You cannot breed a Miniature donkey (30 inches tall) to a Clydesdale mare (18 hands). The foal will be too large for the mare to birth, or the Jack will be unable to mount.
The direction of the cross matters significantly for the physical outcome:
: Horses have 64 chromosomes and donkeys have 62. Their hybrid offspring end up with 63 chromosomes. This odd number prevents the chromosomes from pairing correctly during meiosis, rendering almost all sterile . Horse Mating Donkey
Mules are far more common because mares (female horses) have a larger uterus and birth canal, making the pregnancy safer. Jennies (female donkeys) are smaller, and carrying a hybrid foal (which often has hybrid vigor meaning it grows larger than a pure donkey) can be dangerous.
are less common and typically have the body of a donkey with the extremities of a horse. Quick Genetics Fact You cannot breed a Miniature donkey (30 inches
Hybrid foals often have "contracted tendons" (club foot) because of the conflicting growth rates. They also have a high rate of neonatal maladjustment syndrome (dummy foal syndrome). You will likely need a veterinarian present.
Mules are highly intelligent and possess a strong self-preservation instinct, which is often mistakenly labeled as stubbornness. 2. The Hinny (Stallion × Jenny) Their hybrid offspring end up with 63 chromosomes
Sometimes, the mare’s immune system recognizes the hybrid foal as "foreign" (because half its DNA is donkey) and attacks it. This requires careful veterinary monitoring and immune-suppressing drugs in some high-risk pregnancies.