When addressing mycotoxin issues the fact that multiple ingredients make up a dairy cattle diet can be viewed both positively and negatively. Multiple feeds dilute the toxins from any given feed, resulting in a safer diet. On the other hand, since the effect of toxins can be additive, if there are multiple contaminated feeds, toxicity of individual feeds will be compounded. This article addresses the potential for individual feeds in a typical dairy cow diet to contribute the most significant mycotoxins, aflatoxin B1 and vomitoxin (DON). Mycotoxin concentrations were obtained from feed samples analyzed by Dairy One analytical services between 2000 and 2016. Number of samples analyzed ranged from 20 for soybean meal to 1,480 for corn silage. The figure below shows a dairy cow ration containing corn silage (27.7%), shelled corn (21.0%), low fat distillers’ grains (20%), alfalfa hay (19.3%), Soybean meal (4.1%), grass hay (3 %), and other additives (4.9%). Concentrates are usually the ones most likely contributing mycotoxins to the diet. Of them corn and corn derived feedstuffs are oftentimes the main contributors of mycotoxins, particularly aflatoxins.
Feedstuffs With the Potential to Contribute More Mycotoxins
Dry Shelled Corn
Corn grain samples had on average 17.4 ppb of aflatoxin B1, which was the toxin present in the highest concentration. The maximum value recorded for this toxin in corn was 146 ppb. With corn included at 21% of the diet, and average mycotoxin concentrations as in this data set, it would contribute 3.7 ppb of aflatoxin B1, and up to a worst case scenario of 36.5 ppb if at the highest concentration. Average values for DON in corn were almost 1 ppm reaching a maximum of 3.6 ppm. At 21% inclusion rate the values for DON contributed by corn would be 0.21 ppm and 0.8 ppm for average and high mycotoxin concentrations, respectively.
Aflatoxin B1 was the toxin with the highest concentration in corn silage, right at 1 ppb; its maximum value tested was 8.5 ppb. The second mycotoxin in importance was DON with average values observed at 1.6 ppm and maximum at 4.7 ppm, both higher than for shelled corn. Corn silage included at 27.7% (DM basis) would only contribute 0.28 ppb aflatoxin B1 when at average concentrations, and 2.4 ppb when at its maximum concentration. When considering the inclusion rate for corn silage the DON concentrations would be 0.44 ppm and 1.3 ppm for average and high DON, respectively. The data shows corn silage would probably contribute less aflatoxin B1 to the diet but it could be a more significant contributor of DON than shelled corn.
Distillers Dried Grains (DDGS)
When starch is fermented to ethanol, mycotoxins present in corn grain are concentrated threefold. The quantity of mycotoxins in newly processed DDGS is thus directly related to their presence in the original grain. This has led to concerns by livestock producers and nutritionists that want to include DDGS in cattle diets. Analytical results from 346 samples of DDGS showed that the risk for both mycotoxins is far less with DDGS than with corn grain or even corn silage. Only aflatoxin B1 was detected in the samples and at a concentration of 0.5 ppb on average, less than the average value for dry shelled corn. The highest concentration recorded was 3.5 ppb, lower than the maximum of 146 ppm for corn grain. Average aflatoxin B1 concentration in DDGS was half that observed in corn silage and the maximum was also less than half that in corn silage. Concentration of DON was on average 2.4 ppm with a maximum of 4.8 ppm. These values agree with what was reported by Garcia et al. (2008) who suggested to use DON as a marker for mycotoxin contamination in DDGS samples. It is very likely that the explanation for this difference favorable to DDGS in mycotoxin concentrations is the stringent quality control measures in operation at the bio-refineries, that precludes mold contaminated grain to enter the fermentation process.
Only 20 analyses were reported for soybean meal. It seems however that soybean meal which is less often suspected as a mycotoxin contributor to livestock diets, should also be tested. This might be more important however in non-ruminant diets as well as calf starter diets, since its inclusion is usually higher. Of the samples analyzed soybean meal had on average close to 6.2 ppb of aflatoxin B1. This is nearly 6 times more than corn silage and 12 times more than DDGS. The maximum value observed for aflatoxin B1 was 24.6 ppb, again almost 3 times higher than corn silage and significantly higher than DDGS. However, since soybean meal is included at lower concentrations (4.1 % of the diet in this example) in ruminant diets its contribution would be of little significance, and at 0.37 ppb and 1 ppb for average and high concentrations of aflatoxin B1, respectively.
Although not present in this diet, cottonseeds are oftentimes included in dairy cow rations since they are a good source of protein, energy, and effective fiber. From the point of view of their aflatoxin concentration however cottonseeds can be among the riskiest feedstuffs. According to the 62 analysis performed between 2000 and 2016 by Dairy One, cottonseeds had an average of almost 26 ppb of aflatoxin B1 and a maximum of 188 ppb. This is nearly 50% more than the average, and 29% more than the maximum values reported for corn grain. If cottonseeds were to be included at 6% (3.5 lbs.) of the ration dry matter it would add 1.6 ppb and 11 ppb for average and high concentration of aflatoxin B1, respectively. In a diet with low aflatoxin B1 concentrations the cottonseed mycotoxin contribution might go unnoticed, however it can certainly tip the scale when the overall values of the diet are borderline with toxicity.
High moisture corn is one of the most commonly used high moisture feeds on farms. High moisture byproducts are also oftentimes included in cattle diets, when the distance to the supplier does not increase excessively their transportation cost on a dry matter basis. These feeds are advantageous since they are usually highly palatable for cattle, and help condition otherwise dry rations reducing sorting behavior and feed losses. Among the most frequent high moisture byproduct feeds used in ruminant diets are distillers’ grains, brewers’ grains, and gluten feed.
The average aflatoxin B1 value for high moisture corn was nearly half (8.68 ppb) compared to that observed in dry shelled corn (17.38 ppb). Similarly, its highest value was 42% less compared for the highest value for dry shelled corn (145.85 ppb vs. 102.77 ppb). Vomitoxin content however, showed the opposite trend in high moisture corn where it was higher (2.63 ppm average; 6.40 ppm high), compared to dried shelled corn (0.96 ppm average; 3.63 ppm high).
Wet Distillers’ Grains
This is the co-product obtained after the fermentation and before drying to obtain DDGS. Depending on the bio-refinery there are at least two products available in the market. One is the wet distillers’ grains (usually 65 % moisture) the other one is the modified distillers’ grains (50% moisture) which has been partially dried. In some areas they are just referred as “cake” so it is
very important for the livestock producer and nutritionists to know for sure which product they are dealing with when balancing diets. Wet distillers’ grains analyzed in the Dairy One database were the “true” wet product obtained right after the fermentation process; their moisture content was on average 65%. As it could be expected for a wet corn product its aflatoxin concentration was on average more than 3 times as high as in DDGS (1.80 ppb vs. 0.54 ppb) and the maximum value almost double (3.47 ppb vs. 6.50 ppb). Vomitoxin showed also a reverse trend, with lower concentrations in WDG (1.30 ppm average; 2.5 ppm high) compared with DDGS (2.38 ppm average; 4.81 ppm high).
In certain regions wet brewers grain is a highly sought after feed. It is a good source of protein (usually around 24 %CP) and highly palatable to cattle. Its high moisture content (around 75%) makes its transportation sometimes uneconomical depending on the distance to the brewery. There was a limited number of samples (n= 16) analyzed for mycotoxins in this database. Values for both aflatoxin B1 and vomitoxin were low compared to the other wet feeds.
Wet Corn Gluten Feed
Processes in wet milling are considerably different than those in dry grind ethanol plants. This results in coproducts with differing nutrient profiles. The primary coproducts that result from wet milling include corn gluten feed (CGF), corn gluten meal (CGM), corn germ meal (CGM), and condensed fermented corn extractives (CFCE, also referred to as corn steep liquor). Corn gluten feed (CGF) is comprised primarily of the portion of the kernel that remains after the starch, gluten, and germ have been removed. It is produced by combining the remaining corn bran with steep liquor and is commonly available as either dry or wet CGF. Nutrient composition can vary across different plants, depending on the amount and type of steep liquor added to the bran. For example, CGF is commonly reported as having approximately 24% crude protein (CP) (NRC 2001). There were only 17 samples analyzed in this dataset. Wet corn gluten feed was second only to high moisture corn in its aflatoxin B1 concentration, both for the average (5.59 ppb vs. 8.68 ppb) and the high (13.10 ppb vs. 102.77 ppb) reported values. Vomitoxin content was highest among all wet feeds tested, with and average value of 3.78 ppm and a high value of 13.10 ppm.
Aflatoxin B1 is considered the most potent natural carcinogen. Although rumen microorganisms can degrade up to 42% of this aflatoxin, they are also capable of producing aflatoxicol. Aflatoxin M1 another metabolite is produced from B1 in the liver and can end up in the rumen through the rumino-hepatic circulation. The toxicity of aflatoxicol and M1 is similar to that of B1, and they are readily absorbed by the intestine. Therefore, even when B1 is degraded in the rumen to aflatoxicol and transformed in the liver to M1, the toxic end-result is similar. The metabolite M1 circulates from the liver into the blood and ends up in milk or urine.
The average and maximum contribution of mycotoxins to the dairy cow diet in this example are reported in Graph 1. Cottonseeds were included at 6% of the ration dry matter just for illustration purposes. The riskiest feedstuff to contribute aflatoxin B1 when looking at both the average and maximum concentrations in this data set was corn grain, followed by cottonseeds, and then corn silage. The safest feed was soybean meal, particularly because of its low inclusion in the diet. When DDGS are included at a maximum of 20% its contribution of mycotoxins to the diet was negligible even at their highest mycotoxin concentration reported compared to corn grain, corn silage, and cottonseeds.
When the mycotoxin concentration in the individual feedstuffs is average (as those reported in the Dairy One data set) a ration like the one in the example will have aflatoxin B1 and DON concentrations of 5.57 ppb and 1.44 ppm, respectively. This can increase to high values of up to 49.5 ppb of aflatoxin B1 in the ration, when the individual feed values are also in the higher range. Similarly, DON values for the complete ration would be 1.44 ppm with feedstuffs of average values and 4.9 ppm on the higher end.
The FDA has established “action level” for aflatoxin B1 and DON concentrations in lactating dairy cow diets at 20 ppb and 5 ppm for aflatoxin B1, and DON, respectively. If DDGS supplemented at 20 % would happen to have the maximum observed aflatoxin B1 values, the total in an “average” ration would increase by 3 ppb, to 8.57 ppb still well below the action level suggested of 20 ppb suggested by the FDA. The only feeds that would significantly increase aflatoxin B1 to values above FDA recommendations would be corn grain and maybe even moldy corn silage. With corn grain contaminated at its highest reported value, and the other feeds at average concentrations, then the total aflatoxin B1 in the diet would be 38.4 ppb. This suggests that if the addition of the DDGS results in aflatoxicosis symptoms, then the total ration was already borderline with a dangerous concentration of aflatoxin B1. The same conclusion is valid for DON. If maximum analytical values reported for all feedstuffs are used in the ration, the total DON concentration reaches 4.9 ppm, right below the 5 ppm suggested by the FDA. The only feeds that in the right combination of high individual concentration and high inclusion rates would increase the total beyond the “action levels” are corn grain and corn silage.
Handling Mycotoxin-Contaminated Feeds
Healthy dairy cows usually resist molds in feed unless they are immune-suppressed. Any stress that impairs the dairy cow immune function increases susceptibility to mycotoxicosis. Aflatoxins have a demonstrated effect on immuno-suppression. The effects that have been described are reductions in cellular protein synthesis, cell mediated immunity, and antibody production. It is thus very important to boost the immune system of the animal, aside from the actions taken to decrease the mycotoxin concentration. Boosting the immune system can be accomplished by reducing overall stress and by supplementing the diet with antioxidant compounds (e.g., selenium, vitamins A and E, beta carotenes, etc.) are potentially very efficacious because of their ability to act as superoxide anion scavengers (Galvano et al. 2001).
If aflatoxins become a problem, absorption of the toxin can be reduced by adding anti-caking agents such as sodium bentonite, hydrated sodium calcium aluminosilicates, or a modified yeast cell-culture-based product to the grain. Adsorbent agents sequester the mycotoxins in feed, reducing the bio-availability of mycotoxins and increasing their excretion in feces (Table 11). Advantages of adsorbent agents are their cost, safety, and ease of inclusion. However, clay-type binders appear to be effective against aflatoxins only, not other mycotoxins.
Screening to remove fines from grain can be an effective and practical way to reduce mycotoxin concentrations to levels that pose less of a risk. Research performed at the Virginia Polytechnic Institute (Harper et al. 2006) suggests that mechanical screening of corn can reduce aflatoxin concentration in contaminated corn. Samples from a bin were collected with a probe at depths of 3, 9, and 15 feet. The samples were mechanically shaken to separate fines from intact kernels. The aflatoxin concentration in the whole kernel fractions was 86–89% lower than that in the fines. Total aflatoxin concentration and concentration in the fines was higher in samples collected at 3 feet than the samples taken at other depths. The difference in aflatoxin concentration at different locations within a bin underscores the importance of getting representative samples when assessing mycotoxin concentrations.
DEALING WITH MYCOTOXIN-CONTAMINATED FEEDS DECALOG
- Prevention is key. Add grain preservatives or inoculants when warranted.
- Clean bins from fines from previous seasons before adding the new crop.
- Use best management practices when harvesting, storing, and feeding-out forages.
- Test grain for molds and mycotoxins, and at what concentration.
- Screen the grain to reduce fines concentration and/or blend with clean grain.
- Reduce overall animal stress levels by adequate management and comfort.
- Include antioxidants like vitamin E and selenium in the diet.
- "Dilution may be the solution": blend affected feeds with "clean" feedstuffs.
- Consider using anti-caking agents at feeding time.
- Always remember that more than one feed is possibly contributing mycotoxins.
This article was originally published on iGrow, a service of the SDSU Extension.
- Dairy One Analytical Services. Ithaca, NY.
- Diaz, D. E., W. M. Hagler Jr., J. T. Blackwelder, J.A. Eve, B. A. Hopkins, K. L. Anderson, F. T. Jones, and L. W. Whitlow. 2004. Aflatoxin Binders II: Reduction of aflatoxin M1 in milk by sequestering agents of cows consuming aflatoxin in feed. Mycopathologia. Vol. 157, Number 2 pp. 233-241.
- Kutz, R. E., J. D. Sampson, L. B. Pompeu, D. R. Ledoux, J. N. Spain, M. Vázquez-Añón and G. E. Rottinghaus. 2009. Efficacy of Solis, NovasilPlus, and MTB-100 to reduce aflatoxin M1 levels in milk of early to mid lactation dairy cows fed aflatoxin B1 J. Dairy Sci. 2009. 92:3959-3963.
- Galvano F., A. Piva, A. Ritieni, and G. Galvano. 2001. Dietary Strategies to Counteract the Effects of Mycotoxins: A Review. Journal of Food Protection®, Volume 64, Number 1 pp. 120-131(12) Publisher: International Association for Food Protection.
- Garcia, A., Kalscheur, K., Hippen, A., Schingoethe, D., and K, Rosentratr. 2008. Mycotoxins in Corn Distillers Grains: A concern in ruminants? SDSU Extension Extra 4038.
- Harper, A., J. Zhao, J. B. Meldrum, and M. J. Estienne. 2006. Impact of sample collection location and grain fraction when assessing corn for aflatoxin contamination Journal of Swine Health and Production: pp. 152.