Dairy special

Dairy: Mycotoxins an ever-present threat to cow performance

Mycotoxin contamination of both straights and forage is an issue for every UK dairy producer, according to AB Vista technical director Dr Derek McIlmoyle, and it is one which needs to be taken seriously.

The wet conditions of last summer, which caused high levels of mycotoxin contamination in forages, may not have been repeated this year, but the risks are still significant.

Dr McIlmoyle says: “An analysis of forages and straights by Micron Bio-systems found more than 75 per cent contained mycotoxins and 90 per cent of those contained multiple mycotoxins. Some were at very low levels, but others were much higher.

“One of the challenges is even very low levels of two to three different mycotoxins together can have an additive effect and be more damaging than a single type of mycotoxin at higher levels.”

Reduced condition and milk yields, lower butterfat content, more mastitis and higher cell counts are all symptoms of mycotoxin ingestion. Other key indicators include rough coats, variable manure consistency, the presence of mucus tags (pieces of gut wall) in manure and foot lesions which will not heal.

Dr McIlmoyle says: “In recent years, there has been an increased awareness of the threat posed by mycotoxins, but this is countered by changes in farming practice which have also increased risks.

“Higher yields tend to put cows under more stress, which reduces the rumen’s ability to deal with mycotoxins, as does sub-acute-ruminal acidosis (SARA), which has become more common as yields have risen and higher energy rations are fed.”

In fact, SARA increases the risk from mycotoxins in two ways. It reduces the populations of beneficial microbes able to break down mycotoxins in the rumen and also damages the rumen wall, making passage of mycotoxins into the blood much easier.

Good rumen function is therefore the first defence against mycotoxins, with certain rumen microbes able to either ingest, transform or degrade mycotoxins and render them less harmful.

So it is important to avoid overloading the rumen with too much rapidly fermentable energy and to include both digestible and structural fibre – plus maybe a rumen buffer – to help reduce the lactic acid build-up in the rumen which leads to SARA.

Dr McIlmoyle says: “Last year was particularly bad for mycotoxin contamination in forage and it was common to see yields improve by 2-3 litres/cow/day when a high quality mycotoxin binder was added to the ration.

“Compared to this, the cost for including a mycotoxin binder is relatively low, particularly when you consider that even a 0.5 litre/cow/day improvement would give an easy 3:1 return on investment.”

The most basic of the mycotoxin binders available are based on simple clay minerals which adhere to specific mycotoxins, rendering them harmless until they are carried out in the manure. However, most have been superseded by products which also contain other components, such as fragments of yeast cell wall called manno-oligosaccharides (MOS) which bind to a much broader range of the mycotoxins normally associated with livestock feeds.

“It is important to compare the products available on a like-for-like basis,” Dr McIlmoyle adds. “The most effective will contain a combination of MOS and clay minerals to maximise the mycotoxin-binding range, while some even contain specific enzyme activity to ‘open up’ certain mycotoxins to the binders, together with nutrient supplements to boost cow reserves.

 “When it comes to mycotoxins, it is far better to assume feeds are contaminated with mycotoxins – the chances are high they will be at some point – and take appropriate action to guard against their effects.”

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