Eradication of paratuberculosis is hindered by a lack of effective treatments and the difficulty of developing highly efficacious diagnostic tests. Breeding disease-resilient animals is a potential alternative strategy for controlling paratuberculosis. However, there is limited information available on the estimates of genetic parameters for paratuberculosis in New Zealand dairy cattle. The present study used enzyme-linked immunosorbent assay (ELISA) scores from 2 commercial kits (IDEXX and IDvet) using milk (n = 930 for both IDvet and IDEXX) and serum samples (n = 935 for IDvet and 1,121 for IDEXX) obtained from 4 dairy herds in the Manawatu region of New Zealand during the 2022/23 production season. To estimate the heritability of ELISA scores and their correlations with total milk, and fat yields, we used univariate and bivariate Bayesian animal models with a Markov Chain Monte Carlo sampling framework. Both continuous and binary scales for ELISA traits were modeled to assess whether binarization alters the underlying genetic signal of ELISA measurements. For ELISA scores on a continuous log-transformed scale, point estimates for heritability ranged from 0.21 to 0.34, whereas ELISA scores in binary form ranged from 0.02 to 0.03 with their 95% highest posterior density intervals (HDI) overlapping zero. The genetic correlations between ELISA and milk production traits were compatible with both effect and null effects. Between-kit (IDvet vs. IDEXX) genetic correlations were estimated at 0.48 (95% HDI: 0.14-0.74) in milk and 0.58 (95% HDI: 0.32-0.81) in serum, suggesting that these assays may capture partly distinct genomic architectures. In conclusion, the present study demonstrates low to moderate heritability of the humoral response to paratuberculosis measured using continuous ELISA scores in New Zealand dairy cattle.
Venkatesh et al. (Mon,) studied this question.