When you turn your cow-calves out on pasture, chances are they are going to look alert and healthy. However, as the heat comes on in the heart of the summer, warning signs will begin to appear for those paying attention. The pasture is an increasing hotspot for summer pneumonia and, though the causes are not fully understood, two factors – immunity and exposure – will determine the potential impact of bovine respiratory disease (BRD) on your herd.
Immunity may be affected by the accelerated growth and maturity rates we see in today’s calves, but it is certainly affected by the transition from the mother’s supplemental antibodies to the calf’s developing immune system. Four to six months after first milk, calves enter an immunity “valley” when both sources of natural immunity are at their weakest. Early vaccinations help to keep that valley shallow, which is especially important if it coincides with the summer months when stressors, like heat, dust and humidity, reach their peak. Cattle can adapt to high temperatures, as long as they have access to good water and forage and nights that cool down to around 78 degrees or lower. Sustained temperatures higher than 80 degrees trigger dietary changes and additional stress. Cattle will eat less and drink more, compromising the immune response greater than heat alone.
If summer pneumonia does establish in the pasture, spotting it early and limiting the spread of pathogens is crucial. Isolating infected cattle immediately helps keep the herd healthy and gives sick individuals better access to feed, water and any follow-up treatments they need to recover. Spreading out and periodically moving watering sites and any supplemental feed locations will also help limit crowding and pathogen exposure. Keeping an eye on the health of the herd is important at all times, but especially once an outbreak is in progress. If 10 to 15 percent of your cattle have respiratory symptoms, you and your veterinarian need to consider treating the entire group.
Preventing summer pneumonia is an ongoing process, but it starts with working with your veterinarian to create a comprehensive health program and staying in touch with what is happening in your pasture. You can’t change the weather, but you can vaccinate early to support immunity, stay vigilant and manage your pasture to minimize BRD pathogens. It’s a lot easier to ward off a major outbreak than chase it the rest of the season.