A 340-head dairy in New England experienced eight abortions in the dry cow pen in a two-week period. This is a closed herd that has not received vaccinations in many years. A Jersey bull with unknown vaccine history was introduced to the dry cow pen two weeks prior to the first abortion. Four pigs were housed in a pen in the dry cow barn, one of which escaped from the pen and was found to be sleeping in the lactating cow feed for a few days. Concurrently with the abortion events, there was an outbreak of subclinical mastitis, with high somatic cell counts and positive California mastitis test results (typically 3+).
Serum was collected from dams, and fetuses and placentas were submitted to the AHDC for necropsy and ancillary testing. Multiple dams had high positive titers for Leptospira interrogans serovar Pomona. Histopathology on fetal tissues revealed hepatic pathology, and placenta samples tested positive for Leptospira on PCR. These findings indicated Leptospirosis to be the most likely cause of abortions in this case.
Serum and urine were collected from the pig living in the lactating cow feed. The pig had a high titer for Leptospira interrogans serovar Pomona, and the urine was PCR positive for Leptospira. It is likely that this pig was involved in widespread propagation of Leptospira, including into the lactating cow barn; however, it could be that this positive result is just a reflection of widespread environmental contamination of the farm with the bacterial agent.
Milk collected from lactating cows with high somatic cell counts also tested positive for Leptospira with PCR, which is an atypical etiologic agent of subclinical mastitis presently, but was identified as a common mastitic agent several decades ago [1,2]. This positive result in milk is also concern for zoonotic potential, and reiterates the importance of pasteurization.
Leptospira abortion and mastitis are relatively uncommon in cattle, in part because of widespread vaccination. This herd was unvaccinated, and this case serves as a good reminder of the importance of vaccination for the health and reproductive success of a herd.
 Mitchell D, Boulanger P. Leptospirosis in Canada: IV An atypical mastitis in cattle due to Leptospira Pomona. Can J Comp Med Vet Sci. 1959;23(8):250-255.
 Robertson A, Boulanger P, Mitchell D. Isolation and identification of a leptospire of the Hebdomadis serogroup (L. Hardjo) from cattle in Canada. Can J Comp Med Vet Sci. 1964 Jan;28(1):13-8.