Document Type

Thesis - University Access Only

Award Date


Degree Name

Doctor of Philosophy (PhD)

Department / School

Animal Science


A method is described for the detection of monensin in bovine serum by HPLC. In serum, the HPLC method was linear in the range of 0.25 to 1 μg/ml. Two experiments were conducted to determine the location where monensin-Na (MON) stimulated satiety signaling process and to describe monensin effects on consumption behavior. Experiment 1 consisted of pre-dose, dose and post-dose phases. Treatments included: C) Control; R) 250 mg of MON injected into rumen; P) 125 mg MON infused into portal vein; and H) 3 mg MON infused into hepatic vein. There were four steers (BW = 414 ± 53 .1 kg) in the 4 x 4 Latin square design. MON caused greater suppression (P < 0.10) of DMI compared to Con dose day. Cumulative 12 h changes from pre-dose DMI for C, R, P and H were+ 17.9, -27.5, -14.7 and +3 .2 g/kg MBS respectively. In Exp. 2, 5 steers (BW = 374 ± 22.9 kg) were continuously dosed with MON in an ethanol carrier (8 ml/h) into either: C) the rumen, ethanol only (n=5); R) rumen at 10.4 mg MON/h (n=4); Pl) portal vein at 5.2 mg MON/h (n=3); or P2) at 10.4 mg MON/h (n=4). The experiment consisted of a pre-dose ( 4 d), dose ( 6 d) and post-dose (2 d) phases. Data were analyzed as a completely randomized design. Two steers that received P2 and 1 steer that received Pl had complete inhibition ofDMI within 24 hand dosing terminated within 86 h poststart of dosing. Monensin caused steers to consume greater percentage of daily DMI later in the day (P<0 .10) by d 5 and 6 and caused a difference (P<0 .10) in the distribution of episodes when steers consumed 15% or more of daily DMI within 1 h. Monensin did not reduce daily variation in DMI during d 2 to 4 compared to C but Rand Pl did (P<0.10) during d 5 and 6. Both rumen and portal vein exposure to MON altered consumption behavior. These results indicate that the satiety signal caused by MON is not exclusively a rumen phenomena.

Library of Congress Subject Headings

Beef cattle -- Feeding and feeds
Feed additives



Number of Pages



South Dakota State University