Impact of diseases on milk yield and physicochemical traits in small ruminants: a comprehensive review

Diseases are major determinants of reduced milk production, impaired milk quality, and substantial economic losses in small ruminant farming systems. A wide range of health disorders can adversely affect milk yield and physicochemical traits in sheep and goats by altering mammary gland structure and function, disrupting rumen physiology, reducing feed intake and energy availability or triggering systemic inflammatory responses. These conditions include i) mastitis, ii) lameness-related disorders, iii) abortion-related diseases, iv) systemic infectious diseases such as bluetongue, maedi-visna, caprine arthritis encephalitis, sheep pox, and paratuberculosis, v) parasitic diseases, particularly caused by gastrointestinal nematode infections and ectoparasitic infestations, vi) and metabolic disorders such as subacute ruminal acidosis and pregnancy toxaemia. Beyond mastitis, and despite their importance, the effects of most of these diseases on milk yield and milk physicochemical traits in sheep and goats remain insufficiently quantified. Thereby, the aim of this review was to synthesize and present current knowledge on how infectious and non-infectious diseases affect milk production and physicochemical traits in sheep and goats.