By Marlene Paibomesai
Colostrum is important for passive immunity, neonate nutritional needs and calf development. Colostrum is a source of immune factors, fatty acids and protein that the calf needs early in life.
Colostrum components are absorbed by the small intestine to effectively protect and provide nutrition to the neonate calf.
Circulating IgG and other immune factors, such as lactoferrin or leukocytes, play an important role in neutralizing pathogens, which protects the calf from disease. The window of absorption is close to birth with gut closure occurring about 12 to 24 hours after birth.
What Impacts Passive Immunity Transfer?
- Colostrum quality – Concentration of 50 grams per litre of IgG;
- Timing of colostrum delivery – First feeding within the first hour and no more than six hours for the second feeding;
- Cleanliness of the colostrum – Bacterial count should be under 100,000 colony forming units per millilitre;
- Quantity of colostrum – At least 200 g of IgG or four L in the first meal, followed by two L by eight hours;
- Slow transition to milk or milk replacer – Mix colostrum and milk over three days.
There are ways to assess colostrum standard operating procedures (SOPs) by assessing the calf’s serum total proteins (STP).
STP measures the total protein concentration in circulation in the blood stream. This measurement can be used to estimate the absorption of IgG into the calf. IgG makes up a large portion of the proteins in colostrum and it is a large, but not the only, contributor to passive immunity.
The threshold used to determine passive immunity in a calf is ≥10 g of IgG/L and correlates with a STP of ≥5.2 g per decalitre in circulation. Calves that have less than 10 g of IgG/L (5.2g/dL STP) have an increased risk of morbidity and mortality.
If a calf fails to reach this threshold, it is considered a failure of passive immunity transfer. A recent cross-sectional study of 444 Holstein calves in Ontario showed 24 per cent of calves had failure of passive immunity transfer, indicating there’s room for improvement on colostrum management programs in Ontario (Renaud et al., 2020).
There are some calf-side tests on the market to determine IgG concentration, but there is little research on their accuracy under field conditions. Brix refractometers (optical and digital) can be used to determine total solids and relative IgG concentration in colostrum.
Refractometers can also be used to determine how well the calf absorbed colostrum by assessing STP. It’s important to note refractometers used for STP have a different scale than the Brix refractometer, so be sure to check the refractometer used for STP is intended for that use.
Serum is the clear yellowish liquid left after blood clotting. Serum can be isolated from a blood sample by centrifuging or by leaving a blood sample for 24 hours. Once the serum has separated, researchers, veterinarians or producers can take a small drop and apply it to the well of the digital refractometer or the lens of the optical refractometer, as shown in Figure 1.
Figure 1: Examples of a digital (A) and optical (B) refractometer with samples being applied to the sample well and lens.
STP DIFFERENCE BETWEEN COLOSTRUM REPLACER AND DAM’S COLOSTRUM
Research by Lopez, et al. 2020, evaluated colostrum programs on-farm by testing STP of calves. In this study, researchers aimed to validate the accuracy of digital refractometry to evaluate absorption of colostrum components by the calf when fed the dam’s colostrum (n=927 calves) or a colostrum replacer (n= 1,258 calves).
Researchers used pre-existing data that had pre-colostrum blood samples to confirm the calf had not suckled, and post-colostrum blood samples at 24 to 48 hours after calving to determine STP and IgG concentration. Blood samples were spun by centrifuge to separate the serum.
Calves fed the dam’s colostrum had a STP of 5.8 g/dL and 22.81 g of IgG/L. Serum IgG strongly correlated (81 per cent) with STP measurements.
Of the calves that were sampled, 4.2 per cent of calves had failure of passive immunity transfer. These results suggest STP by digital refractometry is a good measure to determine calves with failure of passive immunity transfer and those that had successful passive transfer.
In contrast, STP was not accurate enough to determine failure of passive transfer of calves fed colostrum replacer. STP of calves fed colostrum replacer was 5.15 g/dL and 12.78 g/L of IgG in circulation.
The failure of passive transfer of calves fed colostrum replacer was 27.26 per cent. Lopez et al., 2020, suggest the STP threshold should be lower than 5.2g/dL. The difference in STP is due to differences in protein content between colostrum replacer and the dam’s colostrum. The suggested threshold was 4.9g/dL.
Even with the lower STP threshold, the accuracy is still poor, and researchers suggested producers who feed colostrum replacer only use STP to determine trends in the herd or evaluate IgG directly using another method. This is an area of continued research.
Monitoring passive immunity transfer in the herd gives an indication of whether there are improvements needed in colostrum management protocols or if protocols are not being followed.
Once gut closure has occurred by 24 hours, it is not possible to increase IgG concentration in circulation in the bloodstream of the calf. The calf will be reliant on low pathogen load and low stress in the environment. There has been some research in feeding colostrum after the first day of life and the benefits to the calves. It may improve gut health but will not increase IgG circulation.
NEW THRESHOLDS TO EVALUATE PASSIVE TRANSFER
Routinely assessing colostrum SOPs by STP to determine successful passive transfer is recommended. Testing STP or IgG in circulation will help determine whether the timing, cleanliness and quantities of colostrum are meeting the needs of the calf.
Recent research in the United States uses four categories to determine poor to excellent absorption of IgG by the calf based on data from the U.S. National Animal Health Monitoring Systems, shown in Table 1 (Lombard et al., 2020).
The categories allow for producers to evaluate their colostrum management program on the entire herd instead of individual calves. This allows dairy producers to increase the number of calves in the good and excellent categories, which is associated with decreased mortality and morbidity.
Recent work shows 24 per cent of calves still experience failure of passive immunity transfer, which puts them at risk of disease early in life. This shows there is room for improvement in colostrum SOPs and consistency.
Testing colostrum quality will ensure adequate colostrum is delivered to every calf. Refractometers are useful tools to evaluate colostrum quality and STP, which are critical to lowering the rates of failure of passive immunity transfer.
Evaluating colostrum absorption in calves fed the dam’s colostrum is to assess STP by refractometry, aiming for ≥5.2 g/dL, which correlates to ≥10 g/L of IgG. Refractometers are not as accurate when assessing colostrum replacer absorption and should only be used to determine trends in the herd.
Ensure the refractometer producers use to determine STP is designed for STP. The different scales could cause confusion when assessing STP. Assessing herd level colostrum management using the four categories in Table 1 will allow for overall improvement and ongoing assessment of colostrum management.
| Category | Serum IgG (g/L) | Serum total protein (g/dL) | Serum Brix % | % of calves |
| Excellent | ≥25.0 | ≥6.2 | ≥9.4 | >40% |
| Good | 18.0-24.9 | 5.8-6.1 | 8.9-9.3 | 30% |
| Fair | 10.0-17.9 | 5.1-5.7 | 8.1-8.8 | 20% |
| Poor | <10.0 | <5.1 | <8.1 | <10% |
References:
Renaud et al. (2020) J. Dairy Sci. 103:8369-8377.
Lopez et al. (2020) J Dairy Sci.104:2032-2039.
Lombard et al. (2020) J Dairy Sci. 103:7611-7624.
Dairy and Beef Cattle Production 