The simple answer is no animal in America is currently at any appreciable imminent risk from radiation to warrant administering Potassium Iodine. Obviously if the risk increases and the radiation level seen by the US West Coast somehow is more then expected then yes it would be a good idea to administer Potassium Iodine. However the Veterinary School at UC Davis cautions over use of this medication in your pets.
If an animal takes too much Potassium Iodine, it could get a severe allergic reaction, vomiting, diarrhea, anorexia, decreased thyroid function and damage to the heart. Too much potassium iodide can even cause death. "While potassium iodide might help protect dogs, cats and other pets, as it would people, from the risks of radiation exposure in the unlikely event that radioactive iodine reaches here in appreciable levels, giving it ahead of time carries risks and would be ill advised," said Michael Kent, a faculty veterinarian at UC Davis who specializes in radiation cancer therapy.
Following a radiological or nuclear event, radioactive iodine may be released into the air and then be breathed into the lungs. Radioactive iodine may also contaminate the local food supply and get into the body through food or through drink. Because non-radioactive iodine acts to block radioactive iodine from being taken into the thyroid gland, it can help protect this gland from injury.
When a person takes Iodine, the stable iodine in the medicine gets absorbed by the thyroid. Because potassium iodine contains so much stable iodine, the thyroid gland becomes “full” and cannot absorb any more iodine—either stable or radioactive—for the next 24 hours.
For both animals and humans you should not use table salt as a substitute for an Iodine tablet. This is not a substitution and will cause its own ill effects on both animal and human as too much sodium can lead to several major health concerns and in large enough doses without treatment even coma. Our bodies can process a much greater amount of sodium then a dog or cat in fact dogs and cats really do not need should not have added table salt to their food.
A single dose Iodine Tablet protects the thyroid gland for 24 hours. A one-time dose is usually all that is needed to protect the thyroid gland. In some cases, radioactive iodine might be in the environment for more than 24 hours. If that happens, local emergency management or public health officials may tell you to take one iodine tablet every 24 hours for a few days. You should do this only on the advice of emergency management officials, public health officials, or your doctor.
Avoid repeat dosing with potassium iodine for pregnant and breastfeeding women and newborn infants. Those individuals may need to be evacuated until levels of radioactive iodine in the environment fall. I am not a veterinarian and haven't found specific information for the plan of action if your animal is pregnant or breast feeding you may want to call your veterinarian or a veterinary teaching hospital to find out if you should administer the tablet to this particular animal. A teaching hospital should also be able to advise on dangers to farm animals like cows and horses who are pregnant or feeding their young as well.
At this point any radiation released by the nuclear plant will primarily affect Japan or blow out to sea and not arrive in the US in amounts that are of major concern. If you are looking for a tool to predict the radiation cloud's path I am told you should look to NOAA's HYSPLIT trajectory model. The model uses the GFS model's winds to track the movement of a hypothetical release of a substance into the atmosphere. They say you should not use it to track the trajectory for a term longer then three days because there are too many variables in the calculations to be accurate.
Basically take steps to be prepared but do not start administering the medication to yourself or your animals in advance of any potential radiation. Doing so can cause adverse reactions. Basically be alert and aware of reports and if and when officials determine those on the West Coast should take potassium iodine this would be the same time you should administer a dose to your animals.
http://www.bt.cdc.gov/radiation/ki.asp
http://www.fox40.com/news/headlines/ktxl-pet-owners-worried-about-radiation-cloud-20110317,0,4078023.story