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Feeding dried distiller grains with solubles (DDGS) to immunologically castrated pigs
Improvest (gonadotropin releasing factor analog - diphtheria toxoid conjugate; Zoetis, Inc., Florham Park, NJ) is a temporary method of immunological castration (IC) in pigs, which captures advantages of lean gain efficiency of boars, while eliminating boar taint in carcasses. Feeding diets high in DDGS to barrows and gilts generally reduces pork fat quality with minimal effects on growth performance. Studies evaluating feeding DDGS to IC pigs are limited. At 8 weeks of age (WOA), entire male pigs (n = 863; initial BW = 21.5 kg) were weighed and randomly assigned to dietary treatments and harvested at 9 (TD9), 7 (TD7), or 5 (TD5) weeks post-second dose of Improvest in a 4 x 3 factorial arrangement (n = 8 pens per treatment). A 4-phase feeding program (phase 1 = 3 weeks, phases 2 and 3 = 4 weeks each, phase 4 = 5 weeks) was used for each dietary treatment: positive control (PCon; 0% DDGS in all phases), DDGS step down (SD; 40%, 30%, 20%, and 10% DDGS in each phase, respectively), DDGS withdrawal (WD; 40% DDGS in phases 1 to 3 and 0% DDGS in phase 4), negative control (NCon; 40% DDGS in all phases). The first Improvest dose was administered at 11 WOA, while the second Improvest dose was administered at 15, 17, or 19 WOA. All pigs were harvested at 24 WOA. A subsample of pigs (n = 2 /pen) were selected for harvest and lean and fat quality assessment. Overall G:F was improved (P ≤ 0.05) in TD5 pigs compared with TD9 pigs (0.428 vs. 0.413 ± 0.005). Pigs fed PCon and SD had improved (P ≤ 0.05) G:F compared with WD and NCon (0.427 and 0.424 vs. 0.414 and 0.413 ± 0.005). Backfat thickness at the 10th rib was greater (P ≤ 0.05) in TD9 and TD7 pigs compared with TD5 pigs (1.83 and 1.82 vs. 1.67 ± 0.05 cm, respectively). Harvest time post-second Improvest dose did not affect lean quality of the longissimus muscle. However, subjective firmness scores of loins from pigs fed PCon were greater (P ≤ 0.05) compared with loins from pigs fed WD and NCon (2.60 vs. 2.28 and 2.24 ± 0.12, respectively). Improvement in G:F occurred independently of diet and harvest time post-second dose of Improvest, and diet and harvest time post-second dose of Improvest had minimal effects on lean quality.
Keywords: dried distillers grains with solubles, growth, Improvest