The 86-year-old, who played space explorer Capt. James Kirk on TV and in flicks, breeds saddlebreds and quarter horses on his 360-acre Kentucky farm and rides the animals in shows.
In his recently released book, Spirit of the Horse: A Celebration in Fact and Fable, Shatner reveals he is "wonderfully, hopelessly in love with the creatures."
Top behavioral expert Dr. Lillian Glass says it's more than love, noting there's a sexual thrill linked to mounting and controlling the large, muscular beasts.
"To ride a horse is very sexy, very sensual," says the doc. "They're beautiful, sensuous animals — and very loving animals.
"There's the rhythmic cant when you ride a horse. The feel of this massive animal — you have control of this massive animal.
"It's a very sensuous and very powerful process."
In his book, Shatner recalls visiting tragic Superman star Christopher Reeve after he was paralyzed in a horse-jumping accident in 1995.
Shatner was amazed Reeve, who would die from complications at the age of 52 in 2004, still loved the animals that had put him in a wheelchair for the rest of his shortened life.
"They spoke — naturally — of horses, and Shatner marvels at the joy that was in Reeve's eyes," a source says.
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