As of this writing, 41 California dairies had been confirmed as infected with HPAI. A handful of additional herds will likely be confirmed this week. A single Merced turkey farm has also been infected and depopulated. As the number of infected herds climbs, producers are understandably concerned, wanting to know how to prevent the disease from entering their herd and how to best manage the disease if it does. On Thursday, September 26, CDQAP, UCCE, and CMAB brought both disease control experts and dairy practitioners together to discuss Managing Cattle Through HPAI. The webinar and was recorded and can be made available to dairy producers and industry partners by contacting CMAB.
Highlights from the Webinar The Virus Started in One Place – Genetic studies suggest that migrating waterfowl carried a strain of Avian Influenza which mutated in the Texas Panhandle in late 2023 or early 2024.These mutations allowed it to easily infect cows, particularly the mammary tissue. All subsequent cow infections in the U.S. have occurred either by cow-to-cow transmission or through mechanical transfer on inanimate objects. Disease spread into California likely occurred through transfer of infected but asymptomatic cattle.
How the Virus Spreads in a Herd is Unclear – Small experimental challenge studies have shown the virus can be transmitted through oral contact and through contamination of the teat surface.
Research continues, however, to determine if the primary method of transmission is through nose-to-nose contact or during milking, or both. How big a role shared equipment (water troughs, feed bunks), flies or “peri-domestic” species (rodents, barn cats, nuisance birds) play in disease transmission is also unclear. Airborne plumes containing virus do occur on infected poultry flocks, but whether this happens on dairies is unknown. CDQAP is partnering with dairy trade organizations to identify potential collaborator dairies for additional research.
Spread to New Herds Doesn’t Require Live Cows – High concentrations of virus are found in milk and movement of infected cows has resulted in disease spread to other herds. At least half of new herd infections, however, have not involved movement of live cows, presumably through contaminated equipment such as trailers or potentially visitors. How much risk is associated with movement of younger and nonlactating cows is under investigation. Sharing of employees with other dairy herds or poultry flocks appears to be a major risk factor. Sampling of wild migratory water fowl (ducks, geese etc.) throughout the U.S. suggest that these birds are not spreading the disease.
Milk Tankers May Not Be High Risk – An initial Michigan study sampled 18 tanker trucks transporting milk from infected farms. A total of 125 samples were taken from wide variety of sites including the external tank, tires, transfer hose, truck cab and the sampling dipper. Only a single sample from a direct load floor was positive, suggesting that milk tankers may not be a primary method of viral transfer. Additional research is needed. CDFA has released guidance for milk haulers.
It’s Unclear if Reinfection is Happening – Some herds, thought to have recovered from the disease, have experienced new infections. It is not yet clear if these new cases represent cattle that initially escaped infection or are rather actual reinfections or relapses of cows that had been previously infected.
It Takes Several Weeks to Move Through a Herd – In a study from one dairy, about 14 days prior to recognition of clinical signs, some cows were shedding enough virus to be detected in the bulk tank. Viral shedding peaked about 5 days after the first clinical signs and decreased as cows developed antibodies. In this herd, virus was no longer detectable about three weeks following the first clinical signs, but viral detection in other herds has been more prolonged. How long
clinical symptoms persist on different farms also varies greatly. In general, the number of clinical cases in the herd seems to peak at about 7 to 14 days and slowly tapers off. The duration of time clinical cows is reported present in the herd varies, ranging in one study from about two weeks to over a month. In California herds it seems that the worst of the outbreak (and the associated constant drenching) lasts about 2 to 3 weeks.
Recovered Cows “Reset” at Lower Production – It appears that the lactation curve is being “reset” in recovered cows. A typical example discussed was a cow producing roughly 100 lbs./day, dropping to about 20 lbs. a week later. Production climbed as the cow recovered, plateauing at about 70 to 80 lbs. Whether this approximate 20 to 30% decrease in production represents a permanent change due to scaring of the udder and will persist in the next lactation is unknown. Losses in total herd production varies greatly. The 3-day rolling average in two herds fell by 6% and 16% during the infection period.
Effective Treatment Focuses on Oral Fluids – Keeping cows hydrated and reestablishing rumination as quickly as possible quickens recovery and minimizes secondary pneumonia, abortions, mortalities and culls. Frequent oral drenching with 5 to 6 gallons using electrolyte solution is effective, with cows being treated 1 to 2 times per day depending on number of affected cows and employee resources. A variety of commercial drench powders (TechMix, MB Restore, Drench-Mate) or homemade electrolyte recipes are being used effectively.
Oral Fluid Therapy – During the peak of the outbreak producers may be treating 30-40% of the herd every day for a week or more, so an efficient system to deliver large volumes of drench is essential. Producers have either constructed or purchased “drench carts” with a fluid reservoir, pump, a one-inch administration hose and mixing equipment. Mixing through the use of a paddle mixer or reservoir recirculation is important to prevent electrolytes and medications from settling out. An inexpensive flow meter attached on the administration hose removes the need to time the pumping duration and ensures a correct volume is given. Using this equipment, a couple of trained employees can safely administer six gallons of drench solution in several minutes. Rapid over hydrating, particularly without electrolytes, can result in brain swelling and death. Intravenous fluids are expensive and impractical. Commercial drench carts can be purchased but may be
back-ordered several months. Producers should begin ordering or constructing their own drenching systems now.
Medications – Anti-inflammatory drugs are typically used, but treatment with flunixin or aspirin to a dehydrated animal can result in cow death through abomasal ulcers, kidney, or liver failure. Exceeding the label doses of antiinflammatory drugs can cause similar problems. In particular, powdered aspirin added to the drenching solution is reported as efficient and effective, but milk from treated cows must be withheld from the bulk tank using a withdrawal time prescribed by the herd veterinarian. Administration of aspirin in the TMR is illegal and ineffective. Antibiotics are only administered to cows with secondary bacterial infections, like pneumonia, and then only when using veterinary prescribed milk withdrawal times.
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