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Influence of Pretransit Zeranol Implant and Receiving Diet Protein and Urea Levels on Performance of Yearling Steers¹

US Department of Agriculture, Bushland, TX 79012 , Texas A&M University Center, Amarillo, TX 79106 , University of Tennessee, Knoxville, TN 37901 and and US Department of Agriculture, El Reno, OK 73036

Abstract

Two trials were conducted to determine the influence of preshipment zeranol implant and protein and urea levels of the feedlot receiving diet on the performance of yearling steers. In each trial, one-half of the steers were implanted with 36 mg of zeranol 30 d before shipment from El Reno, Oklahoma to Bushland, Texas. In trial 1, receiving diets were fed for 14 d and contained 10.6 (LP), 12.6 (MP), or 16.0% (HP) crude protein (DM basis). A fourth diet contained 10.8% protein with 7% of total N from urea (LPU). In trial 2, receiving diets were also fed for 14 d and contained 12.4 (MP) or 16.7% (HP) protein. Two other diets contained about 16% protein with either 15% HPMU) or 30% (HPHU) of total N from urea. After 14 d on the receiving diets, calves were fed a 70% concentrate intermediate diet for 7 d and were fed an 85% concentrate finishing diet until the end of both trials. Zeranol implants did not significantly affect marketing-transit weight changes, but increased (P<.05) daily weight gains at all time periods in both trials. In trial 1 on d 14 steers fed the HP diet tended (P<.10) to have faster gains and greater gain/feed than steers fed the LP and LPU diets, with steers fed the MP diet being intermediate. On d 56 of trial 2, steers fed the HP receiving diet for 14 d tended (P<.10) to have faster gains and had higher (P<.05) gain/feed than steers fed the MP and HPHU diets, with steers fed the HPMU diet being intermediate. Overall, performance from arrival to slaughter was not affected by protein or urea levels in the receiving diet.

¹ Contribution from USDA, Agricultural Research Service, in cooperation with The Texas Agr. Exp. Sta., Texas A&M Univ., College Station, TX 77843.

² USDA-ARS, Bushland, TX 79012.

³ Texas A&M Univ. Res. and Ext. Center, Amarillo, TX 79106.

⁴ Dept. of Anim. Sci., Univ. of Tennessee, Knoxville, TN 37901.

⁵ USDA-ARS, El Reno, OK 73036.

⁶ Mention of a trade name or product does not constitute a recommendation or endorsement for use by the USDA.