So my little dog goes ape whenever she sees and/or hears animals on TV (other dogs, cows, horses, dinosaurs, etc.), but the other day I had her in the park and she completely ignored two horses! First they were across a field, so I held her up in their direction. Nothing. Then they trotted over and, barely two feet away, still no reaction. If she weren’t ten months old I’d say she was blind. Any guesses? Did she just… not care? They were black geldings, as if that makes a difference.
I think it has more to do with territory… at home, that is your dog’s turf that needs to be defended. The park is not her territory, so she has no interest in defending it, and the horses didn’t threaten her, so no issue. Whenever you add new animals to a house, it is recommended to have the new pets meet the old pets on neutral ground for this very reason.
I suppose… but then, she does bark at certain people and dogs she sees or hears in the distance while at the park. I really just thought she should be freaking out at these giant animals before her (though I guess I should be thankful she didn’t).
I have little dogs too, and most of mine are smart enough not to pick fights with things much bigger than they are. One of them isn’t. He weighs all of 5 pounds, and has tried to start fights with a pair of dobermans, a great dane, and is constantly escaping my yard to enter the neighbor’s yard with a german shepherd. He is the most arrogant dog who ever lived, I think. One of my others will bark at people while we are in the car, but she is actually barking because she wants attention. So when your dog barks at the TV, it is defneding territory, but it might be asking to play with other people or dogs when it barks away from home. You’ll learn to tell the difference. Dogs are NOT dumb and realize horses are not people OR dogs. Depending on the dog and their previous experience with horses, that may peak their curiosity, cause indifference, or cause fear.
Also note that sense of smell is more important to your dog than sight, as is hearing. The horses smelled and sounded different from any past experiences.
Posted too soon - I wasn’t done.
How a dog handles a new experience is all determined by how it was raised in the first weeks of life. Ideally, a dog has been exposed to a lot of new experiences in a positive manner, and so it would not react in fear to something like a horse. A dog who was not exposed to new things would react with fear, as would one who was raised with new experiences with bad results. Ideally, a dog is raised to be indifferent to curious about new situations.
I have seven Jacks and ONE of them goes crazy when she hears tv dogs barking. The others ignore them completely. If ANY of them hear a real dog its Katy bar the door! Go figure.
Seven must be the magic number - I have 7 dogs too. 
Mostly chihuahuas, and one miniature dachshund. Combined, they weigh less than 50 pounds. The dachshund and one of them will bark at nearly anything - dogs on TV, car doors outside, the rooster crowing down the block, birds flying through my yard, geese flying overhead. Three of them bark sometimes, mostly at people who come into the house. The other two don’t bark at all, at anything. I currently have a puppy I got at 8 weeks old - have had him for two months now, and still, I have never heard him do anything but whine or growl. He doesn’t even bark at the other dogs when he wants them to play.