Passive Transfer Immunity in Calves: From Colostrum Management to Practical Strategies

Passive transfer immunity (PTI) is a critical determinant of health and survival in neonatal calves, as they are born with an immature immune system and depend entirely on colostral immunoglobulins for early immune protection. Failure of passive transfer (FPT), commonly defined as a serum IgG concentration below 1000 mg dL^-1 at 24 - 48 hours of age, remains a widespread problem worldwide and is associated with increased morbidity, mortality, and reduced growth performance. This review summarizes the fundamental principles and practical aspects of successful passive transfer management. Colostrum management, including quality, quantity, and timing of feeding, is the primary determinant of PTI success. High-quality colostrum (≥ 50 g L^-1 IgG; Brix ≥ 22 - 23 %) should be administered as early as possible after birth, ideally within the first 2 hours of life. Calves should receive approximately 3 - 4 L of colostrum at first feeding, followed by a second feeding within the first 8 - 12 hours to ensure sufficient immunoglobulin intake. PTI status is typically evaluated between 24 and 48 hours after birth, with 48 hours considered the most reliable time point. Direct measurement of serum IgG using radial immunodiffusion (RID) or ELISA remains the gold standard; however, practical on-farm tools such as serum total protein and Brix refractometry are widely used for routine monitoring. In herds with a high prevalence of FPT, systematic evaluation of colostrum management practices and calf-related factors such as dystocia, hypoxia, and metabolic acidosis is required. Optimizing colostrum management and routinely monitoring passive transfer are key strategies to improve calf health and herd productivity.