Effects of Increasing Soybean Meal in Corn-Based Diets on Effects of Increasing Soybean Meal in Corn-Based Diets on Growth Performance of Late Finishing Pigs Growth Performance of Late Finishing Pigs

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Effects of Increasing Soybean Meal in Corn-Based Diets on Growth Performance Effects of Increasing Soybean Meal in Corn-Based Diets on Growth Performance of Late Finishing Pigs of Late Finishing Pigs
Cover Page Footnote Cover Page Footnote Introduction Soybean meal (SBM) is a highly digestible and consistently produced protein source in swine diets that provides many essential AA for the pig. However, swine diets are often Kansas State University Agricultural Experiment Station and Cooperative Extension Service formulated to incorporate feed grade AA as a replacement for some SBM to reduce diet cost. As a result, late finishing swine diets may contain minimal quantities of SBM.
Typically, corn-based diets with feed grade AA can be formulated for late finishing pigs to meet individual AA requirements. However, there is evidence to suggest that beyond meeting individual AA requirements, late finishing pigs require at least 12 to 13% dietary CP to optimize growth performance. 3 Utilizing intact protein sources such as SBM to increase dietary CP may improve growth performance of late finishing pigs. Therefore, the objective of this experiment was to determine the ideal amount of SBM needed to optimize growth performance of finishing pigs from 220 lb to market when provided with corn-based diets.

Materials and Methods
The Kansas State University Institutional Animal Care and Use Committee approved the protocol used in this experiment. This study was conducted at a commercial research facility in southwestern Minnesota. The barn was naturally ventilated and double-curtained-sided. Each pen was equipped with a 4-hole stainless steel dry feeder and a cup waterer to allow ad libitum access to feed and water. Daily additions of feed to each pen were recorded through a robotic feeding system (FeedPro, Feedlogic Corp., Wilmar, MN).

Animals and diets
A total of 1,793 pigs (L337 × 1050, PIC, Hendersonville, TN; initially 231.2 ± 2.4 lb) were used in two groups with 22 to 27 pigs per pen and 12 to 14 pens per treatment (7 per trial). Pens of pigs were blocked by initial BW and randomly assigned to 1 of 5 dietary treatments in a randomized complete block design. Experimental diets were corn-based with feed grade AA. Soybean meal levels gradually increased from 5 to 20% in 3.75% increments and replaced feed grade AA. All diets were formulated using analyzed AA composition and assumed AA SID from the NRC 2 (Table 1). Diets were then formulated to be isocaloric and contained 0.70% SID Lys (Table 2). Dietary additions of feed grade AA were adjusted to ensure identical AA ratios between the two groups.
Pens of pigs were weighed and feed disappearance measured on d 0, 13, and 23 or on d 0, 14, and 35 for group one and two, respectively, to determine ADG, ADFI, and F/G. On d 13 and 21 of the experimental period for groups one and two, respectively, three pigs within each pen were marketed. The remaining pigs were then marketed at the conclusion of the experiment.

Statistical analysis
Data were analyzed using the GLIMMIX procedure in SAS (v. 9.4, SAS Institute, Inc., Cary, NC) and pen was considered as the experimental unit. The statistical model considered fixed effects of dietary treatment, linear, quadratic, and cubic contrasts, and random effects of group and block. Additionally, initial BW was utilized as a covariate in the statistical model. All data are reported as least square means and considered statistically significant at P ≤ 0.05 and marginally significant at 0.05 < P ≤ 0.10.

Results and Discussion
Overall, as dietary SBM increased in the late finishing period, pigs exhibited linear improvements in ADG (Table 3; P ≤ 0.001). Additionally, pigs exhibited a linear improvement in F/G (P < 0.001). There were no linear or quadratic responses on final BW of pigs (P > 0.05) Interestingly, not only were the improvements in overall ADG and F/G linear with increasing SBM, but a cubic response among overall ADG and F/G was also observed (P < 0.05). The greatest improvements in ADG and F/G were observed as dietary SBM increased from 5 to 8.75% and from 16.25 to 20%. Additionally, final BW of pigs tested cubic (P < 0.05) as SBM increased from 5 to 8.75% and from 16.25 to 20%, similar to the responses observed for overall ADG and F/G. We suspect that the observed response may be due to the increased Trp:Lys ratio of 21.6 in the 20% SBM diet compared to 20% in all other diets.
These results suggest that utilizing corn-SBM-based diets with increasing dietary SBM concentrations up to 20% resulted in improved growth performance of late finishing pigs. Moreover, in this experiment, increasing dietary CP up to 15% supplied by increasing SBM optimized the growth performance of late finishing pigs. However, further research is necessary to fully understand the cubic response observed in overall ADG, F/G, and final BW of late finishing pigs in this study.

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