The left table shows mating two normal/healthy horses, they do not carry any dwarfism alleles. In this case only normal/healthy foals will arrive.
On the right table you can see mating dwarfs. Here you will always breed dwarf foals. Both parents are dwarfs and homozygous for their dwarfism, so they will always inherit one dwarfism allele each. So you must get a dwarf foal.
The left side table shows mating a dwarf to a normal/healthy horse. In this case you will always breed carrier foals.
The right side table shows mating carriers. As mentioned above here you can breed normal/healthy foals, carrier foals and dwarf foals.
Misbelief: Normal looking horses will never breed dwarf foals. That´s proven not true! Also "normal" and "healthy" looking horses can be carrier. Mating these can produce dwarf foals. This recessive trait can be inherited over generations without notice.
Warning: Double carriers excist! It is known that horses can carry for e.g. ACAN and Skeletal atavism dwarfism alleles and looking normal.
There are many genetic combinations of this type that are possible
Four known ACAN mutations excist: D1, D2, D3, D4.
D1 is lethal combined with itself and all other ACAN-Mutations.
D3 could also be lethal combined by itself. But no samples homozygous for D3/D3 were found.
D4 is lethal combined with itself or D1.
All other combinations are viable.
Unknown are dwarfs being homozygous on one ACAN-type and on Skeletal atavism. It seems to be possible this combination is not viable.
Carriers on skeletal atavism can also carry different types of ACAN-Dwarfism.
Tip: These gene discoveries may explain, in part, why miniature horses have a noticeably higher miscarriage rate, and lower live foal rate, compared to other horse breeds