A number of factors are combining to raise the risk of mycotoxins negatively affecting milk yields, fertility and cow health, claims AB Vista’s Dr Derek McIlmoyle.
Drier grass silages, greater reliance on third and fourth cuts and reduced availability of good quality straw are all increasing the threat posed by mycotoxins this winter. And according to Dr Derek McIlmoyle, AB Vista’s EMEA Ruminant Technical Director, the scale of the problem continues to be overlooked by many, despite the substantial negative impact on cow performance, health and fertility.
“Forage and straw shortages mean that most dairy units are having to feed the milking herd more late-cut grass silages than normal, and in some cases straw that would normally be used for bedding,” he explains.
“These lower quality forages are undoubtedly more prone to mould growth and the build-up of mycotoxins. Drier silages are also at higher risk of aerobic moulds, and the 2018 grass silage samples analysed so far by Scotland’s Rural College (SRUC) show that average dry matters (DM) could be as much as 4% higher than last year.”
Mycotoxin testing results
Mycotoxin testing of maize samples (grain and silage) from across Europe carried out by Micron Bio-Systems last year confirm the scale of the ongoing challenge posed by in-feed mycotoxins. Of the samples tested, 84% contained one or more mycotoxins, 58% contained at least two and 26% were contaminated with three or more mycotoxins (see Figure 1a).
“The most prevalent mycotoxin was deoxynivalenol (DON), which was present in 62% of the maize samples (see Figure 1b) and is highly damaging to ruminants,” Dr McIlmoyle explains. “DON is also unaffected by simple clay-based mycotoxin binders, and has to be physically transformed using specific active ingredients before it can be neutralised.”
a) Number of samples contaminated with mycotoxins b) Level of individual mycotoxin contamination
Figure 1 – Mycotoxin levels in 2017-18 European maize samples (source: Micron Bio-Systems)
There’s currently little data available to show the full extent to which UK feedstuffs are contaminated with mycotoxins, but it’s an issue that affects more than just forages. Any feed that is grown outdoors, exposed to humidity or stored for any length of time is at risk, with mould growth likely to be accelerated by insect or mechanical damage, contamination with soil or bird faeces, or poor storage conditions.
Previous testing carried out in 2014, for example, found that 92% of all total mixed rations (TMR) tested contained mycotoxins, along with 82% of maize silages, 80% of barley samples and 75% of wheat samples.
Impact on production
“Many of the most damaging mycotoxins – DON, zearalenone (ZON) and T2 toxin – are produced by the Fusarium moulds that commonly affect growing feed crops,” Dr McIlmoyle continues. “Others, such as aflatoxin B1 (AFB1), are generated by the Aspergillus moulds typically seen in stored feeds.
“Some of the mycotoxins produced when crops are growing actually get combined with sugars within the plant. Although these ‘masked mycotoxins’ aren’t detected by standard mycotoxin testing, there’s evidence to suggest they can be released during digestion and add to the overall mycotoxin load on the animal.”
Common symptoms of mycotoxin ingestion are a reduction in milk yields, lower butterfat levels, worsening body condition and infertility (see Figure 2). Other indicators include rough coats, listless activity, variable manure consistency and the presence of mucus tags – pieces of gut wall – in the manure.
Figure 2 – Effects of different mycotoxins on cow health and productivity
“Research has shown that dairy heifer conception rates fell from 87% to 62% where ZON was present in the ration,” highlights Dr McIlmoyle. “Even chronic lameness, foot lesions that won’t heal, or an increase in somatic cell counts, mastitis and cystic ovaries, can indicate a mycotoxin problem.
“The risk is also much greater when cows are suffering from sub-acute ruminal acidosis (SARA), which reduces the ability of rumen microbes to deactivate certain mycotoxins. In addition, SARA causes damage to the rumen wall that eases passage of those mycotoxins into the blood.”
Managing mycotoxin risk
It’s therefore extremely important to minimise the incidence of SARA when facing a mycotoxin threat. Avoid overloading the rumen with excess rapidly fermentable starch, consider adding a slow-release rumen conditioner such as Acid Buf to buffer rumen pH and take steps to reduce stress, such as overcrowding, competition for feed and aggression.
Paying close attention to feed storage, silage clamp management and feed hygiene is also critical to limit additional mould growth. Visibly spoiled or mouldy material should always be discarded and feed-out areas cleaned daily to remove refusals.
“If the ration is heating in front of the cows – a sure sign aerobic fungal growth is taking place – consider feeding less, but more often, to reduce the time available for spoilage,” Dr McIlmoyle advises.
“Many top herds are also now routinely including a high quality mycotoxin de-activator to protect cow health and production.”
A clear performance response within 2-3 weeks of adding a de-activator to the ration is indicative that mycotoxins are present at significant levels, an extra 2-3 litres/cow/day is not unusual.
“Just make sure it’s a broad spectrum, multi-component de-activator like Ultrasorb R that’s been developed specifically for use in ruminants, and can act to ‘open up’ important mycotoxins such as DON for de-activation,” Dr McIlmoyle adds.
“And avoid the basic clay-based binders. They’re not only ineffective against the likes of DON, but they can also bind with minerals and vitamins in the ration, making them less available,” he concludes.