Determining the preference and in situ digestibility of a microalgae co-product for beef cattle

Abstract Text: Two experiments were conducted to determine preference (Exp. 1) and in situ digestibility (Exp. 2) of dried, mechanically de-oiled, milled microalgae co-product (ALG) in beef steers.  In both experiments, 3 ruminally cannulated steers (998 ± 103 kg BW) and 4 treatments were utilized: 1) dry rolled corn-based diet (CON), 2) 15% ALG as a DM replacement of corn (ALG15), 3) 30% ALG (ALG30), and 4) 45% ALG (ALG45).  Exp. 1 was performed in a 3 × 6 Latin square design with six 5-d periods, and 6 paired diet combinations.  Steers were fed the CON diet for 3 d. On d 4 each steer was offered 2 diets, placed in either side of a bunk divider in- tubs.  Steer diet preference was determined based on DM disappearance for the 4-h immediately post-feeding.  On d 5, paired diets were again offered to each steer, on the opposite side of the divider.  Exp. 2 was conducted in a 3 × 4 unbalanced Latin square design with 3 diets fed each period and four 14-d periods.  Steers were limit fed at 2% of BW and adapted to diets for 12 d.  On d 13, dacron bags containing samples of dried and ground corn, soyhulls, or ALG were incubated in the rumen for 6, 12, 24, or 36 h to determine DM disappearance.  Data were analyzed using Glimmix and Mixed procedures of SAS for Exp. 1 and 2, respectively.  In Exp. 1, the proportion of total DM consumed by steers during the 4-h period was affected (P = 0.01) by the paired diet combination.  Intake of ALG45 was lesser (P ≤ 0.008) when offered in combination with the ALG15 or ALG30 diets, but not when offered with CON (P = 0.76).  No other paired diet combinations altered (P ≥ 0.23) DMI.  In Exp. 2, inclusion of ALG in the diet did not affect (P ≥ 0.12) rate of, or overall digestibility of, corn, soyhulls, or ALG (71.5 ± 0.83% DM disappearance for ALG at 24 h).  Additionally, DMI was linearly decreased (P = 0.05) as ALG increased in the diet due to lesser intake (P = 0.05) by ALG45 compared with CON, while ALG15 and ALG30 did not differ from CON (P ≥ 0.19).  In summary, steers readily consumed the microalgae co-product but preferred concentrations of less than 45% of diet DM under the conditions of these experiments.

Keywords: beef, digestibility, microalgae