Updates on calf passive immune status and colostrum management

Targets for serum IgG concentrations in calves at 24 hours old have been increased in an attempt to combat the high morbidity and mortality levels that still persist in rearing systems.

It had been thought that achieving 10g/litre IgG in calf blood serum at 24 hours of age was adequate while less than 10 g/litre was considered a failure of passive transfer.

But new standards (Lombard et al., 2020) are now in place which set more ambitious targets:

• Greater than, or equal to, 25g/litre, is considered Excellent
• 18 – 24.9 g/litre – Good
• 10 – 17.9g/litre – Fair
• Less than 10g/litre – Poor

Table 1 shows the equivalent values when using total protein and Brix percentage measures on the refractometer.

Table 1: Consensus passive immunity categories with equivalent measurements

Proper protocols around colostrum feeding are essential to achieve sufficient passive transfer:

• 1. Feed colostrum promptly, ideally within two hours post-birth
• 2. Feed first milking colostrum at first feed
• 3. Feed 10% of body weight in colostrum, for example four litres to a 40kg calf
• 4. Feed good quality colostrum, one that contains greater than 50g/litre IgG or 22%+ Brix on the refractometer
• 5. Feed a second feed colostrum at 12 hours post-birth
• 6. Ensure colostrum is clean and stored properly to prevent high bacteria levels

Colostrum Quality

IgG Concentration

We know that colostrum quality differs greatly amongst cows and between herds for numerous reasons. Figure 1 by Dunn et al., (2017) illustrates how colostral IgG concentration varies amongst over 1200 cows across Northern Ireland. The gold standard is for colostrum to contain 50g/L IgG. Colostral IgG levels ranged from 1.4 to 204 mg/mL IgG, with a mean concentration of 55 ± 25.5 mg/mL; 56% of the samples contained a minimum of 50 mg/mL IgG.

Figure 1: The distribution of IgG concentration (mg/mL) in colostrum samples from 1,239 dairy cows across Northern Ireland

The IgG intake is a function of the quality of colostrum (IgG in colostrum, grams/litre) × the quantity of colostrum fed (litres). So, if a calf is fed 4 L of poor-quality colostrum (e.g., 30 g of IgG/L), then the calf will consume only 120 grams of IgG (4 × 30) in the first 24 hours instead of the recommended 200g+.

Bacterial Count

In addition to the IgG content of colostrum. Bacteria levels have a huge role to play in the passive transfer of immunity to baby calves.

When colostrum becomes heavily contaminated with bacteria it causes havoc in that it increases the risk of pathogen transfer to the baby calf and reduced ability to absorb IgG in the intestine as these bacteria can bind to IgG in the gut lumen of the calf or block the uptake of IgG through the epithelial cells (Lorenz et al., 2011).

It is recommended that total counts for bacteria and coliforms in colostrum should not exceed 100,000 colony-forming units per mL (CFU/mL) and 10,000 CFU/mL, respectively (McGuirk and Collins, 2004).

Unfortunately, high bacterial loads in colostrum is very common on a lot of farms as often the colostrum is not fed immediately and there is no proper storage in place to refrigerate colostrum until it is ready to be fed. Bacteria rapidly multiply every 20 minutes under the right conditions.

A study by Stewart et al., (2005) looked at the critical contamination points during colostrum harvest and feeding (see figure 2). As expected, bacterial counts were low when collected direct from the udder and 100% of samples collected met the industry standard goal of <100,000 cfu/mL. Whereas there was a significant increase in bacteria in samples collected from bucket and eosophageal tube feeder.

Figure 2: Mean log10 total plate count and mean log10 total coliform count for colostrum samples collected from the udder, the milking bucket, and the esophageal feeder tube. a,b

A few ways to help minimise bacterial contamination:

• · Strict hygiene protocols in place at first milking
• · Ensure cow’s teats and udder are cleaned and disinfected before colostrum collection
• · Milking equipment should be sanitised after every use
• · Minimise the number of containers used to collect and store colostrum – use a lid to prevent dirt/manure.
• · Heat treatment of colostrum may be an option
• · Refrigerate or freeze any excess colostrum immediately
• · Use refrigerated colostrum within 1-2 days
• · Minimise delay between collection and feeding
• · Ensure colostrum feeding equipment is washed and disinfected after every use – use a scrubbing brush and detergents such as washing up liquid to break down fatty colostrum/milk scum.
• · Replace any worn or roughened stomach tubes, teat ends, bottles, or storage buckets – these can harbour bacteria and are difficult to clean properly.
• · Calf rearer should have clean hands/gloves to prevent any contamination during the feeding process.

Failure of passive transfer in calves is a huge issue impacting their health, development, and survival. Therefore, the correct measures must be in place to ensure we can provide them with the best possible source of clean and high-quality colostrum.