In Denmark and Sweden mycotoxins pose an unseen risk to calf development

The next generation of genetics is expected to deliver on performance and carry the profitability of the farm, so why risk the future stars? The value of calves to the future economics of the farm has been preached by researchers and advisors for a long time. Clearly, managers have been listening when it comes to testing and ensuring calves get adequate amounts of high-quality colostrum in a timely manner. Improvements in housing and animal welfare have also advanced considerably over the years. Understanding animal nutritional requirements to meet today’s genetics, beyond protein and energy, but vitamins and minerals as well, continue to be a hot topic with the focus on early rumen development and minimizing health risks.

While the debate on how to best stimulate early rumen development and transition to a forage-based diet will continue for some time, a potentially serious confounding factor facing calves from an early stage, all the way through their adult lives is often underrepresented in the discussion of calf health and development: mycotoxicosis.

What is mycotoxicosis?

Mycotoxicosis relates to the acute or chronic damage to the animal caused by mycotoxins in the diet. Mycotoxins are produced by fungi with the variety dependent on the environmental temperature and humidity. The vast majority of mycotoxins known for their harmful effects are produced in the field, with fungi of the Fusarium family responsible for a wide range of toxins. However, high humidity during storage can also result in considerable contamination from Aspergillus or Penicillum fungi. Mycotoxins are concentrated on the seeds, placing swine and poultry production at a higher risk, however, calves are particularly vulnerable owing to their underdeveloped rumen – in essence, just as vulnerable as a young monogastric. But it is not only cereals typically in starter feed that are a risk; an array of mycotoxins has also been found in corn silages (Panasiuk, 2018, Reisinger, 2019; Gallo 2022) and grass or whole crop silages (Schenck, 2019; Manni, 2022), which are commonly fed as the calf transitions to a post-weaning forage-based diet.

Effects of mycotoxins on calves

The risk posed by mycotoxins is diverse and dependent on the structure of the toxin. For example, deoxynivalenol (DON), a well-researched mycotoxin, is known to inhibit protein turnover in rapidly developing tissues, such as liver, gastrointestinal tract and immune system – very vital tissues for a growing calf! Toxin effects can be compounded through synergies with other mycotoxins, such as culmorin, which could suppress the immune response, thus enhancing the efficacy of other toxins (Gruber-Dorninger, et al., 2017). Moreover, lesser known, emerging mycotoxins such as enniatins and beauvericin have been shown to have the potential to inhibit development of normal microflora, potentially impacting physiological development of the rumen as well as jeopardizing the protective role microflora play in immune defenses (Krizova, et al., 2021).

Recent research using calf epithelial cells demonstrating that nivalenol was more toxic than DON, whereas enniatin B showed similar toxic effect as DON at only 11% higher exposure level (Reisinger et al. 2019). This indicates that damage by mycotoxins to the epithelial cells lining the gastrointestinal tract would result in reduced nutrient absorption as well as increase the risk of particulates or pathogens being able to enter the blood stream.

In terms of animal well-being, it is not only the level of a single mycotoxin that is of concern, more about the array of different mycotoxins that may have synergistic detrimental effects on the animal.

What is in my feed?

When it comes to mycotoxin testing, dairy processers are all well aware of the risk of aflatoxin M1 in milk, a potent carcinogenic for humans, when aflatoxin-contaminated feeds are fed. Given the risk, milk is routinely tested to ensure consumer safety. Wider awareness of mycotoxin risk is growing, with much of the focus centered on the few that are regulated in human or animal nutrition, namely, aflatoxin, DON, zearalenone (ZEN), fumonisins, ergot alkaloids and ochratoxin, however, this is just the tip of the iceberg. Through advanced analytical techniques, over 800 mycotoxins have been identified, with feeds, including both cereals and forages, often contaminated by multiple fungi species and toxins.

How to best protect the future herd

Low mycotoxin contamination levels, often measured in parts per billion (ppb) do not imply no risk to animal welfare or development. European guidance levels do not account for masked or emerging toxins, yet intestinal dysfunctions such as digestion, gut permeability, liver stress and susceptibility to infectious diseases have been noted in monogastrics and young calves below these suggested limits (Valgaeren et al. 2019). As such, a precautionary mycotoxin risk management stance should be taken from an early stage, by monitoring the mycotoxin loads in starter feeds, observing calf performance including unexplained health outcomes, and use of a comprehensive mycotoxin management product.

As scientific knowledge expands about the diversity of mycotoxins and their negative effects, so too does our understanding about how to best defeat the array of mycotoxins that can occur in a typical ruminant feed. Case in point: whereas the European Feed Safety Association recognized that inorganic binders, such as certain sources of bentonite, are capable of adsorbing planer or 2D molecules like aflatoxins (Fig. 1a), research has demonstrated that binders are ineffective for binding more complex molecules as found with A- and B-trichothecenes (Fig. 1b) or zearalenone. These more complex mycotoxins require their structure to be altered thereby detoxifying or biotransforming them into harmless compounds that can be excreted.

Impact on calf performance in practice

A good example of low level contamination inhibiting calf performance comes from a recent commercial trial in Germany, with eight-week old male Fleckvieh calves (n= 110) divided into two groups and monitored for 100 days. Diets were the same, with feed in the pre-weaning period (34 days) having 317 ppb B-trichothecenes, 14 ppb ZEN, 45 ppb enniatins and 274 ppb culmorin. Post-weaning, feed contained 181 ppb B-trichothecenes, 9 ppb ZEN, 35 ppb enniatins and 214 ppb culmorin. One group was fed a product capable of biotransformation of B-trichothecenes and ZEN. Comparing average daily gain while still in the preweaning phase, evidence of how even low-level mycotoxin contamination inhibits growth and development is clear (Fig. 1). By the end of the trial, the calves receiving a comprehensive mycotoxin management product, Mycofix®, were markedly heavier than those that did not (Fig. 2).

Mycotoxin risks in Scandinavia

Based on mycotoxin surveys of raw materials collected from farms conducted in Denmark and Sweden from the 2022 harvest, similar levels of contamination could be found in small grains, corn silage and even cereal straw (Table 1). Moreover, the high prevalence of mycotoxins within each feedstuff shows the extent contamination reaches across feedstuffs: there is no ‘clean’ or mycotoxin-free feed. There is a high likelihood that feedstuffs commonly used for calf rearing are going to be contaminated, and will be contaminated with an array of mycotoxins, thus placing the calf at considerable risk.

Putting calf rearing into perspective

In summary, calves are some of the most vulnerable animals on the farm, being more susceptible to mycotoxins than adult animals owing to limited immune resilience and rumen development. The threat of mycotoxins in Scandinavia is compounded both by the diversity of toxins present and the high likelihood of multiple contamination risk. Proper mycotoxin risk management begins with surveillance and adopting a preventative protection approach with the use of an EU registered product capable of interceding with a wide range of mycotoxin classes.