The symptoms usually occur in the following order:—Swelling of the affected quarter or quarters; appreciable increase in size and sensitiveness; the presence at first of curdled milk in the galactophorous sinus, then of clots mixed with slightly red tinged serosity; complete cessation of the yield of milk, and suppuration in the secreting portions of the gland.
The general symptoms appear only after the objective signs, and vary greatly in intensity, according to the case. As in the interstitial form, there may be marked fever, loss of appetite, cessation of rumination, groaning, and difficulty in walking.
In some grave forms, where development is peracute, infection spreads rapidly from the glandular to the interstitial tissue, and subcutaneous, subabdominal, or perineal interstitial œdema occurs secondarily.
The udder is turgid, tense, shining, and of reddish-violet colour in places, as if a deep-seated abscess were developing.
Pressure on the galactophorous sinus causes the flow of reddish-grey milk, sometimes fœtid or of gangrenous odour. The animals seem exhausted, show signs of profound intoxication, are unable to rise, and appear paralysed.
But besides these grave forms are others, in which the patients seem scarcely to suffer: appetite is preserved and all the vital functions are in full activity. Only the local signs are of importance.
This variability in the clinical symptoms of acute forms of mammitis is entirely due to differences in the pathogenic infecting organisms.
Parenchymatous mammitis may end in resolution in three to four days, with progressive but slow return to the physiological condition. This termination is announced by the gradual disappearance of all the symptoms and the return of milk secretion. It is, however, quite exceptional for the former condition to be fully restored, and in many cases the affected quarter must be regarded as lost from the physiological standpoint.
It gradually becomes hardened, sclerotic and atrophied.
Suppuration is very common. It attacks the galactophorous sinus, the excretory canals, and even the acini. If obstructions occur in the course of the collecting vessels, or if evacuation is not artificially stimulated by milking, the pus collects in the depths of the gland, and enormous diffuse abscesses may form at the expense of the mammary tissue.