233 Inclusion of a multispecies fungal feed additive in forage-based diets fed to beef cattle: Effects on growth performance and ruminal fermentation

Abstract The objective was to evaluate the effect of adding a multispecies fungal feed additive (MFA; Aspergillus flavus, Aspergillus niger, Aspergillus oryzae) to forage-based diets fed to beef cattle on growth performance and ruminal fermentation. Experiment 1 evaluated the effect of supplementing Angus × SimAngus-crossbred steers n = 80; initial body weight (BW) = 370 ± 44 kg with varying doses of an MFA in a randomized complete block design. Steers were blocked by BW and housed in 8 feedlot pens (randomly assigned 2 pens per treatment) where a hay-based diet was fed for 122 d. The hay-based diet was offered with the inclusion of the MFA at 0.02, 0.04, and 0.08 % of the diet dry matter (DM), or without the inclusion of the MFA (CON). Steers were weighed at 28-d intervals. For experiment 2, ruminally cannulated Angus × SimAngus cows (n = 4; initial BW = 569 ± 21 kg) were used in a crossover design with two 21-d study periods to evaluate the effect of dietary inclusion of an MFA on in situ digestion and rumen metabolites. Treatments consisted of a forage-based diet with (WFA) or without (CON) the inclusion of the MFA. In situ digestion was evaluated on d 5, 10, and 20 throughout each period. In-situ bags were incubated in the rumen for 0 to 36 h, sampling every 4 h. On d 20, samples of ruminal fluid were collected to analyze short-chain fatty acids (SCFA) concentration. All data were analyzed using the PROC MIXED procedure of SAS. For experiment 1, a polynomial contrast was used. For experiment 2, the interaction between period and treatment was not significant (P 0.45). In Experiment 1, the final BW, average daily gain (ADG), and gain to feed ratio (G:F) changed cubically (P ≤ 0.04; Table 1) as dietary inclusion of the MFA increased. Steers supplemented with the MFA at a rate of 0.02% of the diet DM were heavier at the end of the 122-d study period and had the greatest ADG and G:F among treatments. No differences between treatments (P ≥ 0.37) were observed for dry matter intake. In Experiment 2, no treatment × time interactions and treatment effects were detected (P ≥ 0.17; Table 2) for the in-situ disappearance rate and degradation kinetics of the diet DM, neutral detergent fiber, and acid detergent fiber. In addition, MFA supplementation did not affect (P ≥ 0.13; Table 3) the SCFA profile and the total SCFA content in the rumen fluid. Results from these studies indicate that dietary inclusion of an MFA might be an effective alternative to increase the feed efficiency of beef cattle-fed forage-based diets. However, the precise mode of action warrants further investigations.