Failure of Passive Immune Transfer in Neonatal Beef Calves: A Scoping Review

Neonatal calves possess an immature and naïve immune system and are reliant on the intake of maternal colostrum for passive transfer of immunoglobulins. Maternal antibodies delivered to the calf via colostrum, are crucial to prevent calfhood diseases and death. Failure of passive transfer (FPT) is a condition in which calves do not acquire enough maternal antibodies, mostly in the form of IgG, due to inadequate colostrum quality or delayed colostrum feeding. The diagnosis and risk factors for FPT have been widely studied in dairy cattle, however, in beef calves research interest in the topic is relatively recent, and the most adequate diagnostic and preventative methods are still developing, making it difficult to define recommendations for assessment and prevention of FPT in cow-calf operations. The objective of this scoping review is to identify literature available on best practices of colostrum management and transfer of passive immunity (TPI) in neonatal beef calves. Literature was searched through three electronic databases (CAB Direct, Scopus, and PubMed) for publications from 2003 to 2025. The search process was performed during the period from May to July 2023 and repeated in January 2025. All screening processes were performed using Covidence systematic review software. A total of 800 studies were initially identified through database searches. After removing duplicates, 346 studies were screened based on their titles and abstracts, leading to the exclusion of 260 studies. The remaining 86 studies underwent full-text screening, and 60 studies were considered eligible for data extraction. Hand-searching of references from published review papers on the subject yielded an additional six studies, bringing the total to 66 included ar-ticles. Prevalence of FPT has been estimated to be between 5.8% and 34.5% in beef calves. Dam-related risk factors studied include breed, dystocia, twinning, dam vaccinations, age, body condition score, prepartum nutrition, genetics, udder conformation, and health. Studies on risk factors related to the calf include calf vigor and suckling reflex, colostrum quality and quantity consumed, timing and method of colostrum feeding, and microbial content of colostrum. Most importantly for beef systems, calves with low vigor and weak suckling reflex are at high risk for FPT, therefore, these calves should be given extra attention to ensure adequate consumption of colos-trum. While serum IgG levels of < 8 g/L or < 10 g/L have been suggested as cutoffs for the diagnosis of FPT, 16 g/L and 24 g/L have emerged as cutoffs for adequate and optimal serum IgG levels in beef calves. Several field-ready diagnostics have been compared in various studies to reference stand-ards for measuring indicators of TPI in beef calves, where results often differ between models or manufacturers. Therefore, care must be taken when interpreting these results.