Heartworm is the one item on the recommended list that is not a vaccine at all. This page explains the difference and what to bring up at your next vet visit.
What the kennel says
The kennel's vaccination page recommends heartworm prevention, describing heartworm as a parasitic roundworm transmitted through mosquito bites that can be deadly to dogs. It suggests asking your veterinarian about the need for monthly prevention. It is not required for boarding and no record is needed to book a stay.
How heartworm works
The American Heartworm Society explains that heartworm disease is serious and potentially fatal in dogs, cats and ferrets. The worms live in the heart, lungs and nearby blood vessels and can grow to about a foot long. A mosquito that bites an infected animal can pass the larvae to the next pet it bites, and the larvae need about six months to become adult worms. The society says heartworm has been diagnosed in all 50 states and that indoor and outdoor pets are both at risk.
Prevention, not a vaccine
There is no commercially available heartworm vaccine for dogs or cats, according to the American Heartworm Society. Prevention is a monthly or injectable medicine prescribed by a veterinarian, and the society advises giving it twelve months a year and testing every twelve months. A late or missed dose can leave a pet unprotected. That is why heartworm sits on the recommended list: the protection is a routine you keep at home, and a kennel stay should not interrupt it.
Bringing it up with your vet
Mosquitoes are part of life near fields and water in the Sacramento Valley, and your veterinarian knows the local picture better than any kennel page can. Ask whether your dog is on prevention, when the last test was, and whether a missed dose needs a recheck. If your dog takes a monthly pill, mark the calendar so the dose does not fall in the middle of a stay. Medications are given at the kennel at no extra charge; the medication FAQ has details.