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Post-Weaning Nutritional Management Affects Feedlot Performance, 12th Rib Fat, andMarbling Deposition of Angus and Wagyu Heifers

A. E. Wertz1, L. L. Berger1, D.B. Faulkner1, F. K. McKeith1, S. Rodriguez-Zas1 andP. M. Walker2

1 University of Illinois, Urbana; 2 Illinois State University, Normal

SUMMARY

Twenty-four heifers, 12 Angus and 12 Wagyu-cross (1/2 Wagyu, ½ Angus) were weaned at 180 dof age and grown on endophyte-infected tall fescue for 16 months prior to entering the feedlot.An additional 20 head of heifers, 11 Angus and 9 Wagyu-cross (1/2 Wagyu, ½ Angus) were early-weaned (140 d of age) and immediately adjusted to a high concentrate diet. Heifers wereindividually fed using Calan® gate-equipped bunks, which allowed feed efficiency to becalculated for each heifer. Serial ultrasound measurements of 12th rib fat and marbling wererecorded at 50-60 d intervals for Angus-sired and Wagyu-sired heifers during feedlot finishing.Regression equations of marbling and 12th rib fat deposition over time were developed usingserial ultrasound measurements. Serial ultrasound data and individual feed efficiency data werecombined to evaluate the relationship of marbling, 12th rib fat and feed efficiency during thefinishing period. As 2-year-olds, Angus and Wagyu heifers performed similarly in the feedlot.However as yearlings, Wagyu heifers gained less efficiently (P < 0.01) than Angus heifers.Twelfth rib fat of 2-year-old heifers increased linearly (P < 0.01) with increased days in thefeedlot. In contrast, 12th rib fat for yearling heifers behaved quadratically (P < 0.01) over time inthe feedlot. Twelfth rib fat was thicker for Angus 2-year-old heifers relative to Wagyu 2-year-olds. However, differences in 12th rib fat that resulted from breed were not significant foryearling heifers. Marbling scores increased quadratically (P < 0.01) for 2-year-old heifers.However, marbling score increased linearly (P < 0.01) for yearling heifers. The pattern of fatdeposition appeared to differ between heifers that were early-weaned and immediately fedconcentrate and heifers that were grazed on endophyte-infected tall fescue 16 months prior tofeedlot finishing. Both yearling and 2-year-old Wagyu heifers had a higher marbling scoreintercept than their Angus counterparts. Additionally, yearling heifers had greater fat extractionvalues than 2-year-old heifers, which indicated yearling heifers might have had a higher degreeof marbling than 2-year-old heifers. Early-weaned heifers immediately adjusted to concentrateproduced a more industry-acceptable carcass than 2-year-old heifers. Yearling hot carcassweights were within industry standard range (250-340 kg), with less 12th rib fat but morechloroform:methanol-extractable fat in the longissimus dorsi muscle. Additionally, yearlingheifers produced less physiologically mature carcasses. Overall, ultrasound technologyunderestimated 12th rib fat and marbling score for Angus and Wagyu yearling and 2-tear-oldheifers.

INTRODUCTION

Palatability is the major factor that drives human consumption of beef. Tenderness, juiciness, andflavor determine the palatability of beef. Although intramuscular fat accounts for a small

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amount of the variation in tenderness, it is closely correlated to the juiciness and characteristicflavor of beef (Horstein et al., 1987).

Fat cell commitment and proliferation occur early in life, while the deposition of fat into thesecells occurs as the animal matures. Smith et al. (1984) suggest that the primary substrate neededfor intramuscular fat deposition is glucose which differs from the use of acetate to synthesizesubcutaneous fat. Grain-fed cattle produce a greater proportion of propionate, a glucoseprecursor, than forage-fed cattle. As a result, it is hypothesized that feeding grain to cattle earlyin life may stimulate the onset of marbling. In support of this theory, Myers et al. (1999b)reported a greater percent of steers weaned at 117 d of age and immediately adjusted to a highconcentrate diet to grade USDA average choice or better than steers grazed on pasture for 82 dprior to entering the feedlot. Additional research conducted by Myers et al. (1999a)demonstrates a similar improvement in the percent of early-weaned (177d) steers that gradeUSDA average choice or better when compared to normally weaned steers grown on pastureprior to feedlot finishing. Research conducted by Loy et al. (1999) demonstrates that Simmentaland Angus steers weaned at 67 d of age and fed concentrate diets until slaughter have highermarbling scores and greater percentage of carcasses that grade USDA choice or prime than steersweaned at 147 d. In addition to improvements to carcass quality, early-weaning steers andimmediately feeding concentrate diets results in improved average daily gains and feedefficiency (Myers et al., 1999a, Myers et al., 1999b). Myers et al. (1999c) further demonstratesthat as age at weaning decreases from 215 d to 90 d, average daily gain and feed efficiencyimprove linearly.

Lunt et al. (1993) reported that American Wagyu steers (Japanese black, and Japanese brown,crossed with Angus and Hereford) to have a greater potential to marble relative to their Anguscontemporaries. Myers et al. (1999a) reported a greater percent of half-blood Wagyu steercarcasses to grade USDA average choice or better when compared to continental crossbred steersfed to the same fat endpoint. Additionally, although Myers et al. (1999a) reported a similarpercent of British crossbred and Wagyu crossbred steer carcasses to grade USDA average choiceor prime, fewer Wagyu carcasses were classified USDA yield grade 3. Further researchconducted by Myers et al. (1999b) supports the premise that Wagyu steers have higher marblingscores and a greater percentage of carcasses that graded USDA average choice or better thanBritish and Continental crossbred steers. Furthermore, Rouse et al. (1999) reported that 351 kgAngus-Wagyu crossbred steers fed concentrate for 97 d have intramuscular fat sufficient to gradeUSDA low choice. In support of this data Cianzio et al. (1985) concludes that the number ofadipocytes/gram of intramuscular tissue is a better predictor of marbling than cell diameter. Dataof May et al. (1994) indicates that intramuscular adipocytes of Wagyu steers are smaller indiameter than those of Angus steers. However, Wagyu steers have numerically moreadipocytes/gram of tissue (May et al., 1993). This in accordance with Cianzio et al. (1985)suggests that Wagyu steers have higher marbling scores. In addition to carcass quality,performance is also affected by Wagyu breeding. Myers et al. (1999a) reported that early-weaned Wagyu steers gain slower and tend to be less efficient in their gain than British crossbredsteers.

This trial is designed to evaluate the effects of Angus and Wagyu breeding on feedlotperformance and the deposition of marbling and rib fat for heifers managed differently post-

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weaning. Additionally, these data were used to relate feed efficiency to marbling and rib fatdeposition.

MATERIALS AND METHODS

The objectives of this trial were three-fold. 1) to evaluate the feedlot performance of Angus andWagyu heifers managed differently post-weaning to slaughter, 2) to establish, through the use ofultrasound technology, prediction equations for marbling, 12th rib fat, and feed efficiency ofAngus and Wagyu heifers over a range of ages and body compositions. 3) to evaluate therelationship of marbling score and 12th rib fat to feed efficiency as well as the relationship ofmarbling to 12th rib fat.

Twenty-four heifers, twelve Angus and twelve ½ Wagyu x ½ Angus were weaned (200 d) andgrazed on endophyte-infected tall fescue for 16 months. Following the 16-month growingperiod, heifers were transported to Illinois State University where they were adjusted to finishingration (Table 1). These heifers were 22 months of age upon entering the feedlot and are referredto as 2-year-old heifers throughout this document. An additional twenty-four yearling heifers, ofthe same genetics, were early-weaned at five months of age and immediately adjusted to an 80%concentrate ration. Yearling heifers were maintained on this diet for four months and thentransported to Illinois State University and immediately adjusted to a finishing ration (Table 1).These heifers were nine months of age upon entering the feedlot and are referred to as yearlingheifers throughout this document. One Angus yearling and three Wagyu yearlings were removedfrom trial. Two-year-old heifers were implanted with Finaplex-H and yearling heifers wereimplanted with Synovex-C at initiation of the trial.

Four heifers were assigned to each of 12 pens so that all breed-age combinations wererepresented within pen. Heifers were individually fed using Calan® gate-equipped bunks andheifers were weighed at 21-d intervals. Dry matter intakes and feed refusals were recorded on adaily basis and individual animal feed efficiency was calculated using these data. As a result of aconflicting trial, 2-year-old heifers were fed on an individual basis for 125 d and pen-fed from d126 to slaughter at 218 d on feed. Dry matter intakes for individual heifers during the pen-fedperiod were estimated by calculating the percent each animal consumed relative to its pen-matesduring the last individual feeding period (d 105-125). This percentage was then multiplied bytotal pen consumption to yield an estimated intake for each animal in the pen during the pen-fedperiod. Yearling heifers were individually throughout the 216 d of the feeding trial and pen-fedfrom d 217-238 during which time an ultrasound measurement was recorded. It was necessary topredict dry matter intake for the purpose of establishing regression equations for feed efficiencyat the time of the final ultrasound measurement. Individual dry matter intake was estimated foryearling heifers by calculating the percent each animal consumed relative to its pen-mates duringthe last individual feeding period (d 190-216). Pen dry matter intake at the time of ultrasoundmeasurement was multiplied by this percent to estimate individual dry matter intake for the finalperiod.

Real-Time (Linear Array) ultrasound was used to monitor rib fat and marbling deposition overthe course of the feedlot-finishing period. Alkoa® 500V ultrasound equipment with Alkoa®

UST-5049-3.5 transducer was used to record an image of the longissimus dorsi, its marbling and

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surrounding fat. Images were interpreted using the CVI Scan Session reporting Version 6.2b incombination with Rib-O-Matic Version 3.01 software. Ultrasound measurements recorded atfour times during the feeding period were used to develop regression equations for 12th rib fatand marbling score. Ultrasound measurements for the 2-year-old heifers were recorded at 44,101, 155, and 211 d in the feedlot and actual carcass measurements were recorded at slaughter(218 d in the feedlot). Ultrasound measurements for the yearling heifers were recorded on 44,101, 187, and 230 d in the feedlot. Yearling heifers were slaughtered at 238 d in the feedlot andfinal carcass measurements were recorded at this time. Carcass characteristics were recorded atslaughter and fat extraction was performed on longissimus dorsi samples to validate grader-called marbling scores (Brackebusch et al., 1991). Intermuscular fat and surroundingsubcutaneous fat were removed from the longissimus dorsi muscle and the muscle washomogenized. Duplicate 5-g samples were dried and repeatedly washed withchloroform:methanol in accordance with the procedures of Riss et al. (1983).

Heifers were slaughtered when it was estimated that approximately 50% of each age groupwould grade low prime or better. Consequently, 12th rib fat was greater for the 2 year-old heiferscompared to the yearling heifers. Therefore yearling and 2-year-old heifer data were statisticallyanalyzed separately with individual animal as the experimental unit. Performance and finalcarcass parameters were analyzed using the General Linear Models procedure of SAS® (SAS,1989). Differences in parameter means that resulted from breed were separated using the LeastSquared Means procedure of SAS® (SAS, 1989). Ultrasound measurements of marbling and ribfat deposition were analyzed as repeated measures in time using the Mixed procedure of SAS®.Marbling and 12th rib fat regression equations were established using the linear and quadraticterms for the effects of days on concentrate. Additionally, differences in rate of marbling and ribfat deposition that resulted from breed were included in the equation. These prediction equationswere used to generate predicted marbling score and rib fat at slaughter.

RESULTS AND DISCUSSION

2-Year-Old Heifer Feedlot Performance. Feedlot performance for 2-year-old heifers andyearling heifers is reported in Table 2. Two-year-old Angus heifers were 23 d younger (P <0.01) at the initiation of the feedlot finishing phase than Wagyu-cross 2-year-olds. Angus heifersweighed more initially (P < 0.01) and gained 0.15 kg/d faster (P < 0.15) relative to their Wagyucounterparts throughout feedlot phase. Lunt et al. (1992) reported a similar difference in ADGbetween purebred Angus and ¾ Wagyu steers fed a corn/barley diet for 552 d. As a result offaster ADG and heavier initial weights, 2-year-old Angus heifers weighed an average of 70 kgmore (P < 0.01) at trial termination. Two-year-old Wagyu heifers consumed less (P < 0.01) drymatter on a daily basis when compared to their Angus counterparts. As a result of slower ADGand lower dry matter intake, Wagyu 2-year-old heifers had similar feed efficiencies relative totheir Angus contemporaries. Feed efficiency of these heifers and of the steers reported by theLunt et al., (1992) were not similar; most likely because the steers were fed for a longer period oftime, to a fatter external fat cover.

The feed efficiency data were used to generate regression equations for 2-year-old Angus andWagyu-cross heifers (Figure 1). Feed efficiency decreased quadratically (P < 0.01) over time.However, no differences in feed efficiency resulted from breed.

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Yearling Heifer Feedlot Performance. Individual feedlot performance was recorded for 216 d onconcentrate. However, yearlings had been on concentrate since weaning at 140 d of age andwere therefore on concentrate for a total of 368 d at slaughter. Four early-weaned yearlingheifers were removed from trial due to rectal porlapse. This trend was not observed for 2-year-old heifers despite their higher degree of subcutaneous fat cover. Wagyu-cross yearlings wereheavier (P < 0.05) at trial initiation than Angus yearlings. Differences in initial weights werelikely a reflection of differences in age at weaning. Wagyu heifers were 17 d older (P < 0.01) atweaning. Despite statistically similar ADG between the Angus and Wagyu yearlings, Angusyearlings gained numerically faster than Wagyu yearlings. As a result, final live weightsbetween heifers of the two breeds were similar. The combination of numerically slower ADGand higher dry matter intakes resulted in significantly (P < 0.05) less efficient gains for yearlingWagyu heifers. Data reported by Myers et al. (1999a) for early-weaned, concentrate-fed steersindicated that Wagyu-cross steers tended to be less efficient than British steers managedsimilarly. This difference in feed efficiency was not apparent among Angus and Wagyu heifersfinished as 2-year-old.

The feed efficiency regression equation generated from the yearling data and is illustrated inFigure 2. Feed efficiency decreased quadratically (P < 0.01) over time and no difference in feedefficiency resulted from breed.

Characteristics of Two-Year-Old Heifer Carcasses. Differences in carcass characteristics thatresulted from breed for 2-year-old heifers and yearling heifers are reported in Table 3. Angus 2-year-olds had heavier (P < 0.01) hot carcass weights than 2-year-old Wagyu-cross heifers whichwas reflective of differences in ending trial weights. Wagyu heifers had a higher percent (P <0.01) kidney, pelvic, and heart fat. Two-year-old heifers had an average bone maturity score of Band differences between breeds were not significant.

Wagyu-cross 2-year-old heifers had less (P < 0.05) 12th rib fat than their Angus-crosscounterparts at slaughter. The 12th rib fat thickness regression equation generated withultrasound data behaved linearly (P < 0.01) over the course of the finishing period. Theregression equation generated for Angus heifers had a slope similar to that of the Wagyu heifershowever, its intercept was higher (P < 0.01). Actual 12th rib fat measurements recorded atslaughter were higher when compared to fat thickness predicted by the regression equation(Table 4). Data reported in Figure 4 illustrate mean marbling scores at each of four ultrasoundperiods and actual marbling scores at slaughter. Actual marbling scores appeared much higher atslaughter than at the fourth ultrasound period 8 days earlier. In actuality, differences between12th rib fat measured at the fourth ultrasound period and at slaughter were due to inaccurateprediction by current ultrasound equipment and/or software. The research of Rouse et al. (1999)suggested that current ultrasound equipment and/or software under predict 12th rib fat.

The Least Squared Means procedure of SAS (1989) did not detect significant differences inmarbling scores between Angus and Wagyu heifers at slaughter. However, Wagyu-cross 2-year-old heifers averaged a slightly abundant marbling score while Angus 2-year-old heifers averageda moderate marbling score. Similar, non-significantly higher marbling scores for Wagyu heifersrelative to Angus heifers were reported by Lunt et al. (1992). Numerically higher fat extract

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values for Wagyu longissimus dorsi muscle supported the numerical differences in marblingscore indicated by the grader. Angus 2-year-old heifers had a mean fat extraction value of 11%.Brackebusch et al. (1991) reported that longissimus dorsi with this percent fat extract had USDAmarbling scores of moderate. Fat extract values for 2-year-old Wagyu heifers averaged 12%,which was equivalent to a slightly abundant degree of marbling. In both Angus and Wagyuheifers, grader-called and fat extract predicted marbling scores were similar. These differencesin marbling scores resulted in 37.5% more Wagyu 2-year-old heifers that graded USDA primerelative to the Angus 2-year-old heifers.

The marbling score regression equation developed from ultrasound measurements behavedquadratically (P < 0.01) over the finishing period (Figure 5). Marbling scores for 2-year-oldheifers that were grown on endophyte-infected tall fescue prior to entering the feedlot increasedmore rapidly with greater days on feed. The marbling score regression equation for Angus andWagyu 2-year-olds had similar slopes but the regression equation for the Wagyu heifers had ahigher intercept and maintained a greater amount of marbling throughout the finishing period.These data supported the data of Rouse et al. (1999) that concludes Wagyu-cross steers depositedintramuscular fat at a faster rate and to a higher level than typical feedlot cattle. Marbling scorespredicted by the regression equations generated with ultrasound data underpredicted actualmarbling scores recorded at slaughter (Table 4). Previously reported data indicated that thecurrent ultrasound equipment and/or software generally underestimate high marbling scores(Rouse et al., 1999). Figure 6 illustrates each ultrasound period and the actual marbling scorerecorded at slaughter. The differences in final ultrasound measurement and actual carcassmeasurements recorded 8 d later reflect the error associated with ultrasound measurement.

Wagyu-cross 2-year-old heifers had similar yield grades but significantly (P< 0.05) less 12th ribfat thickness than Angus 2-year-old heifers. Additionally, marbling scores for Wagyu heiferswere higher (P< 0.01) throughout the course of the finishing period and a numerically greaterpercentage of 2-year-old Wagyu carcasses graded prime. Producers selling on a yield and gradebasis where yield grade four cattle are discounted and premiums are given only to USDA primecattle, may find it economically advantageous to include Wagyu breeding into their program.

Yearling Heifer Carcass Characteristics. Wagyu-cross yearling heifers tended (P< 0.15) to haveheavier hot carcass weights than their Angus counter parts. This difference in hot carcass weightwas reflective of the differences in ending trial weight. As a result of differences in hot carcassweight, longissimus dorsi area was significantly greater (P < 0.05) for the Wagyu yearlingheifers. However, when expressed as centimeters per kilogram of hot carcass weight,longissimus dorsi area was similar (27cm/100kg). Percent kidney, pelvic, and heart fat tended (P< 0.08) to be higher for Wagyu yearlings than Angus yearlings; a trend similar to that of the 2-year-old heifers. In contrast to 12th rib fat for the 2-year-olds, 12th rib fat for the yearlings tended(P < 0.10) to be thicker for the Wagyu yearlings relative to the Angus yearlings.

The 12th rib fat regression equation generated with ultrasound data behaved quadratically (P <0.01) for early-weaned heifers that were immediately adjusted to concentrate diets (Figure 7).Yearling heifers appeared to deposit subcutaneous fat at a decreasing rate beyond 150 d onconcentrate. Differences in 12th rib fat that resulted from breed were not significant. However,as in the case with the 2-year-old heifers, the ultrasound generated regression equation under

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predicted 12th rib fat for yearling heifers as well (Table 4 and Figure 4). This trend is supportedby the data of Rouse et al. (1999).

Statistically, final marbling scores recorded at slaughter were similar between breeds. However,numerically the Wagyu yearlings averaged marbling scores 86 points higher than their Anguscounterparts. The relative differences in grader-called marbling score (approximately onequality grade lower for Angus vs. Wagyu) were substantiated by marbling score predicted fromfat extraction values of the longissimus dorsi. However, grader-called marbling scores werelower than those predicted by the fat extraction values. Fat extraction values for Angus andWagyu yearling heifers were 13% (slightly abundant) and 14% (moderately abundant),respectively. Grader-called marbling scores for the Angus and Wagyu yearlings averagedmoderate, and slightly abundant, respectively. The fat extraction values provided a lesssubjective evaluation of marbling content relative to visual appraisal, however both meansindicated numerically higher marbling scores for Wagyu yearling heifers. The small number ofobservations most likely limited the statistical power to detect a significant difference inmarbling score between Angus and Wagyu heifers.

The marbling score regression equation developed with ultrasound data suggested that the rate ofmarbling deposition for early-weaned heifers immediately adjusted to concentrate was linear (P< 0.01) throughout the finishing period (Figure 8). This differs from marbling deposition in the2-year-old heifers that was quadratic. Wagyu-cross yearling heifers maintained a higher (P <0.01) degree of marbling throughout the finishing period relative to Angus heifers. Despitedifferences in marbling scores, there was no difference in the percent of heifers that gradedUSDA prime as a result of breed. As with the 2-year-old heifers ultrasound technology underpredicted marbling score (Table 4, Figure 6).

Comparison of 2-Year-Old and Yearling Performance and Carcass Characteristics. Carcasscharacteristics of yearling and 2-year-old heifers cannot be statistically compared because of alack of commonality between 12th rib fat measurements or days on concentrate at slaughter.However, some generalizations can be drawn when comparing the two age groups. Two-year-old heifers weighed 115 kg more than yearlings at the end of the feedlot finishing. Wagyuheifers tended (P < 0.15) to gain slower than the Angus heifers as 2-year-olds. Average dailygain followed a similar numerical trend in yearlings, but this trend was not significant. Althoughyearlings and 2-year-olds had similar ADG, yearlings converted feed to gain more efficientlythan 2-year-olds. Over time, efficiency of gain declined quadratically (P < 0.01) for bothyearlings and 2-year-old heifers. However, yearling heifers remained more efficient than 2-year-old heifers throughout their time on feed.

Two-year-old heifers averaged B-maturity while yearlings had an average bone maturity score ofA-maturity. Grader-called marbling scores were similar among yearling and 2-year-old heifers.However, fat extraction values were 2 percentage points higher for yearlings relative to 2-year-olds, which suggested the yearlings may have had a higher degree of marbling than 2-year-oldheifers. Wagyu yearlings and 2-year-olds had similar 12th rib fat thickness. However, Angusyearlings had less 12th rib fat than Angus 2-year-olds.

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Early-weaned heifers fed concentrate from weaning deposited marbling in a linear mannerduring the finishing period. In contrast, heifers finished as 2-year-olds after grazing endophyte-infected tall fescue, deposited marbling quadratically with marbling being deposited at a fasterrate with more time on feed. Yearling 12th rib fat increased at a decreasing rate with greater timeon feed (Quadratic P < 0.01). However, 12th rib fat for 2-year-old heifers increased linearly (P <0.01) throughout the 218 d in the feedlot. Fat extraction values for the Longissimus dorsi of 2-year-old heifers averaged 11.3% (moderate50), while fat extraction values for yearling heifersaverage 13.5% (slightly abundant50) at lower 12 rib fat thickness (1.8 cm yearlings vs. 2.3cm 2-year-olds). If in fact 12th rib fat is quadratic for yearlings and linear for 2-year-olds and marblingis linear for yearlings but quadratic for 2-year-olds, higher fat extraction values at lower 12th ribfat measurements for yearlings suggest that early-weaned heifers fed concentrate from weaningto slaughter deposit greater marbling relative to subcutaneous fat than heifers grazed endophyte-infected tall fescue 16 months prior to entering the feedlot.

Relationship Marbling, 12th Rib Fat, and Feed Efficiency. The graphic illustrations discussed inthis section were not statistically analyzed. However, their content depicted interesting trendsbetween 12th rib fat and marbling, marbling and feed efficiency, and 12th rib fat and feedefficiency.

The relationship between marbling and 12th rib fat for 2-year-olds and yearlings is illustrated byFigures 9 and 10 respectively. The correlation between 12th rib fat and marbling was moderatelypositive. Marbling scores for 2-year-old and yearling heifers were less strongly correlated to 12th

rib fat up to 1.5 cm. Beyond this point, fatter heifers were more likely to have higher marblingscores. Interestingly, heifers with less than 1.5 cm rib fat had marbling scores ranging fromslight to moderate. This large variation suggested that 12th rib fat was a poor indicator ofmarbling potential for heifers slaughtered at industry standard 12th rib fat thickness (1.0 cm).

The relationship between 12th rib fat and feed efficiency for 2-year-olds and yearlings is depictedby Figures 11 and 12 respectively. Feed efficiency relative to 12th rib fat thickness exhibited andinteresting trend. Both low (< 0.2 kg gain/kg feed) and high (> 0.2 kg gain/kg feed) feedefficiency were associated with 12th rib fat thickness <1.25 cm in yearling heifers. In contrast,heifers with greater than 1.25 cm of 12th rib fat were associated solely with low feed efficiency(< 0.20 kg gain/kg feed). The same trend was exhibited by the 2-year-old heifers however, mostheifers with greater than 1.25 cm 12th rib fat had feed efficiencies < 0.15 kg gain/kg feed.

The relationship between feed efficiency and marbling for 2-year-old and yearling heifers isillustrated by Figures 13 and 14 respectively. Marbling relative to feed efficiency behavedsimilarly for the yearlings and 2-year-old heifers. In both cases, heifers with slight to smallmarbling scores gained more efficiently than heifers with marbling scores of modest or better.However, within the group of heifers that had slight to small amounts of marbling, there wasgreater variation in the correlation between feed efficiency and marbling than for heifers withgreater than a modest amount of marbling. When yearling and 2-year-old heifers were comparedat similar marbling scores, yearling heifers were more efficient than 2-year-old heifers.

Twelfth rib fat and marbling score were removed from the regression model for feed efficiencybecause of a lack of significance. These data might be interpreted to suggest that feed efficiency

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decreased with time on feed and animals become fatter with time on feed however, no directcorrelation between deposition of fat in specific depots is correlated with feed efficiency.

CONCLUSIONS

Breed affected feedlot performance of 2-year-old and yearling heifers. Angus 2-year-olds tended(P < 0.15) to gain faster than 2-year-old Wagyu-cross heifers however, the two breeds weresimilar in their efficiency of gain. As yearling heifers, Angus and Wagyu heifer gains werestatistically similar. However numerically, Wagyu yearlings gained slower and consumed moredry matter on a daily basis, which resulted in significantly (P < 0.01) less efficient gains forWagyu yearling.

Breed influenced the carcass characteristics of 2-year-old heifers. At slaughter, 2-year-oldWagyu heifers had less 12th rib fat (P < 0.05), numerically higher marbling scores, and anumerically greater percent of carcasses that graded USDA prime when compared to 2-year-oldAngus heifers. The 12th rib fat regression equation generated from ultrasound data increasedlinearly (P < 0.01) with increased time in the feedlot. Twelfth rib fat regression equations forAngus heifers had a higher (P < 0.01) intercept than the regression equation for the Wagyu 2-year-old heifers.

Significant differences in marbling score at slaughter that resulted from breed of 2-year-oldheifer were not detectable by the Least Squared Means procedure of SAS®. However, althoughthe slopes of the 2-year-old Angus and Wagyu marbling score regression equation were similar,the intercept for the Wagyu heifer regression was higher (P < 0.01) than that of the 2-year-oldAngus.

Breed affected carcass characteristics of yearling heifers as well. In contrast to the 2-year-oldheifers, yearling Wagyu heifers tended (P < 0.10) to have more subcutaneous fat cover atslaughter than Angus yearling heifers. Yearling 12th rib fat regression equation increasedquadratically (P < 0.01), with a diminishing increase in 12th rib fat beyond 150 d on feed.Differences in 12th rib fat regression equation that resulted from breed were not significant.

Grader-called and fat extract-predicted marbling scores indicated numerically higher marblingscores for the Wagyu yearlings relative to the Angus yearlings. The ultrasound-generatedmarbling regression equation increased linearly (P < 0.01) during the finishing period.Additionally, the intercept of the marbling regression equation for the Wagyu heifers was higher(P < 0.01) than that of the Angus heifers.

In general, ultrasound technology underpredicted 12th rib fat and marbling score for bothyearling and 2-year-old heifers. These data supported previously reported data (Rouse et al.,1999).

Post-weaning nutritional management and genetic lineage of feedlot heifers affect rate ofmarbling and 12th rib fat deposition. The inclusion of ½ -Wagyu genetics increases marblingscore throughout the finishing period relative to crossbred Angus heifers. Additionally, ½-Wagyu heifers finished as 2-year-olds have less (P < 0.05) subcutaneous fat cover at slaughter.

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These characteristics may be advantageous to a producer selling on a yield and grade basis.Additionally, these data suggest that the pattern of marbling and 12th rib fat deposition differ as aresult of post-weaning management.

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May, S. G., J. W. Savell, D. K. Lunt, J. J. Wilson, J. C. Laurenz, S. B. Smith. 1994. Evidencefor preadipocyte proliferation during culture of subcutaneous and intramuscular adiposetissue from Angus and Wagyu steers. J. Anim. Sci. 72:3110-3117.

Myers, S. E., D. B. Faulkner, F. A. Ireland, L. L. Berger, and D. F. Parrett. 1999a. Productionsystems comparing early weaning to normal weaning with or without creep feed for beefsteers. J. Anim. Sci. 77:300-310.

Myers, S. E., D. B. Faulkner, F. A. Ireland, L. L. Berger, D. F. Parrett and F. K. McKeith. 1999b.Performance and carcass traits of early-weaned steers receiving either a pasture growingperiod or a finishing diet at weaning. J. Anim. Sci. 77:311-322.

Myers, S. E., D. B. Faulkner, F. A. Ireland, D. F. Parrett. 1999c. Comparison of three weaningages on cow-calf performance and steer carcass traits. J. Anim. Sci. 77:323-329.

Riss, T. L., P. J. Bechttel, R. M. Forbes, B. P. Kline, and F. K. McKeith. 1983. Nutrient contentof special fed veal rib eyes. J. Food Sci. 48:1868.

Rouse, G., M. Ruble, S. Greiner, J. R. Tait, C. Hays, and D. Wilson. 1999. Growth anddevelopment of Angus-Wagyu crossbred steers. Iowa State University Beef ResearchReport AS 641, leaflet R1635. pp. 31-34.

SAS. 1989. SAS/STAT User’s Guide (Version 6, 4th Ed.). SAS Inst., Cary, NC.

Smith, S. B. and J. D. Crouse. 1984. Relative contributions of acetate, lactate, and glucose tolipogensis in bovine intramuscular and subcutaneous adipose tissue. J. Nutr. 792 - 800.

12

Table 1. Ingredient and Nutrient Composition of Finishing Diets Fed to 2-Year-Old Heifers and Yearling Heifers During the Feedlot Period

Ingredient %, Dry Matter Basis

Coarse ground corn 63.48Soybean meal 13.11Ground corn cobs 10.03Trace mineral salts 0.56Calcium carbonate 1.05Dehydrated molasses 5.08Rumensin 1.63Soybean oil 5.03

13

Table 2. Feedlot Performance of Angus and Wagyu Heifers That Initiated the finishing Phase as 2-Year-Olds Grazed on Endophyte-Infected Tall Fescue or Yearling Heifers Early-Weaned and Immediately Adjusted to Concentrate

Item Angus Wagyu SE P <

2-Year-Old Heifers n 12 12 ---- ---- Initial age, d a 704 727 4.6 0.01 Individual Performance days on concentrate 217 217

---- ----

Days on concentrate at slaughter 217 217

---- ----

Initial weight, kg 410.7 371.9 6.76 0.01 Final weight, kg 632.4 561.4 18.01 0.01 Average daily gain, kg/d 1.02 0.87 0.068 0.14 Average dry matter intake, kg/d 9.11 7.34 0.330 0.01 Gain:Feed, kg/kg 0.112 0.118 0.0064 0.52

Yearling Heifers n 11 9 ---- ---- Weaning age, d 133 150 4.3 0.01 Initial age, d a 285 302 4.3 0.01 Individual Performance days on concentrate 216 216

---- ----

Days on concentrate at slaughter 368 368

---- ----

Initial weight, kg 243.5 274.1 8.83 0.02 Final weight, kg 474.9 489.0 17.14 0.55 Average daily gain, kg/d 1.07 0.99 0.055 0.31 Average dry matter intake, kg/d 6.24 6.33 0.327 0.84 Gain:Feed, kg/kg 0.173 0.157 0.0054 0.05

a Initial age reflects the age at which of individual feed intake began

14

Table 3. Carcass Characteristics of Angus and Wagyu Heifers That Initiated the finishing Phase as 2-Year-Olds Grazed on Endophyte-Infected Tall Fescue or Yearling Heifers Early-Weaned and Immediately Adjusted to Concentrate

Item Angus Wagyu SE P <

2-Year-Old Heifers n 12 12 ---- ---- Days on concentrate at slaughter 218 218 ---- ---- Hot carcass weight, kg 396.1 351.5 11.25 0.01 Longissimus dorsi area, cm2 92.5 93.0 2.81 0.89 Bone maturity B11 B28 12.4 0.35 Kidney, pelvic, heart fat, % 2.1 2.6 0.13 0.01 12th Rib fat, cm 2.7 1.9 0.27 0.04 Marbling a 1298 1349 46.6 0.45 Yield grade b 4.1 3.6 0.29 0.30 USDA choice, % 50.0 33.3 ---- 0.35 USDA prime, % 41.7 66.7 ---- 0.35 Ether extract, % 10.9 11.9 1.09 0.54

Yearling Heifers n 11 9 ---- ---- Days on concentrate at slaughter 368 368 ---- ---- Hot carcass weight, kg 285.3 308.9 11.65 0.15 Longissimus dorsi area, cm2 77.0 84.0 2.42 0.05 Bone maturity A45 A49 5.3 0.55 Kidney, pelvic, heart fat, % 2.1 2.6 0.20 0.08 12th Rib fat, cm 1.5 2.1 0.24 0.10 Marbling a 1219 1305 48.8 0.20 Yield grade b 3.1 3.4 0.26 0.33 USDA choice, % 45.5 44.4 ---- 0.96 USDA prime, % 54.4 55.6 ---- 0.96 Ether extract, % 13.2 13.9 1.23 0.64

a marbling score 900 = slight, 1000 = small, 1100 modest,1200 = moderate, 1300 = slightly abundant,1400 = moderately abundant,1500 = abundant

b yield grade = [2.5 + 2.5(inches of fat at 12th rib) + 0.20(%kidney, pelvic, and heart fat) = 0.0038(lb. hotcarcass weight) – 0.32 (inches2 longissimus dorsi area)]

15

Table 4. Relationship of Actual and Predicted marbling Scores and 12th Rib Fat Thickness of Yearling and 2-Year-Old Angus and Wagyu Heifers

Angus WagyuUltrasound Carcass Ultrasound

2-Year-Old HeifersCarcass

12th Rib fat, cm a 2.7 2.4 1.9 1.9 Marbling score b c 1298 1223 1349 1274

Yearling Heifers 12th Rib fat, cm d 1.5 1.4 2.1 1.6 Marbling score b e 1219 1190 1305 1245

a Angus = 1.21 + 0.002 (d on concentrate) + 0.000015 (d on concentrate)2

Wagyu = 0.72 + 0.002 (d on concentrate) + 0.000015 (d on concentrate)2

b marbling score 900 = slight, 1000 = small, 1100 modest,1200 = moderate, 1300 = slightly abundant,1400 = moderately abundant,1500 = abundant

c Angus =994.8 + 34.8 (12th rib fat cm) – 1.51 (d on concentrate) + 0.010(d on concentrate)2

Wagyu = 1062.9 + 34.8 (12th rib fat cm) – 1.51 (d on concentrate) + 0.010(d on concentrate)2

d Angus = 0.61 + 0.001 (d on concentrate) + 0.00001 (d on concentrate)2

Wagyu = 0.81 + 0.001 (d on concentrate) + 0.00001 (d on concentrate)2

e Angus = 934.1 + 80.5(12thrib fat cm) – 0.59(d on concentrate) + 0.005(d on concentrate)2 – 38.9Wagyu = 973.0 + 80.5(12thrib fat cm) – 0.59(d on concentrate) + 0.005(d on concentrate)2

16

Figure 1. Predicted Feed Efficiency of Angus and Wagyu Heifers That Were Grazed Endophyte-Infected Tall Fescue Prior to Entering the Feedlot

0.1

0.125

0.15

0.175

0.2

50 100 150 200 250

Angus YearlingHeifers

Wagyu YearlingHeifers

c d

a

b

Feedlot Days on Concentrate

Gai

n:F

eed,

kg/

kg

a Angus = 0.2058+ 0.0008 (d on concentrate) + 0.000002 (d on concentrate)2

b Wagyu = 0.2067 + 0.008 (d on concentrate) + 0.000002 (d on concentrate)2

c Quadratic P < 0.01; Linear P < 0.01d Breed NS

17

Figure 2. Predicted Feed Efficiency of Angus and Wagyu Yearling Heifers That Were Early-Weaned and Immediately Adjusted to a High Concentrate Diet

0.1

0.125

0.15

0.175

0.2

0.225

0.25

50 100 150 200 250

Angus YearlingHeifers

Wagyu YearlingHeifers

c d

a

b

Feedlot Days on Concentrate

Gai

n:F

eed,

kg/

kg

a Angus = 0.2444+ 0.001 (d on concentrate) + 0.000002 (d on concentrate)2

b Wagyu = 0.2544 + 0.001 (d on concentrate) + 0.000002 (d on concentrate)2

c Quadratic P < 0.01; Linear P < 0.01d Breed NS

18

Figure 3. Predicted 12th Rib Fat of Angus and Wagyu 2-Year-Old Heifers Grazed on Endophyte-Infected Tall Fescue Prior to Entering the Feedlot

0

0.5

1

1.5

2

2.5

50 100 150 200 250

Angus 2-Year-OldHeifers

Wagyu 2-Year-OldHeifers

cd a

b

Feedlot Days on Concentrate

12th

Rib

Fat

, cm

a Angus = 1.07 + 0.0048 (d on concentrate)b Wagyu = 0.67 + 0.0048 (d on concentrate)c Quadratic NS; Linear P < 0.01d Breed P < 0.01

19

Figure 4. Mean 12th Rib Fat Measurements for Ultrasound Periods and at Slaughter of 2-Year-Old Heifers Grazed Endophyte-Infected Tall Fescue Prior to Entering the Feedlot or Early-Weaned and Immediately Adjusted to a Concentrate Diet

a Days from initiation of individual feed intake measurement. Early-weaned heifers were fedconcentrate from weaning until individual feed intake period (152 d)

b Initial four data points connected with the line represent mean measurements recorded at eachultrasound period. The fifth data point, not connected with the line represents the mean measurementcollected at slaughter.

0

0.5

1

1.5

2

2.5

2-Year-Old HeifersYearling Heifers

12 th

Rib

Fat

, cm

Days of Performance a

b

20

Figure 5. Predicted Marbling Scores of Angus and Wagyu 2-Year-Old Heifers Grazed on Endophyte-Infected Tall Fescue Prior to Entering the Feedlot

800

900

1000

1100

1200

1300

50 100 150 200 250

Angus 2-Year-OldHeifers

Wagyu 2-Year-OldHeifers

d eb

cb

Feedlot Days on Concentrate

Mar

blin

g Sc

ore

a

a marbling score 900 = slight, 1000 = small, 1100 modest,1200 = moderate, 1300 = slightlyabundant, 1400 = moderately abundant,1500 = abundant

b Angus = 978 + 0.069 (d on concentrate) + 0.003(d on concentrate)2

c Wagyu = 1029 + 0.069 (d on concentrate) + 0.003(d on concentrate)2

d Quadratic P < 0.01; Linear NSe Breed P < 0.01

21

Figure 6. Mean Marbling Scores for Ultrasound Periods and at Slaughter of 2-Year-Old Heifers Grazed Endophyte-Infected Tall Fescue Prior to Entering the Feedlot or Early-Weaned and Immediately Adjusted to a Concentrate Diet

800850900950

100010501100115012001250130013501400

2-Year-Old HeifersYearling Heifers

Mar

blin

g Sc

ore

a

Days of Performance Trial b

a marbling score 900 = slight, 1000 = small, 1100 modest,1200 = moderate,1300 = slightly abundant, 1400 = moderately abundant,1500 = abundant

b Days from initiation of individual feed intake measurement. Early-weanedheifers were fed concentrate from weaning until individual feed intake period (152 d)

c Initial four data points connected with the line represent mean measurementsrecorded at each ultrasound period. The fifth data point, not connected with the linerepresents the mean measurement collected at slaughter.

c

22

Figure 7. Predicted 12th Rib Fat of Angus and Wagyu Yearling Heifers That Were Early- Weaned and Immediately Adjusted to a High Concentrate Diet

0

0.2

0.4

0.6

0.8

1

1.2

1.4

50 100 150 200 250

Angus YearlingHeifers

Wagyu YearlingHeifers

c d

a

b

Feedlot Days on Concentrate e

12th

Rib

Fat

, cm

a Angus = 0.336+ 0.008 (d on concentrate) + 0.00002 (d on concentrate)2 b Wagyu = 0.457 + 0.008 (d on concentrate) + 0.00002 (d on concentrate)2

c Quadratic P < 0.01; Linear P < 0.01d Breed NSe Days from initiation of individual feed intake measurement. Early-weaned

heifers were fed concentrate from weaning until individual feed intake period (152 d)

23

Figure 8. Predicted Marbling Scores of Angus and Wagyu Yearling Heifers That Were Early-Weaned and Immediately adjusted to an High Concentrate Diet

800850900950

100010501100115012001250

50 100 150 200 250

Angus YearlingHeifers

Wagyu YearlingHeifers

d e f

b

c

Feedlot Days on Concentrate f

Mar

blin

g Sc

ore

a

a marbling score 900 = slight, 1000 = small, 1100 modest,1200 = moderate, 1300 = slightlyabundant, 1400 = moderately abundant,1500 = abundant

b Angus =923 + 0.86 (d on concentrate)c Wagyu = 981+ 0.86 (d on concentrate)d Quadratic NS; Linear P < 0.01e Breed P < 0.01f Days from initiation of individual feed intake measurement. Early-weaned heifers were fed

concentrate from weaning until individual feed intake period (152 d)

24

Figure 9. Relationship Between Ultrasound-Predicted Marbling Score and 12th Rib Fat Over Time in 2-Year-Old Heifers Grazed Endophyte-Infected Prior to Entering the Feedlot

800

900

1000

1100

1200

1300

0 0.5 1 1.5 2 2.5 3 3.5

12th Rib Fat, cm

a marbling score 900 = slight, 1000 = small, 1100 modest,1200 = moderate, 1300 =slightly abundant, 1400 = moderately abundant,1500 = abundant

25

Figure 10. Relationship Between Ultrasound-Predicted Marbling Score and 12th Rib Fat Over Time in Early- Weaned Yearling Heifers Immediately Adjusted to a High Concentrate Diet

800

900

1000

1100

1200

1300

0 0.5 1 1.5 2 2.5 3

Mar

blin

g Sc

ore

a

12th Rib Fat, cm

a marbling score 900 = slight, 1000 = small, 1100 modest,1200 = moderate, 1300 =slightly abundant, 1400 = moderately abundant,1500 = abundant

26

Figure 11. Relationship Between Ultrasound-Predicted 12th Rib Fat and Efficiency of Gain Over Time in 2-Year-Old Heifers Grazed Endophyte-Infected Tall Fescue Prior to Entering the Feedlot

0.1

0.125

0.15

0.175

0.2

0.225

0.25

0 0.5 1 1.5 2 2.5 3 3.5

Eff

icie

ncy

of G

ain,

kg/

kg

12th Rib Fat, cm

27

Figure 12. Relationship Between Ultrasound-Predicted 12th Rib Fat and Efficiency of Gain Over Time in Early-Weaned Yearling Heifers That Were Immediately Adjusted to a High Concentrate Diet

0.1

0.15

0.2

0.25

0.3

0.25 0.75 1.25 1.75 2.25 2.75

Eff

icie

ncy

of G

ain,

kg/

kg

12th Rib Fat, cm

28

Figure 13. Relationship Between Ultrasound-Predicted Marbling Score and Efficiency of Gain Over Time in 2-Year-Old Heifers Grazed Endophyte-Infected Tall Fescue Prior to Entering the Feedlot

0.050.075

0.10.1250.15

0.1750.2

0.2250.25

800 900 1000 1100 1200 1300 1400

Eff

icie

ncy

of G

ain,

kg/

kg

Marbling Score a

a marbling score 900 = slight, 1000 = small, 1100 modest,1200 = moderate, 1300 =slightly abundant, 1400 = moderately abundant,1500 = abundant

29

Figure 14. Relationship between Ultrasound-Predicted Marbling and Efficiency of Gain Over Time in Early-Weaned Yearling Heifers That Were Immediately Adjusted to a High Concentrate Diet

0.05

0.1

0.15

0.2

0.25

0.3

800 900 1000 1100 1200 1300 1400

Eff

icie

ncy

of G

ain,

kg/

kg

Marbling Score a

a marbling score 900 = slight, 1000 = small, 1100 modest,1200 = moderate,1300 = slightly abundant, 1400 = moderately abundant,1500 = abundant