Trouble with minis is they provide much less cart-pulling and load-carrying power than full-size horses. Better to bring breeds like say Morgans, Irish cobs, Fjords, that are smaller than Clydesdales but quite strong; also, unlike pure draft breeds, they’re all-around using horses and tend to be tough and hardy. Need less food, too.
ETA: Medium to large ponies are also good for pulling, carrying, and riding, and are very easy keepers.
Right, that’s why I said “depending on how much time you have”. Nobody expects that the ship will be able to drop off a Colony Starter Kit on the surface and then fly away the next day: You’ll definitely have some span of time when you’re busy establishing the colony, but everything isn’t yet ready. That’s the time when you’re breeding your horses back into work breeds: The initial minis would serve only as brood mares.
Easier, sure, but I’m also pretty sure that embryos are still easy enough, and give you more control over your genomes.
It takes about 11 months to produce a foal after insemination. Any foal that’s too disproportionate to the mare’s size will likely get stuck and die during birth, also killing the dam. Any resulting fillies can’t be bred till they’re at least two, better three years old. Any colts born in the early rounds will be useless for breeding because of size and not much good for anything except pulling carts, perhaps carrying packs, and slaughter for meat and hides after carrying the useless foals for at least a year to get them big enough to use. So trying to build a herd by incrementally breeding for size from minis is less efficient than starting with mares that are at least 12 to 13 hands high.
ETA: The Morgan gelding I owned was barely 15 hands (1 hand = 4 inches) yet he could easily carry his previous owner, a 6’2" guy.
ETA2: Large pony or small horse mares can work while carrying their foals up to very close to foaling.
The idea that a small human colony on a distant planet is going to bring horses is so absurd to me it feels like you guys are taking the piss.
Horses are an expensive commodity - they require a lot of land be dedicated to growing their food, and a lot of hands-on care - why would colonists waste any effort on them when they will have machines that can do hauling and carrying? And you have a few hundred colonists - can one of them really be spared to be a farrier, even part-time?
As for chickens and pigs - naah, any serious human colony should be thoroughly vegan before it even leaves the solar system, anything else is too wasteful to succeed.
A colony should be high tech or what’s the point. Yes, it should definitely have a chip fab. No point in a one-way colony that didn’t. But it doesn’t have to be the giant $billions cleanroom fabs of the big chip manufacturers. For something like a colony, the tech of the “minimal fab” initiative would be plenty good enough.
How about tilapia and some algae they can eat? I feel like when you have lots of space, for animals can make nice high-nutrition-density food for you with very little effort. And if you are despoiling a while planet, if there’s any space you can plant crops in, there’s lots of space.
I also thought the idea of bringing sheep for fiber, milk, leather, and bone has some merit, although growing suitable food for them is harder than food for tilapia.
(I was also going to point out that horses are delicate and high-maintenance. They seem like the last domestic animal you’d bring anywhere.)
Why not just eat the algae?
Animals take effort, though - protecting them, feeding them, etc. If your Earth animals can forage, you can probably eat the native plants yourself. Or if you must, the native animals.
Space isn’t my concern here, human effort is. Every person you’re assigning to be the swineherd or shepherd is a person not working on mining or medicine or any of the other things you actually will need, not just want.
Why are you concerned with wool and leather? If you have modern tech, you can manufacture fibres and fabrics - either from plants or the old oil-based stuff, no animal intermediary needed. Hell, you can grow “leather” from fungal mycelium, Adidas and Stella Macartney are already using it.
I’m dubious of the robustness of our tech with that small colony. We have evidence that smallish groups of people can maintain a pastoral economy.
I thought tilapia often ate the tiny algae that aren’t very practical for humans to eat, and i assume the colonists would have to bring species they can eat. And tilapia, unlike humans, can make vitamin B12. Our colonists will need a source of that, although i suppose if they are high tech they can just extract it from sewage. We’re bringing bacteria that eat our wastes no matter what other choices we make. 
People who have been pastoralists their whole lives.
The issue here is that they also have to be starship pilots.
But if we’re not brining the fish, why bring their food?
So can seaweeds - and other plants like soy, with bacterial fermentation. We don’t have to eat animals to get B12.
This brings to mind the novella (or novelette?) A Billion Eves by Robert Reed. Involves a technology for devices that teleport a smallish (I donno, a couple of hundred feet radius?) area into a parallel Earth. It happens blindly and randomly and the transporter is single-use, burning out after the jump, so if you land on an Earth in the middle of a Snowball Earth or is filled with T-rexes you’re SOL. You would still have the same problems: what would you take with you to have the best chance of surviving on even a shiny new (human-free) Earth?
Depends on the breed. Thoroughbred, say? Terrible choice. But ponies of any size are tough, hardy, longer-lived, and offer lots of power in a smaller size than horses. The Mongolian horse (large pony-sized) is a prime example of what you’d want. The utility and cost/benefit of bringing them would depend on how much manufacturing, let alone raw materials, would be available to produce machines and the things needed to maintain and repair them, also the available fuel[s] to operate them.
If one wants livestock, goats offer milk, meat, hides, and also wool in certain breeds. Assuming a planet with vegetation that’s edible for Earth life, goats are highly effective at grazing away underbrush, weeds, and other growing stuff you want cleared out. We’re talking critters that can and do eat poison ivy here.
Depending entirely on technology to prove every need, without an alternative if it fails, seems unduly risky to me.
I read Anne McCaffrey’s Dragonsdawn. We’ll for sure need a geneticist gifted enough to turn native flying lizards into dragons.
I suggest, for within the community, bicycles or tricycles.
WD 40 and gorilla tape.
Will keep things running smoothly and hold things together.
It’s always good to have a Corkscrew handy.
I realized this way back in the 90s when I was participating in the Bujold mailing list. Why did the people settling Barrayar bring horses? It didn’t make any sense, especially since horses can’t eat the native Barrayaran plants. Couldn’t convince anyone on the list that it would have been a bad idea.
And don’t forget your towel.
Alternatives that act as a large drain on scarce resources are worse than no alternative at all. I mean, you’ll still have the humans themselves, as well as everything on the new planet, including its own ecosystem. If it’s as Earth-like as the OP proposed, then there should be native wildlife that can take the place of Earth draft animals.
They’d have to be domesticated first. That takes lots of time, usually generations of the animals in question.
So would the proposed pony enlargification program, with the added hassle of having to bring the first ponies in the spaceship.
But if they’re anything like Earth wild horses, no, they wouldn’t need to be domesticated initially. Only tamed. Useless for riding, but could pull something.
Except there’s no guarantee anything would be “anything like” Earth anything. Or that anything would be a species that could be domesticated (only a very small fraction of Earth species could be).
Might be better off bringing dogs - they, too, can be used to pull things, can largely eat the same things people do so don’t require a special suite of crops just for them, can be used for meat and hide (despite our cultural taboos against that) and some breeds can even provide fiber.
“What to bring” depends on a lot on how much you can bring.
A successful interstellar colony would need a chip fabricator, a robot fabricator and most important of all, a fabricator fabricator. It would also need an artificial womb (capable of birthing humans, and draught horses if youn really want them) and a food vat, into which you could shovel local plantlife and algae and convert it into flavoured mush.
As I said earlier, beware of local trace elements (and trace element deficiencies); not every solar system has the same metallicity and local abundance of elements. If you are lucky you might get an abundance of gold; gold is a nicely inert substance and could be used as a protective covering against corrosion, although it would be useless as a currency that far from the Terrestrial economy.
Other than the OP explicitly saying it was.