By this point, almost everyone in the dairy industry has heard of highly pathogenic avian influenza (HPAI) H5N1. The first case of HPAI in dairy cattle was identified on a farm in Texas in the spring of 2024. Since then, as of press deadline, 962 farm cases have been identified along with at least 40 cases where the virus was transmitted to humans. Farm cases have been identified in Texas, Kansas, Michigan, New Mexico, Idaho, Ohio, North Carolina, South Dakota, Colorado, Wyoming, Minnesota, Iowa, Oklahoma, California, Utah and Nevada. In the situations where the virus has been transmitted to humans who had contact with dairy cattle, fortunately symptoms have been fairly mild and have included conjunctivitis (eye infection), mild flu-like symptoms and acute respiratory illness. All identified human cases recovered fully.

Stephen B. Blezinger

Nutritionist / Reveille Livestock Concepts

Dr. Stephen Blezinger is a nutritional and management consultant with an office in New Ulm, Texas.

Email Stephen B. Blezinger

As the name implies, the virus is highly infectious and can spread rapidly. In infected farms, morbidity rates have ranged from 10% to 20% and have been as high as 40%. Mortality rates have been much less at less than 5%. In avian species, where the virus got its foothold, mortalities are much higher, with infected flocks experiencing almost 100% in extreme cases and with numerous flocks that had to be terminated when the disease was identified.

One problem in cattle affected by HPAI is the development of secondary diseases or co-morbidities, particularly respiratory infections. Losses from secondary infections have resulted in higher rates of death loss, somewhere around 15%.

While mortality rates in dairy cows are thankfully low, losses in production are more significant. Affected individual animals in herds show production effects including: 

• Decreased dry matter intake
• Concurrent reduction in rumen fill
• Decreased milk production
• More concentrated, thicker milk consistency and color change (yellow to gray)
• Variable increase in somatic cell count
• Change in fecal consistency, which can range from very loose to very firm

Obviously, production losses are an issue. Some herds, overall, have experienced a production decrease up to 30%. The number of animals that recover fully is highly variable. Having a herd infected can be a long-term problem.

Since there is no vaccine currently on the market, a primary way of managing the problem is prevention and avoidance. A variety of biosecurity measures have been recommended to prevent exposure from outside sources including personnel, equipment, feed, etc.  

At this point, effective treatment is still being researched. Currently, treating an infected animal, once identified and removed from the milking string, primarily focuses on supportive care. This largely includes hydrating the patient, supporting the rumen and decreasing fever. Support includes feeding free-choice hay or long-stemmed forage and administering oral drench and IV fluids, probiotics, injectable B vitamins to stimulate appetite, and transdermal or IV flunixin for fever associated with acute mastitis and bovine respiratory disease as directed by a licensed veterinarian.

The critical need for a functional immune system

As with recent experiences with the COVID-19 virus, HPAI highlights the need for a focus on herd immunity and immune response. The immune system in all animals is critical and complex. While there does not appear to be an effective preventative measure for HPAI, managing the herd to optimize the immune system will deter extensive transmission into the herd. Animals with a depressed immune system (immunocompromised) are at much greater risk for the adverse effects of this virus.

Immune function and nutrition are tied directly together. Repeated research over many years has shown a variety of connections to overall nutrition and specific nutrients and how these support the immune system. Beyond HPAI, issues directly related to cow health and immunity include increased mastitis and metritis, respiratory, digestive, and foot/hoof issues in all levels of the dairy – dry, transition and lactating cows; calves; and developing heifers. Animals struggling with health issues will not perform as well or as efficiently and show increased treatment costs. The result is lower production, increased cull rates, greater expense and reduced revenues.

Because the interrelationship between nutrition and immunity (health) is so critical, the following are some basic guidelines to keep in mind when considering mitigants for HPAI. 

1. Basic, sound nutrition. While this sounds overly obvious, maintaining a sound, consistent, properly balanced nutrition program (all nutrients), especially with farm economics as they have been, can be difficult. Often the mineral and vitamin program is compromised when economics are difficult. This is a problem since minerals and vitamins directly affect immune response. Maintaining a proper balance of nutrient delivery to the animal is not nearly as simple as it sounds, particularly when every penny counts. But as a reminder, dry matter intake, protein and energy balance, proper fiber levels, mineral and vitamin levels and overall ration digestibility are all important for production and reproduction as well as animal health.
2. Feed diets appropriate for transitions, stage of production, genetics, age/parity, environment and stress levels. All these factors and more affect nutrient requirements for the animal and should be taken into consideration. The more accurately cows are fed, the better immunity will be supported.
3. Mix and deliver feed as accurately as possible. This goes along with 1 and 2 above. Keep mixers and feeding preparation areas as clean as possible. 
4. Adjust rations as needed when dictated by ingredients (particularly forages) change. This is always important but even more so for proper immune system support. This promotes the consistency of nutrient delivery to the animal.
5. Provide a plentiful supply of clean, fresh water. Thoroughly clean waterers on a regular basis.
6. Take steps to reduce stress (very important). This includes:
   • Ensure adequate bedding and resting accommodations – do not overcrowd.
   • Ensure adequate bunk space.
   • Take steps to reduce heat/cold stress.
   • Monitor foot and leg health. Trim hooves as needed, use effective footbaths, etc.
7. Use a sound internal and external parasite reduction plan. Flies are a significant source of stress, as are internal parasites. Plus, internal parasites consume critical nutrients needed for production and immunity.
8. Keep mycotoxin control plans in place. Mycotoxins are immunosuppressants and are found virtually everywhere. Feed a high-quality, broad-spectrum toxin binder consistently.
9. Consider feeding supplements and additives proven by sound research to enhance health performance.

Numerous additives and products have been identified as having positive effects on the health and performance of the animal. These include yeast and yeast cell wall products, various direct-fed microbials, essential oil (plant extracts), mycotoxin binders, enzyme sources, etc. In many cases, the initial effect of feeding additives of this nature is to aid in stress reduction. There are an unlimited number of combinations of products/additives that may work synergistically in the animal to improve health and performance. Remember, though, that nothing replaces a sound balanced, basic nutrition program.

Conclusions

While there are no proven vaccines or products for the control of HPAI, sound immunity is a core component of the cow’s physiology and ability to produce efficiently and economically. A sound nutrition program supports immunity in both the long and short term and certainly will have positive effects on reducing HPAI incidence.