Evaluation of Black Soldier Fly larvae () as a protein supplement for beef steers consuming low-quality forage.

Black Soldier Fly larvae (BSFL; ) has been the focus of recent feeding trials in poultry, swine, and fish; however, in vivo research has not yet been conducted in cattle. Accordingly, a study was conducted to evaluate the effects of BSFL as a protein supplement in beef steers. Six steers (603 ± 20 kg of BW, = 3 and 404 ± 17 kg of BW, = 3) consuming King Ranch bluestem hay (6.55% dry matter [DM] crude protein [CP]) ad libitum were used in two simultaneous 3 × 3 Latin squares. Steers were provided one of three treatments each period: 1) a control with no supplement (CON), 2) a supplement comprised of conventional feed ingredients with whole cottonseed and soybean meal as the main protein sources (CONV), and 3) a supplement with BSFL as the main protein source (BSFL). Three 14-d periods were conducted with 8 d to adapt to treatments, 5 d to measure intake and digestion, and 1 d to complete a ruminal fermentation profile. DM, organic matter (OM), CP, neutral detergent fiber (NDF), and acid detergent insoluble ash were determined in forage, supplement, ort, and fecal samples. Protein supplementation as CONV or BSFL stimulated forage OM intake ( ≤ 0.01) relative to CON with a trend for a difference ( = 0.08) between the supplements such that CONV steers consumed more FOMI than BSFL steers. Treatment affected total digestible OM intake (TDOMI; ≤ 0.01); TDOMI for CON steers was 47.5 g/kg metabolic body weight (MBW) which was significantly less ( ≤ 0.01) than that of CONV or BSFL steers. Steers supplemented with CONV consumed significantly more TDOMI than BSFL steers ( 0.05; 62.2 vs. 60.1 g/kg MBW, respectively). Treatment did not significantly affect digestibility of DM, OM, or NDF ( 0.32). There was also not a significant effect ( ≥ 0.17) of treatment on ruminal ammonia-N, total volatile fatty acids, or ruminal pH. Overall, these data indicate that BSFL may be an effective protein supplement for beef cattle consuming low-quality forage.