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

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1 Post-Weaning Nutritional Management Affects Feedlot Performance, 12 th Rib Fat, and Marbling Deposition of Angus and Wagyu Heifers A. E. Wertz 1, L. L. Berger 1, D.B. Faulkner 1, F. K. McKeith 1, S. Rodriguez-Zas 1 and P. M. Walker 2 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 d of 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 earlyweaned (140 d of age) and immediately adjusted to a high concentrate diet. Heifers were individually fed using Calan gate-equipped bunks, which allowed feed efficiency to be calculated for each heifer. Serial ultrasound measurements of 12 th rib fat and marbling were recorded at d intervals for Angus-sired and Wagyu-sired heifers during feedlot finishing. Regression equations of marbling and 12 th rib fat deposition over time were developed using serial ultrasound measurements. Serial ultrasound data and individual feed efficiency data were combined to evaluate the relationship of marbling, 12 th rib fat and feed efficiency during the finishing 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 the feedlot. In contrast, 12 th rib fat for yearling heifers behaved quadratically (P < 0.01) over time in the feedlot. Twelfth rib fat was thicker for Angus 2-year-old heifers relative to Wagyu 2-yearolds. However, differences in 12 th rib fat that resulted from breed were not significant for yearling 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 fat deposition appeared to differ between heifers that were early-weaned and immediately fed concentrate and heifers that were grazed on endophyte-infected tall fescue 16 months prior to feedlot finishing. Both yearling and 2-year-old Wagyu heifers had a higher marbling score intercept than their Angus counterparts. Additionally, yearling heifers had greater fat extraction values than 2-year-old heifers, which indicated yearling heifers might have had a higher degree of marbling than 2-year-old heifers. Early-weaned heifers immediately adjusted to concentrate produced a more industry-acceptable carcass than 2-year-old heifers. Yearling hot carcass weights were within industry standard range ( kg), with less 12 th rib fat but more chloroform:methanol-extractable fat in the longissimus dorsi muscle. Additionally, yearling heifers produced less physiologically mature carcasses. Overall, ultrasound technology underestimated 12 th rib fat and marbling score for Angus and Wagyu yearling and 2-tear-old heifers. INTRODUCTION Palatability is the major factor that drives human consumption of beef. Tenderness, juiciness, and flavor determine the palatability of beef. Although intramuscular fat accounts for a small 1

2 amount of the variation in tenderness, it is closely correlated to the juiciness and characteristic flavor of beef (Horstein et al., 1987). Fat cell commitment and proliferation occur early in life, while the deposition of fat into these cells occurs as the animal matures. Smith et al. (1984) suggest that the primary substrate needed for intramuscular fat deposition is glucose which differs from the use of acetate to synthesize subcutaneous fat. Grain-fed cattle produce a greater proportion of propionate, a glucose precursor, than forage-fed cattle. As a result, it is hypothesized that feeding grain to cattle early in 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 high concentrate diet to grade USDA average choice or better than steers grazed on pasture for 82 d prior 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 grade USDA average choice or better when compared to normally weaned steers grown on pasture prior to feedlot finishing. Research conducted by Loy et al. (1999) demonstrates that Simmental and Angus steers weaned at 67 d of age and fed concentrate diets until slaughter have higher marbling scores and greater percentage of carcasses that grade USDA choice or prime than steers weaned at 147 d. In addition to improvements to carcass quality, early-weaning steers and immediately feeding concentrate diets results in improved average daily gains and feed efficiency (Myers et al., 1999a, Myers et al., 1999b). Myers et al. (1999c) further demonstrates that as age at weaning decreases from 215 d to 90 d, average daily gain and feed efficiency improve 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 Angus contemporaries. Myers et al. (1999a) reported a greater percent of half-blood Wagyu steer carcasses to grade USDA average choice or better when compared to continental crossbred steers fed to the same fat endpoint. Additionally, although Myers et al. (1999a) reported a similar percent of British crossbred and Wagyu crossbred steer carcasses to grade USDA average choice or prime, fewer Wagyu carcasses were classified USDA yield grade 3. Further research conducted by Myers et al. (1999b) supports the premise that Wagyu steers have higher marbling scores and a greater percentage of carcasses that graded USDA average choice or better than British and Continental crossbred steers. Furthermore, Rouse et al. (1999) reported that 351 kg Angus-Wagyu crossbred steers fed concentrate for 97 d have intramuscular fat sufficient to grade USDA low choice. In support of this data Cianzio et al. (1985) concludes that the number of adipocytes/gram of intramuscular tissue is a better predictor of marbling than cell diameter. Data of May et al. (1994) indicates that intramuscular adipocytes of Wagyu steers are smaller in diameter than those of Angus steers. However, Wagyu steers have numerically more adipocytes/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 earlyweaned Wagyu steers gain slower and tend to be less efficient in their gain than British crossbred steers. This trial is designed to evaluate the effects of Angus and Wagyu breeding on feedlot performance and the deposition of marbling and rib fat for heifers managed differently post- 2

3 weaning. Additionally, these data were used to relate feed efficiency to marbling and rib fat deposition. MATERIALS AND METHODS The objectives of this trial were three-fold. 1) to evaluate the feedlot performance of Angus and Wagyu heifers managed differently post-weaning to slaughter, 2) to establish, through the use of ultrasound technology, prediction equations for marbling, 12 th rib fat, and feed efficiency of Angus and Wagyu heifers over a range of ages and body compositions. 3) to evaluate the relationship of marbling score and 12 th rib fat to feed efficiency as well as the relationship of marbling to 12 th rib fat. Twenty-four heifers, twelve Angus and twelve ½ Wagyu x ½ Angus were weaned (200 d) and grazed on endophyte-infected tall fescue for 16 months. Following the 16-month growing period, heifers were transported to Illinois State University where they were adjusted to finishing ration (Table 1). These heifers were 22 months of age upon entering the feedlot and are referred to as 2-year-old heifers throughout this document. An additional twenty-four yearling heifers, of the 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 then transported 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 yearling heifers throughout this document. One Angus yearling and three Wagyu yearlings were removed from trial. Two-year-old heifers were implanted with Finaplex-H and yearling heifers were implanted with Synovex-C at initiation of the trial. Four heifers were assigned to each of 12 pens so that all breed-age combinations were represented within pen. Heifers were individually fed using Calan gate-equipped bunks and heifers were weighed at 21-d intervals. Dry matter intakes and feed refusals were recorded on a daily basis and individual animal feed efficiency was calculated using these data. As a result of a conflicting trial, 2-year-old heifers were fed on an individual basis for 125 d and pen-fed from d 126 to slaughter at 218 d on feed. Dry matter intakes for individual heifers during the pen-fed period were estimated by calculating the percent each animal consumed relative to its pen-mates during the last individual feeding period (d ). This percentage was then multiplied by total pen consumption to yield an estimated intake for each animal in the pen during the pen-fed period. Yearling heifers were individually throughout the 216 d of the feeding trial and pen-fed from d during which time an ultrasound measurement was recorded. It was necessary to predict dry matter intake for the purpose of establishing regression equations for feed efficiency at the time of the final ultrasound measurement. Individual dry matter intake was estimated for yearling heifers by calculating the percent each animal consumed relative to its pen-mates during the last individual feeding period (d ). Pen dry matter intake at the time of ultrasound measurement was multiplied by this percent to estimate individual dry matter intake for the final period. Real-Time (Linear Array) ultrasound was used to monitor rib fat and marbling deposition over the course of the feedlot-finishing period. Alkoa 500V ultrasound equipment with Alkoa UST transducer was used to record an image of the longissimus dorsi, its marbling and 3

4 surrounding fat. Images were interpreted using the CVI Scan Session reporting Version 6.2b in combination with Rib-O-Matic Version 3.01 software. Ultrasound measurements recorded at four times during the feeding period were used to develop regression equations for 12 th rib fat and 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 and final carcass measurements were recorded at this time. Carcass characteristics were recorded at slaughter and fat extraction was performed on longissimus dorsi samples to validate gradercalled marbling scores (Brackebusch et al., 1991). Intermuscular fat and surrounding subcutaneous fat were removed from the longissimus dorsi muscle and the muscle was homogenized. Duplicate 5-g samples were dried and repeatedly washed with chloroform:methanol in accordance with the procedures of Riss et al. (1983). Heifers were slaughtered when it was estimated that approximately 50% of each age group would grade low prime or better. Consequently, 12 th rib fat was greater for the 2 year-old heifers compared to the yearling heifers. Therefore yearling and 2-year-old heifer data were statistically analyzed separately with individual animal as the experimental unit. Performance and final carcass 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 Least Squared Means procedure of SAS (SAS, 1989). Ultrasound measurements of marbling and rib fat deposition were analyzed as repeated measures in time using the Mixed procedure of SAS. Marbling and 12 th rib fat regression equations were established using the linear and quadratic terms for the effects of days on concentrate. Additionally, differences in rate of marbling and rib fat deposition that resulted from breed were included in the equation. These prediction equations were 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 and yearling 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 heifers weighed more initially (P < 0.01) and gained 0.15 kg/d faster (P < 0.15) relative to their Wagyu counterparts throughout feedlot phase. Lunt et al. (1992) reported a similar difference in ADG between purebred Angus and ¾ Wagyu steers fed a corn/barley diet for 552 d. As a result of faster ADG and heavier initial weights, 2-year-old Angus heifers weighed an average of 70 kg more (P < 0.01) at trial termination. Two-year-old Wagyu heifers consumed less (P < 0.01) dry matter on a daily basis when compared to their Angus counterparts. As a result of slower ADG and lower dry matter intake, Wagyu 2-year-old heifers had similar feed efficiencies relative to their Angus contemporaries. Feed efficiency of these heifers and of the steers reported by the Lunt et al., (1992) were not similar; most likely because the steers were fed for a longer period of time, to a fatter external fat cover. The feed efficiency data were used to generate regression equations for 2-year-old Angus and Wagyu-cross heifers (Figure 1). Feed efficiency decreased quadratically (P < 0.01) over time. However, no differences in feed efficiency resulted from breed. 4

5 Yearling Heifer Feedlot Performance. Individual feedlot performance was recorded for 216 d on concentrate. However, yearlings had been on concentrate since weaning at 140 d of age and were therefore on concentrate for a total of 368 d at slaughter. Four early-weaned yearling heifers were removed from trial due to rectal porlapse. This trend was not observed for 2-yearold heifers despite their higher degree of subcutaneous fat cover. Wagyu-cross yearlings were heavier (P < 0.05) at trial initiation than Angus yearlings. Differences in initial weights were likely a reflection of differences in age at weaning. Wagyu heifers were 17 d older (P < 0.01) at weaning. Despite statistically similar ADG between the Angus and Wagyu yearlings, Angus yearlings gained numerically faster than Wagyu yearlings. As a result, final live weights between heifers of the two breeds were similar. The combination of numerically slower ADG and higher dry matter intakes resulted in significantly (P < 0.05) less efficient gains for yearling Wagyu heifers. Data reported by Myers et al. (1999a) for early-weaned, concentrate-fed steers indicated that Wagyu-cross steers tended to be less efficient than British steers managed similarly. This difference in feed efficiency was not apparent among Angus and Wagyu heifers finished as 2-year-old. The feed efficiency regression equation generated from the yearling data and is illustrated in Figure 2. Feed efficiency decreased quadratically (P < 0.01) over time and no difference in feed efficiency resulted from breed. Characteristics of Two-Year-Old Heifer Carcasses. Differences in carcass characteristics that resulted 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 which was 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 B and differences between breeds were not significant. Wagyu-cross 2-year-old heifers had less (P < 0.05) 12 th rib fat than their Angus-cross counterparts at slaughter. The 12 th rib fat thickness regression equation generated with ultrasound data behaved linearly (P < 0.01) over the course of the finishing period. The regression equation generated for Angus heifers had a slope similar to that of the Wagyu heifers however, its intercept was higher (P < 0.01). Actual 12 th rib fat measurements recorded at slaughter 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 ultrasound periods and actual marbling scores at slaughter. Actual marbling scores appeared much higher at slaughter than at the fourth ultrasound period 8 days earlier. In actuality, differences between 12 th rib fat measured at the fourth ultrasound period and at slaughter were due to inaccurate prediction by current ultrasound equipment and/or software. The research of Rouse et al. (1999) suggested that current ultrasound equipment and/or software under predict 12 th rib fat. The Least Squared Means procedure of SAS (1989) did not detect significant differences in marbling scores between Angus and Wagyu heifers at slaughter. However, Wagyu-cross 2-yearold heifers averaged a slightly abundant marbling score while Angus 2-year-old heifers averaged a moderate marbling score. Similar, non-significantly higher marbling scores for Wagyu heifers relative to Angus heifers were reported by Lunt et al. (1992). Numerically higher fat extract 5

6 values for Wagyu longissimus dorsi muscle supported the numerical differences in marbling score 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 USDA marbling 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 Wagyu heifers, grader-called and fat extract predicted marbling scores were similar. These differences in marbling scores resulted in 37.5% more Wagyu 2-year-old heifers that graded USDA prime relative to the Angus 2-year-old heifers. The marbling score regression equation developed from ultrasound measurements behaved quadratically (P < 0.01) over the finishing period (Figure 5). Marbling scores for 2-year-old heifers that were grown on endophyte-infected tall fescue prior to entering the feedlot increased more rapidly with greater days on feed. The marbling score regression equation for Angus and Wagyu 2-year-olds had similar slopes but the regression equation for the Wagyu heifers had a higher 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 deposited intramuscular fat at a faster rate and to a higher level than typical feedlot cattle. Marbling scores predicted by the regression equations generated with ultrasound data underpredicted actual marbling scores recorded at slaughter (Table 4). Previously reported data indicated that the current ultrasound equipment and/or software generally underestimate high marbling scores (Rouse et al., 1999). Figure 6 illustrates each ultrasound period and the actual marbling score recorded at slaughter. The differences in final ultrasound measurement and actual carcass measurements 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 12 th rib fat thickness than Angus 2-year-old heifers. Additionally, marbling scores for Wagyu heifers were higher (P< 0.01) throughout the course of the finishing period and a numerically greater percentage of 2-year-old Wagyu carcasses graded prime. Producers selling on a yield and grade basis where yield grade four cattle are discounted and premiums are given only to USDA prime cattle, 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 have heavier hot carcass weights than their Angus counter parts. This difference in hot carcass weight was reflective of the differences in ending trial weight. As a result of differences in hot carcass weight, longissimus dorsi area was significantly greater (P < 0.05) for the Wagyu yearling heifers. 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 12 th rib fat for the 2-year-olds, 12 th rib fat for the yearlings tended (P < 0.10) to be thicker for the Wagyu yearlings relative to the Angus yearlings. The 12 th 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 on concentrate. Differences in 12 th 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 6

7 predicted 12 th rib fat for yearling heifers as well (Table 4 and Figure 4). This trend is supported by 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 Angus counterparts. The relative differences in grader-called marbling score (approximately one quality grade lower for Angus vs. Wagyu) were substantiated by marbling score predicted from fat extraction values of the longissimus dorsi. However, grader-called marbling scores were lower than those predicted by the fat extraction values. Fat extraction values for Angus and Wagyu yearling heifers were 13% (slightly abundant) and 14% (moderately abundant), respectively. Grader-called marbling scores for the Angus and Wagyu yearlings averaged moderate, and slightly abundant, respectively. The fat extraction values provided a less subjective evaluation of marbling content relative to visual appraisal, however both means indicated numerically higher marbling scores for Wagyu yearling heifers. The small number of observations most likely limited the statistical power to detect a significant difference in marbling score between Angus and Wagyu heifers. The marbling score regression equation developed with ultrasound data suggested that the rate of marbling 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 the 2-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. Despite differences in marbling scores, there was no difference in the percent of heifers that graded USDA prime as a result of breed. As with the 2-year-old heifers ultrasound technology under predicted marbling score (Table 4, Figure 6). Comparison of 2-Year-Old and Yearling Performance and Carcass Characteristics. Carcass characteristics of yearling and 2-year-old heifers cannot be statistically compared because of a lack 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-yearold heifers weighed 115 kg more than yearlings at the end of the feedlot finishing. Wagyu heifers tended (P < 0.15) to gain slower than the Angus heifers as 2-year-olds. Average daily gain followed a similar numerical trend in yearlings, but this trend was not significant. Although yearlings and 2-year-olds had similar ADG, yearlings converted feed to gain more efficiently than 2-year-olds. Over time, efficiency of gain declined quadratically (P < 0.01) for both yearlings and 2-year-old heifers. However, yearling heifers remained more efficient than 2-yearold heifers throughout their time on feed. Two-year-old heifers averaged B-maturity while yearlings had an average bone maturity score of A-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-yearolds, which suggested the yearlings may have had a higher degree of marbling than 2-year-old heifers. Wagyu yearlings and 2-year-olds had similar 12 th rib fat thickness. However, Angus yearlings had less 12 th rib fat than Angus 2-year-olds. 7

8 Early-weaned heifers fed concentrate from weaning deposited marbling in a linear manner during the finishing period. In contrast, heifers finished as 2-year-olds after grazing endophyteinfected tall fescue, deposited marbling quadratically with marbling being deposited at a faster rate with more time on feed. Yearling 12 th rib fat increased at a decreasing rate with greater time on feed (Quadratic P < 0.01). However, 12 th 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% (moderate 50 ), while fat extraction values for yearling heifers average 13.5% (slightly abundant 50 ) at lower 12 rib fat thickness (1.8 cm yearlings vs. 2.3cm 2- year-olds). If in fact 12 th rib fat is quadratic for yearlings and linear for 2-year-olds and marbling is linear for yearlings but quadratic for 2-year-olds, higher fat extraction values at lower 12 th rib fat measurements for yearlings suggest that early-weaned heifers fed concentrate from weaning to slaughter deposit greater marbling relative to subcutaneous fat than heifers grazed endophyteinfected tall fescue 16 months prior to entering the feedlot. Relationship Marbling, 12th Rib Fat, and Feed Efficiency. The graphic illustrations discussed in this section were not statistically analyzed. However, their content depicted interesting trends between 12th rib fat and marbling, marbling and feed efficiency, and 12th rib fat and feed efficiency. The relationship between marbling and 12th rib fat for 2-year-olds and yearlings is illustrated by Figures 9 and 10 respectively. The correlation between 12 th rib fat and marbling was moderately positive. Marbling scores for 2-year-old and yearling heifers were less strongly correlated to 12 th rib fat up to 1.5 cm. Beyond this point, fatter heifers were more likely to have higher marbling scores. Interestingly, heifers with less than 1.5 cm rib fat had marbling scores ranging from slight to moderate. This large variation suggested that 12 th rib fat was a poor indicator of marbling potential for heifers slaughtered at industry standard 12 th rib fat thickness (1.0 cm). The relationship between 12 th rib fat and feed efficiency for 2-year-olds and yearlings is depicted by Figures 11 and 12 respectively. Feed efficiency relative to 12 th rib fat thickness exhibited and interesting trend. Both low (< 0.2 kg gain/kg feed) and high (> 0.2 kg gain/kg feed) feed efficiency were associated with 12 th rib fat thickness <1.25 cm in yearling heifers. In contrast, heifers with greater than 1.25 cm of 12 th 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, most heifers with greater than 1.25 cm 12 th 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 is illustrated by Figures 13 and 14 respectively. Marbling relative to feed efficiency behaved similarly for the yearlings and 2-year-old heifers. In both cases, heifers with slight to small marbling 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 was greater variation in the correlation between feed efficiency and marbling than for heifers with greater than a modest amount of marbling. When yearling and 2-year-old heifers were compared at 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 efficiency because of a lack of significance. These data might be interpreted to suggest that feed efficiency 8

9 decreased with time on feed and animals become fatter with time on feed however, no direct correlation 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 were similar in their efficiency of gain. As yearling heifers, Angus and Wagyu heifer gains were statistically similar. However numerically, Wagyu yearlings gained slower and consumed more dry matter on a daily basis, which resulted in significantly (P < 0.01) less efficient gains for Wagyu yearling. Breed influenced the carcass characteristics of 2-year-old heifers. At slaughter, 2-year-old Wagyu heifers had less 12 th rib fat (P < 0.05), numerically higher marbling scores, and a numerically greater percent of carcasses that graded USDA prime when compared to 2-year-old Angus heifers. The 12 th rib fat regression equation generated from ultrasound data increased linearly (P < 0.01) with increased time in the feedlot. Twelfth rib fat regression equations for Angus 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-old heifer were not detectable by the Least Squared Means procedure of SAS. However, although the 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-old Angus. Breed affected carcass characteristics of yearling heifers as well. In contrast to the 2-year-old heifers, yearling Wagyu heifers tended (P < 0.10) to have more subcutaneous fat cover at slaughter than Angus yearling heifers. Yearling 12 th rib fat regression equation increased quadratically (P < 0.01), with a diminishing increase in 12 th rib fat beyond 150 d on feed. Differences in 12 th rib fat regression equation that resulted from breed were not significant. Grader-called and fat extract-predicted marbling scores indicated numerically higher marbling scores for the Wagyu yearlings relative to the Angus yearlings. The ultrasound-generated marbling 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 12 th rib fat and marbling score for both yearling 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 of marbling and 12 th rib fat deposition. The inclusion of ½ -Wagyu genetics increases marbling score 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. 9

10 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 12 th rib fat deposition differ as a result of post-weaning management. 10

11 LITERATURE CITED Brackebusch, S. A., F. K. McKeith, T. R. Carr, and D. G. McLaren Relationship between longissimus composition and the composition for other major muscles of the beef carcass. J. Anim. Sci. 69: Cianzio, D. S., D. G. Topel, G. B. Whithurst, D.C. Beitz, and H. L. Self Adipose tissue growth and cellularity : changes in bovine adipocyte size and number. 60: Horstein, I and A. Wasserman Sensory characteristics of meat. Part 2 Chemistry of meat flavor. In: The Science of Meat and Meat Products. pp Eds. J. F. Price and B. S. Schweigert. 3rd Ed. Food and Nutrition Press, Inc. Westport, CN. Loy, D., D. Maxwell, and G. Rouse Effects of early weaning of beef calves on performance and carcass quality. Iowa State University Beef Research Report AS 641, leaflet R1632. pp Lunt, D. K., R. R. Riley, and S. B. Smith. Growth and carcass characteristics of Angus and Wagyu steers. Meat Sci. 34: May, S. G., J. W. Savell, D. K. Lunt, J. J. Wilson, J. C. Laurenz, S. B. Smith Evidence for preadipocyte proliferation during culture of subcutaneous and intramuscular adipose tissue from Angus and Wagyu steers. J. Anim. Sci. 72: Myers, S. E., D. B. Faulkner, F. A. Ireland, L. L. Berger, and D. F. Parrett. 1999a. Production systems comparing early weaning to normal weaning with or without creep feed for beef steers. J. Anim. Sci. 77: 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 growing period or a finishing diet at weaning. J. Anim. Sci. 77: Myers, S. E., D. B. Faulkner, F. A. Ireland, D. F. Parrett. 1999c. Comparison of three weaning ages on cow-calf performance and steer carcass traits. J. Anim. Sci. 77: Riss, T. L., P. J. Bechttel, R. M. Forbes, B. P. Kline, and F. K. McKeith Nutrient content of special fed veal rib eyes. J. Food Sci. 48:1868. Rouse, G., M. Ruble, S. Greiner, J. R. Tait, C. Hays, and D. Wilson Growth and development of Angus-Wagyu crossbred steers. Iowa State University Beef Research Report AS 641, leaflet R1635. pp SAS SAS/STAT User s Guide (Version 6, 4th Ed.). SAS Inst., Cary, NC. Smith, S. B. and J. D. Crouse Relative contributions of acetate, lactate, and glucose to lipogensis in bovine intramuscular and subcutaneous adipose tissue. J. Nutr

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 Soybean meal Ground corn cobs Trace mineral salts 0.56 Calcium carbonate 1.05 Dehydrated molasses 5.08 Rumensin 1.63 Soybean oil

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 Initial age, d a Individual Performance days on concentrate Days on concentrate at slaughter Initial weight, kg Final weight, kg Average daily gain, kg/d Average dry matter intake, kg/d Gain:Feed, kg/kg Yearling Heifers n Weaning age, d Initial age, d a Individual Performance days on concentrate Days on concentrate at slaughter Initial weight, kg Final weight, kg Average daily gain, kg/d Average dry matter intake, kg/d Gain:Feed, kg/kg a Initial age reflects the age at which of individual feed intake began 13

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 Days on concentrate at slaughter Hot carcass weight, kg Longissimus dorsi area, cm Bone maturity B 11 B Kidney, pelvic, heart fat, % th Rib fat, cm Marbling a Yield grade b USDA choice, % USDA prime, % Ether extract, % Yearling Heifers n Days on concentrate at slaughter Hot carcass weight, kg Longissimus dorsi area, cm Bone maturity A 45 A Kidney, pelvic, heart fat, % th Rib fat, cm Marbling a Yield grade b USDA choice, % USDA prime, % Ether extract, % a marbling score 900 = slight, 1000 = small, 1100 modest,1200 = moderate, 1300 = slightly abundant, 1400 = moderately abundant,1500 = abundant b yield grade = [ (inches of fat at 12 th rib) (%kidney, pelvic, and heart fat) = (lb. hot carcass weight) 0.32 (inches 2 longissimus dorsi area)] 14

15 Table 4. Relationship of Actual and Predicted marbling Scores and 12 th Rib Fat Thickness of Yearling and 2-Year-Old Angus and Wagyu Heifers Angus Wagyu Carcass Ultrasound Carcass Ultrasound 2-Year-Old Heifers 12 th Rib fat, cm a Marbling score b c Yearling Heifers 12 th Rib fat, cm d Marbling score b e a Angus = (d on concentrate) (d on concentrate) 2 Wagyu = (d on concentrate) (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 = (12 th rib fat cm) 1.51 (d on concentrate) (d on concentrate) 2 Wagyu = (12 th rib fat cm) 1.51 (d on concentrate) (d on concentrate) 2 d Angus = (d on concentrate) (d on concentrate) 2 Wagyu = (d on concentrate) (d on concentrate) 2 e Angus = (12thrib fat cm) 0.59(d on concentrate) (d on concentrate) Wagyu = (12thrib fat cm) 0.59(d on concentrate) (d on concentrate) 2 15

16 Figure 1. Predicted Feed Efficiency of Angus and Wagyu Heifers That Were Grazed Endophyte-Infected Tall Fescue Prior to Entering the Feedlot 0.2 Gain:Feed, kg/kg c d Angus Yearling Heifers Wagyu Yearling Heifers a b Feedlot Days on Concentrate a Angus = (d on concentrate) (d on concentrate) 2 b Wagyu = (d on concentrate) (d on concentrate) 2 c Quadratic P < 0.01; Linear P < 0.01 d Breed NS 16

17 Figure 2. Predicted Feed Efficiency of Angus and Wagyu Yearling Heifers That Were Early-Weaned and Immediately Adjusted to a High Concentrate Diet 0.25 Gain:Feed, kg/kg c d Angus Yearling Heifers Wagyu Yearling Heifers a b Feedlot Days on Concentrate a Angus = (d on concentrate) (d on concentrate) 2 b Wagyu = (d on concentrate) (d on concentrate) 2 c Quadratic P < 0.01; Linear P < 0.01 d Breed NS 17

18 Figure 3. Predicted 12 th Rib Fat of Angus and Wagyu 2-Year-Old Heifers Grazed on Endophyte-Infected Tall Fescue Prior to Entering the Feedlot 12 th Rib Fat, cm c d Angus 2-Year-Old Heifers Wagyu 2-Year-Old Heifers b a Feedlot Days on Concentrate a Angus = (d on concentrate) b Wagyu = (d on concentrate) c Quadratic NS; Linear P < 0.01 d Breed P <

19 Figure 4. Mean 12 th 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 12 th Rib Fat, cm b 2-Year-Old Heifers Yearling Heifers 0 Days of Performance a a Days from initiation of individual feed intake measurement. Early-weaned heifers were fed concentrate from weaning until individual feed intake period (152 d) b Initial four data points connected with the line represent mean measurements recorded at each ultrasound period. The fifth data point, not connected with the line represents the mean measurement collected at slaughter. 19

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 Marbling Score a d e Angus 2-Year-Old Heifers Wagyu 2-Year-Old Heifers c b b Feedlot Days on Concentrate a marbling score 900 = slight, 1000 = small, 1100 modest,1200 = moderate, 1300 = slightly abundant, 1400 = moderately abundant,1500 = abundant b Angus = (d on concentrate) (d on concentrate) 2 c Wagyu = (d on concentrate) (d on concentrate) 2 d Quadratic P < 0.01; Linear NS e Breed P <

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 Marbling Score a c 2-Year-Old Heifers Yearling Heifers 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-weaned heifers were fed concentrate from weaning until individual feed intake period (152 d) c Initial four data points connected with the line represent mean measurements recorded at each ultrasound period. The fifth data point, not connected with the line represents the mean measurement collected at slaughter. 21

22 Figure 7. Predicted 12 th Rib Fat of Angus and Wagyu Yearling Heifers That Were Early- Weaned and Immediately Adjusted to a High Concentrate Diet 1.4 c d 12 th Rib Fat, cm Angus Yearling Heifers Wagyu Yearling Heifers a b Feedlot Days on Concentrate e a Angus = (d on concentrate) (d on concentrate) 2 b Wagyu = (d on concentrate) (d on concentrate) 2 c Quadratic P < 0.01; Linear P < 0.01 d Breed NS e Days from initiation of individual feed intake measurement. Early-weaned heifers were fed concentrate from weaning until individual feed intake period (152 d) 22

23 Figure 8. Predicted Marbling Scores of Angus and Wagyu Yearling Heifers That Were Early-Weaned and Immediately adjusted to an High Concentrate Diet Marbling Score a d e f Angus Yearling Heifers Wagyu Yearling Heifers b c Feedlot Days on Concentrate f a marbling score 900 = slight, 1000 = small, 1100 modest,1200 = moderate, 1300 = slightly abundant, 1400 = moderately abundant,1500 = abundant b Angus = (d on concentrate) c Wagyu = (d on concentrate) d Quadratic NS; Linear P < 0.01 e Breed P < 0.01 f Days from initiation of individual feed intake measurement. Early-weaned heifers were fed concentrate from weaning until individual feed intake period (152 d) 23

24 Figure 9. Relationship Between Ultrasound-Predicted Marbling Score and 12 th Rib Fat Over Time in 2-Year-Old Heifers Grazed Endophyte-Infected Prior to Entering the Feedlot th Rib Fat, cm a marbling score 900 = slight, 1000 = small, 1100 modest,1200 = moderate, 1300 = slightly abundant, 1400 = moderately abundant,1500 = abundant 24

25 Figure 10. Relationship Between Ultrasound-Predicted Marbling Score and 12 th Rib Fat Over Time in Early- Weaned Yearling Heifers Immediately Adjusted to a High Concentrate Diet Marbling Score a th Rib Fat, cm a marbling score 900 = slight, 1000 = small, 1100 modest,1200 = moderate, 1300 = slightly abundant, 1400 = moderately abundant,1500 = abundant 25

26 Figure 11. Relationship Between Ultrasound-Predicted 12 th Rib Fat and Efficiency of Gain Over Time in 2-Year-Old Heifers Grazed Endophyte-Infected Tall Fescue Prior to Entering the Feedlot Efficiency of Gain, kg/kg th Rib Fat, cm 26

27 Figure 12. Relationship Between Ultrasound-Predicted 12 th Rib Fat and Efficiency of Gain Over Time in Early-Weaned Yearling Heifers That Were Immediately Adjusted to a High Concentrate Diet Efficiency of Gain, kg/kg th Rib Fat, cm 27

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 Efficiency of Gain, kg/kg Marbling Score a a marbling score 900 = slight, 1000 = small, 1100 modest,1200 = moderate, 1300 = slightly abundant, 1400 = moderately abundant,1500 = abundant 28

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 Efficiency of Gain, 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