Are current cut-points for passive transfer of immunity appropriate for dairy calves fed colostrum replacers?

Abstract

Objective: Passive transfer of immunity (PTI) is a metric used on farm to assess colostrum management. With multiple colostrum replacers available differing in composition, classical total serum protein cut points may not apply to all products. The aim of this analysis was to determine whether calves fed a whey-based colostrum replacer that successfully achieved PTI (serum IgG ≥10 mg/mL) would have been classified as having PTI using typical benchmarks (total serum protein <5.0, 5.2, or 5.5 g/dL or Brix% <8.4). Materials and Methods: In total, 1,220 calves were assigned to 1 of 2 treatments: (1) maternal colostrum (MC) or (2) whey-based colostrum replacer supplying 150 g of IgG (CR). Serum samples were collected at 0 and 24 h of life to determine serum IgG, total serum protein, Brix%, and apparent absorption efficiency. Results and Discussion: When comparing serum IgG values with current on-farm cut points, the proportion of calves incorrectly classified as having PTI failure was greater (P < 0.01) for the CR treatment compared with the MC treatment. The proportion of calves incorrectly classified for CR versus MC using current total serum protein or Brix% cut points were as follows: 5.0 g/dL (31.2 vs. 8.8%, P < 0.001), 5.2 g/dL (52.5 vs. 15.5%; P < 0.001), and 5.5 g/dL (82.0 vs. 34.0%, P < 0.001) or serum Brix 8.4% (73.2 vs. 29.2%; P < 0.01). Implications and Applications: These data suggest when analyzing serum on farm from calves fed a whey-based colostrum replacer, traditional cut points for PTI should be revised.