> Of course, when robots can sentient [...]

But what sort of proclivities would go with the sentience? Not necessarily the sorts of things we'd expect in an evolved animal.
I'm reminded of a scene from Douglas Adams' "The Restaurant at the End of the Universe".

Excerpt from Chapter 17:

A large dairy animal approached Zaphod Beeblebrox's table, a large fat meaty quadruped of the bovine type with large watery eyes, small horns and what might almost have been an ingratiating smile on its lips.

"Good evening," it lowed and sat back heavily on its haunches, "I am the main Dish of the Day. May I interest you in parts of my body?"

It harrumphed and gurgled a bit, wriggled its hind quarters into a more comfortable position and gazed peacefully at them. Its gaze was met by looks of startled bewilderment from Arthur and Trillian, a resigned shrug from Ford Prefect and naked hunger from Zaphod Beeblebrox.

"Something off the shoulder perhaps?" suggested the animal, "Braised in a white wine sauce?"

"Er, your shoulder?" said Arthur in a horrified whisper.

"But naturally my shoulder, sir," mooed the animal contentedly, "nobody else's is mine to offer."

Zaphod leapt to his feet and started prodding and feeling the animal's shoulder appreciatively.

"Or the rump is very good," murmured the animal. "I've been exercising it and eating plenty of grain, so there's a lot of good meat there." It gave a mellow grunt, gurgled again and started to chew the cud. It swallowed the cud again. "Or a casserole of me perhaps?" it added.

"You mean this animal actually wants us to eat it?" whispered Trillian to Ford.

"Me?" said Ford, with a glazed look in his eyes, "I don't mean anything."

"That's absolutely horrible," exclaimed Arthur, "the most revolting thing I've ever heard."

"What's the problem Earthman?" said Zaphod, now transferring his attention to the animal's enormous rump.

"I just don't want to eat an animal that's standing here inviting me to," said Arthur, "it's heartless."

"Better than eating an animal that doesn't want to be eaten," said Zaphod.

"That's not the point," Arthur protested. Then he thought about it for a moment. "Alright," he said, "maybe it is the point. I don't care, I'm not going to think about it now. I'll just ... er ..."

The Universe raged about him in its death throes. "I think I'll just have a green salad," he muttered.

"May I urge you to consider my liver?" asked the animal, "it must be very rich and tender by now, I've been force-feeding myself for months."

"A green salad," said Arthur emphatically.

"A green salad?" said the animal, rolling his eyes disapprovingly at Arthur.

"Are you going to tell me," said Arthur, "that I shouldn't have green salad?"

"Well," said the animal, "I know many vegetables that are very clear onthat point. Which is why it was eventually decided to cut through the whole tangled problem and breed an animal that actually wanted to be eaten and was capable of saying so clearly and distinctly. And here I am." It managed a very slight bow.

"Glass of water please," said Arthur.

"Look," said Zaphod, "we want to eat, we don't want to make a meal of the issues. Four rare steaks please, and hurry. We haven't eaten in five hundred and seventy-six thousand million years."

The animal staggered to its feet. It gave a mellow gurgle. "A very wise choice, sir, if I may say so. Very good," it said, "I'll just nip off and shoot myself." He turned and gave a friendly wink to Arthur. "Don't worry, sir," he said, "I'll be very humane." It waddled unhurriedly off into the kitchen.