Dairy cows produce a lot of milk. That’s great when you’re producing it for sale. It’s not great when you have to get rid of it.

It’s clear that this H5N1 flu virus has an affinity for the udder, and a lot of virus is shed in the milk of infected dairy cattle. It appears that it’s often obvious when a cow’s udder is affected: milk production drops and the milk looks abnormal. Abnormal-looking milk is disposed, so it doesn’t go into the human food chain. With the odd sick cow on a farm, diverting this amount of milk isn’t hard. With a lot of sick cows on a farm, it becomes more problematic – it can be a lot of milk.

There’s also the issue of the clinically healthy cattle on farms with H5N1 infected cows. At this point, we don’t understand enough about the virus in cattle to know if exposed cows could be shedding the virus in their milk before they look sick. With influenza infections in other species, we know that virus shedding in respiratory secretions is common prior to the onset of illness. This “pre-clinical” period is a big problem when it comes to infection control, because individuals can be infectious before anyone has any clue they’re infected.

  • We don’t know yet if this pre-clinical / sub-clinical virus shedding happens in cattle.
  • We might be lucky if when virus is shed in milk, it’s always identifiable by visible changes in the milk.
  • We might not be lucky if virus can also be shed in milk that looks normal (and our luck when it comes to infectious diseases hasn’t really been great in the 2020s).

If cattle have a period where they are shedding virus in milk without any outward signs of illness, we have to consider what that means. We’re pretty confident that pasteurization is highly effective against this virus (the other day @SafeFoodCanuck and I wrote a commentary on why the risk of H5N1 flu from pasteurized milk is likely still low in The Conversation). However, raw milk still poses a risk, and we also need to think about exposure of people who handle milk before it’s pasteurized. That raises the question about whether all milk from infected herds should simply be dumped. That’s a lot more milk. I can argue both ways at this point.

Regardless, with influenza circulating in dairy cattle, we’re going to have to dump milk. Maybe a lot of it. An unfortunate waste to be sure, but dumping that much milk is also not as simple as it sounds.

Dairy farms aren’t plumbed into municipal wastewater systems, and don’t have their own septic systems to handle waste. You can’t just flush hundreds of litres (or more) of milk down a drain. It usually goes into manure pits or lagoons, then is eventually spread on fields. That’s fine for the relatively small volumes of milk that typically are dumped from sick cows, but when we have large amounts of milk potentially contaminated with a concerning virus like H5N1 flu, what do we do with it all? There are a few options, but none are great:

  1. Dump it in the manure pit / manure lagoon as usual.
    • That’s the easiest and most practical means of disposal. However, at this point we don’t know how long the virus would survive in a manure pit / lagoon, or on a field after the manure is spread. So this could result in exposure of lots of wildlife, including more mammals (bad for continued mammalian transmission and adaptation) and wild birds (bad for spillback into birds and subsequent transmission over wide areas).
  2. Pasteurize the waste milk before it’s dumped into the pit / lagoon.
    • Some farms have small pasteurizers on site for milk that’s used to feed to calves. Probably no farms have pasteurizers that could handle their full production capacity, so this isn’t a realistic option if all the milk has to be dumped.
  3. Send the waste milk away for disposal.
    • Sure, farms could conceivably contract someone to come pick up the waste milk and dispose of it another way (perhaps into a wastewater treatment plant?). But, that’s not cheap or easy, and might open up a whole new can of worms.
  4. Cull the affected cows (so they’re not producing milk that needs to be dumped).
    • Not a viable option for many reasons.
    • Animal welfare is one reason. Killing an animal that has a short-term, usually mild, infection is extremely hard to justify.
    • Economics is another reason. Individual dairy cows are valuable animals; dairy cows don’t start milking until they’ve had their first calf, which is usually around 2 years of age, so each one represents a significant investment of time and resources. Some can also have very high genetic value. You can’t just clear out a herd of dairy cattle and repopulate the farm next week and be up and running, like you can with poultry.
    • In addition to the animal welfare issues and economic costs, if the cows were culled then farmers would also need to figure out what to do with hundreds or thousands of dead animals.
    • Last but not least, if a dairy farm was depopulated but the virus is still circulating nearby or present in the environment, any new cattle brought to the farm could be re-infected at any time, and it would all be for nothing.

There might be other options, but none jump to mind as practical to me. For example, there might be some other potential on farm virus inactivation approaches, but the cost, logistics and timeframe would likely not make sense in this scenario.

So, we’re most likely left with the option of dumping the contaminated milk into manure pits, going on the assumption (hope) that the virus will die quickly (since it’s not very tough) and it won’t be a source of further spread. It’s not an unreasonable approach, and is probably the least-bad way, but isn’t ideal.