Monensin effects on digestibility, ruminal protein escape and microbial protein synthesis on high-fiber diets

Faulkner, D.B.; Klopfenstein, T.J.; Trotter, T.N.; Britton, R.A.

Journal of Animal Science 61(3): 654-660


ISSN/ISBN: 0021-8812
PMID: 2999053
DOI: 10.2527/jas1985.613654x
Accession: 001411634

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The influence of monensin 0, 6.1, 12.2, 18.3 or 36.6 mg/kg on diet fibre digestibility, microbial protein synthesis and ruminal escape of dietary protein was evaluated in 2 steer metabolism trials. A growth trial was made to study possible interactions of forage quality and monensin level. In metabolism trial 1, four steers with rumen cannula were assigned to 4 monensin levels in a 4 x 4 Latin square design to measure fibre digestibility, rate of passage and protein metabolism. In metabolism trial 2, five steers with duodenal cannula were assigned to 5 monensin levels in a 5 x 5 Latin square design to measure fibre digestibility, bacterial N flow and plant N flow. In the 2 metabolism trials, the level of monensin influenced organic matter (OM) digestibility, neutral detergent fibre (NDF) digestibility and ruminal NDF digestibility quadratically, with the intermediate levels of monensin being superior to the high level of monensin or no monensin. A quadratic increase in particulate disappearance rate (P = 0.09) and no effect (P = 0.95) on liquid disappearance were also observed in trial 1. In trial 1, monensin level quadratically decreased (P = 0.10) the bacterial protein concentration and increased (P = 0.02) the ratio of total N:diaminopimelic acid in whole rumen contents. In trial 2, no overall difference in duodenal N flow (P = 0.64) or flow of individual amino acids (P = 0.46) was observed. In the growth trial, no interaction of maize stalk quality and monensin was observed (P <0.38). Monensin linearly decreased feed intake (P = 0.09) and quadratically affected daily gain (P = 0.03) and feed/gain (P = 0.07). The 100-mg level, which corresponds to the 18.3-mg/kg level in the metabolism trials, was superior to the 0- or 200-mg level in this trial (P = 0.07).