By Lisa Whitfield

As many of you know, the first feed a calf gets after it is born is one of the most important meals of its life.

Calves are born with very little in the way of an immune system, and so rely on the transfer and absorption of antibodies from their dam through the first milk. This process reduces the susceptibility of the calf to diseases such as calf scours and navel ill, while its own immune system develops over the first few months of life.

Two important factors determine whether the transfer of antibodies from the dam to the calf are successful.

  1. The calf needs to take in a sufficient volume of gold colostrum within six to 12 hours of birth.
  2. The quality of gold colostrum needs to be good – i.e containing a high level of antibodies.

Most people realise the importance of the timeframe between when a calf is born and when it needs to have received its first feed of gold colostrum – in a nutshell, calves absorb antibodies from colostrum through their gut wall, and the ability to do this declines from birth, until it can no longer be absorbed at 24 hours old. There is a sharp drop off in how well antibodies can be absorbed at around six to eight hours after birth.

What many don’t realise however, is that from the moment a cow begins to actively calve, her colostrum quality begins to decrease – think about the impact of this in your calving and calf rearing system – is the colostrum your calves receive good quality?

When we take calves away from their dams, we need to ensure we are not compromising calf health by feeding them poor quality colostrum. Measuring colostrum quality is an incredibly simple test – and it allows us to direct the absolute highest quality colostrum to the youngest calves.

A Brix refractometer is an essential piece of equipment for the dairy shed, and its use is the place where a calving system and calf rearing system need to meet and work together. Measuring the Brix level of gold colostrum gives us an indirect measure of antibody concentration in colostrum. In order to test colostrum quality, all you need to do is take a squirt of colostrum from a fresh cow, place a drop of it on the face of the refractometer, close the flap, and read the scale. It’s an instant result and it takes only seconds per cow to perform.

If the reading measures above 25% it is superior quality, above 21% it is good quality, and below 21% is poor quality. The highest reading we have had from a fresh cow was 33%.

You might wonder what the numbers mean – it roughly reads like this:

  • A calf needs to receive 125g of antibody within six hours of birth in order to absorb enough antibody into its body
  • A Brix reading of 22% correlates to ~50g/L of antibody
  • This means a calf needs to drink ~2.5L of gold colostrum with a Brix reading of 22% in the first six hours of life in order to achieve the transfer of good immunity.

A lot of rearing systems rely on pooling colostrum to feed to the calves – but if you add in a Brix test, you can then pool colostrum strategically – pool the top quality colostrum together, and pool the low quality colostrum separately.

We use a system of coloured buckets to keep our colostrum pooling system simple. Each fresh cow is milked into a test bucket and her colostrum is tested before we pool it. Colostrum measuring over 25% goes into orange buckets, colostrum measuring over 21% goes into white buckets, and low quality colostrum goes into green buckets. This way, no matter who is doing the calf rearing, they know which bucket to reach for to feed the newborn calves. If there is a shortage of top quality colostrum, then we will prioritise the best quality available to heifer replacements. The reality is that you can’t spend all day bringing in freshly calved cows and milking them, and many calves will receive their first feed of gold colostrum by suckling their dam. However, if we are taking a newborn calf away from its dam before its first feed, it is critical that we don’t compromise the health of the calf by doing a poor job of providing it with passive immunity.

A Brix test is a simple, cow-side test which can allow you to step up your game when it comes to rearing healthy, well prepared calves.

  • Lisa Whitfield is a Manawatu production animal veterinarian.