There are many factors mentioned in textbooks, which you can control to maximize the quality of your corn silage with proper silage management. The timing and conditions at harvesting corn silage as well as minimizing the exposure of silage to oxygen during storage to avoid spoilage are crucial to for the nutritional value of the silage to the dairy cow.

What the textbooks don’t tell you is that a lot of those factors can also contribute to the formation of mycotoxins if not practiced properly. Mycotoxins are produced under favourable conditions by certain types of moulds. However, the hidden danger can be that mycotoxins are present without clear visual signs of mould in the silage.

Quality of 2017 corn silage

Read about what you should know about 2017 corn silage here.

Symptoms for a mycotoxin challenge

Typical symptoms of a mycotoxin challenge in a dairy herd are:
• decreased feed intake,
• reduced milk and milk component yields,
• increase in somatic cell counts
• reduced reproductive performance, including decreased conception rates, increase in irregular heats and ovarian cysts.
• increased incidences of metabolic disorders such as ketosis, retained placentas, displaced abomasum

Providing those symptoms cannot be explained by other nutritional or management short-comings on the farm, the cause are most likely mycotoxins in the feed ration.

Economic impact

Subclinical mycotoxicoses decrease profitability by lowering milk production and quality while increasing expenses from inappropriate veterinary therapies.

So, the risk of mycotoxins is one more incentive for best practice at harvesting and storing corn silage.

Mycotoxins produced in corn silage

Mycotoxins can already accumulate in the crop prior to silage making during growth of the corn on the field and often will not be visible. This level of toxin can then continue to increase during poor harvest conditions and on into storage. The primary toxin producing fungi on corn in the field includes Fusarium.

Several mycotoxins of concern are produced by Fusarium and include:

deoxynivalenol (DON),

zearalenone

and T-2 toxin.

Zearalenone is a mycotoxin, which can cause fertility problems after its ingestion due to its structure being very similar to the hormone oestrogen. DON can have a negative impact on rumen efficiency and hence on milk solid yields. Read more about DON in dairy cows in the following link  How cows can adapt to DON

Frost increases risk of mycotoxins in silage

Corn silage harvested after frost is at even greater risk of toxin contamination. When the corn is chopped and placed in a silo, the frosted and now drier silage is difficult to pack properly. The oxygen level in the silo takes longer to deplete during tilling and the fungus can continue to grow and produce toxin for several days.

Mycotoxins in grass silage

Mycotoxins, such as zearalenone, have also been found in grass silage, however the levels are generally much lower than on corn silage (Driehus et al 2009)

Managing the risk of mycotoxins in silage

Pre-harvest events

While silage-making practices impact fungi and mycotoxin levels, environmental conditions likely have the largest impact Environmental conditions, such as excessive moisture, temperature extremes, drought conditions, insect damage, crop systems and some agronomic practices, can cause stress and predispose plants in the field to mould and determine the severity of mycotoxin contamination.

Despite progress made in prevention through breeding of resistant varieties and improvement in agronomic practices hazardous concentrations of mycotoxins may occur as a result of annual weather fluctuations.

Post-harvest management

Excellent silage management can reduce the incidence of mycotoxins. Prevention of mycotoxins in silage includes following accepted silage making practices aimed at preventing deterioration, primarily by quickly reducing pH and the elimination of oxygen (Figure 1 below). This decreases the growth of moulds and mycotoxin contamination.

Figure 1 The 3 major events that make good silage and factors that can affect silage fermentation
(Kung 2000, Tangni et al 2013)

DM content

DM content of the forage can have major effects on the ensiling process via a number of different mechanisms.
1) Drier silages do not pack well and thus it is difficult to exclude all of the oxygen from the forage mass during the confection of the silo.

2) As the DM content increases, growth of lactic acid bacteria is inhibited and the rate and extent of fermentation is reduced.

3) If the forage is too moist and pH decline is not sufficient, clostridia, which ferment lactic to butyric acid and amino acids to ammonia, might become active. This process results in increases in pH and losses of silage DM content.

Rapid feed-out

When the silo is opened for feeding, oxygen becomes available to the front of the mass and the activity of the yeasts and molds, as a result of survival of fungal spores or a re-colonization of these microorganisms, could reduce aerobic stability of ensiled mass, thus favoring potentially toxigenic fungi development. Silo size should be matched to herd size to ensure daily removal of silage at a rate faster than deterioration. In warm weather, it is best to remove a foot of silage daily from the feeding face. The feeding face of silos should be cleanly cut and disturbed as little as possible to prevent aeration into the silage mass. Silage (or other wet feeds) should be fed immediately after removal from storage. Spoilage should not be fed and feed bunks should be cleaned regularly.

Silage Inoculants

As part of the best ensiling practices the use of an appropriate silage inoculant, depending on various conditions, should be considered.

Regular monitoring
Monitoring the forage quality during the preservation process is the only real way to assess the given situation.

References

Cheli et al 2013. Fungal populations and mycotoxins in silages: From occurrence to analysis 

Driehuis et al 2009. Occurrence of mycotoxins in maize, grass and wheat silage for dairy cattle in the 

Gallo et al 2015. Review on Mycotoxin Issues in Ruminants: Occurrence in Forages, Effects of Mycotoxin Ingestion on Health Status and Animal Performance and Practical Strategies to Counteract Their Negative Effects

Tangni E. K., Pussemier L. and Van Hove F. 2013, Mycotoxin Contaminating Maize and Grass Silages for Dairy Cattle Feeding: Current State and Challenges, J Anim Sci Adv 2013, 3(10): 492-511