I notice my breeding barn has a limit of five horses.

Is there a way of increasing this?

As far as I know the breeding barn doesn't seem to have a limit on horses - I think however many you have in there it displays as the limit? So if you have five it says Breeding Barn - 5 horses, Capacity - 5 horses, but if you retired another horse to breeding barn it would update the capacity to 6. I think that's how it works?

no limit in breeding barn but most 2yo's that can be bought into game is 150 and you need 150 free slots in your yard

Unless Mark changed it, there was a different limit in previous games. I had something like 40 mares in my breeding barn in SO5 and used the computer mares which brought me over 70 yearlings. I had plenty of room in my barn since I tend to only keep 20 or fewer racing at a time. I lost 10 2-year-olds because my barn cap was 100. They didn't go to other trainers. They just went *poof*. Annoyed me because some of them were by a top NPC stallion (computer owned).

So the barn cap (I could have sworn unless this changed in SO6) is:
150 - # of horses you have in the barn - # of foals
Put another way, the game counts your breeding horses in the barn as well as your foals. It doesn't include NPC horses.

Example 1: If you have 75 horses in the breeding barn, most amount of yearlings you can get ultimately is 75. You lose any over that.

Example 2: You have 2 horses in the barn (1 mare, 1 stallion), you can have 148 yearlings. Chances of you getting that many with a single stallion is unlikely, though.

I haven't really done any extensive breeding in SO6, though, so not sure if it's the same case as SO5. Since the game hasn't really changed that much, I don't see that not being the case.

Simply put: cap's 150. Same as your racing stable's cap. It auto increases as you put horses into it.

I thought it was 100 ?

When i try to retire horses when their is 100 horses in my breeding barn the retired horses stay in my stable.

On SO6 I've fully upgraded everything and have a limit of 150 horses in the stables, however my breeding barn only has a capacity of 6. I've been putting my three best mares in there along with my top 3 stallions to breed them (and then let my stallions breed with game owned).

Playing an USA game, both one with the default database and another with the StartUp mod. Both have the limit of 6 in the breeding barn so I had the impression that it was the limit - however there doesn't seem a limit on foals apart from the number of mares and fillies I can breed my horses to in a given year.

That's the limit because you only have 6 horses in there. Put 10 in and 10 will be the limit. I didn't realise there was an upper limit, but I tend to only keep about 20 in there at a time anyway.

Wow, I never realised that - thanks SuperCat!

I simply saw the limit was 6 when I built the barn and it always kept with that limit. Guess I should have just tried putting more in rather than believing the number on screen. Now I can get my breeding program fully operational and see how my bloodlines develop over the seasons.

limit would be 150 you'd imagine