Avian Influenza Viruses in Dairy Cows: What is the role of biosecurity? by: Russ Daly Professor, SDSU Extension Veterinarian, State Public Health Veterinarian

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The March 2024 finding of an avian influenza virus in dairy cows suffering from a previously unknown disease syndrome has brought attention to disease control and detection methods on dairy operations.

While dairy cows affected with the syndrome were first identified in Texas and New Mexico, the illness has been detected in cows in other states as well. Individual cows affected by the syndrome have drastic drops in milk production, along with clinical signs, such as going off feed, firm-dry manure, the production of thick milk, and fevers. Within affected herds, up to 10% of cows in the middle of their second (or greater) lactation are disproportionately affected; first-lactation cows, heifers, and dry cows do not appear to be significantly affected.

The avian influenza virus detected in samples from a few of these affected cows is the same virus that has caused substantial death losses in wild birds and domestic poultry, demonstrating the ability of influenza viruses to change over time to potentially infect “non-target” animal species.

In the midst of a new disease event such as this, animal health officials encourage producers and their veterinarians to stay abreast of new developments and fall back on the basics of supportive care, prompt diagnostics, and disease prevention.

Understanding Biosecurity

A common disease prevention recommendation during any new disease occurrence is to pay close attention to biosecurity. What does biosecurity for a dairy farm look like in the context of the potential for an avian influenza virus to adversely affect lactating cows?

Biosecurity can be defined as, “interventions that prevent the introduction of novel infectious disease agents into a specified population of animals.” It’s a term that’s thrown around a lot, but it’s also a concept that deserves closer examination and refinement for individual farms.

Compared to swine and poultry farms, disease control methods on dairies typically focus more on containing existing germs (for example, mastitis, Johne’s Disease, and salmonellosis) rather than keeping new germs off the farm. The emergence of a disease agent such as avian influenza should have dairy producers at least consider how they might prevent the germ from entering their animal populations.

A common challenge for livestock producers in implementing biosecurity processes is trying to “check all the boxes.” Lists of preferred biosecurity efforts can be lengthy, addressing everything from vehicle traffic, to visitors, to equipment, to rodents and wildlife. Instead of trying to implement all of those management practices on a specific farm (some of which may not be possible), dairy operators should examine how the specific threat (avian influenza in this case) can enter the farm and what processes could be implemented to prevent that entry.

Routes of Virus Entry

While much still needs to be learned about how this particular virus infects cattle, two routes of entry (and the potential for preventing them) are worth examining.

  • Cattle movement. Very little is currently known about whether this strain of influenza is easily transmitted from cow to cow, but at least one dairy has implicated cattle imported from a state with affected cattle as a probable source for their infection. Isolation of newly arrived cattle away from the resident herd for a period of 30 to 60 days has been a standard recommendation and would greatly reduce the chance of this virus entering a herd from an incoming infected animal. This period of time gives the new animals (which are often stressed from transport) a chance to go through any incubating disease they may have brought with them, recover, and stop shedding the virus.
  • Wild bird contact with feed and animal buildings. For dairy farms, this is a more-challenging biosecurity intervention to accomplish. Avian influenza strains are predominantly associated with droppings from wild waterfowl (ducks, geese) and shorebirds (gulls). Open water or especially feed sources that attract these bird species can result in birds contaminating feed, resulting in the efficient spread of the virus to cows. Feed storage and animal housing on modern dairies are relatively open compared to poultry operations, for which effective influenza prevention has still proven elusive. Therefore, we shouldn’t expect preventing wild bird exposure to dairy cattle or their feed to be simply accomplished.

Taking Action

Producers should promptly contact their veterinarian when this, or any other novel disease occurrence, is suspected. Working closely with state animal health officials and diagnostic laboratories is important to efficiently identify potential causes – and potential ways to prevent further introductions.