Evaluation of increasing digestible threonine to lysine ratio in corn-soybean meal diets without and with distillers dried grains with solubles on growth performance of growing-finishing pigs.

Corn distillers dried grains with solubles (DDGS) is commonly available and often can lower diet cost for swine diets. This corn co-product is recognized to be a source of dietary insoluble fiber, which can not only increase the villous length of the gut mucosa but also increase intestinal production of mucin. Mucin structure, functions, and synthesis are correlated to Thr intake; consequently, the dietary Thr level may need to be increased when feeding an insoluble fiber source such as corn-DDGS. Thus, the objective of this study was to evaluate if feeding standardized ileal digestible (SID) Thr:Lys ratio at or above the estimated requirement in diets without and with DDGS would influence growth performance in finishing pigs. A total of 2,160 pigs (PIC 337 × 1,050; initially 35.1 ± 0.5 kg) were used in a 112-d growth trial. Pigs were randomly assigned to pens (27 pigs per pen) in a randomized complete block design by body weight (BW) with 20 replications per treatment. Pens of pigs were allotted to one of four dietary treatments that were arranged in a 2 × 2 factorial with main effects of dietary Thr level (normal vs. high) and DDGS (without or with). Treatment diets were formulated in four phases from 34 to 57, 57 to 79, 79 to 104, and 104 to 130 kg BW. Diets with high DDGS were formulated to include 40% DDGS in phases 1 and 2, 30% in phase 3, and 15% in phase 4. The normal Thr diets were formulated to contain 61%, 62%, 63%, and 65% SID Thr:Lys ratios for the four dietary phases, respectively. High Thr diets had SID Thr:Lys ratios of 67%, 68%, 69%, and 72%, respectively. There were no interactions ( > 0.10) observed in any phase or overall between Thr level and added DDGS. For the overall period (day 0 to 112), pigs fed diets without DDGS had increased ( < 0.001) average daily gain (ADG) but reduced ( < 0.001) average daily feed intake (ADFI), leading to increased ( < 0.001) feed efficiency (gain-to-feed ratio [G:F]). There was no evidence for difference ( > 0.10) between pigs fed diets formulated at normal or high SID Thr:Lys ratio. In summary, feeding high levels of DDGS decreased ADG and increased ADFI, which resulted in decreased G:F and lower final BW, regardless of the dietary SID Thr:Lys ratio level. In the current study, increasing the level of digestible Thr in a diet that contained a highly insoluble fiber source did not increase the growth performance of grow-finish pigs.