Aiken, G. E.

Kerby, Joel L.

Nimr, Gary H.

Rouquette, F. M., Jr.

Tabler, S. F.

English

Texas A&M University

Ultrasonic Measures of Backfat Depth and Ribeye Area for Steers Grazing Rye-Ryegrass at Three Stocking Rates

Texas A&amp;M Repository

    PUBLICATIONS 2000 ULTRASONIC MEASURES OF BACKFAT DEPTH AND RIDEYE AREAFOR STEERS GRAZING RYE-RYEGRASS AT THREE STOCKING RATESG. E. Aiken, S. F. Tabler, J. L. Kerby, G. H. Nimr, and F. M. Rouquette, Jr.Background. Visual estimates of body condition scores (BCS) use degree of fatness topredict existing and future nutritional requirements for an array oflivestock class, sex, and functions.One of the most widely acceptable uses ofBCS is that for estimating r:eproductive·functi~n. Withrecent developments in ultrasound technology and computer software, real-time ultrasound has usein predicting carcass compositional traits, genetic selections, etc. A cooperative experiment betweenUSDA!ARS Booneville, Arkansas and TAMU-Overton was initiated to determine the effect ofstocking rate (SR) ofrye-ryegrass pastures on compositional traits ofsteers prior to feedlot fattening.Winter-born Angus x Brahman (AxB) and Simmental-sired steers from both AxB and Brahman xHereford dams were weaned late-Sep, backgrounded on pasture, hay, and supplement until initiationof grazing pastures in early Dec, 1998. Steers were scanned ultrasonically between the 12th and13th ribs at initiation and termination (May 12, 1999) from low (':-0), medium (ME), or high (ID)SR, 1.5,2.1, or 2.7 steers/acre, respectively. These scans allowed for estimates ofbackfat (BF) andribeye area (REA). Companion reports present pasture, feedlot, and carcass data.Researc~ Findings. Both BF and REA measures decreased linearlywith increasing SR Fig.I). Steers grazed on LO stocked pastures had more external fat and larger REA than steers whichgrazed at either ME or HI SR. This. negative linear relationship was expected since final bodyweights ranged from 1066 Ibs (LO). 904 Ibs (ME), and 701 (HI) stocked pastures. The moreimportant information was how BF compares with REA. An index-calculation that converts BF toa relative area basis (BF:REA) estimated BF at 8.6% (LO), 6.6% (ME), and 5.8% (ID) (Fig. 1).Steers on LO stocked pastures had more deposition ofBF relative to deposition oftissue in the REAApplication. The LO stocked pastures resulted in heavier steers with higher BCS whichsuggested these calves could be finished in the feedlot at a reduced number of days. Feedefficiencies in the feedlot, however, may compensate for reduced conditioning at the time offeedlotentrance. Implementation of stocking strategies requires estimates of gain, final weight, BCS,continued ownership, cost of gain on pasture vs feedlot costs per Ib gain, carcass quality, extent offinancial risk, etc. The use of ultrasound data can allow for better predictions of carcass attributesand information upon which to base management decisions.210.30 _--------------------------------,0.100.152BF = 0.4 - 0.1 SR; r = 0.890.050.25-.=.--- 0.20.c-Q.,~"C-.~..::.::CJC':==0.00 ...----or----------,....---------r-------12 _-------------------------------,- 10 •N .=.---C': 8~-.C':~>.6 •~.cQ24 REA = 13 - 2.4 SR; r2 =0.914--. ---------...,.---------......~------I3•21BF:REA = 19.0 - 9.5 SR + 1.7 SR2; R2 = 0.937958....~ 6=--.~ 10 _-------------------------------,fIlC':.cC':~-.C':~~.--C':~~Stocking rate (steers/acre)Fig. 1. Trends in backfat depth, ribeye area, and BF:REA (percentagebackfat relative to ribeye area) as stocking rate increases for rye-ryegrasspastures.22

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Ultrasonic Measures of Backfat Depth and Ribeye Area for Steers Grazing Rye-Ryegrass at Three Stocking Rates

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Texas A&M University

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Ultrasonic Measures of Backfat Depth and Ribeye Area for Steers Grazing Rye-Ryegrass at Three Stocking Rates

Abstract

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Full text

Available Versions

Texas A&M University

Texas A&amp;M Repository

Texas A&M Repository