Ischemic Teat Necrosis
By CS McConnel, Veterinary Medicine Extension
Earlier this year an unfortunate case came into the Washington Animal Disease Diagnostic Laboratory (WADDL) with the following background: “History of a teat lesion that slowly worsened and became excessively pruritic in the last 3-4 days leading to self-mutilation of the teat by the cow. This cow was a high producing individual in her 1st lactation, 155 days in milk when the teat was removed. The sample was removed with little pain response by the cow and very minimal blood loss indicating poor blood flow to the affected teat because of possible necrosis.” On a separate dairy located nearby, a similar issue was ongoing and as time went on well over 10 animals were affected and culled over a period of approximately 6 months.
Primary histologic diagnoses from the case submitted to WADDL demonstrated:
- Neutrophilic teat duct inflammation and perivascular dermatitis with superficial dermal and epithelial necrosis and hemorrhage, severe, multifocal.
- Teat canal epithelial hyperplasia with hypergranulosis and orthokeratotic hyperkeratosis, severe, focal, chronic (presumed teat end hyperkeratosis).
That’s quite the mouthful but the gist of the situation was that no infectious causes of teat necrosis were identified and if causes of teat trauma could be ruled out clinically then bovine ischemic teat necrosis (ITN), as recently described in the UK, was considered likely.
So, what is ischemic teat necrosis?
Well, according to a recent publication in the Journal of Comparative Pathology, it is “an emerging disease of unknown etiology affecting mostly dairy cows in the early stages of first lactation and a substantial welfare concern frequently leading to premature culling and economic losses.” According to the article, it is common for ITN lesions to be highly irritating or pruritic with cows licking their teats until the tissue is further traumatized and eventually removed. ITN is extremely difficult to treat, and many animals are culled on welfare grounds due to the severity of the lesions. Anecdotally, the head milker from the dairy with the case described above claims to see a small ‘bruise-like’ lesion at the medial base of the teat at the onset of the disease process (Figure 1). The lesion feels mildly hardened compared to the rest of the teat surface, almost like a callous. When he observes this lesion, he changes the post-dip for those particular cows to a ‘Winter Dip’ with increased levels of emollient that he thinks helps keep the lesion from worsening into the typical ITN lesions.
It should be mentioned that ITN is a differential diagnosis for several other diseases of the skin of the teat, most of which have a better prognosis. Such diseases include bovine herpes mammillitis, the main differential diagnosis, caused by bovine herpesviruses 2 and 4, the bovine parapox viruses, cowpox virus and bovine warts caused by multiple bovine viruses. Also, to continue with the biosecurity theme above, I’ll mention that foot-and-mouth disease virus (FMDV) may also affect the skin of the teats, although systemic signs of FMDV in the same animal and herd would lead to a rapid diagnosis.
Although there are many unknowns regarding ITN, another British study published in Frontiers in Veterinary Science set out to investigate potential risk factors and economic impacts. The take-home message was that at the animal level, 47% of the cases occurred during the first lactation and 79% within the first 90 days in milk. Only 21% of the cases were reported to recover, whereas 23% of the cases required culling. The remaining cases
experienced complications such as loss of a teat and/or mastitis. The presence of udder cleft dermatitis (odds ratio 2.80; p < 0.01) and chapped teats (odds ratio 6.07; p < 0.01) in the milking herd was associated with the presence of ITN at the farm level. The bottom line is that this is a frustrating and potentially costly emerging disease. For some additional practical advice regarding ITN management, you might want to check out this UK Farmers Weekly site, or this video regarding a herdsman’s tips on beating ITN.