Effects of energy and/or mineral supplementation in combination with monensin on performance of steers grazing winter wheat pasture

¹ Department of Animal Science, Oklahoma Agricultural Experiment Station, Stillwater, OK 74078
² Department of Plant and Soil Sciences, Oklahoma Agricultural Experiment Station, Stillwater, OK 74078

^* To whom correspondence should be addressed. E-mail: gerald.horn{at}okstate.edu.

	Abstract

A 2-yr study was conducted during the 2004 to 2005 (YR1) and 2005 to 2006 (YR2) winter wheat grazing seasons to determine effects of supplementation strategies and delivery methods on supplement intake and growth performance of grazing steers (YR1: n = 253, initial BW 255 ± 25 kg; YR2: n = 116, initial BW 287 ± 14 kg). Five treatments were 1) negative control (NC), no supplemental nutrients; 2) free-choice, non-medicated mineral (MIN); 3) free-choice, medicated mineral with 1,785 mg monensin/kg mineral mixture (RMIN); 4) RMIN and soybean hulls (SH/RMIN); 5) a soybean hull-based energy supplement containing 165 mg monensin/kg (GRNGOLD). Energy supplements were hand-fed on alternate days (average daily intake = 0.91 kg/steer). Inclusion of monensin in the free-choice mineral mixture decreased intake of the mineral mixture by 63% in YR1 and 55% in YR2 when no other supplement was offered. Consumption of RMIN provided between 129 and 161 mg monensin/steer on average, while GRNGOLD provided 150 mg monensin/day. Compared to NC, MIN did not affect ADG in YR1 (P = 0.38) but increased (P = 0.01) ADG by 0.22 kg/steer in YR2. Conversely, ADG of RMIN steers was greater (P = 0.03) than MIN during YR1 (0.72 vs. 0.55 kg/steer) but not different (P = 0.35) in YR2. Providing supplemental energy increased ADG by 0.13 kg/steer (0.85 vs. 0.72 ± 0.053) in YR1, compared with RMIN, but no increase in ADG was observed in YR2. No difference (P > 0.24) was observed in ADG between SH/RMIN and GRNGOLD in either year. Conversion of the energy supplements was excellent in YR1, resulting in 1 kg of BW gain for each 3.1 kg of supplement consumed. However, due to smaller increases in ADG with the energy and monensin supplements in YR2, supplement conversion for YR2 averaged 17.6. The absence of a difference (P > 0.24) in ADG between steers that received SH/RMIN and GRNGOLD suggests that the method of delivery (separate packages vs. a single package) for energy, monensin, and mineral supplementation is not important.

Key Words: energy supplementation, mineral supplementation, monensin, wheat pasture