South Dakota State University Extension Veterinarian Russ Daly said some South Dakota producers are seeing AIP (atypical interstitial pneumonia) and grass tetany in cattle herds on pasture.
"The fact that these conditions are popping up in pastures this fall is related to rapid regrowth of grass after these last rains we've had," Daly said. "It is somewhat unusual, because we usually see these conditions in the spring, when grass is first going through its rapid growth phase."
AIP. AIP is an acute (rapid onset) respiratory disease that affects cattle after they are moved from poor pasture to lush pasture. It usually affects mature cows instead of younger animals. The type of pasture (grass or legume, etc.) does not seem to matter, rather it is the "lushness" and abrupt change that is important.
It occurs because these pastures contain higher levels of L-tryptophan, a naturally occurring amino acid. In the rumen, it is converted to 3-methyl indole ("3-MI") and absorbed into the bloodstream, where it leads to toxic changes in the lungs.
They will breathe with their mouths open, salivate, and stand with their necks extended. Severely affected animals are in real distress, and sudden stresses like handling them or moving them will cause them to collapse.
There is no specific treatment. Veterinarians may try diuretics or anti-inflammatories, but they are not completely successful in all cases. Animals can be removed from pasture but new cases may still occur over the next two to three days.
Prevention can be management or medical or a combination of both. Adapting cattle to lush pasture, limit feeding, section grazing are all management practices that can decrease the risk. In addition, feeding monensin (Rumensin�) or lasalocid (Bovatec�) can reduce the occurrence of AIP, but must be consumed at full dose, which can be challenging in a pasture situation.
Grass tetany also occurs when animals graze rapidly in growing pastures. It can occur if grass does not contain enough magnesium. Since cattle need to consume all the magnesium their body needs, deficiency symptoms show up when their forage does not contain enough of this mineral.
In contrast to AIP, certain types of pastures, especially such as grass pastures and small-grain regrowth are more commonly cited as problems. It is also more of a function of animals consuming this pasture in the rapid growth-phase, and not so much due to an abrupt change. Waiting until the rate of growth slows down will help avoid the occurrence.
Lactating cows are more at risk than younger animals or non-lactating cows, and cows with younger calves (less than four months) are at more risk than cows with older calves.
As with AIP, prevention of grass tetany is also based on feed and management practices.