Mycotoxin contamination of feedstuffs used in swine diets continues to be a problem for producers. Research recently conducted at the Prairie Swine Centre in Saskatoon, Saskatchewan, has specifically focused on deoxynivalenol, also known as vomitoxin, as it commonly contaminates corn, wheat, barley and other important feed ingredients.

According to Biomin (2019), 85% of all grain samples and 90% of finished feed samples in North America contained DON. Data for wheat in Saskatchewan show an increase in the incidence of fusarium, with 80% to 90% of wheat downgraded due to DON contamination. With advances in mycotoxin analysis it has become clear that the mycotoxin problem is much larger than thought and the costs associated with mycotoxin contamination will continue to increase.

Contaminated grains are commonly downgraded for use in livestock feed and, while the best strategy for livestock producers is to avoid feeding mycotoxin-contaminated grain altogether, with the increased incidence and level of contamination this is no longer a viable option. Therefore, many strategies have been proposed to eliminate or reduce the negative effect of mycotoxins in animal feeds. Most of these strategies are based on deactivation of the mycotoxin through binding of the mycotoxin using adsorbents, such as silicate clays and activated carbon, which can be included in feed as non-nutrient additives.

In general, however, current feed additives are relatively ineffective in mitigating the negative effects of mycotoxins and may not be effective for all mycotoxins. For example, some adsorbent agents have proven effective at reducing the negative effects of some mycotoxins, such as aflatoxin, but have shown little or no impact in pigs fed DON-contaminated diets.

Recent studies have examined the use of additives consisting of different blends of yeast/yeast product, preservatives, antioxidants, amino acids and probiotics which have shown potential for success in DON-contaminated diets in grower-finisher and weaning pigs. There are currently no additives available in Canada for use to mitigate the effects of DON.

As swine are one the most susceptible livestock species to the negative effects of DON, there has been an abundance of research on DON in pigs. In general, however, the majority of studies have been performed in young animals with the assumption that the negative effects of consuming mycotoxin-contaminated feed are highest in the young animal. Moreover, previous studies have examined the impact of mycotoxins over a relatively short period of time. Therefore, we sought to answer the following questions:

What did we find?
Two growth performance studies were conducted to examine the impact of long-term feeding of graded levels of DON in finisher (75 to 120 kilograms) and grower-finisher (35 to 120 kilograms) pigs.

In Study 1, 200 finishing pigs with an initial body weight of 76.6 ± 3.9 kilograms were group housed in pens with five pigs per pen. In Study 2, 240 grower pigs with an initial body weight of 35.9 ± 1.1 kilograms were group housed in pens with six pigs per pen. In both studies, pens were assigned to one of four dietary treatments (n=10 pens per treatment).

Dietary treatments consisted of a control diet (CON) containing no DON or a diet containing 1, 3 or 5 parts per million DON (DON1, DON3 or DON5). The basal diet was wheat-barley-soybean meal based and formulated to meet or exceed nutrient requirements. The dietary DON levels were achieved by replacing DON-free wheat with DON-contaminated wheat and wheat screenings. Individual pig body weight and per pen feed intake were measured weekly for the duration of the studies (42 days for Study 1 and 77 days for Study 2) for determination of average daily gain, average daily feed intake and feed efficiency.

In finisher pigs, we found that there was a rapid negative response to >1 part per million DON intake, resulting in a decrease in average daily gain and feed intake as well as reduced body weight within the first week (Table 1). The reduction in body weight was maintained throughout the study, however, after a period of approximately four weeks, the feed intake and average daily gain of all pigs had recovered.

In grower-finisher pigs, the response to DON intake was less pronounced and not as rapid, resulting in variability in the response over time and across treatments (Table 2). Overall, there was reduction in average daily gain, feed intake and body weight in pigs fed >1 part per million DON, however, this negative effect was less than observed in finisher pigs.

There was no impact of dietary DON content on feed efficiency in either study. Overall, these studies provide further evidence for an upper limit of 1 part per million DON in finished feed to avoid reduced performance. While there was an initial reduction in performance, pigs seem to be able to adapt to DON intake of >1 part per million and <5 parts per million.

What will this cost you?
The Prairie Swine Centre Enterprise Model was used to assess the economic impact of feeding DON-contaminated grain to pigs. It is important to note that the following assessment was based on the results of the current studies as well as a number of other assumptions (e.g., grid, market weight, current market prices). Therefore, these results are meant only as an indicator of the potential economic impact and the specific economics will be dependent on individual production parameters.

Producers need to weigh several factors when considering feeding DON-contaminated grains in their operations, the most important being — What are the costs associated with it?

Results from this project have shown, that pigs consuming high levels of DON, in complete diets, will be 5 to 8 kilograms lighter by the time they reach market weight. However, these pigs also consumed less total feed. Does this drop in feed consumption and total feed cost, outweigh the drop in market revenue from the sale of hogs at a lighter weight? The simple answer is no, however it depends when pigs are introduced to DON in their diets.

Figure 1 shows the margin over feed cost when pigs (at average market conditions) are fed varying levels of DON in complete diets and when DON is introduced at different stages in the production cycle. Results indicate little to no change in returns when pigs are fed diets containing 1 part per million of DON, regardless of when it was introduced. In both studies, no significance was found in final market weight between control and diets containing 1 part per million of DON.

Results also indicate an inverse relationship between margin over feed cost and the level of DON in the diet for both studies. In other words, increasing DON reduces producer returns. However, the negative impact on margin over feed cost is far greater when pigs are first introduced to DON in the finishing period. This indicates the negative impacts of DON are less when introduced earlier to pigs in the production cycle. Based on the results of this study we would estimate between a $2 to $7 per hog drop in revenue under average market conditions. Therefore, it would be in the producer's best interest to avoid contaminated grains when possible.

In order to balance the drop in returns (margin over feed cost), producers will need to buy DON-contaminated grains at a discount, compared to clean grain, in order or make feeding DON-contaminated grain a viable option. Figure 2 shows the estimated drop in finished feed cost (per metric ton) for various levels of DON-contaminated diets required to have no impact to margin over feed cost (returns) to the producer. The finished diet will need to drop in price between $11 and $63 per ton, depending on level of contamination and exposure to DON, in order to have no change in margin over feed cost.

Figure 3 displays the drop in (DON-contaminated) ingredient price required when that ingredient would make up 40% of the total finished diet. If we assume clean grain can be purchased at $225 per metric ton, producers will need to purchase the DON-contaminated ingredient at a significant discount, up to $155 metric ton, in order to justify feeding 3 or 5 parts per million of DON in a diet.

It is important to remember an ingredient containing 2.5 parts per million making up 40% of the diet translates to 1 part per million in the final diet, and it would take 12.5 parts per million of DON in an ingredient to achieve 5 parts per million in a diet.

There are additional considerations that producers must take in account when feeding DON-contaminated. In theory, if we could simply purchase DON-contaminated grains cheaper we could maintain margin over feed cost, however, it is not that simple in practice and may not be possible. If these savings cannot be achieved, pigs fed DON-contaminated diets will need to be kept in the barn longer due to slower growth, increasing costs and reducing throughput. Adding five days to market adds approximately 4.5% to fixed costs, as fewer pigs can be marketed from the barn in a year. In farrow-to-finish operations, many facilities simply cannot afford to keep pigs five days longer. Logistics are another important consideration. If farms do not have the ability to separate the DON-contaminated ingredients from clean grain, the entire herd would receive the DON ingredient — perhaps creating additional challenges in other parts of the production system. It is also important to note that this economic analysis examines the impact of feeding DON based on one specific grading grid. As packers have different requirements, the change in margin over feed cost would be packer specific and shipping at lighter weights (associated with higher levels of DON) may be more detrimental in some cases.

Finally, the use of DON-mitigating feed additives, while potentially effective, also result in increased feed costs, therefore, producers would need to weigh the potential benefits against the costs of these products.

Take home message
In finisher pigs, feeding of diets with >1 part per million DON results in an initial reduction in feed intake and average daily gain. This results in a reduction in body weight which is sustained over time. Growth performance recovers after a period of time, indicating that pigs may be able to adapt to DON intake. The response to DON appears to be reduced and more variable in grower pigs than in finisher pigs.

Acknowledgements
These studies were supported by the Saskatchewan Ministry of Agriculture and the Canada-Saskatchewan Growing Forward 2 bilateral agreement, the Barley Development Commission of Saskatchewan, Biomin Holding GmbH and Mitacs. General program funding for the Prairie Swine Centre is provided by the Government of Saskatchewan, Saskatchewan Pork Development Board, Alberta Pork, Manitoba Pork and Ontario Pork.

References

Wellington M.O., Bosompem M.A., Petracek R, Nagl V, and Columbus D.A. (2021) Effect of long-term feeding of graded levels of deoxynivalenol on growth performance, nutrient utilization, and organ health in finishing pigs and DON content in biological samples. J. Anim. Sci. In press. doi:10.1093/jas/skaa378.

Sources: Dan A. Columbus, Michael A. Bosompem and Ken Engele, who are solely responsible for the information provided, and wholly own the information. Informa Business Media and all its subsidiaries are not responsible for any of the content contained in this information asset.