More than half of P in soybeans are bound to phytate which causes a low digestibility of P when fed to pigs. However, new varieties that have different characteristics are sometimes developed and an example is the Photoseed variety of soybeans that captures more carbon and sunlight leading to a more nutrient rich ingredient and a reduced footprint from crop production. There is, however, no information about the nutritional value of the soybean meal produced from the Photoseed variety of soybeans. Therefore, the objective of this research was to test the hypothesis that the apparent total tract digestibility (ATTD) and the standardized total tract digestibility (STTD) of P is not different in soybean meal produced from Photoseed soybeans compared with control soybean meal when fed to pigs.

Material and methods

Soybean expellers produced from either the Photoseed variety (PhotoSeed, Zeakal Inc., San Diego, CA) or a control variety were use. Forty-eight growing pigs (initial BW: 12 ± 1.6 kg) were allotted to a completely randomized design with 6 diets, and 8 replicate pigs per diet. Pigs were housed individually in metabolism crates. Six diets were formulated and arranged in a 2 × 3 factorial with 2 SBM types (control vs. Photoseed) and 3 levels of microbial phytase (0, 500, or 1000 phytase units (FTU) per kg; Quantum Blue, AB Vista, Marlborough, UK). The initial 5 days were considered the adaptation period to diets, and fecal samples were collected for 4 days following the adaptation period. Diets, ingredients, and fecal samples were analyzed for P to calculate ATTD and STTD of P in each diet.

Results and discussion

Concentration of P and Ca were greater in the Photoseed soybean meal than in the control meal (Table 1). Concentrations of phytic acid and trypsin inhibitors were also slightly greater in the Photoseed ingredient than in the control ingredient. In contrast, stachyose and raffinose contents were slightly greater in the control compared with the Photoseed soybean meal.

Values obtained for ATTD and STTD of P for the Photoseed soybean meal (Table 2) were slightly greater than values reported for conventional soybean meal by NRC (2012). This may be a result of the greater crude fat in the soybean meal used in this experiment compared with NRC values because digesta passage rate is reduced with greater fat, which increases digestibility. There was no interaction between type of soybean meal and phytase level for STTD of P, and there was no difference in the STTD of P between the two sources of soybean meal. Addition of microbial phytase to both sources of soybean meal increased STTD of P (P < 0.05). Microbial phytase also increased (P < 0.05) the ATTD of Ca in both Photoseed and conventional soybean meals. The lack of differences in STTD of P between the 2 sources of soybean meal demonstrates that the Photoseed soybean meal provide more phosphorus to the diets without any reduction in digestibility. As a consequence, the concentration of digestible P is greater from Photoseed soybean meal than from conventional soybean meal.

Key points

• Photoseed soybean meal had greater nutrient concentration compared with conventional soybean meal.
• There were no differences in STTD of P between the two soybean meals with or without phytase inclusion demonstrating that despite the greater concentration of P in Photoseed soybean meal, digestibility was not compromised.
• The STTD of P was increased to the same degree in Photoseed soybean meal as in conventional soybean meal when microbial phytase was added was added to the meals.

Table 1. Analyzed composition of the test ingredients, as-fed basis.

¹DM = dry matter. GE = gross energy. AEE = Acid hydrolyzed ether extract. CP = crude protein. ND = not detectable.

²Phytate-P was calculated by multiplying the analyzed phytate by 0.282 (Tran and Sauvant, 2004).

³Nonphytate-P was calculated as the difference between total P and phytate-P.

⁴Calculated using a conversion factor: TIU/mg = 1.9 × TI, mg/g (Hamerstrand et al. 1981).

Table 2. Effects of phytase on apparent total tract digestibility (ATTD) and standardized total tract digestibility (STTD) of P in soybean expellers and ATTD of Ca in diets fed to growing pigs, as-fed basis, Experiment 3¹.

¹Data are least square means of 10 observations for all treatments, except for SBM-CV with 0 FTU and FSBM and FFFSB with 500 FTU, which represent 9 observations.

²The basal endogenous loss (BEL) of P expressed as milligram per day was calculated by multiplying the basal endogenous loss (mg/kg DMI) by the daily DM feed intake (kg/d) of each diet.

⁴Values for the STTD of P were calculated by correcting values for the ATTD of P with the basal endogenous loss (i.e., 190 mg/kg DMI, NRC, 2012).

^a-dMeans within a row that do not have a common superscript differ, P<0.05.