Characterization of risk from FB₁ dietary exposure was estimated by using a conceptual model, which consists of three major components: toxicological effects (levels of concern, LOC), swine management, and agronomic management as described in Delgado and Wolt [4]. Six scenarios were developed to consider FB₁ exposure influenced by corn and DDGS as the primary protein source in diets:

Scenario 1: Blended diet (Bt grain, non-Bt grain, Bt-DDGS and non-Bt DDGS)

Information necessary to forecast FB₁ exposure and model parameterization needed to estimate risk consistent with the conceptual model is presented in the following subsections. Each diet scenario required separate sets of worksheets (Microsoft Excel 2010) to describe the FB₁ exposure. Deterministic inputs (Table 1) used average, maximum, midpoint or fixed parameter estimates and all probabilistic modeling (Table 1) used Palisade @Risk 5.7 with random Latin hypercube sampling [6]. The term semi-stochastic will be used to refer to the non-deterministic modeling which does not contain distributions for the inputs of specific week in grower-finisher phase, Bt use fraction in diets and estimations of FB₁ in corn. Refer to Table 1 for descriptions of model input assumptions.

Swine Management. Model parameterization required for diet development included the following: mycotoxin exposure assessed by weekly intervals during the production phase, changes in body weight (BW) over time (i.e., weekly), and total corn intake fraction (TCIF). Information for modeling the diet reflected a typical corn-soybean diet for swine facilities in the Midwestern USA.

Duration of Exposure (Weekly). For the purpose of this dietary exposure assessment, weekly intervals were modeled in order to estimate variations of FB₁ in diets. Estimating exposure by daily intervals was not conducted due to limited changes in diet composition. The sampling of the weekly intervals (i.e., 20 weeks) during production allows for an estimated correlated BW and expected TCIF in accordance with the Kansas State University Growth and Feed Intake Curve Calculator (FICC, see BW and TCIF below). All deterministic modeling scenarios used the 10^th week of production to represent the midpoint of duration. For the semi-stochastic analysis a total of 20 weekly intervals of production were partitioned into six timeframes representative of weight ranges corresponding to the TCIF (Table 2 and Table 3) and sampled by a discrete uniform distribution to estimate the body weight associated with weekly interval.

Bodyweight (BW). Determination of BW was calculated by the Kansas State University Growth FICC as a function of the specific week during production [7]. Parameterization inputs for the FICC included initial nursery average BW of 5.67 kg and an average daily gain of 0.39 kg. Initial BW of grower-finisher production was 22.68 kg with an average daily gain of 0.82 kg, and 120.20 kg as the close out average BW. Values of BW were calculated at the end of the indicated week after placement into the grower-finisher phase (Table 2).

Total Corn Intake Fraction. Estimation of the TCIF in diet is based on the BW intervals associated within the 20 week production duration (Table 3) [9].

Bt vs. non-Bt Corn Fraction in Diet. Estimation of the fraction of Bt and non-Bt corn in swine diets was conducted by using the percentage of US hectares planting Bt and non-Bt seed corn. The USDA National Agricultural Statistics Service (NASS) estimated in 2010 that 15% of corn planted in the state of Iowa was insect-resistant (Bt) and 61% of all corn planted in Iowa was stacked gene varieties (Bt plus herbicide resistance) [10]. Therefore, in our deterministic model we assume that the TCIF in swine diets has a maximum Bt use fraction (BUF) representing 76% of Iowa corn planted, whereas the stochastic analysis distribution was developed from hectares planted in the major corn production states of the US [10]. For stochastic analysis Bt-corn adoption fractions were estimated by using a beta generalized distribution as described by Delgado and Wolt (Table 4) [4].

DDGS Fraction in Diet. In the Midwestern USA DDGS is increasingly used as an alternative feed source due to increased prices of corn and the widespread availability of DDGS as a by-product of ethanol production. Producers usually design the diets to use the maximum allowed percentage of DDGS. Therefore, DDGS distributions were not used in the models. Both deterministic and semi-stochastic modeling used a maximum of 30% DDGS in the diet formulation, since this value represents acceptable growth performance for swine in the grower-finisher phase [8].

Fumonisin B₁ Concentrations in Bt-hybrids, Non-Bt Hybrids, and DDGS. Paired trials of Bt and non-Bt hybrids were used for estimates of FB₁ in diets, which were expressed as cumulative distribution functions (CDF) describing the empirical data (Figure 1) [11–21]. For specific details pertaining to the CDF calculations, see Delgado and Wolt [4]. Estimates of FB₁ concentration in DDGS used a 3-fold scaling for both deterministic and semi-stochastic analysis as a typically reported value [3].

Information used to generate CDF contains both US and non-US data. We considered very carefully the source data and rationale for inclusion of non-US data sites. Rationale for inclusiveness is to better represent the potential variation in FB₁ due to diverse genetic backgrounds and environments (e.g., location and years). The inclusion of non-US data represents 8.31% (i.e., 32 observations in a total of 385) of the total data used to represent FB₁ in corn (Figure 2).

Chronic toxicological adverse effects associated with FB₁ concentrations relevant to dietary exposure in the grower-finisher production phase for formulating the incipient level of concern (LOC) are reviewed in depth by Delgado and Wolt [4] and include the toxicological study of Rotter et al. [22]. The LOC for this QEA is 1.0 mg of FB₁/kg of diet, which is consistent with the lower LOC used by Delgado and Wolt in the QEA for swine in nurseries [4].

Existing data were used to forecast long-term FB₁ exposures in feeding scenarios which may occur in the swine industry. Risk findings were expressed as the probability for exposures to exceed the LOC for long-term effects (1 mg FB₁/kg diet). All diet scenarios predicted some level of FB₁ exposure exceeding the LOC (Table 5). Diet scenarios where the source of grain or DDGS is derived from non-Bt corn (scenarios 3 and 6) pose the greatest opportunity for exceeding the LOC. Scenarios including only Bt grain (scenario 5) without DDGS exhibited the least mycotoxin exposure. The blended diet design (scenario 1) containing Bt and non-Bt grain and DDGS was ranked intermediate relative to other diet scenarios.

FB₁ exposures exceeding the LOC were forecasted for all diet scenarios (Figure 3). Variation of FB₁ exposure among scenarios and worst-case incidences representing the 90th percentile of exposure (Table 5) showed the least risk when the diets were developed with Bt grain only (scenario 5) while non-Bt and non-Bt DDGS diets (scenario 3) showed the highest LOC exceedance in 95% of cases. The percentile exceedance of LOC (1 mg FB₁/kg diet) forecasted were:

Scenario 1: Blended diet (95% of occasions)

Our current model did not include environmental factors inputs, such as temperature, insect pressure, and storage practice variations [24]. However, since we have used data for FB₁ corn spanning multiple use environments and seven growing seasons, the effects of environmental factors is represented in our sampling distribution.

Estimating the DDGS concentration factor of a 3-fold increase is an overestimate of FB₁ in diets. Preliminary research to determine the DDGS FB₁ concentration factors is estimated to range from 1.5 to 2.8 fold [25]. Inclusion of 30% DDGS throughout the entire grower-finisher production phase has been documented to induce softer pork fat due to high concentrations of linoleic acid in the oil of DDGS, resulting in pork fat iodine that are not acceptable. Therefore, recommendations suggest the removal of DDGS at least 3 weeks before slaughter [8]. The current model included DDGS in diets throughout the production phase without removal.