Final Answer:
The differentials for the presented case include dermatophytosis (ringworm), bovine papular stomatitis, and photosensitization.
Step-by-step explanation:
The clinical presentation of a Friesian heifer with a thick adherent crust on the dorsum of the muzzle, confluent crusts over the pinnae/neck with extensive alopecia, patchy hypotrichosis with thick scales on the trunk, and alopecia with scales/crusts around the hocks suggests several potential differentials. Dermatophytosis, commonly known as ringworm, is a fungal infection that aligns with the observed symptoms, especially the crusts and alopecia.
Bovine papular stomatitis, a viral disease, is another consideration given the widespread crusts and alopecia, particularly in areas like the pinnae. Photosensitization, characterized by skin lesions on non-pigmented areas, could also be a differential, considering the equal involvement of white and black areas. Importantly, the absence of pruritus is notable and can help differentiate these conditions, as ringworm and bovine papular stomatitis are typically pruritic, while photosensitization is not.
To delve deeper into the differentials, it's essential to consider each possibility in the context of the specific symptoms observed. Dermatophytosis is a common fungal infection in cattle and is characterized by circular lesions with alopecia and crusts. Bovine papular stomatitis manifests as papules and vesicles on the oral mucosa and skin, with subsequent crust formation. Photosensitization occurs when the skin reacts to sunlight, resulting in inflammation and lesions, but pruritus is usually absent. Considering these factors aids in a more precise diagnosis and appropriate treatment plan.
In summary, the differentials encompass common skin conditions in cattle, with a focus on dermatophytosis, bovine papular stomatitis, and photosensitization. Thoroughly evaluating each possibility based on clinical signs and considering the absence of pruritus provides a comprehensive approach to arriving at an accurate diagnosis for the Friesian heifer's skin condition.