How mycotoxins can Iimpair milk production

If your cows, goats or sheep have gone off feed and milk production has dropped off, mycotoxins in their ration could be the culprit. An ear corn mold survey last fall has shown elevated levels of mycotoxins in some parts of Ontario.

Mycotoxin is a generic term for toxic chemicals produced by mold that colonize crops and stored feed. One mold species may produce more than one type of mycotoxin, and various mold species may produce the same mycotoxin. Examples of these toxic chemicals are Aflatoxin, Zeralenone and Vomitoxin (DON).

Molds can develop on various feed types at various growth stages-before harvest or during storage. When weather conditions are right for their growth, molds can grow on grain kernels still attached to plants in the field and produce mycotoxins. Corn and wheat, for example, can show significant mycotoxin levels at harvest. Molds can also proliferate on stored feed such as corn silage if oxygen leaks into the silage mass.

Moldy feeds can typically cause performance losses of five to 10 per cent, even if they don't produce mycotoxin. Cattle find moldy feeds less palatable and may reduce their dry matter intake. This lowered nutrient intake reduces weight gains or milk production.

When mycotoxins do contaminate feed, they can cause problems when cattle consume them even at extremely low levels. The toxins can impair performance and change normal metabolism, mainly targeting an animal's immune function. Young, pre-ruminant calves and high-producing cows are most susceptible to mycotoxins, and cows already stressed by lameness, high temperatures or improper rations are also more at risk. The transition period and at calving time are critical, too.

Last fall's ear corn mold survey, conducted by the Ontario Ministry of Agriculture, Food and Rural Affairs, revealed some fields had elevated levels of DON. Severity varied across the province, but about 12 per cent of fields sampled showed levels between two and four parts per million (ppm). A few fields even had levels in excess of four ppm.

Other sources have reported even greater concentrations in feed samples. In one case, a silo of high moisture corn has been analysed at 12 ppm of DON. Other data suggest Zearalenone could be trending higher, more so than DON.

Mycotoxin contamination can come from purchased feed sources as well as your fields or silos. Before buying a load of corn distillers grains or similar material, ask for a laboratory report for mycotoxins.

The fermentation process does not break down mycotoxins in contaminated grains. In fact, the process concentrates toxins in corn distillers grains to three times higher than the level in the original grain corn.

You can't tell just by looking at a feedstuff whether it has mycotoxin contamination. Visible mold is not a sure sign mycotoxins are present, and absence of visible mold is not a sure sign your feed is mycotoxin-free. Only laboratory testing can provide answers.

If you believe mycotoxins have contaminated your feed, have all individual ingredients-grains and silage-laboratory tested for mycotoxins. If positive, this testing will also determine total dietary mycotoxin levels and let you assess potential problems and solutions.

The table on page xx shows the levels at which you should be concerned about mycotoxins. Further testing may be required, especially if your cattle show moderate symptoms. Limit the amount of suspect feed included in the ration, especially if performance or health symptoms persist.

When mycotoxins reach potentially harmful levels, the toxins might be involved in depressed performance, acute clinical symptoms or both. If severe production decreases occur or acute clinical symptoms appear, stop using the suspected feed until you have it tested further.

You can consider several strategies to alleviate mycotoxins' effects. For instance, cleaning moldy grains to remove fine particles, dust and lighter grains can substantially reduce mycotoxin concentration. Diluting problematic feed with tested, toxin-free-feeds can also reduce the amount of mycotoxins in your total ration to acceptable levels.

However, mycotoxins may not be the sole culprit hurting production. Before setting an inclusion rate of a contaminated ingredient, consider moldy ingredients that may also reduce a ration's palatability and total dry matter intake.

If you suspect mycotoxin contamination, also consult your veterinarian and nutritionist. They can help you determine an appropriate management strategy to deal with your situation.

Mario S. Mongeon is an OMAFRA livestock specialist, based at the Alfred Resource Centre, Alfred, Ont., and Tom Wright is OMAFRA's dairy cattle nutritionist, based at the University of Guelph.

References: www.ontario.ca/feedquality, www.ontario.ca/qualitedesaliments. Suggested guidelines on mycotoxin levels in the ration

Total Ration (on a Dry Matter basis)

(Adapted from Penn State)

Various molds produce mycotoxins in feed.

Which one has toxins? Only testing tells your for sure.

This article first appered in the Janaury 2012 Milk Producer magazine.