Immune-associated traits measured in milk of Holstein-Friesian cows as proxies for blood serum measurements

Previous work has highlighted that immune-associated (IA) traits measurable in blood are associated with health, productivity and reproduction in dairy cows. The aim of the present study was to determine relationships between immune associated traits measured in blood serum and those simultaneously measured in milk as well as their association with disease phenotypes. All animals were Holstein-Friesian cows from the Langhill research herd (n=546) housed at the SRUC Dairy Research Centre in Scotland. Milk and serum samples were collected on 20 separate occasions between July 2010 and March 2015 and analyzed by ELISA for haptoglobin (Hp), tumor necrosis factor alpha (TNF-α) and for natural antibodies binding keyhole limpet hemocyanin (NAbKLH) and lipopolysaccharide (NabLPS). Data were analyzed using mixed linear models that included pedigree information. Analyses revealed positive phenotypic correlations between milk and serum NAb (0.59 ≤ r ≤ 0.77), Hp (r=0.37) and TNF-α (r=0.12). Milk and serum NAb were also found to have a strong genetic correlation (0.81 ≤ r ≤ 0.94) and were both genetically correlated with cow lameness (0.66 and 0.79 for milk NAbKLH and serum NAbLPS respectively). Clinical mastitis was found to be phenotypically correlated with both milk and serum Hp (0.09 ≤ r ≤ 0.23). Serum Hp was also strongly genetically correlated with other cellular immune-associated traits such as %NKp46+ (0.35) and %PBMC (-0.90). Similarly, genetic correlations were found to exist between serum TNF-α and %NKp46+ (0.22), %PBMC (0.41) and %lymphocytes (0.47). Excluding serum Hp, all milk and serum IA traits were repeatable ranging from 0.11 (milk Hp) to 0.43 (serum NAbLPS). Between-animal variation was highest in milk and serum NAb (0.34 – 0.43) and significant estimates of heritability were also observed in milk and serum NAb (0.17 – 0.37). Our findings show that certain immune associated traits, such as NAbKLH and NAbLPS, found in milk and serum are strongly correlated and highlight the potential of using routinely collected milk samples as a less invasive and cost-effective source of informative data for predictive modeling of animal immune associated traits.