Mycotoxins in Swine: A Complete Overview

swine, pigs, animal nutrition, animal health

Fungi, which are commonly referred to as molds, are microorganisms that live and grow on feedstuffs when moisture, temperature, and other conditions favour their growth. Some, but not all, molds produce toxins that cause disease in livestock and poultry. These toxins are referred to as mycotoxins.

More than 200 different types of mycotoxins have been identified and new ones are continually being discovered. In Ontario, there are two types of mycotoxins that cause serious problems to the swine industry: feed refusal and estrogenic mycotoxins.

Feed Refusal Mycotoxins

Vomitoxin (Deoxynivalenol or DON) and other trichothecenes (e.g. T-2 toxin, HT-2 toxin, DAS) are the two groups of toxins most commonly associated with feed refusal in swine. The reduction in feed intake is proportional to the concentration of these toxins in the diet. The reduction in growth rate and feed conversion of pigs is primarily due to a reduced intake of energy, amino acids, minerals, and vitamins. At high concentrations in the diet, vomitoxin also causes vomiting in pigs.

The other trichothecenes are far more toxic than vomitoxin in that they cause nervous disorders, irritation of the skin and digestive tract, birth defects, reduced disease resistance, and hemorrhaging in addition to a reduction in feed intake. Fortunately, their occurrence and levels are generally lower than vomitoxin in Canadian grains.

The symptoms, such as vomiting and large reductions in feed intake, caused by high concentrations of these mycotoxins will be readily observed by all pork producers. However, smaller reductions in feed intake, which may be of great economic significance, may go unnoticed if feed intake is not monitored.

VOMITOXIN

<1 ppm        very little influence on feed consumption

1-2 ppm      limited influence on feed consumption

>2 ppm        reduced feed intake & growth noticeable after 7 days

                    can be difficult to detect at farm level unless you monitor feed intake or usage.

>3 ppm       reduced intake will be noticeable within 3 days

                   dilution may be effective at this level

>5 ppm       30% - 50% reduction in consumption and growth rate

7 ppm         intake problems are very obvious

                   dilution may not be a practical solution at this level

10 ppm       almost complete feed refusal

It is very difficult to interpret assay values and accurately predict the impact on pig performance. There is a possibility that the assay reading is not representative of the grain source being used in the ration formula. It is also possible that other toxins may exist in the grain that will reduce performance more than what typically would be expected. Synergies between toxins can occur, but most known interactions are with feed additives. However, naturally contaminated grains are recognized to produce more severe effects when containing a certain level of one mycotoxin than a diet containing clean grains and tainted with the same level of the single, purified mycotoxin. The values above for vomitoxin are suggested guidelines.

Estrogenic Mycotoxins

ZEARALEONE

Zearalenone is the mycotoxin that affects reproductive efficiency but generally not feed intake. Once absorbed by the pig, zearalenone mimics the action of estrogen, a key reproductive hormone. Relative to other species, swine are extremely sensitive to this mycotoxin.

In gilts and sows, the vulva and reproductive tract become enlarged and vaginal and rectal prolapses occur. Heats become irregular and litter size is reduced. In boars, zearalenone causes degeneration of the testes and reduced libido. The loss of boar fertility alone will have a large negative impact on herd productivity if it goes unnoticed.

Market animals may show signs of increased irritability causing tailbiting and fighting. As a result of mucosal irritation and straining, vaginal and rectal prolapses may occur. Growth decline or stall out has been noticed in market weight animals.

0.1 – 0.2 ppm (100-200 ppb) will initiate estrogenic syndrome, and mucosal irritation.
0.3 – 0.5 ppm (300-500 ppb)  some interference with reproductive performance
0.6 – 0.9 ppm (600-900 ppb)  serious reproductive problems
                                                failure to show heats
                                                reduces sex drive in boars

It is very difficult to interpret assay values and accurately predict the impact on pig performance. There is a possibility that the assay reading is not representative of the grain source being used in the ration formula. For any mycotoxin analysis, the method for sampling is critical as it is widely recognized that the mycotoxin is not evenly distributed within the field and the grain lots. It is also possible that other toxins may exist in the grain that will reduce performance more than what typically would be expected. The values above for zearaleone are suggested guidelines.

Feed Formulation

Several strategies can be employed to minimize the effect that mycotoxin contaminated ingredients will have when mixed in swine rations. In many cases, the situation can be “managed” through adjusting the feed formula.
Practical options include:
a) dilution of the contaminated grain,
b) increasing nutrient density to offset feed intake reductions

The Trouw Nutrition/Shur-Gain program for Managing Mycotoxins recommends a combination of these methods to reduce the negative effects from feeding rations with toxins. In some cases, the best option is to feed suspect grain to less sensitive species.


DILUTION

The severity of symptoms produced by any mycotoxin is proportional to the amount present in the diet. Therefore, at low to moderate levels of contamination, dilution with clean grain is the first option to consider in order to reduce the concentration of mycotoxins in swine diets.
If zearalenone levels exceed 1 ppm and vomitoxin levels exceed 2 ppm, a 50:50 dilution with clean grain is recommended.
If you are unable to dilute your contaminated grain due to bin restrictions or storage requirements, Shur-Gain can make a custom large inclusion crumbled supplement based on our Shurlock or Excel lines in order to help you dilute the myco-toxin from the overall complete feed.

INCREASE DIET DENSITY

Growth rate and feed conversion of swine are adversely affected by feed refusal mycotoxins because daily intake of energy, amino acids, minerals and vitamins is not sufficient to support maximum growth rate.

By increasing the nutrient density, energy and nutrient intake can be maintained while the intake of mycotoxin-contaminated corn is reduced. There is some evidence that fat may also reduce intestinal absorption of vomitoxin and T-2 toxin.


REDUCE ABSORPTION OF MYCOTOXINS

If swine do consume feeds containing mycotoxins, some products are suggested to prevent the adverse effects by reducing the absorption of the mycotoxins. Nutreco Canada Agresearch has tested numerous feed additives of this category.


FEED TO LESS SENSITIVE SPECIES

Because of the action of microflora in the rumen, ruminants (Beef primarily) are relatively resistant to the effects of mycotoxins. If possible, the cleanest grain should be fed to swine and mycotoxin-contaminated grain should be fed to ruminants.

RECOMMENDED MAXIMUM MYCOTOXIN GUIDELINES

In November 2014, Andrew Pharazyn completed a summary of government and university recommendations for various mycotoxin limits in swine feed. The final guidelines (per mt of complete feed) for Trouw Nutrition/Shur-Gain are as follows:

Species/Stage

DON

(Vomitoxin)

ppb

Aflatoxin

ppb

Zearalenone

ppb

T-2 Toxin

ppb

Fumonisin

ppb

Ochratoxin

ppb

Swine            
All classes 1000 20    200 5000 50
Nursery Pigs     100      
Grow Finish Pigs      250      
Breeding Gilts     100      
Sows     250