Why does a stallion refuse a new mare?

Answer 1

The mare may have a caslicks. The stallion may be large or starting to flower a bit which will make it difficult for him to penetrate especially if she is small.

Mare may be tall and not breaking down so that the stallion cannot reach her effectively.

Answer 2

Without any information on the stallion's history and how he has been

bred to mares (breeding in hand, AI, pasture breeding or a combination of any of the three) the possible reasons for his refusal to breed a new mare are numerous.

Some possible reasons:

Stallions that have been used for pasture breeding are generally the most savvy about mare behavior and are more careful about breeding. They generally know if a mare is fully receptive and will ignore a mare until she is in full standing heat. They don't want to be injured trying to breed an uncooperative mare.

Some of these stallions breed mostly at night so the mare may be ignored and bred later.

Stallions used for AI only who are being switched over to hand breeding or

pasture breeding may be confused by the change in routine, refusing to breed

a live mare because they have been highly disciplined to ignore mares (ex. during competitions).

Stallions that are hand bred may never have been presented with a mare that is not receptive but the routine may have changed in some way that is enough of a

distraction that he won't breed. These stallions are the most likely to be injured

in an uncontrolled breeding situation and an uncooperative mare or too many

people standing around wanting to observe the process can be an issue for some

stallions. Shy breeders, slow breeders also fall into this category.

If a stallion has been injured/kicked by a mare in the past he may refuse to breed her, or a mare that appears to be like her. (Ex. A stallion kicked by a gray mare refuses to breed gray mares. While this sounds ridiculous considering most stallion's libidos, it has happened.)

The stallion doesn't feel well.

It's late in the year and the stallion's interest in mares is waning.