There are a few challenges in farming and one of the toughest definitely has to be receiving the call that the tank of milk you sent away has failed an antibiotic test.

Thankfully, we hadn’t received any such calls on the farm since before I started university over 10 years ago.

However, on 25 January 2024, we got a message saying our milk sample had tested positive for antibiotics.

I honestly couldn’t believe the news and initially thought it couldn’t be my sample. We hadn’t started calving our spring herd and there were no cows being treated in the parlour at that time.

However, after taking a sample of the bulk tank, that evening’s milking also tested positive.

Therefore, we thought there had to be a cow within the herd affecting it. After checking that all the dry cows were in the right house and none had made it into the milking group, we decided to test all of the cows at 10.30pm that night to try and identify the problem cow before the morning milking.


That sampling found 29 cows were positive for antibiotics out of 128 milking. Therefore, we came to the conclusion that something the milking herd had eaten must have caused it.

Originally, we thought it was the meal or perhaps the maize silage, as it was our first year feeding it. However, after sending samples of all feedstuffs, the results came back showing that the grass silage had extremely high levels of Penicillium mycotoxins, twice the level that would be flagged as high.

We changed the mycotoxin binder and fed it at double the rate, hoping this would alleviate the problem. Unfortunately, six weeks later, the same issue occurred again.

Silage pit

Looking at the silage pit and asking everyone who had entered the yard over the last few months to inspect it, you wouldn’t think there would be any issues with the silage - it looks clean with very little spoilage.

After the second failure, we changed to an algae-based binder and fed it at triple the rate, costing approximately £45 daily. We have also been sending milk samples daily to the dairy to check for antibiotics.

Last Thursday, for the second time this month and third time this year, our tank failed the antibiotic test. We had to discard the previous two milkings, and the evening milking also tested positive.

The Penicillium mycotoxins are relatively short-lived, as the following morning the tank was clear again. The mycotoxins don’t seem to be impacting the animals in any other way, as they are milking well and conception rates to AI are good.

We have considered what could have happened, and we think it may be a combination of a poorly mown first cut with too much stubble left and slurry applied via the dribble bar, causing the Penicillium mycotoxins in the second cut.

Mycotoxin pockets

Slurry was only applied to 10 acres after first cut as the rain that was forecast didn’t materialise, and we believe this is why the cows are testing positive randomly as there are just mycotoxin pockets in the pit from this area that had slurry applied.

Thankfully, a neighbour has come to the rescue and is going to sell us silage until the cows are out grazing full-time (hopefully soon).

However, it’s difficult to know where to go from here. There does not seem to be a mycotoxin binder that can effectively bind the high levels of Penicillium mycotoxins in our silage pit.

Although I would have very few complaints about the dribble bar up until now, it will be used cautiously this year. My intention is only to apply slurry via the dribble bar to well-cut or grazed swards and when there is a decent amount of rainfall forecast after application.