Effects of Wheat Middlings Inclusion, Grinding, and Carbohydrase Supplementation in Isoenergetic Diets on Growth Performance and Carcass Characteristics of Grow-finish Pigs

Abstract This study evaluated the response of grow-finish pigs to varying wheat middlings inclusion in isoenergetic diets and the potential of carbohydrase supplementation and wheat middlings grinding to improve nutrient digestibility. A total of 1,231 crossbred boars and gilts Pietrain × (Landrace × Large White); initial body weight (BW) 33.8 ± 4.14 kg were housed in 96 single-sex pens, blocked by BW, and randomly assigned to 4 dietary treatments, with 12-13 pigs/pen and 24 pens/treatment. Pigs were fed experimental diets for 89 d and weighed on d 0, 19, 40, 61, 77, and 89. Wheat middlings inclusion in growing diets (d 0-61) was 0.0, 6.0, and 12.0% (diets 3 and 4), and in finishing diets (d 61-89) was 0.0, 10.0, and 20.0% (diets 3 and 4). To maintain isoenergetic diets, diets 3 and 4 included 1.80% added animal fat in the growing phase and 1.40% animal fat plus 1.00% soybean oil in the finishing phase. Diet 2 was a 50:50 blend of diets 1 and 3. All diets, except diet 4, included wheat middlings grinding (average particle size 536 vs. 596 µm unground) and carbohydrase supplementation. Performance data were analyzed using a linear mixed model with treatment and sex as fixed effects and block as random effect. Carcass data were analyzed with treatment and sex as fixed effects, hot carcass weight as a covariate, and pen and marketing group as random effects. During the growing phase, pigs fed 12.0% wheat middlings had lower ADFI than those fed 0.0% (1.59 vs. 1.65 kg; P = 0.002). As no differences were observed in ADG, FCR improved (1.95 vs. 1.99; P = 0.001), regardless of grinding or carbohydrase supplementation. In the finishing phase, ADFI differed among treatments (2.16, 2.19, 2.10, 2.12 kg; P = 0.046), being lower in pigs fed 20.0% wheat middlings. Overall, high inclusion reduced ADFI by 3.6% (P = 0.008) without affecting final BW. High wheat middlings diets improved fat digestibility in both phases (P 0.001) and neutral detergent fiber digestibility in the growing phase (P 0.001) but reduced gross energy and organic matter digestibility in the finishing phase (P 0.001). Hot carcass weight was lower in pigs fed the highest inclusion compared with those fed diets without wheat middlings (92.2 vs. 93.7 kg; P = 0.006), with increased carcass leanness (64.1 vs. 63.6%; P = 0.007) and reduced backfat thickness (13.97 vs. 14.66 mm; P 0.001). In conclusion, at equal dietary energy, moderate wheat middlings inclusion (6-10%) had no effect on growth, feed efficiency, or carcass composition. High inclusion levels (12-20%) reduced feed intake, increased carcass leanness, and decreased fat deposition. Grinding and carbohydrase supplementation had no additional effects on performance or carcass characteristics.