Mice in hay

When mice levels are high, producers should be mindful that stored hay, or the hay you are buying in, could have some level of contamination from mice.

What's the risk of mice contaminated hay?

Mice not only do damage, they carry disease that can pose a risk to livestock.

It is important producers consider their options before using or purchasing potentially contaminated hay, as it can carry risks, such as:

• Livestock avoiding hay due to smell
• Leptospirosis in cattle
• Botulism in livestock.

A major risk is that mice urine can spread Leptospirosis, commonly known as “Lepto”.  There are more than 250 different serovars (or “strains”) of Lepto. Two of these strains (L.hardjo and L.pomona) are known to cause abortion in cattle, and there is a vaccine available to prevent this. Hence, I would strongly recommend if you are planning on feeding out hay that has been contaminated by mice, that you fully vaccinate your cattle for Lepto well in advance of feeding (this means giving them two shots, 4-6 weeks apart). There is no vaccine available for sheep, but Lepto is not thought to cause clinical disease in sheep.

Mice carry many more strains of Lepto than just two though, and these other strains may infect humans that are handling the hay. Lepto is a debilitating zoonotic disease and there is no vaccine for people, therefore the best way to reduce the risk is to limit contact with mice urine. You may choose to do this by electing not to use the hay, using mechanical methods to move the hay so that people aren’t handling it, or wear appropriate PPE (long clothing, gloves, eye protection and a mask) when touching the hay.

Another real risk that can come from mice contamination of hay is Botulism. Botulism comes from a bacterial toxin that lives in the dead mice carcasses. When livestock eat the hay and pieces of the carcasses, they may become infected.  It causes flaccid paralysis which results in animals that go down, cannot eat and drink and eventually die. Large numbers of stock may be affected and there is no treatment. Vaccination is available for cattle and sheep for botulism, but two shots are needed for most products available on the market, so again, plan ahead.

It may be prudent to vaccinate for botulism, regardless of whether you are planning to feed hay, due to the extreme contamination of paddocks with mice carcasses. Stock that are phosphorus or protein deficient will actively select to chew on carcasses and bones and are at a higher risk.

Assessing damage to hay bales

Monitoring is key when identifying the impact of mice on hay bales. Where possible, open them up and examine from various positions or sections of the haystack or shed. An assessment of the damage can be made by identifying the number and depth of mice holes and the amount of carcasses, urine of feces found.

For low levels of damage, it may be possible to remove damaged sections, and destroy them separately. However, this would only reduce your risk, not fully remove the possibility of the fodder source continuing to be contaminated.

When inspecting bales, it is important to wear personal protective equipment (PPE) and implement good hygiene practices. Mice damaged also pose a hazard because they can collapse.