled with laboured breathing will present itself. Movement can also become difficult and the animal may appear to be more rigid than usual.
Prevention and control
Animals should be vaccinated timeously and livestock that have already contracted pneumonia must be treated as soon as possible to ensure the best prognosis. According to Doc Faffa, injectable vaccines are sometimes less effective than those administered via the nose.
Most combination vaccines aimed at fighting respiratory infections include all the viruses that can cause pneumonia.
“It is vital to follow a good immunisation programme. Cows must be vaccinated prior to calving so that the antibodies in the colostrum can protect the calf. The calf must ingest enough colostrum within the first eight hours post calving. Good birth management is therefore essential in order to build up your herd’s resistance to diseases such as pneumonia,” explains Doc Faffa.
Early treatment with antibiotics is extremely important to avoid chronic conditions in the herd and to optimise calf growth. Although antibiotics can only help fight bacterial infections in the lungs, the elimination of stress factors will help cattle to regain immunity, which will reduce the outbreak of viral infections. – Claudi Nortjé, Stockfarm
For more information, contact Dr Faffa Malan on 082 908 8666 or firstname.lastname@example.org.