Eight hectares of land that is certified for organic production at the WCROC were used for organic winter camelina production between 2018 and 2019. Four hectares were used as a monocrop (camelina only) field and the remaining 4 ha were used as a relay-crop (camelina relayed with soybean) field. Winter camelina (var. “Joelle”) was seeded using a grain seed drill on Oct 1st, 2018, after harvesting corn for silage in both the mono and relay crop fields. The camelina sowing time was later than desired (mid-September; Gesch et al., 2014) due to rain and wet fields, which prevented proper functioning of the seed drill. Row spacing was 15 cm for the camelina in the monocrop field, with a seeding rate of 8 kg ha⁻¹. In the relay-crop field, camelina was seeded the same way except that a row was skipped every 76 cm as described by Gesch et al. (2014). The skip-rows were designed for relay inter-seeding soybean the following spring. The seeding rate of camelina in the relay-crop field was 6 kg ha⁻¹. Camelina germinated 17 days after seeding and emerged before the first snowfall. During the planting and growing phase, the crop was managed organically in both fields. No herbicides or pesticides were applied.

On June 3, 2019, before the camelina flowered, organically certified soybeans were seeded at 445,000 seeds ha⁻¹ in the skip-rows in the relay-crop field. Camelina in both the mono- and relay-crop field was harvested on July 13, 2019. At harvest, soybeans in the relay cropped field were in the 4-leaf stage, still small enough so as not to be damaged by harvesting the camelina. Harvesting camelina seed was performed with a standard combine with sieves and screens adjusted to the setting for canola due to the small size of camelina seed. During harvest, camelina was cut about 20 cm above the ground in the monocrop field and about 30 cm above the ground in the relay-crop field to avoid cutting the soybeans. At harvest, camelina seeds were sampled and measured for moisture content by drying the samples at 60°C for 48 h. The seeds then were air-dried and stored according to the Organic Production Protocol of the WCROC, which was developed based on the National Organic Standards [National Organic Program (NOP), 2020].

Camelina seeds were cold-pressed (at room temperature) for oil at a commercial organic oil processing plant (Healthy Oilseeds, Carrington, North Dakota). Camelina seeds and CPC were sampled and analyzed for concentration of moisture, crude protein, crude fat, crude fiber, neutral detergent fiber (NDF), total calcium, phosphorus, and minerals (iron, sodium, potassium, magnesium, manganese, copper, and zinc) at a commercial lab (Midwest Laboratories, Omaha, Nebraska), and for amino acid profiles at the Experiment Station Chemical Laboratories (University of Missouri, Columbia, Missouri). Additionally, camelina oil, seeds, and CPC were analyzed for anti-nutritional compounds (glucosinolates and trypsin inhibitors) at BioProfile Testing Labs (St. Paul, MN). Fatty acid profiles of camelina seed, oil, and CPC were quantified at the same lab as amino acids. The CPC produced was used as a feed ingredient for pigs in the feeding trial described below.

A feeding trial was conducted between 2019 and 2020 to evaluate the impact of including dietary CPC on growth performance of pigs, pork quality, and costs and returns of organic pig production. The experimental protocol used in the study was reviewed and approved by the University of Minnesota Institutional Animal Care and Use Committee (IACUC#: 2006-38189A).

The market for camelina seed, oil, and CPC is not currently well-established to provide reliable estimates of future market prices. In the absence of reliable estimates of future market prices, the economical feasibility of growing winter camelina and feeding CPC to pigs was evaluated by calculating a set of minimum required sale prices and maximum allowable purchase prices for camelina seed, CPC, and oil that would be required to make an organic crop rotation and pig feeding enterprise with camelina as economically feasible as similar ones that do not include camelina.

A typical crop rotation with small grains in the Midwest is a 3-year rotation of corn grain—spring wheat—soybeans. In the economic analysis, camelina was considered a cover crop and the camelina production follows wheat production. This is because some or all organic producers seeded cover crops after organic wheat between 2017 and 2019 [University of Minnesota Center for Farm Financial Management (CFFM), 2021]. The economic analysis is organized in a partial budgeting format (Boehlje and Eidman, 1984) which looks at the differences in costs and returns compared with such a typical three-crop rotation that does not include camelina. In the relay-planting scenario, soybeans are planted after camelina in the third year of the typical rotation. In the monocrop camelina scenario, the camelina replaces the soybeans in the third year. Thus, the soybean growing cost is incurred in the relay-planting scenario but is avoided in the monocrop scenario. Another minor cost savings in the camelina scenarios compared with the University of Minnesota Center for Farm Financial Management (CFFM) (2021) summaries is the elimination of the cover crop expense following the wheat that the organic wheat enterprises in the University of Minnesota Center for Farm Financial Management (CFFM) (2021) summary incurred on average. In the analysis, replacing those existing cover crops with camelina would result in a savings that offsets some of the camelina growing cost.

The calculation of a crop producer's minimum required sale price for camelina seed draws on several data sources. The camelina seed cost, camelina yield, and the soybean yield reduction of the following relay-planted soybean crop were from the current study. The soybean yield reduction was compared with average organic soybean yield between 2017 and 2019 in the Midwest [University of Minnesota Center for Farm Financial Management (CFFM), 2021]. The average organic soybean yield was 2,268 kg ha⁻¹ with growing costs of $630 ha⁻¹ in the University of Minnesota Center for Farm Financial Management (CFFM) (2021) summary. The machinery costs per hectare were based on types and sizes typical of a commercial crop operation (Lazarus, 2020), which were based on prices of new machinery purchased in 2020 as listed in Table 2.

The minimum required camelina sale price from the crop budget was converted to a per-kg of CPC basis based on the percentage of CPC in camelina seed in the current study. It was then compared with the maximum price that a hypothetical pig producer would be willing to pay for CPC to make pig feeding as profitable as feeding a non-camelina diet. Feed cost per pig was calculated based on average growth performance of pigs in each treatment group, and cost of feed ingredients used for the current study, with CPC replacing organic corn grain and soybean meal in the treatment diets. Organic corn grain was valued at $0.35 kg⁻¹, soybean meal at $0.88 kg⁻¹, and base mix at $1.23 kg⁻¹ based on market conditions in west-central Minnesota in 2020. Given that camelina oil is a co-product of CPC, the difference between the minimum sale and maximum purchase prices of CPC is assumed to be made up by marketing the oil. A minimum required sale price for the oil was calculated as the residual from the calculations. Economical feasibility of the whole system hinges on whether it would be possible to market the camelina oil at a sale price at or above that minimum required oil sale price.

Data collected from the feeding trial were analyzed using SAS software (Version, 9.4; SAS Institute Inc., Cary, NC). The Glimmix procedure with the Gaussian regression model was used for analysis of continuous variables (growth performance, hot carcass weight, dressing and lean percentage, backfat thickness, liver weight, carcass length, loin eye muscle area, belly thickness and hang angle, pork post-mortem pH, water holding capacity, and shear force value), and the Poisson regression model for analyses of count data (subjective color and marbling score of pork chops). All models included dietary treatment as a fixed effect, with pen serving as a random effect and the experimental unit. For data collected over time, repeated measures statistical models were used that included week and interaction between treatment and week as fixed effects. Initial body weight at 10 weeks of age was used as a covariate for analyses of final body weight and hot carcass weight. Final body weight was used as a covariate for the analysis of dressing percentage. Hot carcass weight was used as a covariate for analyses of backfat thickness and loin eye muscle area (Zhu et al., 2021). Morbidity and mortality data were combined due to low incidence and analyzed using the Frequency procedure with chi-square analysis. Both belly hang angle and adjusted belly hang angle with belly thickness as a covariate were analyzed (Schieck et al., 2010). All tests were two-tailed tests. Differences were considered significant when P ≤ 0.05, and trends when 0.05 < P ≤ 0.10.

At harvest, camelina yield was 1,575 kg ha⁻¹ and 772 kg ha⁻¹ in the monocrop and relay-crop field, respectively, both with 25% moisture content. After drying, moisture content dropped to 14%. Camelina yield with 14% moisture content was 1,394 kg ha⁻¹ in the monocrop field, and 684 kg ha⁻¹ in the relay crop field.

Camelina seeds contained 34.6% crude fat (oil) on an as-is basis (Table 3). Camelina press-cake contained 34.4% crude protein and 9.3% crude fat, suggesting that CPC can be a useful protein and energy source for livestock feed. However, compared to corn and SBM, CPC had higher concentration of NDF, which may negatively affect digestibility of a diet supplemented with CPC. Concentrations of crude protein and amino acids, especially essential amino acids, in CPC were lower compared to those in SBM. Particularly, concentration of lysine, the first limiting amino acid for pigs, in CPC accounted for only 64% of lysine in SBM.

Total saturated fatty acids (SFA) in camelina oil, seeds, and CPC were lower compared to SFA in corn and SBM (Table 4). But, camelina oil, seeds, and CPC had higher concentrations of monounsaturated fatty acids (MUFA) compared to corn and SBM. One of the MUFA in camelina was erucic, which potentially can reduce palatability of camelina for pigs (Meadus et al., 2014). Erucic concentrations in camelina oil, seeds and CPC in the current study ranged from 2.3 to 2.4% of total fatty acids which is typical for winter camelina (Matthaus and Zubr, 2000; Walia et al., 2021). While the total PUFA concentrations in camelina oil, seeds, and CPC were lower compared to those in corn and SBM, concentrations of omega-3 fatty acids (Linolenic: C18:3n3, and Homo-a-linolnic: C20:3n3) in camelina oil, seeds, and CPC were much higher than in corn and SBM. On the other hand, the concentration of the omega-6 fatty acid, linoleic (C18:2n6), was much lower in camelina oil, seeds, and CPC than in corn and SBM. The concentration of glucosinolates in camelina seeds and CPC were almost identical. The concentration of glucosinolates was negligible and trypsin inhibitors were not detected in camelina oil. Concentrations of trypsin inhibitor in camelina seeds and CPC were similar to that reported previously (Matthaus and Zubr, 2000; Woyengo et al., 2017). Because anti-nutritional factors were not expected in corn and SBM, glucosinolates and trypsin inhibitors were not analyzed for corn and SBM.

Pigs fed diets supplemented with CPC consumed less feed (P = 0.05; Table 5), gained less weight (P = 0.001), and were lighter (P = 0.001) at conclusion of the study compared to pigs fed control diets. Gain efficiency (G:F) was not affected by dietary treatment. Twelve pigs (6%) in the control group and six pigs (3%) in treatment group could not be marketed at the end of the study because they were too light, were lame, displayed a belly rupture or died. But no statistical differences in total mortality and morbidity were detected between control and treatment groups. For pigs that were marketed and harvested at the meat processing plant, hot carcass weight was lighter (P = 0.001), dressing percentage was lower (P = 0.03), backfat thickness at the last rib was less (P = 0.04), and lean percentage was greater (P = 0.04) for pigs fed treatment diets compared with pigs fed control diets.

Interactions between dietary treatment and week were detected for ADFI, ADG, and body weight. Pigs fed treatment diets displayed reduced ADFI (P < 0.05) during the initial 4 weeks of the study, compared to pigs fed control diets (Figure 1). After 4 weeks, no difference was detected in ADFI between the two groups. Similar to ADFI, ADG was reduced during the initial 4 weeks in pigs fed treatment diets compared with pigs fed control diets (Figure 2). After 4 weeks, differences in ADG between the two groups were not significant. Body weight of pigs fed treatment diets was lighter (Figure 3; all P < 0.05) at weeks 14, 18, 22, and 24 compared to pigs fed control diets.

For focal pigs harvested to evaluate pork quality, body weight at harvest and hot carcass weight were lighter (all P < 0.05; Table 6) in pigs fed treatment diets compared to pigs fed control diets. Differences in dressing and lean percentage between the two groups were not statistically significant. Additionally, dietary treatment had no effects on any other carcass, pork or belly traits measured except for backfat thickness at the last lumbar vertebra. Backfat thickness at the last lumbar vertebra was less (P = 0.03) in focal pigs fed treatment diets than that in pigs fed control diets. In addition, focal pigs fed treatment diets had heavier livers (P = 0.03 for liver weight, and P = 0.04 for liver weight as a percentage of final body weight) than pigs fed control diets.

For the scenario of the typical 3-year rotation, the average net return to land during the year of planting organic soybeans was $708 ha⁻¹, assuming that the average organic soybean yield was 2,268 kg ha⁻¹ and growing costs was $630 ha⁻¹ [University of Minnesota Center for Farm Financial Management (CFFM), 2021].

The soybean yield in the relay-cropping field in the current study was 1,210 kg ha⁻¹, which was a reduction of 1,058 kg or 46.6% compared with the University of Minnesota Center for Farm Financial Management (CFFM) (2021) average. At a price of $0.59 kg⁻¹, the soybean yield reduction if relay planting results in a revenue reduction of $624 ha⁻¹ (Table 7). It is assumed that the soybean growing costs of $630 ha⁻¹ are unchanged regardless of mono- or relay-cropping camelina. If the camelina is monocropped with no soybeans following it, the entire 2,268 kg soybean yield is lost which results in lost soybean revenues of $1,338 ha⁻¹. However, this lost revenue is partially offset by the avoided soybean growing cost of $630 ha⁻¹, so that the reduction in net return is $708. Conventional tillage is assumed for the camelina seeding, and costs $246 ha⁻¹ based on machinery purchased new in 2020. Adding the cost of the camelina seed and interest on the preharvest expenses until harvest, and deducting a small amount of cover crop expense that organic wheat enterprises are currently incurring, the total of the costs and reduced revenues is $883 ha⁻¹ for the relay-planting scenario and $967 ha⁻¹ for the monocropping scenario. Dividing by the relay-planted camelina yield (684 kg ha⁻¹) shows that the camelina seed would need to be sold at a minimum price of $1.29 kg⁻¹ to cover those costs and reduced revenues. For the monocrop scenario, dividing by the camelina yield of 1,394 kg ha⁻¹ translates to a minimum sale price of $0.69 kg⁻¹ for the camelina seed.

Lower minimum sale price indicates improved economic feasibility. The lower minimum sale price of camelina seed in the monocrop scenario ($0.69 compared with $1.29 in the relay scenario) is counterintuitive because the camelina yield in the monocrop field was lower than the total yield of camelina plus soybeans in the relay-cropping scenario, but the economical feasibility is improved by the difference in the soybean growing cost. Thus, growing cost savings is an important factor affecting economical feasibility along with the yield differences.

A maximum allowable purchase price for CPC was calculated based on the difference in per-pig gross income and feed cost between the two treatment groups (control vs. treatment, Table 8). The average feed cost for the control diet was $140 pig⁻¹ while the average feed cost for the treatment diet was $121 pig⁻¹, which would be a feed cost savings of $19.12 pig⁻¹ if not accounting for the CPC cost. Dividing this $19.12 by the 26.3 kg of CPC in the treatment diet shows that the CPC can be purchased for no more than $0.73 kg⁻¹ in order for the total treatment diet cost to remain at or below the cost of the control diet, ignoring the 5.8 kg difference in weight gain between pigs in the two groups.

The reduction in total weight gain (5.80 kg pig⁻¹) of pigs fed the treatment diet in the current study represents a gross income reduction of $13.94 pig⁻¹, based on a sale price for organically-grown pigs of $2.40 kg⁻¹ live weight. Subtracting this gross income reduction ($13.94 pig⁻¹) from the feed cost savings ($19.12 pig⁻¹) leaves $5.18 pig⁻¹ as the maximum amount that a producer should be willing to pay for CPC in order to achieve a net return at or above that of the control diet. Dividing this $5.18 pig⁻¹ maximum by the 26.3 kg of CPC fed to pigs shows that the maximum allowable price for the CPC is $0.20 kg⁻¹.

Pressing camelina seed yields CPC at 80.5% in the current study. For the relay-planting scenario, the minimum camelina seed price of $1.29 kg⁻¹ translates to a minimum CPC price of $1.60 kg⁻¹ after pressing if no value is assigned to the oil (Table 9). The difference between the minimum CPC sale price ($1.60 kg⁻¹) and the maximum allowable CPC purchase price ($0.20 kg⁻¹) that the pig producer should be willing to pay for the CPC leaves a deficit of $1.41 kg⁻¹ of CPC or $1.13 kg⁻¹ of seed. It may be possible to make up this deficit by marketing the camelina oil. Camelina oil yield was 14.7% of seed weight in the current study, so that 6.8 kg of seed is required to produce one kg of oil. Multiplying 6.8 kg seed by the deficit of $1.13 kg⁻¹ of seed, the minimum oil price required to make up the deficit is $7.71 kg⁻¹ of oil for the relay-planting scenario.

The minimum CPC sale price is $0.66 kg⁻¹ in the monocrop scenario, which translates into a minimum oil sale price of $3.59 kg⁻¹ for the monocrop scenario based on similar calculations.