Why is boarding stressful for my pet?
Boarding can be stressful. Boredom, strange noises, change of lighting, strange smells, change of food, unfamiliar people, and recognition of the stress of other animals increases stress in your pet. Pet's security is compromised when they are moved. Remember, animals are sensory based. Your pets notice small details and these details can be very scary. Interestingly it’s very easy for animals to create negative associations with “innocent” items. For example, feeding areas, sleeping locations, different areas to go to the bathroom, repetitive behaviors, and other fear memories are very difficult to eradicate. It’s best to try to minimize these.
Vocalizations in animals are generally signs of stress. If a number of dogs in a kennel are barking and/or whining, they are stressed. If cows are mooing, they are stressed. These sounds will make the other animals/pets in the vicinity stressed also. Remember pets are driven by emotions and they are very sensitive to emotions of those in their surroundings! Have you ever listened to the sounds in a boarding kennel?

But I’m worried about my animals being bored at home.
Dogs, and most other animals, have a strong “seeking” behavior, therefore to keep them engaged and out of trouble when you are away, give them things to SEEK such as new toys, toys that have treats “hidden” inside of them, or hide their current toys in unique spots.
You might consider putting out some common (non harmful) objects in the yard that the animal can explore at their leisure. I’ve personally found that placing furniture (benches, chairs or the like) that enable my animals to see out the windows helps to decrease boredom.

What do my pets NEED?
For their safety and security, pets need some type of human interaction daily. The time of interaction depends on the type of animal. Dogs need about an hour a day, whereas cats can get away with ½ hour or less. Horses need about ½ hour per day.
Food, clean water and a general check of their well-being is a daily MUST!
Our pets and animals need physical activity. If they are able to achieve this on their own (dog doors, horses in pasture, etc.) that is a benefit. If not, be sure to have someone that will take them out and allow them time to “stretch their legs”.

What about the benefits of pet socialization?
There absolutely are benefits to animals being able to socialize. Chances are, if you have more than one animal in your home, there is sufficient social interaction. Most animals are social creatures and not only do they need socialization, animals like horses, who are herd animals, have a biological drive for being associated with other animals and pets for safety.
Socialization with strange animals can increase the exposure of YOUR animals to diseases and other health problems plus behavioral problems and stress.

Development of bad habits
Repetitive behaviors, like licking, pacing, cribbing and obsessive chewing are a sign of stress and/or fear. Sudden reversal of a house broken pet can be experienced after stress and insecurity.
Such behaviors are very difficult to stop and it is therefore best to find ways to prevent development of such behaviors. Development of these behaviors can occur when animals are confined in small spaces or taken to unfamiliar location (such as boarding kennels) where they experience extreme levels of stress. By keeping their environment consistent you increase your pet's security and feeling of safety.
References:Grandin T. and Johnson C. (2009) Animals Make Us Human. Creating the best life for animals. Houghton Mifflin Harcourt (Boston).
Dr. Dolittler veterinary blog. Kennel Cough nightmares courtesy of a boarding facility near you. Vet School 101. www.dolittler.com/2008/0207/pet.vet.dog.cat.kennel%20cough.bordetella.vaccine.veterinary.html
Dr. Temple Grandin lecture, May 6, 2009
Spotlight on CSU: Intricacies of animal behavior, May 5,2009