Preliminary Assessment of the Productive Impact of Theileria buffeli / orientalis Infection in Dairy Cattle on São Miguel Island, Azores

Abstract

The Azores archipelago is one of Portugal’s most prominent regions for cattle production. Previously, our group found a prevalence of 45% for asymptomatic Theileria buffeli/orientalis infections across ten dairy farms on São Miguel Island. This study aimed to monitor productivity on a selected farm to evaluate potential subclinical impacts of infection. On this farm, all animals in the milking facility—including lactating and pre-calving cows, but excluding calves, heifers, and dry cows—underwent PCR screening for Theileria buffeli/orientalis. Of the 74 samples, seven were confirmed positive, resulting in a 9.5% infection rate. This prevalence is lower than in our previous study, though some previously surveyed farms also showed low infection rates with only one positive case. Over the six months following sampling, the negative group showed a higher average milk yield per cow (31.726 kg) compared to the positive group (29.574 kg). The negative group also exhibited higher protein content (3.447) than the positive group (3.362), while the positive group showed slightly higher butterfat content (4.086 vs. 4.032). Statistically, no significant association was found between these productivity measures and infection status, which is expected given that only 7 of the 74 animals tested positive. Follow-up studies on this farm may offer further insights into the impact of Theileria buffeli/orientalis infections on dairy production in endemic areas. With this study ongoing, extended research across more farms and over longer periods is essential to fully capture subclinical effects, enabling a deeper understanding of the parasite's influence on productivity and animal health. By monitoring these subclinical impacts, this study contributes to advancing evidence-based management practices, supporting more informed strategies for herd health and optimizing dairy production in affected areas.