Review of Nutrient Requirements of Dairy Cattle: Update on Mycotoxins

By Rainey Rosemond

The National Academies of Sciences, Engineering, and Medicine: Nutrient Requirements of Dairy Cattle Eighth Addition incorporates and summarizes new information and research on various topics related to dairy cattle nutrition. This document serves as a tool for the dairy industry, students, and educators to improve the efficiency of milk production with consideration for animal health. The following information is summarized from the recently published 2021 Eighth Revised Edition of the Nutrient Requirements of Dairy Cattle.

Mycotoxins are toxins produced by molds and appear frequently in dairy feeds, like silage. Mold growth, and therefore the prevalence of mycotoxins, depends on field and environmental conditions, harvest practices, and potential damage to plants prior to harvest. Fortunately, the presence of mold in feeds does not immediately mean that mycotoxins are present. However, feeds with mold contamination should be tested to identify mold variety and mycotoxin presence to ensure animal health and performance. Mycotoxins are known to impact animal performance and to have antibiotic action, impacting rumen microbiota. Unfortunately, mycotoxin prevalence is not always evenly distributed throughout feed, which can impact sampling frequency. Common mycotoxins are aflatoxin, deoxynivalenol, fumonisins, ochratoxin, and zearalenone.

Aflatoxins are produced by Aspergillus flavus and Aspergillus parasiticus and can be found in commonly produced dairy feeds like corn, sorghum, and cottonseeds. Aflatoxins are associated with above-average temperatures and dryer conditions during growing seasons. For dairy animals consuming feeds with high aflatoxin levels, their health could be impacted, leading to reduced feed intake and lower milk production. Besides animal performance, aflatoxins are of high concern in dairy rations since they can carry over into milk. Because of this, the FDA regulates allowable aflatoxin levels in dairy diets to 20 µg/kg.

Deoxynivalenol, commonly known as DON or vomitoxin is produced by Fusarium spp. DON contamination has been reported in all major grain commodities. DON contamination can lead to reduced feed intake and reduced microbial protein synthesis. Dairy cattle are largely resistant to DON toxicity due to microbial activity which converts DON to de-epoxy DON (DOM- 1), which has not been shown to inhibit the growth of yeast cells.

Fumonisins are additionally produced by a variety of Fusarium spp., including Fusarium verticillioides and Fusarium proliferatum and are commonly found in corn grain products. Contamination of feeds is commonly associated with hot, dry weather followed by high humidity during growing seasons. Ruminants are expected to be tolerant of fumonisins because of low absorption, recommended maximum tolerable levels for dairy cattle include a sum (i.e., FB₁ + FB₂ + FB₃) total of 15 mg/kg in rations.

Ochratoxin A is not commonly an issue for dairy cattle as it is extensively degraded to ochratoxin α. However, concentrations over 12 mg ochratoxin A/kg BW at one time can impact animal health. While recommended levels have not been defined, it is produced by Aspergillus and Penicillium spp. and can be found in small grains and corn.

Zearalenone is commonly found with deoxynivalenol as they are both produced by Fusarium spp and is found in grains, silages, and grass or legume pastures. Zearalenone has been associated with reduced reproductive performance when dietary levels are greater than 10 and 20 mg/kg.

If mycotoxins are expected of impacting animal performance, testing for mycotoxin identification and levels is necessary before acting. Identifying and isolating individual contributing feeds can allow for intervention methods through dilution of contributing feeds to reduced total dietary levels. Toxin binders are commonly added to rations as an additional approach to managing mycotoxins. However, these should be carefully selected and proven effective against the identified toxin by independent research. While issues with mycotoxins can be managed, like most things, prevention is better than management. Harvesting feeds at the proper moisture and storing these feed properly can help prevent mold formation. Quickly harvesting, densely packing, and quickly removing oxygen can all help mold growth prevention. Inappropriate feed out rates can also allow for mold growth due to prolonged oxygen exposure.

As previously stated, visible mold does not immediately mean mycotoxins are present. Feeds suspected of high mycotoxin concentrations should be tested for toxin concentrations and identification. Various control methods can be identified and implemented depending on which feeds are contributing and additional feeds available. Mycotoxins can impact animal health and performance and issues are commonly associated with reduced feed intake and reduced milk production.