Mastitis can present with and without clinical signs. Cows affected by sub clinical mastitis will demonstrate no visual signs of the disease and will require additional diagnostic tests to identify affected individuals (California mastitis test/milk sampling). Clinical disease can be identified and graded based on visual signs. Any alteration in the colour (off white/yellow/red) or consistency (clotted/thickened) of the milk and or changes to the udder (hot, hard, swollen, painful, sloughing) can be indicative of clinical mastitis. Cattle affected by mastitis can also become systemically ill. Often systemically affected cows will present with a range of clinical signs from a cow that shows reduced productivity to an animal that is collapsed and will die imminently without veterinary attention. The severity of the disease can be graded on clinical grounds using a simple three point scale:
Grade 1 (mild): Changes to the milk only (colour/consistency).
Grade 2 (moderate): Changes to the udder (heat, swelling, pain).
Grade 3 (severe): Changes to the cow (sick cow) and or gangrenous sloughing of the teat.