lol, after my dumb moment before, I've done more testing today and have some more realistic results to share. Apologies to all for my inaccurate claims earlier.
First up, when my sim makes the granola bars, the 'glitch' where she only uses one fruit happens a lot more frequently than I first thought. Not sure if it has to do with cooking skill as I hadn't noticed it before she reached level 9 but since paying attention, so far every second batch she makes up only uses one fruit and it's always the apple, even if the other fruit is before the apple in her inventory.
When I realized my earlier mistake, I also came to the conclusion that the type of fruit used didn't seem to matter. After that, I continued the testing with just two horses. Horse Two got bars that had been made using two fruits. I made bars with various fruits including life fruit, plasma fruits, and plain everyday fruits. Horse Three got the bars that had been made using only an apple.
I've tested with giving them 1 bar a day, 2 bars a day and 3 bars a day.
So far the tests suggest that the plain apple bars give the best result when the horse has 2 or 3 each day although this was only over a short time, so it might just be about the same over the life of a horse. Over a period of 15 days (5 days of each amount) Horse Three who was getting the apple bars gained 5 days added to their adult life. Horse Two, who was getting the bars made with two fruits only gained 2 days over the same period. Both horses got the extra days after they were having 2 or more bars a day.
So at the end of the test period so far, Horse Two has 23 days before aging (at the beginning of the 15 days, it had 36). Horse Three has 25 days to go and it started with 35.
A few things I noticed:
You can check a horses life bar straight after it eats a bar to see if the number of days has gone up.
Granola bars can be fed to Omni plants where the other gourmet pet foods can't be.
The bars can be put on the ground and you can have the horse eat them this way (not sure if this changes how effective they are though)
The bars can be put in the fridge where the other pet foods can't.
