J. Anim. Sci. 2005. 83:679-685
© 2005 American Society of Animal Science
Comparison of characteristics of lambs fed concentrate or grazed on ryegrass to traditional or heavy slaughter weights. I. Production, carcass, and organoleptic characteristics1
R. J. Borton*,2,
S. C. Loerch
,
K. E. McClure and
D. M. Wulf
* Agricultural Technology Institute and
and
Department of Animal Sciences, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster 44691; and
and
Department of Animal and Range Science, South Dakota State University, Brookings 57007
 |
Abstract
|
|---|
The objectives of this study were to determine the effects of finishing lambs on concentrate (C) or by grazing ryegrass forage (F) to slaughter end weights of 52 (N) or 77 kg (H) on carcass characteristics and organoleptic properties. This experiment included 64 Targhee x Hampshire lambs (average BW = 24 ± 1 kg) in a 2 x 2 x 2 factorial arrangement of treatments to compare wethers vs. ewes, C vs. F, and N vs. H slaughter weights. No interactions (P > 0.10) were observed between gender and other main effects. Hot carcass weight and dressing percent were greater (P < 0.001) for C- than for F-fed lambs. Backfat thickness also was greater (P < 0.001) for lambs fed C than for those fed F. Moreover, USDA lean quality score and USDA yield grades were higher (P < 0.001) for C- than for F-fed lambs, as well as for lambs slaughtered at H vs. N market weights. There was a higher (P < 0.005) incidence of off odors and off flavors in cooked muscle from F- vs. C-fed lambs, and also from H vs. N slaughter-weight lambs. The heavy C-fed lambs had juicier (P < 0.001) meat than other treatment combinations. Cooked meat from C-fed lambs received higher (P < 0.001) overall acceptability scores. Concentrate-finished lambs produced fatter carcasses and more palatable meat than forage-finished lambs; however, forage finishing allowed for slaughter at heavier weights without excessive fat deposition.
Key Words: Carcass • Concentrate-Finished • Fat • Forage-Finished • Lamb • Palatability
|
Introduction
|
|---|
Traditional slaughter weights of lambs in the United States are approximately 60% of the physiological mature size of the dam (Snowder et al., 1994
). Many packers and retailers indicate they prefer larger carcasses; however, nutrition and management traditions may influence the ability to produce lambs with larger carcasses. Lamb meat is defined as being from an ovine not older than 1 yr without permanent teeth and spool joints (AMSA, 2001). Despite meeting this classification, leanness and palatability of meat of heavier lambs is of concern. Recent research has shown that lambs finished on concentrate were fatter than lambs grazed on perennial ryegrass forage (McClure et al., 1994, 1995; Murphy et al., 1994) or alfalfa (McClure et al., 2000). However, no information has been published on the efficacy of using grass-based finishing systems to increase carcass weight, while maintaining desirable carcass composition and organoleptic properties. Although the mature size of the ram and ewe influences the optimal market size of the lamb, rearing management also may be involved. Thus, this study was undertaken to compare the effects of grazing ryegrass vs. feeding a high-concentrate diet in a dry lot on growth of lambs, carcass characteristics, and organoleptic properties of muscle from lambs fed to 65 and 100% of the physiological mature size of the dam.
|
Materials and Methods
|
|---|
Sixty-four Targhee x Hampshire lambs (32 ewes and 32 wethers) were randomly assigned by gender to two dietary/management treatments and two final slaughter weights. Lambs born in March 1997 were offered creep feed for the last 14 d before weaning at approximately 55 d of age. The experiment began 23 d after weaning. The dietary management treatments were 1) high-concentrate diet (Table 1) fed in a dry lot, or 2) all-forage (rotationally grazed on perennial ryegrass until late October 1997, and fed medium-quality grass hay and grazed on grass, if possible, through the winter until April 15, 1998, and then returned to ryegrass pastures until finished). For lambs fed the high-concentrate diet, groups of four lambs of the same gender were placed in eight dry-lot pens, and assigned randomly to a slaughter treatment of either 52 or 77 kg (two pens per treatment combination). The 32 lambs assigned to the forage treatment were allotted randomly within gender to eight groups for slaughter at either 52 or 77 kg. Four groups (two heavy and two normal slaughter weight) of four ewes each were assigned randomly to four 1.28-ha pastures. Likewise, four groups of wethers were assigned randomly to the same four pastures, such that each pasture had four ewes and four wethers. Each ryegrass pasture was divided into eight 0.16-ha paddocks for rotational grazing. An eight-paddock rotation (0.16 ha per paddock) of ryegrass was used, where lambs grazed for 3 to 4 d per rotation, with a 9- to 12-d regrowth period allowed between grazing periods. Grazing lambs were provided with Se-fortified trace mineral salt and dicalcium phosphate (2:1 ratio). Protocols concerning animal care followed guidelines recommended in the Guide for the Care and Use of Agricultural Animals in Agriculture Research and Teaching (FASS, 1999).
Lambs were weighed every 2 wk until they reached their end weight. Daily gains were determined for both concentrate- and forage-fed lamb treatments. When the targeted end weight for each group was reached, lambs were slaughtered at The Ohio State University Meat Laboratory. One normal-slaughter-weight, concentrate-fed lamb performed poorly due to physical problems, three normal-slaughter-weight, forage-fed lambs performed poorly due to health problems, and one heavy-slaughter-weight, forage-fed lamb died; therefore, these lambs were removed from the data set. Six heavy-slaughter-weight, forage-fed lambs exhibited no or very slow growth rates late in the trial and did not reach the specified slaughter weight by the end of the trial. These lambs weighed at least 10 kg less than the target end weight, and they were not slaughtered to avoid bias in this slaughter weight treatment. Carcass weights were recorded and visual evaluations of leg conformation, carcass conformation, body wall thickness, lean quality, quality grade, yield grade, and maturity (lamb or mutton) were determined by trained Ohio State University personnel. Carcasses were split in half, and right sides were used for further analyses. Right sides were separated between the 12th and 13th ribs, and LM area was measured with a planimeter. Then, right sides were further fabricated into wholesale cuts. Two 1.27-cm-thick chops were taken from the caudal end of the rack, packaged, and frozen for organoleptic evaluation at a later date. After all lambs were slaughtered, these chops were thawed in a cooler (4°C) for 24 h, wrapped in aluminum foil, and baked for 30 min at 173°C. After cooking, chops were evaluated for off odor, lamb odor, off flavor, lamb flavor, juiciness, tenderness, and overall acceptability by a 10-member panel. Panelists consumed lamb at least once yearly, and they evaluated the chops on a 10-point scale, with 0 representing the least amount of odor, flavor, juiciness, tenderness, and overall acceptability, and 9 representing the most. They were exposed to the procedure and evaluation expectations in a preliminary session. During the preliminary session, panelists evaluated two samples of lamb from a 3-yr-old ewe and two samples of lamb purchased from the meat case of a local supermarket.
Data were analyzed as a completely randomized design using the GLM procedure of SAS (SAS Inst., Inc., Cary, NC). The 2 x 2 x 2 factorial model for performance and carcass characteristics included main effects of diet, end BW treatment, gender, and all interactions. Treatment least squares means were compared using the PDIFF option of SAS protected by a significant (P < 0.05) F-value. Each treatment combination group of four lambs served as the experimental unit for performance and carcass data analyses.
|
Results and Discussion
|
|---|
Gender was included in the model as a main effect, but no (P > 0.10) interactions were noted between gender and other main effects; therefore, only diet and BW treatments, along with their interactions, are discussed.
Lamb Performance
All Lambs.
The ADG by concentrate-fed lambs was nearly three times (P < 0.001) that of forage-fed lambs (Table 2). Chestnutt (1994) reported similar differences in growth rate between concentrate- and forage-fed lambs. McClure et al. (1994, 1995) also compared growth rate characteristics of forage- and concentrate-fed lambs, and demonstrated that lambs grazing ryegrass gained approximately 140 g/d, whereas those fed concentrate gained approximately 280 g/d. In the present study, lambs grazing ryegrass (and fed hay in the winter) gained 120 g/d, whereas those fed concentrate gained 330 g/d. The normal-slaughter-weight lambs gained 18% more (P < 0.05) per day than the heavy-slaughter-weight lambs. Days on test showed an interaction between dietary and slaughter weight treatments (P = 0.001). For concentrate- and forage-fed lambs, 79 and 264 additional days on test were required to reach the heavy target end weight compared with the normal end weight, respectively. This difference in days on test due to slaughter weight was calculated using the mean days on test when heavy weight groups were slaughtered. However, as noted previously, six lambs in the forage-fed, heavy-slaughter-weight treatment did not attain the target slaughter weight (due to very slow growth rate). Therefore, the 264-d difference in days on test between normal and heavy slaughter weight should be considered a minimum value for forage-fed lambs. These results are similar to those reported by McClure et al. (1994). As planned in the experimental design, the final BW and the total gain for lambs fed the concentrate and forage dietary treatments were similar, whereas heavy slaughter lamb weights were higher (P < 0.001) than normal slaughter weight lambs.
View this table:
[in this window]
[in a new window]
|
Table 2. Effects of diet and endpoint slaughter weight of all lambs and slaughtered lambs on production characteristics
|
|
Slaughtered Lambs.
For the lambs slaughtered that completed the trial, there was an interaction (P < 0.03) between diet and slaughter treatment for ADG (Table 2
). For concentrate-fed lambs, ADG did not differ between normal and heavy slaughter weights; however, for forage-fed lambs, those slaughtered at a normal weight gained 33% faster than those slaughtered at a heavy weight. This decrease in overall ADG by heavyweight lambs fed forage occurred during their last 25 kg of gain (results not shown).
Lamb Carcass Characteristics.
Weights off-test and at slaughter were greater (P < 0.01) for concentrate- than forage-fed lambs (Table 3). As a result, the percentage of shrink tended to be greater (P = 0.07) for the forage-fed than for the concentrate-fed lambs. Hot carcass weights of concentrate-fed lambs were 3.7 kg greater than those of forage-fed lambs due to lower (P < 0.001) dressing percent for forage-fed lambs. Forage finishing systems likely increase digestive tract size and decrease external fat cover, which both result in lower dressing percents. Fluharty et al. (1999) reported that intestinal tracts represented a greater proportion of live weight for forage-fed lambs than for concentrate-fed lambs. McClure et al. (2000) reported that lambs finished on forage had heavier intestinal weights than those finished on concentrate, whereas reticulorumen weight was not affected by diet. In the present study, concentrate-fed lambs were fatter (P < 0.001) than the forage-fed lambs slaughtered at similar weights. As expected, HCW of heavy-slaughter-weight lambs were greater (P < 0.001) than those of normal-slaughter-weight lambs. Ely et al. (1979) slaughtered early-weaned lambs at 41 or 50 kg, and reported a 4% increase in dressing percents for the heavier slaughter weight lambs. Lloyd et al. (1980) slaughtered lambs at 54 and 64 kg and reported similar increases in dressing percent for lambs slaughtered at the heavier weight.
In the present study, fat thickness of concentrate-fed lambs was 4 mm greater (P < 0.001) than that of forage-fed lambs. In an earlier report with lighter-weight lambs, McClure et al. (1995) reported that concentrate fed lambs had 2 mm greater fat thickness than those grazed on alfalfa. In the present study, increasing slaughter weight from 48 to 70 kg resulted in a 5 mm increase (P < 0.001) in fat thickness. With lighter-weight lambs (36 kg), Kemp et al. (1970, 1972) also reported that a 20-kg increase in slaughter weight increased fat thickness by 5 mm. When Lloyd et al. (1980) increased slaughter weight from 54 to 64 kg, fat thickness was increased by 2 mm. The LM area of concentrate-fed lambs was 16% greater (P < 0.001) than that of forage-fed lambs, which is similar to an earlier study (McClure et al., 1994). Longissimus muscle area of heavy slaughter-weight lambs was 27% greater (P < 0.001) than that of normal-slaughter-weight lambs. Lloyd et al. (1980) reported that a 10 kg increase in slaughter weight resulted in a 19% increase in LM area.
We hypothesized that forage feeding would prolong the growth curve and allow for increased muscle mass at heavier slaughter weights without excess fat deposition. The interaction between diet and slaughter weight for fat depth was not significant (P = 0.17). Increasing slaughter weight resulted in a 115% increase in fat depth for forage-fed lambs and an 89% increase for concentrate-fed lambs. Feeding to a heavier weight increased LM area 28% for both groups. Slaughtering lambs at a heavier weight resulted in a 68% increase in body wall thickness when fed concentrate, but an 86% increase when fed forage (diet x slaughter weight interaction; P < 0.02). For leg and carcass conformation, heavy-weight carcasses had slightly more than one-third of a grade greater (P < 0.001) conformation than normal-weight carcasses. Lean quality of concentrate-fed lamb carcasses was approximately one-third of a grade greater (P < 0.001) than for those fed forage, and heavy-weight carcasses had a similar improvement compared with the normal-weight carcasses. Feeding concentrate increased (P < 0.02) overall quality compared with feeding forage, but weight at slaughter did not affect (P > 0.10) quality grade. Carcasses of forage-fed lambs had lower (P < 0.001) USDA yield grades than did those of concentrate-fed lambs, and normal-slaughter-weight lambs had lower (P < 0.001) USDA yield grades than heavy-slaughter-weight lambs. This resulted because concentrate-fed lambs and heavy slaughter weight lambs were fatter than their counterparts at slaughter. In this study, there was one spool joint present, indicating a yearling mutton carcass, and this carcass was in the forage-fed, heavy-carcass-weight treatment.
Organoleptic Evaluation.
Sensory panelists found a higher (P < 0.02) incidence of off odors and off flavors in forage-fed lambs compared with concentrate-fed lambs (Table 4). There was a higher (P < 0.04) incidence of off flavors in heavy-slaughter-weight lambs than in those slaughtered at normal weights. These results are similar to those noted in a review by Field et al. (1983), who reported forage-fed lambs had a more undesirable flavor than concentrate-fed lambs. As there was no interaction (P > 0.80) between diet and slaughter weight, these negative effects on flavor of forage feeding and feeding to a heavier weight were consistent across main effects. Lamb flavor was rated higher (P < 0.001) for meat from concentrate-fed lambs than for forage-fed lambs, but slaughter weight did not affect (P > 0.13) lamb flavor. Lloyd et al. (1980) also found no difference in flavor of lambs slaughtered at light (54 kg) and heavy (64 kg) BW. Kemp et al. (1980) found that meat from pasture-fed lambs had less flavor than concentrate-fed lambs. Surprisingly, in the present study, heavy slaughter weight tended to increase tenderness for concentrate-fed lambs, whereas tenderness was not affected by slaughter weight of forage-fed lambs (diet x slaughter weight interaction; P = 0.06). Juiciness was rated higher for heavy than normal slaughter weight when lambs were fed concentrate, whereas juiciness of samples from forage-fed lambs was not affected by slaughter weight (diet x slaughter weight interaction; P < 0.01). This could be related to the fatness of carcasses from heavy-weight, concentrate-fed lambs. Kemp et al. (1980) found no difference in juiciness between pasture-fed and concentrate-fed lambs, and Lloyd et al. (1980) found no difference in juiciness between light- and heavy-weight lambs. Forage finishing decreased overall acceptability by 9% at normal slaughter weights, but decreased overall acceptability scores by 20% vs. concentrate finishing when lambs were fed to heavy slaughter weights (diet x slaughter weight interaction; P = 0.07).
View this table:
[in this window]
[in a new window]
|
Table 4. Effects of diet and endpoint slaughter weight of all lambs and slaughtered lambs on organoleptic properties on boneless rib chops
|
|
|
Implications
|
|---|
Feeding lambs to heavier-than-traditional slaughter weights using high-concentrate diets results in excessively fat carcasses. Large, lean lamb carcasses can be produced through forage finishing; however, forage finishing may result in much lower daily gains, much longer finishing periods, and less palatable lamb meat. Future research should examine the effectiveness of growing lambs on forage for an extended period of time followed by a short period of high-concentrate finishing to produce large, lean, highly palatable lamb carcasses.
|
Footnotes
|
|---|
1 Salaries and research support provided by state and federal funds appropriated to the Ohio Agric. Res. and Dev. Center, The Ohio State Univ., Wooster 44691-4096. The authors acknowledge the assistance of D. D. Clevenger for animal and forage management; G. D. Lowe for technical assistance, data tabulation, and statistical analysis of results; and G. D. Dunlap for lamb slaughter and carcass measurements. 
2 Correspondence: 1328 Dover Rd. (phone: 330-287-1310, ext. 1314; fax: 330-287-1333; e-mail: borton.1{at}osu.edu).
Received for publication February 3, 2004.
Accepted for publication December 9, 2004.
|
Literature Cited
|
|---|
AMSA. 2001. Meat Evaluation Handbook. Am. Meat Sci. Assoc., Savoy, IL.
Chestnutt, D. M. B. 1994. Effect of lamb growth rate and growth pattern on carcass fat levels. Anim. Prod. 58:77–85
Ely, D. G., B. P. Glenn, M. Mahyuddin, J. D. Kemp, F. A. Thrift, and W. P. Deweese. 1979. Drylot vs pasture: Early weaned lamb performance to two slaughter weights. J. Anim. Sci. 48:32–37.[Abstract/Free Full Text]
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.
Field, R. A., J. C. Williams, and G. J. Miller. 1983. The effect of diet on lamb flavor. Food Technol. 37:258–263.
Fluharty, F. L., K. E. McClure, M. B. Solomon, D. D. Clevenger, and G. D. Lowe. 1999. Energy source and ionophore supplementation on lamb growth, carcass characteristics, visceral organ mass, diet digestibility, and nitrogen metabolism. J. Anim. Sci. 77:816–823.[Abstract/Free Full Text]
Kemp. J. D., J. D. Crouse, W. Deweese, and W. G. Moody. 1970. Effect of slaughter weight and castration on carcass characteristics of lambs. J. Anim. Sci. 30:348–354.
Kemp, J. D., M. Mahyuddin, D. G. Ely, J. D. Fox, and W. G. Moody. 1980. Effect of feeding systems, slaughter weight, and sex on organoleptic properties, and fatty acid composition of lamb. J. Anim. Sci. 51:321–330.[Abstract/Free Full Text]
Kemp, J. D., J. M. Shelley, Jr., D. G. Ely, and W. G. Moody. 1972. Effects of castration and slaughter weight on fatness, cooking losses, and palatability of lamb. J. Anim. Sci. 34:560–562.[Abstract/Free Full Text]
Lloyd, W. R., A. L. Slyter, and W. J. Costello. 1980. Effect of breed, sex and final weight on feedlot performance, carcass characteristics and meat palatability of lamb. J. Anim. Sci. 51:316–320.[Abstract/Free Full Text]
McClure, K. E., M. B. Solomon, and S. C. Loerch. 2000. Body weight and tissue gain in lambs fed an all-concentrate diet and implanted with trenbolone acetate or grazed on alfalfa. J. Anim. Sci. 78:1117–1124.[Abstract/Free Full Text]
McClure, K. E., M. G. Solomon, N. A. Parrett, and R. W. Van Keuren. 1995. Growth and tissue accretion of lambs fed concentrate in drylot, grazed on alfalfa or ryegrass at weaning, or after backgrounding on ryegrass. J. Anim. Sci. 73:3437–3444.[Abstract]
McClure, K. E., R. W. Van Keuren, and P. G. Althouse. 1994. Performance and carcass characteristics of weaned lambs either grazed on orchardgrass, ryegrass, or alfalfa or fed all-concentrate diets in drylot. J. Anim. Sci. 72:3230–3237.[Abstract]
Murphy, T. A., S. C. Loerch, K. E. McClure, and M. B. Solomon. 1994. Effects of grain or pasture finishing systems on carcass composition and tissue accretion rates of lambs. J. Anim. Sci. 72:3138–3144.[Abstract]
NRC. 1985. Nutrient Requirements of Sheep. 6th ed. Natl. Acad. Press, Washington, DC.
Snowder, G. D., H. A. Glimp, and R. A. Field. 1994. Carcass characteristics and optimal slaughter weights in four breeds of sheep. J. Anim. Sci. 72:932–937.[Abstract]
This article has been cited by other articles:
|
|
|
|
 
R. J. Borton, S. C. Loerch, K. E. McClure, and D. M. Wulf
Characteristics of lambs fed concentrates or grazed on ryegrass to traditional or heavy slaughter weights. II. Wholesale cuts and tissue accretion
J Anim Sci,
June 1, 2005;
83(6):
1345 - 1352.
[Abstract]
[Full Text]
[PDF]
|
|
|
Top
Abstract
Introduction
