Table 2.

Characteristics of symptoms at different stages of BDD.

M stage	Stage of the disease	Clinical manifestations
M0	Healthy Skin	Hoof skin is intact with no discoloration, and palpation reveals no pain response.
M1	Early stage	Hoof skin infection caused by one or more pathogenic microorganisms, resulting in small localized lesions gradually developing on the skin. The affected area measures less than 2 cm in diameter and presents as a gray or red, rough ulcerated surface. When pressure is applied to the lesion, the cow exhibits a pain response.
M2	Acute phase	The infection is intensified, with the lesion gradually expanding to at least 2 cm in diameter, accompanied by symptoms such as ulceration and fissures between the toes.
M3	Healing stage	The affected area gradually forms a scab and hardens, turning brown. Pressing firmly on the lesion elicits no response or pain.
M4	Chronic stage	The skin between the toes becomes hardened and develops grayish-white or brown filamentous and crust-like growths, which are painless upon pressure.
M4.1	Chronic-active stage	Transitional stage with small (< 0.5 cm) ulcerative changes within a chronic M4 lesion containing a small active M1 focus, preceding relapse to the acute M2 stage; reflects inadequate hoof management during the chronic phase.

Adapted from Döpfer et al., 1994; Döpfer et al., 1997.