Selective breeding for aesthetic traits can result in significant anatomical and physiological compromise. In Arabian horses, breeding for exaggerated concave facial profiles (“dished faces”) has raised concerns regarding potential impacts on respiratory function and dental alignment. Studies such as those by Goodarzi et al. (2021) and Pompermayer et al. (2023) demonstrate that variations in skull morphology can influence sinus structure, airway dimensions, and surgical accessibility, highlighting the biological consequences of aesthetic selection. From a welfare perspective, any alteration that compromises respiratory efficiency directly impacts the health domain, while chronic breathing difficulty can negatively affect the mental state through discomfort and stress. This raises important ethical questions regarding the prioritization of aesthetic traits over functional anatomy.

Selective breeding can also lead to less visible but equally significant internal dysfunctions. Research by W. M. Rauw emphasizes that selection for production traits can result in physiological trade-offs, where resources are diverted away from immune function and stress resilience. In poultry (as a comparative example), rapid growth rates have been linked to cardiovascular issues and skeletal disorders, illustrating how extreme selection pressures can exceed biological limits. While not the primary focus of large animal breeding here, this principle is directly transferable to cattle, pigs, and other livestock species. From a welfare perspective, these trade-offs compromise both health and mental state, as animals experience increased disease susceptibility and reduced capacity to cope with environmental challenges.

The nasal cavities of pugs have evolved to be more condensed, resulting in a desirable short or scrunched-like face that humans have chosen to prefer. Compared to normal domesticated dogs, the nasal passage of a pug is more condensed and tilted upwards, whereas a normal dog's airways would be straighter, as the shape of a longer snout allows for clearer airways. Both pugs and French hound dogs breeds are what's considered extremely brachycephalic dogs, which are categorized based on their flat faces and shorter skulls. When pugs were originally domesticated, they had longer muzzles and clearer airways, but based on aesthetic demands, pugs were bred for the shorter skull and flat face traits to meet consumer preferences. One of the more common diseases seen within pugs due to their flat face is turbinate hypertrophy, which is caused by the shortening of the skull but not the shortening of the turbinates', leaving it anatomically unbalanced. The breeding of pugs is now highly debated and not ethical, based on the obvious and unavoidable respiratory issues it will have throughout its life due to its morphology.

Ear cropping involves the surgical removal of the ear flap, leaving behind a more pointed and standing-up ear shape. Tail docking is a similar procedure where the tail of a dog is cropped at a specific point, often for aesthetic purposes rather than functionality. Dobermans, especially, are known for being subjected to both of these procedures on a routine basis to maintain their standard breed “reputation” with the intent of making them more intimidating and sharp-looking. While highly controversial, many breeders and owners continue to have this procedure done on a routine basis for the overall look of the animal. Medical alterations to an animal's appearance should always be out of medical necessity to be ethical, and it is not recommended for cosmetic purposes, as it can lead to an increased chance of further complications and chronic pain that can impact the animal's overall health and well-being