What are biomarkers and how can we use them to improve male dairy calf health?

By Dr. Dave Renaud, ACER Consulting Ltd.

In simple terms, biomarkers are biological cues that can be measured to better understand calf health and disease. Finding biomarkers for calf health requires the collection of a blood sample for analysis to identify calves at high risk for disease.

Recently in Ontario, a number of different studies have been performed to evaluate if blood samples collected at arrival to a veal facility are associated with future risk of disease development. One study collected blood samples from 992 calves arriving at a grain-fed veal facility, whereas a separate study collected blood samples from 405 calves at a milk-fed veal facility. These studies found several interesting biomarkers that are useful in identifying calves at high risk of disease, including markers of colostrum intake, inflammation, and energy status.   

Immunoglobulin G | A marker of colostrum intake

High levels of immunoglobulin G (IgG) in the blood stream of calves has consistently been shown to improve levels of growth and reduce risk of disease and death. Specifically, for every one gram/litre (g/L) increase in IgG, the risk of mortality decreases by three per cent. This is not a new finding and shows just how critical it is that calves receive excellent colostrum at birth.

To maximize IgG, calves need to be provided with an ample quantity of colostrum (three to four litres at first feeding), that is of good quality (greater than 50 g/L for IgG or greater than 22 per cent on a Brix refractometer, which can be used to measure colostrum quality), clean (low bacterial contamination), and fed promptly after birth (ideally within four hours after birth).

Following this protocol will protect calves against disease. Unfortunately, it is still very common for male calves arriving at veal and dairy-beef facilities to have low levels of IgG. This means changes are necessary to provide male dairy calves with improved resistance against disease. 

Haptoglobin | A marker of inflammation

Haptoglobin is a protein that is released in response to tissue damage and is higher in calves with bacterial or viral disease. Haptoglobin levels should be low in healthy calves and it is not surprising that calves that arrived at veal facilities with high levels of this protein in their blood had a greater risk of being treated for disease.

Haptoglobin levels at arrival to veal facilities are likely related to the condition of calves entering into the facility, where those with an umbilical infection or diarrhea would have highest levels. Haptoglobin will also be increased as a result of stress, like transportation. Ensuring that calves are in the best condition possible when they leave and are transported can help to reduce the burden of disease.    

Cholesterol | A marker of energy status

One of the most interesting findings in both of these studies is that calves arriving with high concentrations of cholesterol in their bloodstream had an increased average daily gain and reduced risk of mortality. This result could be for several reasons. As cholesterol plays a critical role in energy mobilization, low levels may be related to when they had their last meal and the duration of transport. Low levels could also be related to age, with higher levels found in older calves, or to colostrum intake, as colostrum has high levels of cholesterol. Finally, it could be related to a genetic defect in Holsteins called cholesterol haplotype deficiency. This genetic defect causes calves to not gain as well and leads to higher levels of diarrhea and mortality.

What does all this mean?

Many of these factors relate back to how calves are managed in early life. Therefore, ensuring calves receive excellent colostrum and nutritional management as well as preventing the marketing of calves with disease can go a long way towards reducing the burden of disease and risk of death at veal facilities. 

This project was funded by the Canadian Agricultural Partnership, a five-year federal-provincial-territorial initiative.