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This Article Full Text Full Text (PDF) All Versions of this Article: jas.2007-0263v1 85/11/3090    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Abney, C. S. Articles by Galyean, M. L. Search for Related Content PubMed PubMed Citation Articles by Abney, C. S. Articles by Galyean, M. L.

Effects of ractopamine hydrochloride on performance, rate and variation in feed intake, and acid-base balance in feedlot cattle¹

C. S. Abney^*, J. T. Vasconcelos^*,2, J. P. McMeniman^*, S. A. Keyser^*, K. R. Wilson^*, G. J. Vogel and M. L. Galyean^*

^* Department of Animal and Food Sciences, Texas Tech University, Lubbock 79409-2141; and and Elanco Animal Health, Greenfield, IN 46140

² Corresponding author: judson.vasconcelos{at}ttu.edu

Two experiments evaluated effects of ractopamine hydrochloride (RAC) on performance, intake patterns, and acid-base balance of feedlot cattle. In Exp. 1, 360 crossbred steers (Brangus, British, and British x Continental breeding; initial BW = 545 kg) were used in a study with a 3 x 3 factorial design to study the effects of dose [0, 100, or 200 mg/(steer·d) of RAC] and duration (28, 35, or 42 d) of feeding of RAC in a randomized complete block design (9 treatments, 8 pens/treatment). No dose x duration interactions were detected (P > 0.10). As RAC dose increased, final BW (FBW; P = 0.01), ADG (P < 0.01), and G:F (P < 0.01) increased linearly. As duration of feeding increased, ADG increased quadratically (P = 0.04), with tendencies for quadratic effects for FBW (P = 0.06), DMI (P = 0.07), and G:F (P = 0.09). Hot carcass weight increased linearly (P = 0.02) as dose of RAC increased. Thus, increasing the dose of RAC from 0 to 200 mg/(steer·d) and the duration of feeding from 28 to 42 d improved feedlot performance, although quadratic responses for duration of feeding indicated little improvement as the duration was extended from 35 to 42 d. In Exp. 2, 12 crossbred beef steers (BW = 593 kg) were used in a completely random design to evaluate the effects of RAC [0 or 200 mg/(steer·d) for 30 d; 6 steers/treatment] on rate of intake, daily variation in intake patterns, and acid-base balance. To assess intake patterns, absolute values of daily deviations in feed delivered to each steer relative to the total quantity of feed delivered were analyzed as repeated measures. There were no differences (P > 0.10) in feedlot performance, urine pH, blood gas measurements, or variation in intake patterns between RAC and control cattle, but steers fed RAC had increased (P = 0.04) LM area, decreased (P = 0.03) yield grade, and increased (P < 0.10) time to consume 50 and 75% of daily intake relative to control steers. Our results suggest that feeding RAC for 35 d at 200 mg/(steer·d) provided optimal performance, and no effects on acid-base balance or variation in intake patterns of finishing steers were noted with RAC fed at 200 mg/(steer·d) over a 30-d period.

Key Words: ß-adrenergic receptor agonist • beef cattle • feed intake • performance • ractopamine