J. Anim. Sci. 2005. 83:2752-2761
© 2005 American Society of Animal Science
ANIMAL GROWTH, PHYSIOLOGY, AND REPRODUCTION |
Growth rate, body composition, and meat tenderness in early vs. traditionally weaned beef calves1,2
D. L. Meyer*,
M. S. Kerley*,
E. L. Walker
,
D. H. Keisler*,
V. L. Pierce
,
T. B. Schmidt*,
C. A. Stahl*,
M. L. Linville
and
E. P. Berg*,3
* Division of Animal Sciences,
and
Division of Agriculture Economics, and
and
Office of Animal Resources, University of Missouri, Columbia 65211; and
and
Southwest Missouri State University, Springfield 65804
 |
Abstract
|
|---|
One hundred forty spring-born Angus x Gelbvieh and purebred Angus steers were selected for study as early weaned (EW; average age at weaning = 90 ± 30 d) or traditionally weaned (TW; average age at weaning = 174 ± 37 d) steers that were non-implanted or implanted (Synovex-S, Fort Dodge Animal Health, Overland Park, KS). Initially, steers were sorted by age, sire, and farm, and then allotted randomly in a 2 x 2 factorial arrangement of treatments of EW implanted (EWI), EW nonimplanted (EWN), TW implanted (TWI), or TW nonimplanted (TWN). Ultrasound measurements (US) of LM area (LMA), 12th rib fat thickness (US-BF), and marbling (US-M) were collected every 28 d during the time that steers were on feed. At 202 d of age, EW calves had larger US-LMA, US-BF, and BW than TW calves (37.9 vs. 32.3 cm2, 0.38 vs. 0.26 cm, and 271.6 vs. 218.9 kg, respectively; P < 0.001). At slaughter, EW calves had heavier HCW (290.4 vs. 279.7 kg, respectively; P < 0.05) and greater USDA marbling scores (51.25 vs. 46.26, respectively; P < 0.05) than TW calves; more EW steers graded USDA Choice or greater (P = 0.05). However, no differences were detected in BW (P = 0.15), LMA (P = 0.39), BF (P = 0.45), or liver abscess scores (P = 0.41). Twenty-four implanted steers were selected from the original group of 140 and sorted into two slaughter groups of 12. Twelve implanted steers from each weaning group, matched in slaughter BW but differing in age, were subsampled at slaughter to assess the effect of weaning age and chronological age on muscle tenderness. Younger animals had lower Warner-Bratzler shear force values (P < 0.001) than older calves after 14 d of postmortem aging; however, no differences were found in tenderness after 21 d of aging. Furthermore, there was greater variance (P < 0.001) in Warner-Bratzler shear force values among younger, EW steers vs. older, TW steers. These data provide evidence that early weaning of beef calves may be used as a tool to more effectively manage the cow-calf production system without compromising the quality of the offspring.
Key Words: Beef • Early Weaning • Growth • Tenderness
|
Introduction
|
|---|
Numerous early weaning studies have been conducted with beef cattle in the past several decades (Green and Buric, 1953
; Fluharty et al., 2000; Schoonmaker et al., 2003), yielding evidence that early weaned (EW) calves have more efficient gains than traditionally weaned (TW) calves (Myers et al., 1999b; Wertz et al., 2002). Furthermore, early weaning studies have thoroughly investigated BW gain over time as well as endpoint carcass attributes (Fluharty et al., 2000; Wertz et al., 2002). Recent early weaning studies also have investigated the potential of EW calves to compete with, if not outperform, TW calves in terms of USDA yield and quality grades. Most studies have documented that EW cattle require a greater number of days on feed to reach acceptable BW compared with TW calves (Myers et al., 1999a; Schoonmaker et al., 2002). In addition, USDA quality grade comparisons between EW and TW calves reveal that EW cattle are capable of grading USDA Choice or greater in a time frame comparable with TW calves (Fluharty et al., 2000; Schoonmaker et al., 2002). Most importantly, the same studies have reported this to be true while both groups were able to maintain an acceptable yield grade (USDA yield grade of 
3).
The objectives of this study were 1) to characterize changes in LMA and 12th rib fat depth in implanted vs. non-implanted calves from weaning to slaughter via serial ultrasound analysis of EW vs. TW calves, 2) to determine whether EW calves generate a greater percentage of USDA Choice or greater quality grade and carcasses with a yield grade of 3 compared with TW calves, and 3) to determine whether ribeye steaks from EW calves are more tender than steaks from TW calves.
|
Materials and Methods
|
|---|
Experiment 1
Growing Period.
The experimental procedure used in this study was approved by the University of Missouri Animal Care and Use Committee. One hundred forty spring-born Angus x Gelbvieh and purebred Angus steers were selected for study as EW (average age weaned = 90 ± 30 d) or TW (average age weaned = 202 ± 37 d) steers that were nonimplanted (n = 70) or implanted (Synovex-S, Fort Dodge Animal Health, Overland Park, KS; n = 70). Farm production records for date of birth and sire were used as a means of sorting initial treatment groups allotted randomly across age, sire, and farm into a 2 x 2 factorial arrangement. The treatments were EW implanted (EWI), EW nonimplanted (EWN), TW implanted (TWI), or TW nonimplanted (TWN). This list of treatments was provided to the farm managers, who then sorted the EW calves for delivery to the University of Missouri South Farm feedlot (Columbia). The TW calves followed approximately 110 d later. The EWI steers were implanted with Synovex-S at the time of weaning and re-implanted after 80 d in the feedlot. Similarly, TWI steers received a Synovex-S implant at the time of weaning and were re-implanted after 80 d in the feedlot. All steers were purchased from within the University of Missouri beef cattle production system to minimize breed and previous management differences.
Steers in both weaning groups entered the South Farm feedlot and were allowed a 21-d acclimation period. Day 0 of the experimental period, and thus all measurements pertaining to this study, began at the completion of the acclimation period for EW steers. Early weaned calves were placed on a high-by-product, no roughage (hay) orientation diet for 28 d (Table 1). After 28 d, EW calves were placed on an EW diet (Table 2), which introduced hay as a means of preventing bloating, which began to occur in some of the research steers. At the time of traditional weaning (174 d of age; d 112 of the experiment), a palatability issue was identified relative to a new batch of rice bran included in the diet. Furthermore, EW calves had health issues (primarily bloating) at the start of the experiment, most likely because of introduction of a high-concentrate diet and the small particle size (Cheng et al., 1998) of the rice bran. As a result, rice bran was removed from the finishing diet (Table 3) and was compensated by the addition of whole soybeans and additional whole-kernel corn. Both groups remained on this diet for the duration of the feedlot period (Table 3). Steers were assigned randomly to 24 pens (six steers per pen and 12 pens per treatment). Feed delivery was based on the quantity of residual feed (from the previous day’s offering, allowing the researchers to monitor daily consumption [CON]) by pen. Pens exceeded size (9.14 m x 18.29 m) and bunk space (6.10 m) allowance per calf recommended by FASS (1999) and also contained a shaded area for use by the calves in extreme weather conditions. Initial BW for each weaning group were determined at d 1 by averaging BW taken on two consecutive days (d 0 and 1) to minimize the effect of gut fill variation. Ultrasound (US) measurements and BW were taken from calves every 28 d, starting at d 0 (90 d of age) and continuing until EW calves had been in the feedlot for 280 d and TW calves had been in the feedlot for 168 d, reaching an average BW of 523 kg. Average daily gains for each 28-d feed period were calculated.
Ultrasound Images.
Ultrasonic images were captured using the AUSkey System Software (Animal Ultrasound Services, Ithaca, NY) using a 500V Aloka (Corometrics Medical Systems, Inc., Wallingford, CT) ultrasound machine with a 3.5-MHz transducer fitted to a custom beef animal standoff (a gel fitted to contour the shape of the beef animal at the 12th and 13th rib). The US technician was trained by Animal Ultrasound Services for live beef evaluations, transducer head placement, image collection, and interpretation. The same trained technician was used throughout the study. Longissimus muscle area (LMA) and 12th rib fat images were captured between the 12th and 13th rib on the right side of each steer. Generous amounts of commercial vegetable oil were applied to the site of measurement to decrease sound wave attenuation associated with hair coat. Final LMA and 12th rib fat images were approved by the Animal Ultrasound Services general manager. The final live US image was taken 1 d before animals were shipped to slaughter.
Carcass Data Collection.
The experiment was terminated after all calves reached approximately 370 d of age. The EW calves had been on test for 280 d, and TW calves had been on test for 168 d (total average final BW = 523 ± 46 kg). Twenty-four steers remained in the feedlot as a subsample for Exp. 2 (explained later). A total of 116 steers were transported to a commercial packing plant for humane slaughter and carcass data collection. Hot carcass weights were documented for each animal. Liver abscess scores were recorded by a licensed veterinarian for each animal as an index of health issues related to aggressively feeding a high-concentrate/by-product diet (Nagaraja and Chengappa, 1998). Abscesses were assessed using scores of A–, A, or A+ based on Brink et al. (1990). A liver score of A–indicated the presence of one or two minor abscesses; a score of A indicated the presence of two to four well-established abscesses; and a score of A+ indicated the presence of large, active abscesses that might have contained inflammation on the abscess periphery. Livers that did not contain any apparent abscesses were scored with a zero.
After a 24-h chill period (at 5°C), additional carcass measurements were collected. The LMA was measured using the reverse blot image technique (Martin, 1991), which allows LMA to be obtained at grading chain speeds. The 12th rib fat thickness (BF) was determined using a USDA preliminary yield grade ruler (USDA, 1997) at an anatomical location perpendicular to the vertebral column and 0.75 the distance caudal to the LM. To determine preliminary yield grades, the fat measurements were then adjusted, correcting for any atypical fat distribution. Marbling scores were identified by an experienced USDA grader using the USDA marbling standards (Abundant, Moderately Abundant, Slightly Abundant, Moderate, Modest, Small, Slight, Traces, and Practically Devoid; USDA, 1997). Maturity scores also were assessed using the USDA standards (USDA, 1997) for animals older than "A" maturity.
Experiment 2
Subsample Selection.
Using statistical sample size determination, 24 implanted steers were selected from the original research group (Exp. 1) and sorted into two slaughter groups of 12 each. The calves were repenned at six steers (three TW and three EW) per pen (n = 2 per slaughter group). They continued to receive the same feedlot diet described for Exp. 1. As a means to further analyze shear force data on two separate age groups, both slaughter groups 1 (average age = 404 ± 10 d) and 2 (average age = 442 ± 10 d) included six EW and six TW steers. Calves chosen for slaughter group 1 were selected based on their BW of 523 kg. These steers were delivered for slaughter at the University of Missouri abattoir 21 d after the termination of Exp 1. The 12 steers selected for slaughter group 2 were chosen based on their BW and growth projection estimates, which put them at 523 kg of BW 50 d after the slaughter of group 1. The 50-d period between the slaughtering of groups 1 and 2 was intentionally planned to create a diverse spread between animal days of age. Beef striploin steaks were then analyzed for tenderness by a Warner-Bratzler shear force (WBSF) instrument (G-R Elec. Mfg. Co., Manhattan, KS) after 0-, 7-, 14-, and 21-d periods of wet-aging.
For both slaughter groups, carcasses were allowed a 24-h chill period at 2°C, after which the striploin (IMPS, 180; NAMP, 1997) was removed from the right side of each carcass. Four strip steaks were cut 2.54-cm thick, immediately vacuum-packaged, and assigned randomly to one of four aging treatments (wet-aged for 0, 7, 14, or 21 d). After appropriate aging, the steaks were immediately prepared for WBSF measurements.
Warner-Bratzler Shear Force.
After the appropriate wet-aging periods, the steaks were removed from the vacuum package and cooked on a MagiKitch’n electric belt grill (Blodgett Co., Quakertown, PA) set for a 6-min cycle at 118°C (both top and bottom plate temperature) preheated for 2 h, as suggested by Lawrence et al. (2001). Cooking degree of doneness and shear force on a standard WBSF apparatus were conducted in accordance with AMSA (1995) standard procedures.
Statistical Analysis
Experiment 1.
Steers were blocked by age, sire, and farm of origin and were allotted randomly to the 2 x 2 factorial arrangement of treatments: EWI, EWN, TWI, or TWN (six steers per pen [three implanted and three nonimplanted] and 12 pens per weaning group). To evaluate the 2 x 2 factorial arrangement, the Mixed procedure of SAS (SAS Inst., Inc., Cary, NC), using compound symmetry as a variance covariance matrix, was used to analyze BW and ultrasonic tissue deposition at 28-d intervals throughout the feeding period and carcass composition and quality after slaughter. The fixed effects of age at weaning, implant strategy, and time, as well as all interactions, were tested for significance at a level of P < 0.05 for differences relative to fat and lean tissue deposition and feed consumed over time. Similarly, fat and lean tissue deposition and CON were expressed as a ratio of live BW and analyzed at 28-d intervals for the first 168 d that both groups were on feed. Pen was considered the experimental unit for differences in feed CON, resulting in 12 experimental units per weaning group. Animal was the experimental unit for ADG, BW, ultrasonic tissue measures, and carcass measurements. Least squares means, SE, and probabilities were calculated using the Type III mean squares for individual animal (implant x weaning age) as an error term.
Experiment 2.
Steers selected from Exp. 1 were blocked by BW into two slaughter groups of 12 and penned with six steers per pen (three TW and three EW); two pens were established per slaughter group. Data were analyzed using the Mixed procedure of SAS. Least squares means evaluated for LSD in a general linear model setting; weaning age and slaughter date were the fixed effects, and animal was the experimental unit. Differences in striploin steak WBSF values at each wet-aging period were considered significant at P <0.05.
|
Results
|
|---|
Days of Age
Early weaned calves were heavier (P < 0.05) than TW calves at the time the TW calves were weaned (202 d of age; Figure 1) and remained heavier until just before slaughter (370 d of age). Average daily gains fluctuated throughout the feed period for both TW and EW calves. Comparing BW gains from 230 d of age and older, exclusive of the 230-d BW collection, TW calves had greater (P < 0.001) ADG than did EW calves until 370 d of age (Table 4). The TW calves consumed more feed (P < 0.001) than did EW calves during the final 84 d before slaughter (Table 5).
View this table:
[in this window]
[in a new window]
|
Table 5. Average feed intake (kg·animal–1·d–1) on an as-fed basis for early weaned and traditionally weaned calves on a day-of-age basis
|
|
There were no differences among or between implant strategies of EW and TW calves on a time-on-feed basis for US-BF (P = 0.538 for implant x weaning age x time interaction) and US-LMA (P = 0.174 for implant x weaning age x time) variables (data not shown).
Implant strategy and the age at weaning x implant strategy interaction were not significant within the model for US-BF (P = 0.525 and 0.372, respectively) and US-LMA (P = 0.486 and 0.394, respectively) on a day-of-age basis for growth end points (data not shown). Ultrasonically determined LMA and BF were compared between TW and EW calves on a day-of-age basis. From 230 d of age throughout the feeding period of TW calves, the EW calves maintained a thicker BF (P < 0.001) from feeding to slaughter (Figure 2). Similar to BF, EW calves maintained larger (P < 0.001) US-LMA than TW calves on a day-of-age basis (Figure 3). Traditionally weaned calves had greater ADG for four of six weigh periods during the initial feeding period (Table 4
).
Time on Feed
To evaluate differences on a time-on-feed basis, US-BF, US-LMA, and feed CON were compared as a ratio of BW over the first 168 d each group was placed on a feedlot diet immediately after weaning. This was done because the EW calves started on feed at approximately 90 d of age, and the TW calves started at approximately 174 d of age. Traditionally weaned calves had a greater (P < 0.001) US-BF relative to live BW (US-BF:BW) than EW steers (Figure 4). The reverse was true for LMA; EW steers had a greater (P < 0.001) US-LMA:BW on a days-on-feed basis than TW steers (Figure 5).
Age at weaning (P < 0.001) and implant strategy (P < 0.015) affected US-BF:BW (Figure 4); however, age at weaning x implant was not significant (P = 0.367). Early weaned steers had a lower (P < 0.001) US-BF:BW (0.026 cm/kg) than did TW steers (0.029 cm/kg). As expected, implanted steers averaged a lower (P = 0.015) US-BF:BW (0.028 cm/kg) than non-implanted steers (0.029 cm/kg). A weaning age x time interaction was observed (P = 0.001; Figure 4). Early weaned calves entered the feedlot (d 0) with a greater US-BF:BW than did TW steers. The ratio was equal after 28 d, and from d 56 through the remainder of the feeding period, TW steers had greater (P < 0.001) US-BF:BW.
Similar to the US-BF:BW results, age at weaning (P < 0.001) and implant strategy (P = 0.014) affected US-LMA:BW (Figure 5); however, the age x implant interaction was not significant (P = 0.342). Furthermore, the influence of implants did not manifest itself throughout the time on feed (implant x time; P = 0.953). Overall, EW steers had a larger US-LMA:BW (1.08 cm2/kg) than did TW steers (0.94 cm2/kg). Surprisingly, implanted steers had a lower (P = 0.014) US-LMA:BW (0.99 cm2/kg) than non-implanted steers (1.03 cm2/kg). A weaning age x time interaction was observed (P < 0.001; Figure 5). Early weaned calves entered the feedlot with greater US-LMA:BW than did TW steers; however, the differences between the two age groups diminished over time (Figure 5).
Traditionally weaned calves consumed more feed (P < 0.001) for the first 168 d on feed than did EW calves (data not shown); however, TW steers had a greater (P < 0.001) CON:BW, which peaked at approximately 56 d when EW steers consumed more feed relative to their BW. The EW CON:BW continued to increase until d 84, maintained a plateau through d 140, then fell below that of the TW steers (P = 0.027) at the final weigh period (Figure 6).
Implant strategy had an influence on the amount of feed consumed per pen. The implanted steers consumed less feed (P = 0.003) relative to their BW than non-implanted counterparts (implanted CON:BW = 2.48 kg/kg vs. nonimplanted CON:BW = 2.63 kg/kg). The lower CON:BW of the implanted steers may be partially responsible for the lower US-LMA:BW also observed in the implanted steers. Overall, weaning age had no influence (P = 0.261) on CON:BW; however, the influence of weaning age over time (age x time interaction) was significant (P < 0.001). Figure 6 illustrates that TW CON:BW peaked at approximately 56 d, whereas EW CON:BW continued to increase until d 84, reaching a plateau through 140 d on feed. No significant interaction between weaning age and implant strategy was observed (P = 0.847).
Overall Carcass Data
Implant Groups.
The main effects of implant strategy (P < 0.01) and age at weaning (P = 0.048) explained differences in HCW; however, their interaction term was not significant (P = 0.475). Implanted EW calves had heavier (P < 0.05) HCW than did both EWN and TWN, but they did not differ (P = 0.113) from TWI steers. The TWI carcasses were heavier (P = 0.013) than TWN carcasses, but they did not differ from the EWI (P = 0.086) or EWN (P = 0.113) carcasses (Table 6). The EWN steers had more marbling than did TWI (P = 0.012) and TWN (P = 0.043) groups, but were statistically equal to EWI (Table 6).
View this table:
[in this window]
[in a new window]
|
Table 6. Carcass measurements for early weaned, nonimplanted (EWN); early weaned, implanted (EWI); traditionally weaned, nonimplanted (TWN); and traditionally weaned, implanted (TWI) calves
|
|
Implanted EW steers had deposited more fat adjacent to the 12th rib than EWN steers (P = 0.04). The LMA and liver abscess scores did not differ among the four treatments (main effect; P = 0.794 and 0.528, respectively).
EW vs. TW Beef Steers.
Early weaned steers had a heavier (P = 0.048) HCW than did TW steers (Table 7), and EW marbling scores were greater than (P = 0.023) those for TW steers. There were no differences between treatments for liver abscess scores (P = 0.243), LMA (P = 0.396), or BF measurements (P = 0.722; Table 7). For USDA quality grade, 57% of the EW calves graded Average Choice or greater, whereas only 37% of the TW steers graded Average Choice or greater (P = 0.034). Within those percentages, five EW carcasses and one TW carcass graded Low Prime or greater (Table 7).
Experiment 2: WBSF.
Shear force values were taken to indicate the level of tenderness, as well as the rate of tenderization, according to age of the steers and duration of meat aging. In addition, SD derived from the six cores of each steak were analyzed as an indication of the uniformity of tenderness within a treatment group. Although tenderness scores dropped 1 kg after 7 d of aging, there were no differences in tenderness among treatment groups aged for 0 or 7 d (Table 8). At 14 d of aging, differences (P = 0.001) were noted between group 1 (404 ± 10 d of age) and group 2 (442 ± 10 d of age) independent of weaning treatment, whereby the EW and TW steaks from group 1 (the younger animals) were more tender than either the EW or TW steaks from group 2 (the older animals). Within the second, older animal slaughter group, steaks from EW were more tender (P = 0.045) than TW steaks aged 14 d. At 21 d of aging, no differences in WBSF were noted across treatment groups (P = 0.354).
Standard deviations of the shear forces were calculated to estimate uniformity within the steaks for each treatment (Table 8). At the time of carcass processing (0 d aged), steaks representing TW animals in group 2 were more variable (P < 0.05) than the steaks from EW and TW animals in group 1. At 7 d of aging, uniformity was consistent among treatments; however, a trend (P = 0.055) was observed for EW WBSF to be more variable (higher SD) than TW WBSF SD. Steak samples aged 14 d from EW steers slaughtered in group 1 (EW1) were more uniform (P < 0.05) than either the steak samples from EW or the TW animals in group 2. There were no differences (P > 0.05) among samples from the EW animals in group 2, or those from TW animals in groups 1 or 2 after 14 d of aging. Finally, after 21 d of aging, samples from EW animals in group 1 had less tenderness variability (P < 0.05) than those from TW animals in group 2.
|
Discussion
|
|---|
Early weaned calves had more US-BF than TW calves, most likely because EW calves were on feed 112 d before the TW calves were weaned. Consequently, TW calves were never able to compensate for the shorter period of time in the feedlot than EW calves and maintained lower US-BF measurements throughout the seven measurement periods after weaning. Similarly, EW calves had larger US-LMA relative to the additional time spent in the feedlot before the arrival of the TW group. Because EW calves began on feed at approximately 90 d of age and the TW calves at approximately 174 d of age, US-BF, US-LMA, and feed CON were evaluated as a ratio of live BW over the first 168 d each weaning treatment was on feed immediately after weaning.
Although weaning age x implant strategy and weaning age x implant x time were not significant, the influence of implants was observed. All calves associated with the implanted treatment were implanted at weaning and again 80 d later. Early weaned calves had a decreased US-BF:BW, as d 0 measurements differed from d 28 and d 56 measurements. The US-BF:BW reached d 0 status at d 84, which differed from d 112 until slaughter. Anabolic implants function to alter composition of gain in feedlot cattle by improving protein accretion and decreasing fat deposition (Guiroy et al., 2002). In the current study, implanting seemed to repartition energy away from fat deposition in the EW steers for the first 56 d on feed. A similar, less dramatic effect was observed for the TW calves. They too were implanted at weaning (d 0); however, these older steers did not record a lower US-BF:BW, as d 0 and d 28 measurements did not differ and each subsequent US-BF:BW was greater than the previous from that point until slaughter. This increase in US-BF relative to BW is similar to that reported by Hornick et al. (2000), who noted a rapid increase in BF within 28 to 56 d immediately following initial exposure to a feedlot diet. Implant strategy x time was not a significant factor relative to these body composition ratios in the current study. This is likely due to the timing of the implants. The EW steers had received two sets of implants (90 and 170 d of age) by the time the TW steers entered the feedlot at 174 d of age. The same implant strategy was employed for the TW cattle: implanted on entry to the feedlot and again 80 d later. The ratios of LMA or BF to BW were calculated from US data recorded during the periods both weaning groups overlapped in the feedlot. Thus, the effect of implants might have been diluted because the EW steers received their last implant approximately 200 d before slaughter, whereas the TW received their last implant approximately 88 d before slaughter.
The same observations can be made comparing US-LMA and time on feed, whereby physiological age seems to have more of an influence on growth than time on feed. The age at weaning x time interaction suggests that the EW calves showed a much more marked decrease in the US-LMA:BW than the older TW steers, likely because of frame and organ growth and development. By the time the TW steers entered the feedlot, the majority of frame and organ growth had occurred; therefore, additional BW might have been more attributed to muscle and fat accretion (Blaxter, 1962). In the current study, a gradual increase in muscle and fat was noted, and physiological age seemed to be more of a factor than days on feed.
As a result of TW calves gaining more BW than EW calves over four of the six feeding periods, the TW calves compensated for their lighter BW at weaning, thereby finishing with a BW equivalent to the EW calves at the end of the growth period. The idea of compensation is further accentuated by the fact that feed CON by EW calves did not drastically fluctuate in their final 140 d on feed, but TW calves seemed to become less efficient. This result is observed in Figure 6, showing that CON:BW peaked at 56 d on feed, which was also the point TW steers began to deposit a greater level of BF relative to their live BW. Although some investigators have addressed the subject of nutrient partitioning in cattle (Neesse and Kirchgessner, 1975; Eisemann et al., 1996; Turner et al., 1998), more specific physiological evaluations may be beneficial in determining whether there is an age component to calf feed efficiency and growth rate. For example, future research should investigate how age of cattle from birth to approximately 17 mo affects nutrient use for growth (i.e., nutrients for skeletal, connective tissue, and organ growth vs. protein and fat accretion).
The carcass data results just reported are common to early weaning studies, as well as implant studies. In the current study, slaughter weights (final BW) of EWI calves were equivalent to the TWI calves. This result is notable, given that the EWI calves were on feed 112 d longer than TWI calves. Even though the TWI calves weighed more than the TWN calves, they did not outweigh the EWN calves. This result could be attributed to the longer feeding period for EWN calves than for TWI calves.
Carcasses representing EWN steers had more marbling than did TWI calves, which could be attributed to repartitioning of nutrients by implants into protein deposition rather than fat deposition (Solis et al., 1989). With this same point in question, the EWN marbling scores also exceeded those of the TWN, likely because of their longer feed period. There were no differences between EWN and EWI marbling scores, likely because of the length of time on feed.
The EWI steers had more BF than EWN steers; however, because there were no differences found among or between the TWI and TWN calves, this greater BF is most likely due to the extensive time the EW calves spent on a high-concentrate/high by-product diet. As stated previously, the implant effects might have diminished because of the interval between final implantation and slaughter (198 d). A more rigorous implant regimen, more similar to industry protocols, is recommended for future studies.
Feedlot diets low in forage put cattle at a greater risk for ruminal acidosis. In a review of bloat in feedlot cattle, Cheng et al. (1998) stated that calves consuming a higher proportion of rapidly fermented feedstuffs destabilize the ruminal microbial population through proliferation of more acid-tolerant bacteria. Nagaraja and Chengappa (1998) reported that liver abscesses observed at slaughter could be an indication of previous feedlot acidosis resulting from aggressive grain-feeding programs. Given that liver scores were found to be equivalent across treatment groups in the current study, extended durations on a high-concentrate/high by-product diet did not seem to affect overall calf liver health late in the feed period. The initial EW diet shown in Table 1 contained a high proportion of corn, rice bran, and dried distillers grains. Despite the lack of liver abscesses as an indicator of poor health, the EW calves required more intense management and slight adjustments in feed early in the feed period (first 56 d on feed) to maintain acceptable performance. This finding may indicate that liver abscess scores are not a good indicator of health throughout the entire feeding duration, but perhaps are only a good indicator for a period of time closely leading up to slaughter.
Final carcass LMA were not different among treatment groups, despite the implant strategy or feeding durations imposed. This result was surprising given that the EW calves had larger US-LMA than TW from 202 d of age until 2 d before slaughter (Figure 3); however, the gap between the two treatments was shrinking, which illustrates the potential for misrepresentation of estimating carcass variables from live US measurements.
The similarity in BF is interesting considering the differences in marbling scores. Wertz et al. (2002) noted that EW calves had greater marbling scores at any given fat thickness and that the EW calves deposit less subcutaneous fat relative to marbling. Myers et al. (1999b) also observed greater marbling scores and USDA quality grades in EW vs. TW calves. These findings suggest that there might be two separate mechanisms for dictating subcutaneous and i.m. fat deposition at different stages of development. Greater marbling scores in younger calves might indicate a physiological mechanism manipulating fat deposition for specific needs at varying stages in life. For instance, it might be unnecessary for younger calves being fed high-concentrate diets to metabolize i.m. fat for other processes because ample nutrients are provided through the feed. The TW calves, however, might be lacking sufficient nutrients (especially by the end of the dam’s lactation) to provide a sufficient combination of dietary energy and nutrients necessary to accommodate both muscle growth and i.m. fat deposition.
Similar to the findings of Myers et al. (1999b), a greater proportion of EW carcasses graded USDA Choice or greater in the current study, and a greater number graded Prime. This result could reflect the lengthened period on feed or the age-dependent mechanism suggested previously as it relates to nutrition and fat deposition.
In Exp. 2, steaks from EW and TW steers in group 1 were more tender than steaks from EW and TW steers in group 2 after 14 d of aging. These results support past data, which indicated that younger animals are more tender than older ones (Hiner and Hankins, 1950; Shorthose and Harris, 1990). Nonetheless, after 21 d of aging, there were no differences in tenderness, which is likely due to previous findings indicating that 14 d of postmortem aging is optimal for maximum LM tenderness (Calkins and Seideman, 1988; Mitchell et al., 1991). The rate at which the younger calves reached maximum tenderness relative to the older calves might indicate a difference in the ratio of muscle proteases available in younger muscle tissues, as younger animals in active growth have a greater protein turnover (Huff-Lonergan et al., 1995). Another possibility, as suggested in Shimokomaki et al. (1972), is that collagen crosslinking in older animals is more advanced, resulting in less heat-soluble collagen and tougher meat. As the animal ages, this crosslinking becomes increasingly complex, and it could be expected that younger animals would have lower tenderness variability (smaller SD) within ribeye steaks. Supporting this theory, there were consistent differences in SD between the EW steers in group 1 and TW steers in group 2; steaks from EW steers in group 1 had lower SD at 0, 14, and 21 d of postmortem aging.
|
Implications
|
|---|
The results of this study indicate that calves introduced to a high-concentrate/high-by-product diet at 90 d of age are heavier, have more 12th rib back fat, and have larger longissimus muscle area at the time their contemporaries are weaned at a more traditional 174 d of age. The early weaned calves in this experiment generated heavier carcasses that had a greater propensity for grading USDA Choice or greater than traditionally weaned steers of the same age. We conclude that the improvements in hot carcass weight, longissimus muscle area, and USDA quality grade can be attributed to the extra time spent in the feedlot. The health problems experienced early in this experiment were not realized at slaughter through evaluation of liver abscesses or scarring. Based on liver evaluation, there was little evidence to conclude that the diets fed in this experiment adversely affected animal health.
|
Footnotes
|
|---|
1 This research was supported in part by the Missouri Agric. Exp. Stn. Project No. 0569 and the Missouri Beef Industry Council. 
2 The authors thank P. Brooks, P. McCarty, and P. Lancaster for their support at the UMC Beef South Farm and also thank D. Davis and R. Smoot for supplying valuable preweaning records from the calves on this study. We also thank R. Stouffer and R. Wanner of Animal Ultrasound Services for their invaluable knowledge and services pertaining to the ultrasound images captured throughout the duration of this study.
3 Correspondence: 920 East Campus Dr. ASRC S133B (phone: 573-882-3176; fax: 573-882-6827; e-mail: bergep{at}missouri.edu).
Received for publication February 4, 2005.
Accepted for publication August 1, 2005.
|
Literature Cited
|
|---|
AMSA. 1995. Research Guidelines for Cookery, Sensory Evaluation and Instrumental Tenderness Measurements of Fresh Meat. Am. Meat Sci. Assoc. Natl. Livest. Meat Board, Chicago, IL.
Blaxter, K. L. 1962. Some further indirect approaches: The comparative slaughter technique. Pages 64–69 in The Energy Metabolism of Ruminants. Hutchinson Sci. Tech., London, UK.
Brink, D. R., S. R. Lowry, R. A. Stock, and J. C. Parrott. 1990. Severity of liver abscesses and efficiency of feed utilization of feedlot cattle. J. Anim. Sci. 68:1201–1207.[Abstract]
Calkins, C. R., and S. C. Seideman. 1988. Relationships among calcium-dependent protease cathepsins B and H, meat tenderness and the response of muscle to aging. J. Anim. Sci. 66:1186–1193.[Abstract/Free Full Text]
Cheng, K. J., T. A. McAllister, J. D. Popp, A. N. Hristov, Z. Mir, and H. T. Shin. 1998. A review of bloat in feedlot cattle. J. Anim. Sci. 76:299–308.[Abstract/Free Full Text]
Eisemann, J. H., G. B. Huntington, and D. R. Catherman. 1996. Patterns of nutrient interchange and oxygen use among portal-drained viscera, liver, and hindquarters of beef steers from 235 to 525 kg body weight. J. Anim. Sci. 74:1812–1831.[Abstract]
FASS. 1999. Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching. 1st rev. ed. Fed. Anim. Sci. Soc., Savoy, IL.
Fluharty, F. L., S. C. Loerch, T. B. Turner, S. J. Moeller, and G. D. Lowe. 2000. Effects of weaning age and diet on growth and carcass characteristics in steers. J. Anim. Sci. 78:1759–1767.[Abstract/Free Full Text]
Green, W. W., and J. Buric. 1953. Comparative performance of beef calves weaned at 90 and 180 day of age. J. Anim. Sci. 12:561–572.[Abstract/Free Full Text]
Guiroy, P. J., L. O. Tedesch, D. G. Fox, and J. P. Hutcheson. 2002. The effects of implant strategy on finished body weight of beef cattle. J. Anim. Sci. 80:1791–1800.[Abstract/Free Full Text]
Hiner, R. L., and O. G. Hankins. 1950. The tenderness of beef in relation to different muscles and age in the animal. J. Anim. Sci. 9:347–353.
Hornick, J. L., C. Van Eenaeme, O. Gerard, I. Dufrasne, and L. Istasse. 2000. Mechanisms of reduced and compensatory growth. Domest. Anim. Endocrinol. 19:121–132.[Medline]
Huff-Lonergan, E., F. C. Parrish, Jr., and R. M. Robson. 1995. Effects of postmortem aging time, animal age, and sex on degradation of titin and nebulin in bovine longissimus muscle. J. Anim. Sci. 73:1064–1073.[Abstract]
Lawrence, T. E., D. A. King, E. Obuz, E. J. Yancy, and M. E. Dikeman. 2001. Evaluation of electric belt grill, forced-air convection oven and electric broiler cookery methods for beef tenderness research. Meat Sci. 58:239–246.
Martin, E. L. 1991. A rapid method to determine beef ribeye areas at grading chain speed. J. Anim. Sci. 69(Suppl. 1):341. (Abstr.)
Mitchell, G. E., J. E. Giles, S. A. Rogers, L. T. Tan, R. J. Naidoo, and D. M. Ferguson. 1991. Tenderizing, aging, and thawing effects on sensory, chemical, and physical properties of beef steaks. J. Food Sci. 56:1125–1129.
Myers, S. E., D. B. Faulkner, F. A. Ireland, and D. F. Parrett. 1999a. Comparison of three weaning ages on cow-calf performance and steer carcass traits. J. Anim. Sci. 77:323–329.[Abstract/Free Full Text]
Myers, S. E., D. B. Faulkner, F. A. Ireland, L. L. Berger, and D. F. Parrett. 1999b. Production systems comparing early weaning to normal weaning with or without creep feeding of beef steers. J. Anim. Sci. 77:300–310.[Abstract/Free Full Text]
Nagaraja, T. G., and M. M. Chengappa. 1998. Liver abscesses in feedlot cattle: A review. J. Anim. Sci. 76:287–298.[Abstract/Free Full Text]
NAMP. 1997. The Meat Buyers Guide. North Am. Meat Processors Assoc., Reston, VA.
Neesse, K. R., and M. Kirchgessner. 1975. Changes in the nutrient and energy content in defined parts of the veal calf (Author’s translation–Abstract only). Z. Lebensm. Unters. Forsch. 159:193–203.[Medline]
NRC. 2000. Nutritional Requirements of Beef Cattle. 7th rev. ed. Natl. Acad. Press, Washington, DC.
Schoonmaker, J. P., M. J. Cecava, D. B. Faulkner, F. L. Fluharty, H. N. Zerby, and S. C. Loerch. 2003. Effect of source of energy and rate of growth on performance, carcass characteristics, ruminal fermentation, and serum glucose and insulin of early-weaned steers. J. Anim. Sci. 81:843–855.[Abstract/Free Full Text]
Schoonmaker, J. P., S. C. Loerch, F. L. Fluharty, H. N. Zerby, and T. B. Turner. 2002. Effect of age at feedlot entry on performance and carcass characteristics of bulls and steers. J. Anim. Sci. 80:2247–2254.[Abstract/Free Full Text]
Shimokomaki, M., D. F. Elsden, and A. J. Bailey. 1972. Meat tenderness: Age related changes in bovine intramuscular collagen. J. Food Sci. 37:892–896.
Shorthose, B. B., and P. V. Harris. 1990. Effect of animal age on the tenderness of selected beef muscles. J. Food Sci. 55:1–14.
Solis, J. C., F. M. Byers, G. T. Schelling, and L. W. Greene. 1989. Anabolic implant and frame size effects on growth regulation, nutrient repartitioning and energetic efficiency of feedlot steers. J. Anim. Sci. 67:2792–2801.
Turner, N. D., R. Knapp, F. M. Byers, and J. J. Kopchick. 1998. Expression of mutant bovine growth hormone genes in mice perturbs age-related nutrient utilization patterns. J. Nutr. 128:520–524.[Abstract/Free Full Text]
USDA. 1997. USDA Official United States Standards for Grades of Carcass Beef. USDA, Agric. Marketing Service, Washington, DC. Available: http://www.ams.usda.gov/lsg/stand/standards/beef-car.pdf. Accessed Sep. 22 2005.
Wertz, A. E., L. L. Berger, P. M. Walker, D. B. Faulkner, F. K. McKeith, and S. L. Rodriguez-Zas. 2002. Early weaning and postweaning nutritional management affect feedlot performance, carcass merit, and the relationship of 12th rib fat, marbling score, and feed efficiency among Angus and Wagyu heifers. J. Anim. Sci. 80:28–37.[Abstract/Free Full Text]
Top
Abstract
Introduction
) vs. traditionally weaned (TW = 
) calves on a day-of-age basis. Within a specific day of age, means with *** differ at P < 0.001 and those with * differ at P < 0.05.
