# Evaluating a Rapid Immunity Test to Predict Dairy Calf Mortality Risk

## TL;DR

A new rapid immunity test called D2Dx better predicts early calf mortality risk than the traditional Brix test in dairy calves.

## Contribution

The D2Dx immunity test is shown to outperform Brix values in predicting neonatal dairy calf mortality risk.

## Key findings

- Calves that survived had higher D2Dx scores and Brix values at 2–3 days of age compared to those that died.
- On the low-mortality farm, D2Dx scores showed significantly better sensitivity and AUC than Brix values.
- The D2Dx test is most effective in predicting mortality risk when no other factors are involved.

## Abstract

Transfer of passive immunity (TPI) is critical for the survival of pre-weaned dairy calves. Plasma or serum Brix values measured by a refractometer are often used in farm settings to estimate circulating immunoglobulin (Ig) G concentration as a proxy for TPI. However, the Brix value only estimates the total solid percentage in blood and does not directly reflect the immune status of the calf. The D2Dx (from diameter to diagnostics) immunity test is a new nanoparticle-enabled rapid blood test to measure humoral immunity in humans and animals. In this study, we compared the performance of Brix value and the D2Dx immunity test in predicting neonatal dairy calf mortality risk. Our study found that the D2Dx immunity test outperforms Brix value when predicting neonatal diary calf mortality risk within their first 30 days of life if no other risk factors are involved. The D2Dx immunity test can potentially be used as a new tool in farm settings for dairy calf health management.

The study objective was to compare the ability of Brix values and the D2Dx immunity test to predict the mortality risk of calves under 30 days of age. Heifer calves at 2–3 days of age were enrolled from two farms: Farm A, which has a low calf mortality rate (n = 849, 2.9% mortality), and Farm B, which has a high calf mortality rate (n = 698, 11.7% mortality). Serum samples were collected from the calves when they were 2–3 days of age. The D2Dx scores and Brix values of serum samples were compared between calves that died or survived between 3–30 days of age. For both farms, calves that survived their first 30 days of life had greater serum Brix values (9.05 vs. 8.48, p = 0.002 for Farm A; 9.26 vs. 8.99, p = 0.05 for Farm B) and D2Dx scores (0.0281 vs. 0.0036, p < 0.001 for Farm A; 0.0342 vs. 0.0286, p = 0.05 for Farm B) at 2–3 days of age compared with calves that died. On Farm A, the D2Dx score shows significantly better sensitivity (96% vs. 48%) and Area Under the Curve (0.87 vs. 0.69) than the Brix value in predicting calf mortality. However, similar results were not observed for the high-mortality farm (Farm B) due to other factors in addition to calf immune status that influenced calf survival. This study concludes that the D2Dx immunity test can be used to identify newborn dairy calves with low immunity and increased mortality risk; however, the prediction is most effective if no other risk factors are involved.