Have you ever given vaccinations to an entire group of calves only to have a large number of them still end up getting scours or BRD? You may be blaming it on vaccine storage or handling. While this is always a possibility, there is also a strong chance that you are experiencing the negative effects of stress on vaccination efficacy.
No vaccination program can completely eradicate the possibility of disease in your cattle herd. Vaccines are meant to augment and strengthen immunity against the wide variety of diseases that can infect cattle and impact production. Even a fully vaccinated animal can contract any number of diseases if they are not in optimum health and receiving nutrition adequate enough to support a latently strong immune system. It is necessary to ensure that calves and adult cattle are in top shape before receiving vaccines, or the results will be sub-par at best.
It’s been established that there is a direct connection between the strength and effectiveness of a cow’s immune system and the amount of stress they experience. Stress hormones, namely cortisol, have a direct impact on the functioning of the rumen. Stress from any source (i.e. transport, poor or excessive handling, inadequate nutrition, cramped or unsanitary living conditions, heat stress, transitions from pasture to the feedlot, etc.) can create a myriad of problems, including a decreased positive response to herd vaccination programs.
Hormonal Stress Response and Vaccinations
When cattle are stressed, a complex physiological process takes place with the release of hormones such as cortisol, adrenaline, and norepinephrine. Although essential to help an animal escape danger, stress hormones can remain elevated due to environmental or health factors. Careful management of herds through proper handling, adequate nutrition, and immune support can markedly reduce the overall exposure of the body’s systems to the aforementioned hormones.
The most abundantly released of the stress hormones, cortisol is beneficial in normal amounts, but at elevated levels, it can start to have negative effects. When detected at heightened levels, it has been noted to result in less time spent in rumination; thus, a correlation exists between poor digestion and higher serum levels of cortisol. If cortisol concentration is elevated for extended periods of time, it suppresses immune defense, lowering the cow’s ability to fight off diseases.
Frequent release of cortisol and other hormones into the bloodstream can upset the delicate pH balance of the rumen by causing a die-off of the gut’s beneficial bacteria, allowing harmful bacteria to take hold, upsetting the pH balance. Gut flora is an integral element in a healthy rumen and allows for proper digestion and utilization of nutrients. Cattle depend on the fermentation processes of the rumen to break their feed down into easily assimilated components. When the bacterial balance is disturbed, fermentation doesn’t take place at the same rate or efficacy, creating a firestorm of problems throughout the cow’s entire system. In extreme cases, this can lead to acute or sub-acute acidosis. It has been established that at least 80 percent of a cow’s immune defenses lies within the rumen, emphasizing the importance of lowering stress levels in the herd.
As a result of the release of stress hormones during a stress response, body tissues can be broken down, potentially causing an inflammatory reaction. When this occurs, yet more cortisol is released. Further, stress hormones are metabolized by the liver and kidneys, placing an additional burden on the body as it attempts to break down and clear these neurochemicals. Reducing stress in cattle is of utmost importance to guarantee a healthy herd, and thus an effective vaccinations program.