When it comes to potential problems with forages, most producers concentrate on potentially toxic weeds and nitrates in times of drought. However, several of our primary forages can have anti-nutritional factors that can decrease or limit growth and reproduction. Alkaloids and mycotoxins can rob producers of production and should be considered as potential causes when cattle underperform for no apparent reason.
Fescue and ryegrass can both be carriers of alkaloids. Endophytes are organisms, often bacteria or fungi, which live within the plant and produce alkaloids. Alkaloids, primarily ergotamine and ergonovine in these cases, can cause vasoconstriction. Severe toxicosis is relatively rare, but can result in uncontrolled muscle contractions and can even be fatal.
In these very severe cases, the animal becomes delirious in the final stages. More commonly, problems are seen with restricted blood flow. Again, in more severe cases we can observe gangrene in the ears, tails, teats and possibly limbs.
The most common problems observed are lameness and abortions. Lameness can occur with swelling of the fetlock and may also be observed as a reddening of the coronary band.
Alkaloid poisoning also affects the thermal regulation of animals. As a result, cattle become more sensitive to heat stress. Heat and humidity conditions that could normally be tolerated with minor negative effects can cause animals to experience complications associated with severe heat stress.
This can result in both reduced growth, through decreased feed intake, and poorer reproduction, as typically seen in cattle under heat stress.
A third major effect of alkaloid poisoning can be abortions. The direct cause can come from multiple effects of alkaloids including their effect on smooth muscles, vasoconstriction and reduced heat tolerance.
One of the problems with alkaloid toxicity is that these compounds can accumulate in the body. When a problem is recognized, reversal takes time due to the accumulation of toxins. The primary “fix” is the logical one, which is to get cattle off of these affected fields. However, this resolution is not always possible.
There are products that can help reduce the effects on cattle that must remain on “infected” fields. Some, but not all, of the inorganic, clay-related products that have been demonstrated to bind aflatoxins may also bind alkaloid compounds.
However, producers have to remember that even if such products are effective at preventing additional accumulation of alkaloids, time will be required for animals to clear the toxins that have already accumulated.
Deoxynivalenol is a mycotoxin known more commonly as “vomitoxin” and can cause the implied problem in swine. You will also find it referred to simply by the initials DON. DON is produced by Fusarium fungi that are also responsible for the production of the mycotoxin zearalenone.
Many people think of mycotoxin contamination as the result of grain storage or silage preservation issues. However, DON contamination occurs in the field, so crops are already contaminated at the time of harvest. Over the past several years we have seen an increase in the occurrence of DON in corn crops with the advent of more low-till or no-till farming methods.
Therefore, it should not come as a surprise that DON can be incorporated into some of our common grasses.
This past year’s wheat crop has shown particularly high levels of DON with the mycotoxin being found in the plant as well as the grain. Some of the newer varieties of wheat may actually have greater DON activity because DON can be bound to parts of the plant.
This can be deceiving since the bound DON may not appear as being present to standard analytical methods such as enzyme-linked immunosorbent assay and high-performance liquid chromatography (ELISA and HPLC). However, when the plant is consumed by cattle, the bound DON is released from the plant cell walls and can have an active effect on the animal.
These “hidden” mycotoxins can be measured by the newer liquid chromatography-tandem mass spectrometry (LC/MS-MS) methods.
DON interferes with the production of proteins at a cellular level. It can have a pronounced effect on liver function and the intestinal system which both contribute greatly to a mammal’s immune system. Since the first two organs that are faced with a DON challenge are the gut and the liver, immune function can be compromised.
From a production standpoint, this can contribute to infections across a wide variety of systems. Calves coming off pasture may be prone to more issues such as “shipping fever,” while cows may have more problems with mastitis and metritis.
DON can also be responsible for reducing “gut integrity” or causing what is called leaky gut syndrome. DON can reduce the strength of the junction between cells lining the digestive tract.
This tight junction is important to not only help protect the animal from potential pathogens and other toxins in the diet, but also to assure that absorbed nutrients are kept in the body for utilization. Amino acids and other important nutrients are absorbed via processes that require energy; if the gut leaks, the efficiency of absorption drops and so does animal performance.
Additionally, proteins can leak from the body back into the lumen of the gut. These proteins become a rich source of nutrients for Clostridium perfringens Type A, a gram-positive bacterial pathogen which produces enterotoxin and can further damage the intestines.
The isolation of C. perfringens Type A has occurred from a high number of cases of hemorrhagic bowel syndrome (HBS) or “bloody gut.” The cause of HBS is not clearly understood, but HBS is often lethal and therefore can be costly to producers.
Unlike alkaloids or aflatoxin mentioned above, DON is not absorbed to any appreciable amount by either clay or yeast products, although some yeast products may help support and aid the animal in recovery during a challenge. There are commercial products available which offer specific enzymes that have been shown to convert the active form of DON to the inactive compound DOM-1.
Zearalenone (ZEN) is produced by the same fungi that produce DON. Zearalenone acts by mimicking the effects of estrogen. This increased estrogen “activity” can play havoc on heat cycles in livestock and can lead to abortions and difficulties in getting animals rebred.
ZEN levels may be elevated in grasses associated with tropical and subtropical environments. It certainly has the potential to contribute to breeding difficulties in southern states that may have historically been attributed to heat stress, but may in fact have been a ZEN issue.
Similar to DON, zearalenone is not easily bound by clay or yeast products, but can be transformed to non-active forms through the use of specific enzymes.
Forages that are commonly fed can have toxic qualities that make them less-than-ideal feeds for growing and producing cattle. These factors can change from year to year based upon weather conditions, forage growth rate and cattle grazing patterns. Good cattle observations and production records may be the best way to detect potential problems.
However, many times the effects can be “subclinical” in nature. If cattle seem to be underperforming, and there are no other more obvious potential mediating factors, one should consider testing their feeds for both alkaloids and mycotoxins.
Identification of these potential challenges can help guide producers to potential resolutions and improved animal performance. There are commercial products available which can assist animals to overcome the toxin challenges they face.
PHOTO: Alkaloids produced from fescue endophytes affect the thermal regulation of animals. As a result, cattle become more sensitive to heat stress and are often seen trying to cool themselves in standing water. Staff photo.
- Ruminant Technical Support Manager
- BIOMIN America Inc.
- Email Bryan Miller