In the dairy and beef industries, bovine respiratory disease (BRD) is one of the main causes of morbidity and mortality of animals in early life.
Dr. Tiago Tomazi, cattle technical services veterinarian with Merck Animal Health, said a USDA study identified BRD as the second most frequent cause of morbidity in dairy calves, resulting in economic losses to the industry.
“Overall, the cost of BRD in young calves is reflected in both the immediate cost of treating the disease and the lifetime impairment of the reproductive performance,” said Tomazi, “even reducing the weight of animals in pre-weaning period.”
The cost of death loss amounts to more than the market value of the calf and treatment cost. Inputs for the dam such as forage, grain, supplements, water and fuels are also wasted.
For dairy or dairy x beef crosses entering the beef sector, BRD can also result in significant economic loss. BRD during the feedlot period decreases average daily gain, marbling, quality grade and increases mortality risk.
While economic losses can be significant, there’s another aspect to consider. Tomazi believes recognizing and treating BRD promptly is the right thing to do for calves and has an impact on consumers’ perception about the dairy industry.
“BRD is a multi-factorial syndrome triggered by a combination of factors – environmental factors, the calf [host] and the infectious agent,” said Tomazi. Poor colostrum management, transportation, weaning, feed changes, weather conditions, insufficient ventilation and overcrowding can all lead to immunosuppression and stress, making animals more susceptible to viruses and bacterial disease.
Tomazi urged dairy farmers to consider the stressors that can lead to bacterial colonization of the calf’s upper respiratory tract. Age, weaning, dietary changes, transportation stress, co-mingling, antibiotics and vaccinations, disease and pathogen exposure affect the microbiome that inhabits the calf’s respiratory tract and can disrupt the interaction between the host’s immune system, mucosal epithelial tissue and resident microbiota. The result is a compromised respiratory tract that’s predisposed to pathogenic and virulent microorganisms that lead to pneumonia.
“Cattle are more susceptible to pneumonia than other species because of their anatomy,” said Tomazi. “The total lung capacity of an adult cow is only 2.5 times greater than that of an average man, yet its resting oxygen requirement is more than 10 times greater.”
BRD management begins with prevention. “The goal is to make the calf more resilient to the challenges associated with BRD and other diseases,” said Tomazi. “It always starts during the prenatal period. If a cow faces severe challenges while pregnant, such as nutritional deficiencies or chronic stress, the organs of the fetus will not develop properly, which can affect the calf’s capacity to respond to challenges later in life. Everything starts when the calf is still in the cow.”
Good calving hygiene is also key to prevention, starting with a maternity area that’s used only for calving. Prevent the entry of disease into the calf area by limiting access by those who have worked with sick animals. When possible, remove calves promptly, prior to them standing up, and prevent them from ingesting manure in the pen or attempting to nurse a dirty udder.
An important factor in preventing BRD and other diseases is colostrum management. “Colostrum is the single most important meal the dairy animal will ever receive in their life,” said Tomazi. “Colostrum ingestion is the baseline for building robust, immune competence in cattle.”
While vaccines can play a key role in reducing the incidence of BRD, Tomazi said calves benefit more from vaccines if a good health program is in place. “If we cover all the basics (nutrition, comfort, well-being), we promote good organ development and immunity,” he said. “Immunity can be boosted by the use of proper and efficacious vaccines.”
High infection pressure can overwhelm immunity, even in a well-immunized animal, and result in disease. Calves affected by pneumonia will likely develop permanent lung lesions. Lung consolidation (airways filled with fluid) due to infection with pneumonia is the reason calves die or perform poorly if they survive. As adults, cows affected as young calves typically produce less milk.
Tomazi believes the extent of lung damage in an affected calf is related to recognizing early signs and appropriate treatment. “Diagnosis at the first signs of BRD plus timely treatment with effective antibiotics can make a huge difference in controlling BRD,” he said.
Several challenges may hamper recognizing early signs of BRD. One is that as prey animals, cattle tend to hide illness. This makes it more difficult for calf caretakers to recognize early signs. “By the time signs of illness are noticeable, the animal has likely been sick for at least a few days,” said Tomazi. Clinical signs are less evident when disease is first present, but the chance of good response to treatment is greater.
It’s easy to single out sick animals for treatment, but noticing signs of illness before lungs are damaged is critical. Screening for BRD must be timely and done by those who are willing to learn to look for early, subtle signs. Tomazi urged dairy farmers to focus on less obvious initial signs to reduce losses.
Those early signs of BRD include mild depression, lethargy, less interest in surroundings, reluctance to eat or drink and slow movement. There’s usually excessive drooling and nasal discharge, which is initially clear. Calves with excessive nasal discharge will clean their nostrils more frequently. This is a subtle sign that can help with early diagnosis.
One barrier to early BRD detection and treatment is inadequate employee training. Tomazi believes training employees to recognize early signs helps them understand the importance of recognizing them. Many workers on large farms don’t have prior livestock experience and aren’t familiar with subtle signs of illness, but this issue can be overcome with training.
Another problem is insufficient personnel who are already struggling to finish tasks. Language barriers can be problematic, but good dairy managers facilitate communication.
Tomazi said it’s a matter of when – not if – BRD will occur on the farm. Even dairy operations with the best management practices can experience BRD, but early detection and prompt treatment can help protect calf health and long-term outcomes.
by Sally Colby