PSI-7 Evaluation of Form of Supplement with or Without Ionophore on Stocker Steer Performance While on Bromegrass

Abstract

Abstract Cattle producers have a wide variety of supplements available to increase gains, extend forage, and balance for forage deficiencies; however, this becomes challenging with determining the correct supplement for a specific operation. Therefore, the objective of this study was to evaluate form of supplementation with or without the addition of ionophore on cattle gains while grazing bromegrass during the summer. Growing steers (n = 72; initial weight 245 ± 22 kg) were used in a 2 x 2 + 2 factorial treatment and grazed 18 bromegrass pastures from March through August. Factors include base form of supplement at two levels [pressed block (Mintrate) or hand-fed 50:50 corn:DDG blend offered 3x weekly at 0.25% BW] and ionophore at two levels (Rumensin; none or 90 g/ton). Other treatments were liquid supplement (Mix30) and control (free-choice mineral). Cattle were weighed at beginning and end of 150 d grazing period and every 28 d, with carcass ultrasound on d 150. Data was analyzed with ProcMixed (SAS v. 9.4, Cary, NC) with pre-planned contrasts. Hand-fed supplemented steers had greater ADG than steers on free-choice supplements (P = 0.05). Between d 56 and d 140 on grass, hand-fed steers had greater ADG than steers on the block treatment with liquid supplemented steers being intermediate (P < 0.10). Addition of ionophore did not result in differences in ADG (P = 0.43). There was not difference in ADG between steers that were supplemented or only received free-choice mineral (P = 0.48). Marbling score tended (P = 0.08) to be greater for control steers than all other supplemented. Backfat tended (P = 0.08) to be greater with hand-supplemented steers than steers on a free-choice supplement. Even though supplemented steers did not outperform non-supplemented steers during this project, there was gain advantages to hand-feeding supplement instead of a free-choice feed.