The associative effects of sunflower straw, sunflower plate, sunflower seed shells associated with concentrate and alfalfa evaluated by using an in vitro gas production technique

This study aimed to evaluate the multiple-factor associative effects (AEs) of concentrate (C) to sunflower straw (SS) to alfalfa (A) ratios, concentrate to sunflower plate (SP) to alfalfa ratios, concentrate to sunflower seed shell (SSS) to alfalfa ratios at 40 : 60 : 0, 40 : 45 : 15, 40 : 30 : 30, 40 : 15 : 45, 40 : 0 : 60 and 30 : 70 : 0, 30 : 55 : 15, 30 : 40 : 30, 30 : 25 : 45, 30 : 10 : 60, 30 : 0 : 70, respectively, by using an in vitro gas production (GP) method. Thirty-three feed combinations and nine single feeds C, SS, A; C, SP, A; C, SSS, A were incubated respectively for 72 h in a GP tube. A total of 42 treatment combinations were tested, including 33 feed mix combinations [(5 + 6) × 3] and nine single raw materials, a total of 42 sample culture tubes. Each sample culture tube was repeated 20 times, totalling 840 (42 × 20) sample culture tubes. In this study, a total of 12 batches of in vitro culture tests were carried out. Seventy sample tubes and six blank tubes were cultured in each batch (eliminating systematic errors). A total of 912 sample culture tubes were used. The GP values of 0, 2, 4, 6, 9, 12, 24, 36, 48, 72 h were recorded. The GP parameters a, b, c, a + b were calculated by a single exponential equation. The AE values were calculated based on 72 h GP and weighted estimation value of 33 feed combinations. In the incubation fluid pH, ammonia nitrogen (NH3–N) and volatile fatty acids (VFA) after 72 h incubation were determined and dry matter digestibility (DMD), organic matter digestibility (OMD) were measured in the residue. The single-factor associative effects index (SFAEI) and multiple-factor associative effects index were calculated. The results indicated that groups 40 : 45 : 15 (C:SS:A), 30 : 25 : 45 (C : SS : A), 40 : 60 : 0 (C : SP : A), 40 : 45 : 15 (C : SP : A), 30 : 40 : 30 (C : SP : A), 40 : 45 : 15 (C : SSS : A), 40 : 30 : 30 (C : SSS : A), 30 : 25 : 45 (C : SSS : A) and 30 : 10 : 60 (C : SSS : A) had higher a, b, GP72h, NH3–N, DMD, OMD, moreover, higher SFAEI (the AE of GP72h, NH3–N, total VFA, DMD and OMD) than other groups (P < 0.05). It was concluded that the optimal feed combinations occurred when concentrate/sunflower straw/alfalfa ratios were 40 : 45 : 15 and 30 : 25 : 45; concentrate/sunflower plate/alfalfa ratios were 40 : 60 : 0, 40 : 45 : 15 and 30 : 40 : 30; concentrate/sunflower seed shell/alfalfa ratios were 40 : 45 : 15, 40 : 30 : 30, 30 : 25 : 45 and 30 : 10 : 60.