Molds and Mycotoxins in Dairy Cattle Production

The name mycotoxin combines the Greek word for fungus 'mykes' and the Latin word 'toxicum' meaning poison. 'St Anthony's fire' was one of the earliest recognized diseases caused by mycotoxins well known by the end of the first millennium. This was the result of eating rye contaminated with ergot alkaloids produced by the mold Claviceps purpurea. The epileptic fits and excruciating burning sensation experienced led many pilgrims to the shrine of St Anthony in France in hope of a cure.

Molds can affect animals causing mycosis, when a mold infection results in disease. Ex: Aspergillus fumigatus is known to cause mycotic pneumonia, mastitis and abortions, or cause mycotoxicosis, which is a mycotoxin-induced disease. Mycotoxicosis will be the focus of this note. 

Mycotoxins are organic compounds that are produced by a fungus to increase its virulence as a plant pathogen by reducing the ability of the plant's resistance. During colonization fungi secrete enzymes to digest organic materials into simpler compounds. The simpler compounds are primary and secondary metabolites. The secondary metabolites are called mycotoxins. These metabolites give molds competitive advantages over other surrounding molds growing in the same proximity.

Table 1 – Fungal genera and mycotoxin production

In field situations, the occurrence of mycotoxins can be simultaneously affecting the toxicity of the animals. Deoxynivalenol (DON), zearalenone, T2 toxin, and fumonisin are all produced by molds of the genus Fusarium. Molds in this genus collectively are capable of producing 70 different mycotoxins. Some strains of Fusarium may produce as many as 17 mycotoxins simultaneously. Aflatoxins are extremely toxic, mutagenic, and carcinogenic compounds produced by Aspergillus flavus and A. parasiticus. The FDA limits aflatoxin to no more than 20 ppb in lactating dairy feeds and to 0.5 ppb in milk. The University of Vermont found toxins in haylage, corn silage, dry hay, grains, and all commodities. 

Mycotoxins may cause acute health or production problems in a dairy herd but more likely, they will contribute to chronic problems including a higher incidence of disease. Mycotoxins affect dairy cattle by: a) reducing feed consumption, b) reducing nutrient utilization, c) altering rumen fermentation, d) suppressing immunity (perhaps the most important), e) altering reproduction.

Symptoms of mycotoxicosis vary depending on the mycotoxins involved and their interactions with other stress factors and can result from a progression of effects, or of opportunistic diseases. Animals that are already under stress like transition cows and very high producing cows may be the first to show the symptoms.

Diagnosis of a mycotoxicosis is difficult, since the symptoms may be nonspecific and wide ranging and include: rumen disorders, reduced microbial digestion, intermittent diarrhea (sometimes with bloody or dark manure), reduced feed consumption, reduced production (milk production may drop by more than 15%), elevated milk somatic cell counts, decline in fertility, abortions, weight loss, and hormonal- like changes such mammary gland enlargement in virgin heifers. More occurrences of displaced abomasum, ketosis, retained placenta, metritis, mastitis, fatty livers and death can be observed.

In the last two decades, the total feed ingestion per cow per day has increased significantly, which means that the toxin ingestion has also increased and this can account for the increase in reported mycotoxin problems. 

Prevention of mycotoxins in silages includes good ensiling practices aimed at inhibiting mold growth through elimination of oxygen and reducing the pH. The molds grow and proliferate under the presence of oxygen, near neutral (except penicillium) pH (6.0- 7.0), at high grain moisture (30-40 %) and at different temperatures depending on the type of mold. When corn is ensiled, pH is reduced by fermentation (or by the addition of an additive) to 4.0-4.5, the environment of the ensiled mass becomes anaerobic (without oxygen), and ensiled mass temperatures range from 25-90oF during fermentation and storage. Silo size should be matched to herd size to ensure daily removal of silage at a rate faster than deterioration. Feed bunks should be cleaned regularly. Since mycotoxins are highly soluble in water, do not allow rain to wash through upper layers of spoiled feed. 

Management of crops and storage is important to reduce mycotoxin contamination in grains. When the environmental conditions for a particular fungus occur, the growth cycle begins. When that happens, the crop damage has started and cannot be reversed.

A special concern exists with Dried Distillers' Grains (DDGs). If the original corn is contaminated with mycotoxins, the DDGs produced from it can contain two to three times the amount of the original mycotoxin concentration. This is because only about one-third of the original grain remains as DDG residue, resulting in a concentration of the mycotoxins. 

Testing for mycotoxins should be considered when signs of potential effects on performance and health exist and cannot be readily explained or if you are concerned that mold risks could be a problem.

Samples must be representative of the lot and of sufficient size to compensate for the non-uniform distribution of the contaminant, as well as, the ultralow levels (parts per billion) that must be detected.

Information about how to take samples can be obtained in the paper "Mold and mycotoxin problems in livestock feeding", from Penn State University or requested to Edmar Freitas at VBN (edmarf@vanbeek nutrition.com). 

*References omitted due to lack of space are available upon request