Monensin Supplementation Levels Effects on Rumen Fluid and Blood Parameters of Steers Receiving Warm-Season Grass

Abstract Text: Variable effects of monensin on performance of beef cattle grazing warm-season grasses have been reported in the literature. Lack of response is generally associated with low levels of monesin; thus increasing monesin levels on the animal diet may be an effective management approach to improve its efficiency and positive effects on beef cattle performance. The objective of this study was to evaluate the effects of levels of monensin on rumen fluid and blood parameters of beef steers (Bos sp.) receiving warm-season grass. The experiment was conducted in Ona, FL from July to September 2013. Treatments were three levels of monensin, 10, 20, and 30 ppm and control (no monensin) tested in a 4 × 4 latin square with 10 d adaptation period and 5 d of rumen fluid collection and total DM intake evaluation. Blood samples were collected on d 4 and 5 of the collection period. Ground stargrass (Cynodon nlemfuensis) hay (9% CP, 51% IVDOM) was offered daily and adjusted to allow 10% refusals. The steers received 0.4 kg of a concentrate supplement (14% CP and 78% TDN) daily. Total DM intake was similar among treatments (P = 0.64, mean = 2.0% BW). There was a linear increase (P < 0.01) in propionic acid concentration in the rumen (from 16.9 to 19.4 mol/100 mol) with increasing levels of monensin; however, there was no effect of monesin levels on pH (P = 0.19, mean = 6.6), acetic acid (P = 0.14, mean = 72.3 mol/100 mol), isobutyric acid (P = 0.47, mean = 0.73 mol/100 mol), butyric acid (P = 0.83, mean = 8.3 mol/100 mol) and NH4-N (P = 0.53, mean = 6.8 mg/dL). In addition, there was no effect of monensin levels on blood glucose (P = 0.75, mean = 62.0 mg/dL), insulin (P = 0.82, mean = 3.5 uIU/mL), IGF-1 (P = 0.73, mean = 12.4 ng/mL), and blood urea nitrogen (P= 0.83, mean = 26.4 mg/dL). Increasing levels of monensin alone may not be effective to increase performance of beef cattle receiving warm-season grasses with limited nutritive value.

Keywords: ionophore, monensin, warm-season grasses