Investigating the effects of direct-fed microbials on beef cattle during an acidosis challenge

Ruminal acidosis is a prevalent and costly metabolic disorder in beef feedlot cattle characterized by low ruminal pH and can lead to a multitude of health problems and poor animal performance. Direct-fed microbials (DFM) are naturally occurring microorganisms that can be used to improve rumen fermentation and alleviate nutritional disorders. The objective of this study was to investigate the effect of two DFM dosing strategies on beef cattle during an acidosis challenge model. Eighteen ruminally cannulated steers (BW = 328 ± 20 kg) were used in a randomized block design with 6 steers in each block. Two steers in each block were assigned to one of three treatments: blank media (NCON), a single strain of Megasphaera elsdenii at a minimum of 108 CFU per dose (DFM1), and a combination of Megasphaera elsdenii and proprietary microbial strains at 1010 CFU per dose (DFM2). Each block was fed for a period of 18 d. All treatments were dosed through the rumen cannula. On d 1, DFM1 was dosed once and DFM2 and NCON were dosed daily at 0700 on d 1-15. A basal diet (45% forage) was fed ad libitum on d 1-7. To induce acidosis, steers were fasted for 24 h on d 8 and were fed the challenge diet (10% forage) ad libitum on d 9-15. On d 16-18, all steers were fed the basal diet for the recovery phase. Ruminal pH was continuously measured on d 7-18 using an indwelling pH probe. Rumen fluid samples were collected before, during and after the acidosis induction. Data were analyzed as repeated measures using the MIXED procedure of SAS 9.4. Dry matter intake was not affected (P = 0.76) by treatment. However, a treatment × time effect (P = 0.04) was observed for ruminal pH on d 9, the initial day of the acidosis challenge. Administration of DFM2 resulted in greater (P < 0.05) ruminal pH at 17, 18, 19, and 24 h after feeding on d 9 compared with NCON and DFM1. In addition, ruminal lactate tended (P = 0.06) to be reduced by DFM2 when compared with NCON and DFM1. Within the rumen microbiome, alpha-diversity tended (P = 0.08) to be greater in NCON and DFM2 treatments than in DFM1. Bray-Curtis similarity, used to measure beta-diversity, indicated an effect of treatment (P < 0.01) and time (P < 0.01). Overall, results indicate the microbial treatment used in DFM2 may decrease the risk of acidosis in feedlot cattle.LimitedAuthor requested closed access (OA after 2yrs) in Vireo ETD syste