Karen Trebilcock

It’s the milking that you need all hands on-deck – herd testing. Pottles everywhere, tag numbers not making sense and extra rubberware that needs to be cleaned.

But it’s important to do. Herd testing shows you just how well your cows are getting along, whether they are living up to their genetics and if they have undiscovered mastitis which they could be passing to the rest of your cows.

Don’t shy away from the early herd test.

Your cows might not be all calved, there’s still a lot in the colostrum herd, you’re battling spring mastitis, but it is still important, especially for heifers that have calved early – it will be the first milking data for them.

The more herd tests you do, the more accurate the information is for all of your cows.

DairyNZ recommends four double-sample herd tests each season and says completing fewer, or opting for a single sample, although it saves time and money, gives less-accurate data to use onfarm.

And that is what herd testing is all about – getting accurate data on your cows.

In many countries herd testing is done monthly. In New Zealand most farmers opt for three to four per season.

Herd testing gives you information on the milk volume, fat, protein and lactose percentages and somatic cell count for every cow in your herd.

It can also show whether the animal has BVD, Johnes and its A2 status.

The calving date should already be in the data base so the equations used includes where each cow is in their lactation and its age, BW (breeding worth), PW (production worth) and LW (lactation worth) and potential live weight.

The results will also show how well a cow is doing compared to others in your herd, in your region, and nationally.

NZ farmers have been herd testing since the early 1900s, starting off by simply weighing the amount of milk each cow gave and recording the information. It allowed them to pick and choose between the calves from the best milking mums to go into their herd.

Instead of keeping calves simply because they looked good, they could choose the ones which had higher genetic potential to produce more milk than others.

It was the start of early breeding programmes. Farmers back then knew that keeping the calves from their top cows would give them a better producing herd in the future.

But now, although there is so much more information available from herd testing, only 71% of herds were tested at least once in NZ last season. Taranaki and North Canterbury had the highest number of herds tested.

It was a better result than the season before when only 64% of herds were tested.

Back in the late 1990s, 84% of herds were tested and it has been dropping ever since.

It goes up a little in good payout years and when times get tough, herd testing seems to be often the cost that gets cut first.

There’s also been a drop because some farms have invested in dairy technology that does the testing for you such as in-line milk meters and robotics.

Herd testing usually starts with the van of equipment arriving during the day. The herd testing company’s staff will usually set up the meters ready for the evening milking.

The equipment used is approved by the International Committee for Animal Recording or historically approved via the Dairy Industry Herd Testing and New Zealand Dairy Core Database Regulations so it is accurate and reliable.

If it is the first time you have done a herd test in the dairy it is likely a shed inspection will have happened a few weeks earlier to discuss what is required.

Then, depending on what service you have booked, they either leave you to it, or help out collecting the flasks and washing the equipment when it’s finished.

Either an evening milking followed by morning milking can be done, or just one of those. Farms on 16-hourly milking can be herd tested too.

Herd testing for two milkings gives a more accurate result as it is measuring a 24-hour production sample from each cow.

If you choose to test just one milking, the morning milking is the one to do as cows produce more milk in the morning so there is a greater volume to test for protein and fat percentages and somatic cells.

Your herd test results, whether for one milking or for two, will be assessed against all other herds in your region tested that day so variations for weather, grass growth and stage of lactation are accounted for as much as possible.

Two companies are certified to do herd testing in NZ – LIC and CRV Ambreed. Both offer a choice of frequency of testing and can add the information from your herd test into the NZ Dairy Core Database.

So before you herd test make sure all your cows are tagged and the tags are easy to read.

Make sure your herd records are up to date. If there are gaps, or wrong information such as incorrect calving dates entered, the information from the herd test will be compromised.

If more than 5% of your herd is not tagged, or more than 25% of your herd has no calving date entered, then you cannot receive the full results from your herd test.

This is because the Dairy Core Database, which is where your results end up, is used by the whole industry and not just you.

It is the largest dairy database in the world and was computerised in the mid-1980s. It holds millions of records of genetic and production data going back decades on cows and sires.

So if the information from your herd test is not backed up by accurate cow identification and calving dates then it’s not added because no one wants your bad data affecting other farmers’ herds, not in a database so big and so important.

Your herd test results will change the BW and PW of all the cows in the database which have the same sire or come from the same daughter family.

So if you enter a wrong calving date, or no calving date, the prediction of what the cow should be producing on the herd test date, which will be so many days into the season’s lactation, won’t match up with the test result. It’s the old story of rubbish in, rubbish out.

The value and reliability of the database depends on the quality of the data put in.

So when your herd testing is done, the last of the rubberware cleaned and loaded into the van along with the flasks of milk, what do you do with the information you are soon to have?

First, look at somatic cell count (SCC) results from your herd test. Cows exceeding a threshold of 150,000 SCC and two-year olds exceeding 120,000 SCC are considered infected with mastitis.

Do a rapid mastitis test on these cows to double check the results and get them treated as soon as possible.

Cows which have SCC in the millions, those which have had multiple cases of clinical mastitis and those that had dry cow therapy in the winter and have still high SCC counts show up in the herd test probably should be dried off and culled as soon as possible.

Their mastitis may be untreatable and they will pass it to other cows. Talk to your vet.

If you have had BVD and Johnes testing, act quickly if the results are not good. Again talk to your vet.

If you are about to start mating, identify high BW cows – these are the ones you want mated to the best sires so you can keep their calves.

If you are about to dry off, look at the low PW cows.

PW should be used for culling as it is the best indication of a cow’s performance over its lifetime while BW is the genetic ability for breeding good replacements.

Also a herd test will show up missing tags and double ups of tag numbers. Get them sorted before your next herd test to make sure your data is as good as it can be.