STUD NOTES

IgG – THE ULTIMATE TEST

When IgG testing of foals was first introduced as a diagnostic tool, it was surprising how slow farms were to embrace it.
The first commercial IgG test we used was the GCT test (Glutaraldehyde Clot Test) and these were produced by Dr Angela Begg who was then based in the Hunter Valley. Angela spent a great deal of time on the issue of immunoglobulin in foals, their levels and - most significantly - creating a way to measure them.

At the time, the GCT test was regarded as an expensive addition to foal care, with little understanding as to the significance of this new tool we had at hand. Initially, it was largely used to test foals at 24 hours of age- only later did earlier testing become the more common practice.

At that time, ordering these tests and getting them down from NSW was not an easy task, as they were made up by hand (usually by Angela herself), plus they needed to remain cooled. The other issue was that a serum sample was required. Settling blood, allowing a clot to form to separate serum off took time. For vets in the field, this test could only be performed with the owner’s permission or request (who of course saw it as another cost), or if there was already a problem with the foal. These tests were not easy to perform ‘on the run’, so were usually taken back to the clinic for processing.

At Yallambee Stud it was not long into testing foals (at 24 hours old) that we realised how many foals were in fact failing the test. Two changes needed to be made on how we managed IgG testing. All foals needed to be tested, and they had to be tested earlier so we could do something productive (i.e. colostrum supplementation) to get them over the line.

This concept though, presented a few problems:
The IgG tests then (and still today) require serum samples. Back then to get serum you had to separate the red blood cells, probably by simply standing the blood for a period of time. It takes about two hours to settle sufficiently for this to occur.

This certainly slowed people down to using IgG tests across the board in the early days: by the time you took the sample and settle off the serum, the window of opportunity to supplement the foal more colostrum was closing quickly. We wanted to adopt effective early blanket testing of all foals born on the farm, and Dr. Des James gave us the solution by providing an address of a company that sold second hand hospital gear and suggesting what piece of we equipment we needed. Rick promptly went and purchased a very cumbersome but affordable centrifuge so we could spin the blood. With this new machine we were now able to spin blood and have our serum sample in 10 minutes. This must have been one of the first centrifuges to be located on a breeding farm such as ours. The old girl went to heaven just the other day, so returning to the same place Rick purchased a new one that takes up considerably less bench space!

This changed everything. Testing across the board of all foals was now faster and simpler for us and what I learned was how much I didn’t know! This whole concept of IgG testing completely changed the way I approached the subject, and I think this is the second most important tool introduced to our breeding industry after the ultrasound scan.

The rudest shock was how many foals that I thought were receiving adequate colostrum intake were, in fact, failing these tests. For foals that failed their initial IgG test we now were able to learn and understand what it took in terms of time frames and colostrum supplement quantities and quality (measured by refractometer). Added to this we also developed an idea of what was required in a ‘top up’ prior to the initial test. It wasn’t long before we had a completely different approach and mindset of how we managed neonate’s immunoglobulin levels: from building a colostrum bank and using the test at a timeframe, whereby we still had a window of opportunity to top up a foal that failed to get the desired IgG levels.

Finally we were able to test what goes in the gob, actually ends up in the blood stream of the foal in the form of antibodies, basic IgG levels and develop an understanding our time frames.

In the space of a breeding season we had gone from taking on board the idea of IgG testing all foals with this new GCT kit. We could now perform the blood test and have the opportunity in terms of time to thaw, and tube the foal extra colostrum, with an educated idea of what would subsequently constitute a ‘pass’ in IgG levels of the foal.

The original IgG tests were basic in their measurement capacity. They had three levels of measurement: <400mg/dl, 400-800mg/dl and greater than 800mg/dl. At the time a bit below 800mg/dl was thought to be OK. The problem was … what was a bit below?

Joint ill, pleuro pneumonia and rattles (rhodococcus equi), scouring and other digestive related illnesses, were all things we commonly faced prior to IgG testing. I wish I could find my figures I did at the time, but we turned around the incidence of these problems in just one year, mainly as a direct result of our foals having the benefit of adequate immunity to these challenges. Joint ill is the most notable absentee of foal illness since IgG testing. Scouring in younger foals dropped by amazing levels and lung related problems; the early pneumonia and number of foals with rattles has all but disappeared.

It wasn’t long before insurance companies took notice of the significance of improved health in foals as a result of IgG testing and on the basis of scientific research, set a bench mark of IgG level >800mg/dl as a prerequisite to foal insurance. Accordingly, this was now regarded as industry benchmark. Insurance involvement probably prompted much more acceptance of the IgG testing being performed universally if you were a farm that was promoting ‘best practice’ in young foals. However, there were still many foals out there getting the IgG test performed due to insurance purposes only.

The next IgG test that came onto the market which got my attention was the SNAP test. This is still very much in use in veterinary practices due to its portability (for use in the field for quick results), the ability to use either whole blood (with anticoagulant) or serum and, as it is individually packaged. This is ideal for the small owner, providing the opportunity to do their own testing at the right time and they can buy individual units that store easily. Vets who do on-farm consultations and insurance testing will probably opt for this product as it is easy to transport and store ‘in the car boot’ and for its quicker whole blood technique and have a result in 10 minutes, allowing for appropriate follow up procedures should the foal fail the test.

The SNAP test also has three levels of IgG results: <400mg/dl, 400-800mg/dl and >800mg/dl. It essentially works by using the ELISA (Enzyme Linked Immuno-Sorbent Assay) technique where a manufactured antigen reacts with an antibody of unknown level (IgG in this case), followed by the addition of an enzyme leading to an antibody quantity dependent colour change.

I have found that there is a bit too much ‘grey’ area in interpreting the result. Firstly, my shaky hands quite often did not properly drop the single drop over the ‘sample spot’. Maybe that was just me. Once the test was performed I found the colored spots often looked very similar in intensity.

This is a great product, but not ideally suitable for us as a larger farm.

However, the ‘daddy’ of all IgG testing - in my mind - is the DVM test, which takes IgG testing to another level.

Again we were using this product in its first year of introduction (thanks to Dr. Ian Douglas for bringing it to our attention). This product provided us with a precise reading, for example: 104mg/dl (the lowest reading of the test), 752 mg/dl (which is obviously not greater than 800mg), 949mg/dl (my desired lowest reading) or 2802mg/dl (definitely this foal has a great start, and there was plenty of room to pinch colostrum from this mare. I always feel I have been cheated of opportunity to boost the colostrum bank if I get this reading). <3000mg is ‘off the scale’ with this test. What a wonderful tool. I took great delight in making sure the exact mg/dl was put on insurance certificates for foals. It was amazing how many rang and asked what the number meant … quite clearly, 1079mg/dl is greater than 800mg/dl by quite a lot!

In saying this, this product is probably not practical for the small owner as tests are bought in bulk, there are initial set up costs with the reader, and serum seems to be better to use so a centrifuge is also required.

So, now the protocol at Yallambee is this: if we are looking at collecting colostrum from a mare with big boobs and qualify as a good donor prospect, then we will check quality with a refractometer. If this passes, then we will collect. (Due to learning from accurate IgG testing and mare histories we have an idea of how much we can take). We will label the colostrum with date of collection, mare name quantity and quality grading. Everything we collect is Grade 1. We would keep the colostrum in the fridge until the donor’s foal has passed its own IgG level before freezing. If it fails, then we just ‘return to sender’ at 10-12 hours or so old.

We will collect colostrum of lower quality should a mare loses her foal or some other similar event allows us to boost our bank. In this case we would have to use more in terms of quantity on foals being supplemented with lower grade colostrum, but it is useful to have in a pinch.

I have found supplementing colostrum much after 16 hours to have significantly reduced impact on the follow up IgG testing, which means we endeavour to test at around 10-12 hours, and have colostrum supplementation completed by at latest 14 hours.

Even today we still hear of farms that use only the refractometer to measure the quality of colostrum as their idea of giving the foal a good start - but it is better than nothing. The only time an IgG is done on these foals is for insurance purposes.

Referring to an earlier statement I would like now to amend it:  “Finally we were able to test what goes in the gob, actually ends up in the blood stream of the foal in the form of antibodies, and precisely at what levels with and clear understanding our time frames. Knowing the exact immunoglobulin level we now have a much better idea of how much colostrum to supplement a foal”

So ... what happens if the foal fails the IgG test and the window of opportunity has closed to use colostrum? The answer is Plasma.
Expensive but very effective and, despite cost, is still much better and cheaper in the long haul than running the gauntlet and exposing the foal to possible illness.

Story Link: PLASMA - A BLOODY GOOD BACK UP!