Effect of Time on Feed on Performance of Feedlot ...

Effect of time on feed on performance of feedlot steers, carcass characteristics, and tenderness and composition of longissimus muscles M. T. Van Koevering, D. R. Gill, F. N. Owens, H. G. Dolezal and C. A. Strasia J ANIM SCI 1995, 73:21-28.

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Effect of Time on Feed on Performance of FeedlotSteers, CarcassCharacteristics,andTendernessandComposition of LongissimusMuscles' M. T. VanKoevering2,D.

R. Gill, F. N. Owens3, H. G. Dolezal,and

Department of Animal Science, OklahomaState

University,Stillwater

C. A. Strasia

74078-0425

~~

ABSTRACT:

Two hundred fifty-six British and (329 kginiContinental crossbred yearlingsteers tially) were fed to study the effect of time on feed on live performance, carcass characteristics, tissue composition, andsteaktenderness.Steers were divided into four slaughter groups and fed for either 105, 119, 133, or 147 d. Daily gains (carcass weight-adjusted basis) increasedinaquadratic manner ( P < .05; maximum at 119 d ) , whereas feed intake tended to increase linearly ( P < .08) as cattle were fed longer. Feed conversion (carcass weight-adjusted basis) for steers fed 119 d was superior to that of steers fed for 147 d. Carcassweight, S.C. fat thickness,kidney, pelvic, andheartfat, overallcarcassmaturity, and yield grade increased linearly ( P < .01) with time on

feed. Marbling score andthe percentage of cattle grading U.S. Choice increased (linearly; P < .01) with time on feed but at a decreasing rate (quadratic; P < .05). Cholesterol andtotal lipid concentrationsin longissimus muscle increasedlinearly ( P < .O 1j as time on feed increased,whereas the percentage of protein and moisture tended to decrease linearly ( P < . l 0 and P < .O 1).Tenderness of ribeye steaks tended ( P < .07) withtime on feed, to increaselinearly primarily due to a linear decrease ( P < .03) in the percentage of steaks considered tough (shear force above 4.50 kg). Performance and carcass characteristics indicate that a feedlot finishing period of 119 to 133 is dideal for British Continental crossbred yearlingsteers (329 kg).

Key Words: FeedlotSteers,Cholesterol,Tenderness

J. h i m . Sci. 1995. 73:21-28

Introduction

150 to 180 d, Zinn et al., 1970b), after which animal age may have a greater influence, resulting in reduced tenderness. The objective of this study wasto evaluate the effects of different durations of feeding on animal performance, carcass quality, andtendernessand cholesterolcontent of ribsteaks.

Seasonal changes in feed and cattle costs usually dictate the length of time that cattle are fed. Longer feeding periods for cattle of a given starting weight typically increase final live weight, hot carcass weight, longissimuscross-sectional area, S.C. fat thickness, 1970a; yield grade,andqualitygrade(Zinnetal., Hicks et al., 1987; Dolezal et al., 1982). Some of these changesincrease the value of cattle;otherchanges decreasevalue.Increasesin S.C. fat thickness and yield grade arenot appealing to consumers. Additional quality factors include cholesterol content and tenderness of ribeye steaks. Tenderness increases with time on feed up t o some point (139 d, Epley et al., 1968;

Materials and Methods

Animals and Diets. Two hundred fifty-six crossbred steers (329 kg) were selected from a larger group ( n = 570) based on uniform size, weight, and breed-type. Steers visually appraised to possess greater than 25% Bos indicus or Anguscharacteristics were removed, of British x Continental leavingsteersprimarily breed-type. Steers were processed routinely ata commercial feedlot and implanted with an estrogenic implant (24 mg of estradiol;Compudose@, Elanco, Greenfield, IN). Upon arrival atPanhandleState University in Goodwell, OK steers were individually weighed, identified, and blocked into four weight groups based on initial weight.Sixteen steers from each weight group were assignedrandomly to pens

'Journal article no. 6421 of the Oklahoma State Agric. Exp. Sta., Stillwater 74078-0425. This research was supported by the Oklahoma Beef Industry Council. 'Feed Division, Farmland Industries, Dept. #57, P. 0. Box 7305, Kansas City, MO 64116. 3To whom correspondence should be addressed. Received November 12, 1993. Accepted September 7, 1994.

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VAN KOEVERING ET AL.

22

Table 1. Composition of diet dry matter Diet sequence Ingredient

2

1

3

4

Finala

70.20 10.00 10.00 4.00 5.80

82.20

%

Rolled corn Pelleted alfalfa hay Cottonseed hulls Cane molasses Pelleted supplementb

40.20 25.00 25.00 4.00 5.80

50.20 20.00 20.00 4 .OO 5.80

60.20 15.00 15.00 4.00 5.80

4.00

4.00 4.00 5.80

aCalculated composition (DM basis) from NRC (1982):11.904 CP; 1.77 mcal of NE,,'kg; 1.14 mcal NE /kg; .70% K, .54% Ca; ,3292 P. bSuppyement composition: cottonseed meal, 65.9%; calcium carbonate, 16.6%; urea, 9.49%; salt, 6.04%; dicalcium phosphate, 1.22%; vitamin A, D, E, .20%;manganese dioxide .02%. Half the cattlereceived , 0 3 7 ~ of their diet as P-hydroxy-@-methyl butyrate, which composed .52% of the supplement.

(eightsteersipen),and two pens from each weight group were assigned to each slaughter date before the trial began. One of each pair of pens was fed hydroxymethyl butyrate as discussed in another paper (Van Koevering et al., 1994). In total,eight pens (two from each weight group) were assigned to be fed 105, 119, 133, and 147 d. Steers had ad libitum access to a high-concentrate diet for the entirefeeding period. Cottonseed hulls and as roughage sources, were chopped alfalfa, used removed stepwise from the diet to adapt cattle to their final diet. Diet compositions and analyses are shown in Table 1. Steers were receiving their final diet by d 19 of thestudy. Steers were weighed directly off the truck; these initial weights were used for allocation. Weight gain and feed conversion were calculatedbased on this initial (shrunk) weight and final live weights (5 d before slaughter) as measured or as calculated from hot carcass weight /.6495. This calculation is based on the mean dressing percentage (64.95%) for all cattle based on final weight obtained 5 d before slaughter. A 5-d withdrawal period was required by the Food and Drug Administration for testing effects of hydroxymethyl butyrate. This presumably increased the dressingpercentage by about 1.8 percentage units. Net energy values were calculated for each treatment using the 1977 equation for yearling steers as reported by Hays et al. (1986). Steers were trucked to Dodge City, KS for slaughter. At slaughter, livers were examined for the presence and severity of abscesses. Plasma Sampling. Plasma was obtained 16 h after feeding 5 d before slaughter for each group. Plasma was collected in NazEDTA tubes and stored at -20°C until it was analyzed. Cholesterol concentrations were determined using Sigma Kit # 352 (Sigma Chemical, St. Louis, MO.).

CarcassDataandLongissimusMuscleSampling. Carcass data for all slaughter groups were obtained approximately 48 hpostmortem; yield andquality grades were determined (USDA, 1989).A 20-cm-thick section of the longissimus muscle ( LM) corresponding

to the 9th through 12th rib section was removed from the left side of each carcass; it was vacuum-packaged and shipped to the Oklahoma State University Meat Laboratory. These LM sections were aged at 2°C for 14 d postmortem, frozen ( -3O"C), and faced (uneven portion removed from the posterior end) before being fabricated into steaks for determining composition. A 1.3-cm-thick LM steak wasremoved from the posterior end of each LM section; it was denuded of exterior fat and epimysia1 connective tissue and stored for proximate analysis. Immediately anterior t o the steak used for proximate analysis, the remainingLM was cut into steaks 2.5 cm thick to be used for cholesterol analysis andshear force determination. LongissimusMuscleChemicalAnalysis. Samples were prepared in duplicate for chemical analysis by immersing themin liquidnitrogenand powdering them in a Waring Blendor (Model 34B122; Waring, New Hartford, CT). The duplicate frozen 3-g samples of powdered LM were subjected t o proximate analysis according to procedures outlined byAOAC (1984). Cholesterol content of duplicatesampleswasdetermined through a procedure described by Lepage and Roy (1986).

Longissimus Muscle Cooking Properties and Shear Force. Cooking properties and shear force determinations were conducted as described by the AMSA (1978j . To determineshear force, LM steaks were thawed at 2°C for 24 h, trimmed of S.C. fat, weighed, and broiled on an open hearth broiler (Faberware, Bronx, NY) to a final internal temperature of 70°C. Cooking time(minutes/100 g of raw steak) and cooking shrinkage(percentage weight loss) were calculated for each steak. Steaks were allowed to cool to 25"C, after which six cores (1.27 cm in diameter) were removed parallel to the direction of the muscle fibers. Each core then was individually sheared crossways usingaInstron Model SD-50 WarnerBratzlershearapparatus(Instron,Canton, MA) to determinethe peak force. Data Analysis. Beta-hydroxy-P-methyl butyrate ( HMB) , a metabolite of leucine, was beingincluded in

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23

TIME ON FEED

Table 2. Effects of days on feed on performance of feedlot steersa Observed significance level ( P andQ responses ( P < .08). In contrast, Miller et al. (1987) detected no increasein lean,skeletal, or overall maturity when cattle were fed for up to 168 d. When overallcarcass maturity was adjusted for fat thickness, the effect of slaughter group became cubic ( P < .04); this response is difficult to explain. The percentage of condemned livers was not affected by slaughter group; this is similar to the findings of Hicks et al. ( 1987) for steers fed a comparable length of time. When time on feed is extended, marbling score and percentage of cattle grading Choice or greater generally increase (Dolezal et al., 1982; Miller et al., 1987; May et al., 1992). In our study, marbling scores and the percentage of cattlegrading Choice (Table 4) increased (L; P < .01) across slaughter group, but the valuesreachedmaximum a at less than 147 d; consequently, we detected a Q ( P < .02) response. Steers fedfor 105 dhad lower ( P < .05) marbling scores and fewer ( P < .05) steers grading Choice than of steers otherslaughtergroups.Thepercentage grading Select and Standard decreased ( L ; P < .O 1) with increased time fed. Steers used by Hicks et al.

(198 7) were of a breed-type and had weights and slaughter dates similar to those of steers in our study; our results were similar to theirs for marbling score and percentage of Choice cattle. When marbling scores were adjusted for fat thickness, marbling scores were greatest ( P < .05) for steers fed between 119 and 133 d. Steers in our population, similar to those of Hicks et al.(19871,continued to deposit fat subcutaneously, butthey did not deposit an increased amount of intramuscular fat after 133 d on feed. When marbling scores were adjusted for S.C.fat thickness, no advantage from feeding steers more than 119 was d detected. Thus,steersin bothstudiesmayhave reached their geneticpotential to grade Choice between119and133d.Thisagreeswithresults of Williams et al. (1989) in which steers fedfor 112 d had similar quality grades as those fed for 140 d. This point of optimum marbling may vary with genetics andmature size.

Chemical Composition

of Longissimus Muscle.

Chemical compositions of blood andthe LM are concentrations presented in Table 5 . Cholesterol (milligrams/deciliter)inplasma increased (L; P < .01)with time on feed; steers fedfor 105 d had the lowest ( P