In the past week or so I’ve investigated three separate cases of rock fern toxicity in cattle. Unfortunately, multiple deaths occurred on each property. Although the risk of poisoning is probably low for most herds in the district, it makes sense to be on the lookout.
Clearly seasonal conditions have favoured the growth of rock fern - one producer told me last week that he’s never seen as much rock fern as he has this year. This is mostly due to the combination of a dry summer with early autumn rain across the district. Rock fern responds very rapidly to rain, so it can grow quickly before other pasture species do.
In all the cases I’ve investigated, the paddocks in which deaths occurred had dry, stalky feed (summer grasses) and very short green pick coming through, but not much (other than rock fern) in between. The result is that in some patches rock fern made up a high proportion of the bulk of green feed.
The other common factor in all three cases is that it was relatively young (12-18 month old) and/or recently introduced cattle which were affected. We know that young cattle can be quite inquisitive, and are more likely to eat things they shouldn’t. Introduced cattle can have the same problem, and can also be unfamiliar with local plants.
Take a look at the paddocks currently holding your weaner or young cattle to see if there are any areas where rock fern is dominant. Although there might be a reasonable amount of dry, stalky feed from summer, cattle will often preferentially eat fresh, green rock fern if it’s there. If there is a substantial amount of rock fern, be careful not to overgraze the paddock – as stock run out of other options there’s a greater chance they’ll eat the rock fern.
Be aware of the symptoms of rock fern poisoning so that you can intervene quickly. In the cases I’ve investigated in the past week, producers generally only noticed cattle looking lethargic, weak on their legs, or reluctant to move. In some cases there was nasal discharge and difficulty breathing. Unfortunately, symptoms can go unnoticed and sometimes animals are simply found dead. Any cattle showing symptoms or found dead should be checked by a veterinarian.
What about sheep? I see rock fern poisoning almost exclusively in cattle, and I think this is mostly because sheep are far more selective in their grazing. They can still be affected (and can develop a slightly different neurological form of poisoning), but the risk is low.
If you have any concerns, give me (or your private vet) a call.
Nigel Gillan is the district veterinarian for the Central Tablelands Local Land Services. Contact the Mudgee office: 02 6378 1700