Performance and Carcass Characteristics of Feedlot Steers: Effects of Delayed Implanting and Programmed Feeding During the Growing Period1

Professional Animal Scientist, Apr 2004 by Scaglia, G, Greene, L W, McCollum, F T III, Cole, N A, Montgomery, T H

Abstract

This experiment was conducted to determine the effect of programming the rate of gain and delaying the first implant in feedlot steers on feedlot performance and carcass characteristics. Ninety-six growing steers (269 � 16.2 kg) were assigned to 12 pens in a completely randomized design. Treatments were implant (Synovex-S�; 20 mg estradiol benzoate and 200 mg progesterone; Fort Dodge Animal Health, Overland Park, KS) on d 1 or no implant and programmed feeding to gain at a slow (0.68 kg/d) or fast (1.14 kg/d) rate during the growing period; these treatments were randomly assigned (n = 8) to pens of steers in a 2 � 2 factorial arrangement. Steers were fed a growing diet and after 88 and 60 d (for steers fed to gain at a slow or fast rate, respectively), steers were transitioned to ad libitum consumption of a high concentrate finishing diet. Growing period implant treatments did not affect ADG but did affect (P

(Key Words: Steer, Rate of Gain, Implant, Carcass Characteristics.)

Introduction

Anabolic growth agents are routinely used in beef cattle to increase growth efficiency, feed conversion, protein deposition, carcass weight, Longissimus area, and carcass yield and to decrease production costs (Montgomery et al., 2001). Managing feed intake by restriction or programmed feeding for specific rates of gain may yield performance advantages to beef cattle feeders (Galyean, 1998). In addition, increasing pressures on beef cattle feeders to meet environmental standards may increase the use of feed intake management techniques as a means of altering nutrient excretion and manure loads from confined feeding operations. The use of restricted intake or programmed feeding as a best management practice has the potential to reduce the cost of production (Galyean, 1998). This application is especially attractive when roughage, or pasture costs, or both are high or when pasture is unavailable. Programmed feeding of high concentrate diets has been particularly useful for small- to medium-framed cattle as a means of adding carcass weight at harvest (Loerch and Fluharty, 1998). Simplifying bunk management, avoiding overconsumption of feed when starting cattle on feed, improving feed efficiency, and decreasing manure loads are among the factors that give restricted or programmed feeding the potential to decrease costs. Feeding high concentrate diets at less than ad libitum intake can decrease feed waste and improve feed efficiency (Hicks et al., 1990; Galyean, 1998; Loerch and Fluharty, 1998).

The objective of this experiment was to determine the effects of management strategies (time of implant and programmed feeding for slow or fast rate of gain) used during the growing period on subsequent feedlot performance and carcass characteristics at harvest.

Materials and Methods

Two hundred and thirteen British � Continental steers (average BW = 195 �11 kg; approximate age = 8 mo) were received at the James Bush Research Farm, Texas Agricultural Experiment Station, in Bushland, Texas. (Forty-two bulls were castrated upon arrival.) Approval for animal use was provided by the Cooperative Research, Education, and Extension Triangle Animal Care and Use Committee of the Texas A & M University Agricultural Research and Extension Center (Amarillo); USDA-ARS (Bushland), and West Texas A & M University. all steers were provided a metaphylaxis treatment with Micotil� (tilmicosin; Elanco Animal Health, Indianapolis, IN) for bovine respiratory disease upon arrival. Liquamycin LA-200� (oxytetracycline; Pfizer Animal Health, New York, NY) was used as a second antibiotic if followup treatment was required. all steers received Ivomec� (ivermectin; Merial, Duluth, GA) and were vaccinated with Bovishield 4� (IBR, BVD, PI3, BRSV; Pfizer, Newark, NJ) and 7-way Clostridial� (Merial). Horns were tipped, and steer BW was obtained upon arrival. Steers were revaccinated 10 d after arrival. Steers grazed on a dormant short grass prairie pasture and were supplemented with 0.84 kg (DM basis) of pelleted canola meal per steer three times a week for 92 d before the start of the experiment. On January 26, 96 steers (average BW = 269 � 16.2 kg) were randomly selected and transported 5 km to the Texas Agricultural Experiment Station/USDA-ARS Experimental Feedlot in Bushland. Steers were assigned to 12 experimental pens in a completely randomized design (8 steers per pen) and were fed a grower diet (Table 1). Three steers died within the 1st mo in the feedlot because of complications attributable to pneumonia and were not replaced.

Pens of steers were randomly assigned to one of two implant treatments, implant (Synovex-S�; 20 mg estradiol benzoate and 200 mg progesterone; Fort Dodge Animal Health, Overland Park, KS) on d 1 of the growing period or no implant, and two programmed feeding management strategies during the growing period, fed to gain at a slow (0.68 kg/d) or fast (1.14 kg/d) rate (NRC, 1996) in a 2 � 2 factorial arrangement of treatments. From d 1 to 88 (for steers fed at the slow rate of BW gain) and until d 60 (for steers fed at the fast rate of BW gain), the amount of feed offered to steers was increased at 7-d intervals to account for changes in NE^sub m^ and NE^sub g^ requirements. Using the NRC (1996) model and assuming an increase in BW as expected (0.68 and 1.14 kg/d for slow and fast rate of gain), projected DMI was calculated, and that amount was fed for the following 7-d period.