Factors that Influence the Concentration of Immunoglobulin A in Bovine Milk

Natural levels of Immunoglobulin A (IgA) in bovine milk provide the opportunity to generate added‐value nutrition and immune milk products. This article investigated the concentration of IgA in milk from both individual cows and dairy herds over multiple lactations, with a focus on parameters which may inform the establishment and maintenance of dairy herds with high IgA concentrations. Considerable variation in IgA was observed at both the herd and individual animal level. Heritability of IgA was moderate (0.33–0.37) and both cow age and milk percent protein had a significant positive correlation with IgA concentration. In the second part of the study, the maintenance of IgA concentrations in a High IgA herd, selected from the multiherd cohort, were profiled over two seasons. The IgA:protein ratios in the herd were 55% higher than in unselected animals and stabilised by mid late lactation. Older animals tended to maintain their high, intermediate, or low status both within a season and between years. Together, this article provides information which will assist in the design of High IgA herd selection and maintenance policies, which may lead to the development of future functional foods and ingredients.