While the majority of producers and nutritionists regularly analyze forages for the basic chemical properties, a far smaller number look at factors such as mold count, mold identification and mycotoxin levels of silage. This information can provide valuable insight as to the quality of silage and the way in which it may affect cow health and productivity.

Why should I care about molds and mycotoxins?
As producers and nutritionists, the sight of mold on forages is likely not uncommon and, generally speaking, it is understood that as spoilage organisms, molds will reduce the nutrient content of forage by using the energy preserved within it. Therefore, from a feed quality standpoint, contamination of silage by mold reduces milk production efficiency by decreasing the level of nutrients that silage ultimately delivers to the cow. From a health standpoint, certain types of molds have also been identified as a possible cause of hemorrhagic bowel syndrome (HBS) and respiratory diseases, so there is the possibility of a direct impact of mold on cow health, although the exact nature of this is still to be determined.

In his review of mycotoxin levels in feedstuffs, Jouany highlighted the numerous different ways in which mold and mycotoxin levels can be influenced both pre and postharvest. Different types of mold species impact the silage at different stages, with some species such as Fusarium predominantly acting preharvest, while others such as Penicillium and Aspergillus tend to have their impact postharvest during storage.

The challenge that faces silage makers, particularly preharvest, is that so many factors are out of their control. This is currently being demonstrated through large parts of the Midwest. Any conditions that stress either the plant or the molds that grow on them can lead to increased mold infestation as well as mycotoxin production.

A second challenge for silage makers is that ensiled forage can provide all of the necessary elements for mold growth, particularly water, oxygen and energy. With this in mind, it is important producers do what they can to reduce the potential of mold growth on crops and forage pre and postharvest, respectively. Some of the key areas mentioned by Jouany in his article are listed in Table 1*.

While preharvest conditions can be more difficult to manage, postharvest producers have most elements under their control and as can be seen from the list above, good silage management practices are important in reducing further mold growth and mycotoxin formation.

Mycotoxins are toxic compounds produced by molds when they become stressed. The principal molds of concern to the feed industry include Fusarium, Penicillium and Aspergillus, as these are capable of producing many of the mycotoxins known to us.

As mentioned previously, Fusarium molds are predominantly found in the field. Therefore, mycotoxins produced by these molds such as vomitoxin (DON), zearalenone, T-2 and fumonosin will be produced while the plant is growing and will be brought into the silage bunker with the fresh crop. Fusarium species tend not to thrive under ensiled conditions due to the reduction of oxygen, but the ensilage process cannot remove the mycotoxins produced before harvest.

Fusarium mycotoxins are often the focus of a mycotoxin screen as they have been well documented to impact animal health and productivity by various researchers including Dr. Trevor Smith, who has published a number of papers including one in 2007 which demonstrates their ability to affect metabolic, immune and productivity parameters in dairy cows.

During storage, Penicillium and Aspergillus tend to predominate along with other nontoxin-producing molds such as the Mucor species. Recent data from Dairyland Laboratories suggested Penicillium molds tend to contaminate silages most frequently, as can be seen in Figure 1*.

This information provides an interesting angle as most producers and nutritionists are focused on Fusarium mycotoxins as well as Aflatoxin which is a principal mycotoxin of the Aspergillus species, while relatively scant time has been dedicated to the mycotoxins produced by Penicillium and their potential effects in the cow.

The challenge is therefore two- fold: first, the industry is not looking for Penicillium-based toxins; and second, if it were, it would find it very difficult to find commercially available tests for Penicillium mycotoxins that are of interest to the dairy industry such as roquefortin C, penicillic acid and mycophenolic acid.

Why should I be concerned about Penicillium mycotoxins?
Perhaps the most well-known compound produced by the Penicillium species is the antibiotic penicillin. Based on our knowledge of this compound, it is not surprising then that some Penicillium mycotoxins have antibiotic properties. A number of in vitro (laboratory) studies have examined the impact of the mycotoxin patulin on rumen fermentation parameters. Tapia and co-workers demonstrated that true organic matter – acid detergent fiber (ADF) and crude protein (CP) – digestibility were all affected with the addition of different levels of patulin.

On top of this, bacterial nitrogen flow was also impacted as well as volatile fatty acid (VFA) production being affected at the highest level of patulin inclusion. Morgavi et. al. furthered this when they concluded that rumen cellulolysis (fiber digestion) in particular is inhibited as a consequence of the antimicrobial activity of patulin. Several Penicillium mycotoxins have been implicated in ruminal dysbacterioses and ruminitis and these conditions have been reported in the field as a consequence of exposure to moldy silage.

Summary
Mycotoxins truly can be the root cause of many health, reproduction and production problems on the dairy. A quick review of the information described above shows that they can potentially impact rumen function – Penicillium toxins predominantly, while Fusarium and Aspergillus toxins are well documented to impact digestive tract health, protein metabolism, reproduction and immune function.

Silage remains an important vehicle for mycotoxin contamination of the dairy cow diet due to its characteristics and the nature of its production, management and feedout.

Mycotoxin screens can provide useful information. However, the results of these should not be taken in isolation. Due to the narrow spectrum of toxins analyzed, sampling error based on the fact that mycotoxins often occur in “hot spots”, and the fact that recent studies suggest we can underestimate certain mycotoxin levels by as much as 80 percent, all mean that it is possible to get false-negative results with mycotoxin analysis.

Dairyland Laboratories has seen an increase in the number of mold count and mold identification analyses being requested. This simple test is more cost-effective than a mycotoxin screen and will give an idea as to the level of mold contamination of the silage and the types of mold present. This is not a perfect system either as there is no direct correlation between the presence of mold and the presence of mycotoxins, but it provides producers and nutritionists with another angle from which to look.

The bottom line for producers and nutritionists is that cows remain the best indicator of mold and mycotoxin presence. Therefore, if cows are not performing to their fullest or unexplained symptoms persist within the herd, consider the role that molds and mycotoxins may be playing. A final comment made by Jouany in his review suggested that the use of an organic mycotoxin sequestering agent is one way in which producers and nutritionists can help negate the impacts of mycotoxins within the cow, given that so many of the other factors that affect this are out of their control.  PD

References omitted but are available upon request at editor@progressivedairy.com

Table and Figure omitted but are available upon request to editor@progressivedairy.com.

Nick Adams
Alltech
Western sales manager
nadams@alltech.com

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