Once regarded as a benign, clinically overlooked organism, Theileria orientalis has undergone a paradigm shift in its perceived status and is now recognised as a tick-borne haemoparasite of clinical and economic importance. Severe outbreaks characterised by haemolytic anaemia, reproductive losses, and mortality, primarily associated with the Ikeda and Chitose genotypes, have been increasingly reported in Australasia, Asia, and North America. In Europe and parts of Africa, however, the epidemiological status of T. orientalis remains poorly defined, despite increasing molecular evidence of circulation and reports of predominantly subclinical infections. The parasite is transmitted transstadially in ixodid ticks, with Haemaphysalis longicornis as the principal confirmed biological vector, although vector competence remains unverified for most suspected tick species. This narrative review was based on a comprehensive PubMed search from database inception up to the date of initial manuscript submission, supplemented by reference-list screening and targeted searches. This review synthesises current knowledge on taxonomy, life cycle, transmission, genetic diversity based on the major piroplasm surface protein gene, global epidemiology, pathogenesis, clinical manifestations, co-infections, production losses, diagnostics, and control strategies. Key gaps include limited understanding of the mechanisms driving erythrocyte destruction, insufficient experimental confirmation of vector competence, absence of licensed vaccines, and incomplete epidemiological data in several regions. Future research priorities are discussed in the context of climate change and the expanding geographic distribution of tick vectors.

The transfer of passive immunity (TPI) is vital for newborn calf health and is typically assessed through blood sampling to measure serum or plasma IgG or total protein levels. Saliva offers a less invasive alternative. This study evaluated the potential of saliva for assessing TPI. Saliva and serum samples were collected from 20 calves at birth and on days 1, 2, and 7 of life to measure IgG, IgA, IgM, and total protein concentrations. Colostrum fed to the calves was also analyzed for gross composition and immunoglobulin content. Colostrum intake and composition were associated with saliva IgG (R² = 0.48; p = 0.019), saliva IgM (R² = 0.73; p = 0.02), and saliva total protein (R² = 0.41; p = 0.043). Serum IgG and IgA levels were predicted by saliva IgG (p < 0.001; R² = 0.33) and IgA (p < 0.001; R² = 0.13), respectively, though predictive accuracy varied by calf age (IgG: p < 0.001; R² = 0.40; IgA: p < 0.001; R² = 0.91). In conclusion, the results suggest that both saliva IgG and IgA concentrations could be used to predict IgG and IgA serum concentrations. Nevertheless, further studies are still needed to clarify the best time for sample collection.

Lameness has been identified as a major welfare challenge in sheep farming production. The most common causes of lameness include several types of foot-related lesions. Accurate diagnosis of hoof lesions, particularly differentiating footrot from other foot disorders, is critical for implementing effective control strategies. This study assessed the ability of sheep farmers in Alentejo, Portugal, to recognise footrot lesions among other hoof disorders. A pictorial questionnaire depicting several hoof lesions, including footrot, interdigital dermatitis, contagious ovine digital dermatitis (CODD), toe granuloma, foot abscess, and shelly hoof, was applied to 61 Alentejo sheep farmers. Respondents identified which images represented footrot lesions and which of them they had previously observed in their flocks. Among the footrot images, the individual correct identification rate ranged from 95.1% to 100%. For other hoof disorders, the identification rate ranged between 88.5% (CODD) and 96.7% (shelly hoof). Eighty percent of the farmers (49/61) correctly answered all the eight questions. Farmers who reported no footrot in their flocks had a slightly higher accuracy (82.1%) compared to those who did (77.3%), though the difference was not statistically significant. In general, Alentejo sheep farmers evidenced a high level of accuracy in diagnosing footrot lesions, suggesting CODD does not look like to be an important confounding factor in Alentejo, as it mainly occurs in Great Britain.

Gastrointestinal nematodes (GIN) are one of the main constraints affecting sheep production worldwide. For decades, control methods based on anthelmintics have been extensively used, which ended up in multiple drug‐resistant helminth strains. Selective breeding for disease resistance is a long‐term and sustainable strategy to improve animal health, welfare and productivity. Therefore, we performed a genome‐wide association study using a customized SNP panel to identify genomic regions and molecular mechanisms associated with GIN resistance/susceptibility among Portuguese Merino and Merino‐related sheep. Two SNPs located within centromere protein K (chr 16; 14 439 999 bp) and NADH: ubiquinone oxidoreductase complex assembly factor 2 (chr 16; 19 366 442 bp) genic regions reached genome‐wide Bonferroni significance ( p = 2.08 × 10 ⁻⁶ ). Additionally, five genome‐wide suggestive SNPs were detected within genic regions of adenomatous polyposis coli regulator of WNT signaling pathway (chr 7; 1 050 994 bp), regulator of G protein signaling 8 (chr 12; 68 278 650 bp) and hypoxia inducible factor 3 subunit alpha (chr 14; 57 059 428 bp), as well as in intergenic regions near calcium binding and coiled‐coil domain 1 and ATP synthase membrane subunit C locus 2 (chr 3 142 391 546 bp) and semaphorin‐6D (chr 7; 65 321 727 bp). Candidate genes located in these regions are involved in intestinal homeostasis, epithelial barrier reinforcement, and regulatory mechanisms of immune response. These results provide new and useful information about the genetic architecture underlying GIN infection in Portuguese Merino sheep. Further analyses are needed to validate these SNPs and assess their contribution to selection strategies focused on breeding animals with enhanced GIN resistance.