Traveling with Pets to Mexico

I've been combing over internet entries about traveling to and from Mexico with a dog.  And, few agree on the exact regulations and requirements for transporting a pet to and from Mexico.  This is partly because they may or may not ask for specific papers on a particular day at a particular port of entry, and because it appears that the regulations can vary from state to state .  Transporting a pet by air is much more complicated, and most say that by car is less complicated and much less stressful for the pet and owners.  Valentina is a puppy now (she weighed in at 16.8 lbs. when we last took her in to the vet on Oct. 16, 2012 -- 'shroom incident) and I'm sure she weighs more now.  But she is still small (considering).  Neither Tom nor I plan on transporting her via airline carrier.  I've heard horror stories about poorly pressurized luggage compartments. But, still, we want to have all the possible documentation that they might ask for when we cross the border.

A very nicely done website is: www.gringodog.com
It has a section on pet-friendly hotels in Mexico (as well as one for pet-friendly hotels in the U.S.). It has a series of Questions and Answers sent in and responded to over time about requirements, and experiences traveling to and from Mexico. The website authors are well-traveled with 2 dogs and have many solutions to challenges that the dog owner may face when traveling in Mexico.
A helpful Mexican website which contains what may be the latest version of regulations, (they may change frequently.), is :
Spanish:  http://www.senasica.gob.mx/?id=623
English: http://www.senasica.gob.mx/?Idioma=2&id=623
Today, the website states the following regulations:
If you are traveling with up to three pets you do not have to pay the import fee.  With 4 pets, the import fee for the import certificate for the fourth pet is 1,817 pesos. (Other sites say that two are free and there is a charge for the third pet.)
"In order to travel with your pet (dog or cat) to Mexico, you must present a Health Certificate issued by a medical veterinarian, in original and copy, at the Office of Agriculture Health Inspection (OISA) at your port of entry. This document can be in the form of a letter issued by your private medical veterinarian, on the medical center’s letterhead, including the license number (and, if you wish, a copy of the vet's license) and  the information required below:
1. Name and address of exporter and importer.
2. That the animal has been vaccinated against rabies, indicating the date of application of the vaccine and its valid expiration date. Animals under 3 months of age are exempt of this requirement.
3. Certify that the animal has been inspected and found clinically healthy prior to export."
(I read one response that said that they asked for two ORIGINAL Health Certificates instead of an original and a copy. One source recommends that the original be "signed and stamped" by the vet.Some sources recommend that you bring 2 copies, just in case.)
(There is also a warning on the SENASICA site that says the rules may be different at your port of entry.  -- I believe someone mentioned that it differs from state to state.)
Gringodog has a recommendation for the Health Certificate letter wording: "I certify that I have examined the above-named animal and have found it to be clinically healthy and free from external and internal parasites." They also recommend that the letter/health certificate state that the dog has undergone a parasitic prevention treatment, and then describe the treatment.
Many websites have recommendations for what to bring with/for the animal: pet identification tag for the collar, microchipping, first aid kit, current rabies tag for the collar, antibiotic cream, hydrogen peroxide (!) (to induce vomiting (!) in the event the dog eats/swallows something toxic.
Some internet sources state that the dog must be vaccinated for rabies within 12 months prior,  30 days in advance, or 15 days in advance, or,  just vaccinated before you cross.  
Most websites recommend a copy of the vaccinations info (there is a vaccination card that is frequently recommended.)
Some sites say that the health certificate is good for 10 days from the date signed.  Some say 5 days, some say 72 hours, and I have heard from others around the Lake Chapala area that the certificate is good for only 48 hours!
An alternative to the letter Health Certificate is  the Health Certificate that is USDA official format.  Some sites say that this form can be downloaded and printed off the internet.  If you get it directly from the USDA Office (by walk-in or mail,) it has an official folio number.  I read one story about a traveler at an airport who had a computer printed copy of the form that was actually filled out and signed as an original, but did not have a folio number.  The official was ready to reject the validity of the form until another offical came over and talked him into accepting it. They recommended getting the original form with a folio number and not using a printed out copy to be absolutely certain it is acceptable.

Email contact for questions or comments is: contacto@senasica.gob.mx

Even if you are not traveling to the Yucatan area, the website Yucatan Expatriate Services has a lot of good information: http://www.yucatanexpatriateservices.com/