K.E. McClure,*, M.B. Solomon+, S.C. Loerch*,
D.D. Clevenger*, and G.D. Lowe*
*Department of Animal Sciences and
+Meat Science Research Laboratory, USDA/ARS, Beltsville, MD
Fifty Targhee Hampshire lambs (initial weight, 50.6 pounds) were used to compare the effect of an anabolic implant on lambs fed a concentrate diet with alfalfa grazing as a means to promote lean tissue accretion and minimize fat accretion. Lamb live body weight gains and bone, lean and fat gains were evaluated. Treatments were: 1) all-concentrate offered ad libitum in drylot to end body weight (DL); 2) DL with lambs implanted with trenbolone-acetate:estradiol-benzoate (DLTBA) at 79.2 pounds body weight; 3) DL with lambs switched to alfalfa grazing (DLALF) at 79.2 pounds body weight until end live weight; 4) alfalfa (ALF) to end live weight. Target end weight was 105 pounds for ewes and 111 pounds for wethers. During Phase 2, ADG for lambs on the DLTBA treatment was higher (P = 0.001) than those on the other three treatments. Fat gain was more for both leg (P = 0.006) and loin (P = 0.0003) in lambs fed the DL diet than for those grazed on ALF. Lean gain in loin of DLTBA lambs was more (P = 0.004) than for the other three treatments. This experiment suggests that fat accretion was more for concentrate-fed lambs than for alfalfa-grazed lambs before they reached the intermediate weight. The trenbolone acetate:estradiol benzoate implant at intermediate weight resulted in increased lean accretion in the loin compared to the other treatments.
Recent research in Ohio has shown that daily accretion of carcass lean has been more for lambs fed all-concentrate, offered ad libitum, than for lambs grazed on cool-season grasses or alfalfa (McClure et al., 1994; Murphy et al., 1994; McClure et al., 1995). However, daily accretion of carcass fat was more for concentrate-fed lambs than for lambs grazed on grass or alfalfa. In those studies, daily accretion was determined over the entire growing-finishing period.
Objectives of this experiment were to determine the effects of feeding an all-concentrate diet offered ad libitum during the first half of the finishing period to attain early lean accretion, followed by either an anabolic implant or alfalfa grazing to continue lean accretion and minimize fat accretion. This was compared to alfalfa grazing or concentrate feeding throughout the finishing period.
Fifty Targhee Hampshire lambs (25 wethers, 25 ewes; average weight 50.6 pounds) were used to measure live ADG and carcass tissue accretion (bone, lean, and fat). Treatments were: concentrate fed ad libitum in drylot (DL); DL to intermediate weight (79.2 pounds) then implanted with trenbolone acetate:estradiol benzoate (DLTBA); DL to 79.2 pounds then to alfalfa grazing (DLALF); and alfalfa grazing throughout (ALF). Concentrate diets are shown in Table 1. Diet 1 was fed to lambs which were on DL treatment to 79.2 pounds (Phase 1), and diet 2 was fed to lambs which were on DL or DLTBA treatments (Phase 2). The DLTBA and DLALF treatments were initiated when the pen average weight reached 79.2 pounds. Six lambs (3 wethers, 3 ewes) were slaughtered as baseline controls at 50.6 pounds live weight. Twelve lambs were assigned as intermediates and slaughtered at 79.2 pounds live weight. They were in either DL or ALF treatments until slaughtered.
The remaining 32 lambs were allotted at 4 per pen (4 wethers or 4 ewes) with two replicates per treatment. Target finish body weight was 111 and 105 pounds for wether and ewe lambs, respectively. Intermediate and end lambs were slaughtered when they reached individual target weights.
Lambs were weighed for treatment assignment then weighed again the next day at the start of the experiment. Concentrate diets were fed once per day with diets increased at the rate of 0.1 pounds per lamb per day to full feed level of intake. Thereafter, concentrate diets were offered ad libitum.
Lambs grazing alfalfa were on an 8- paddock (0.2 acre per paddock) rotation system. Lambs grazed for 3 to 5 days on each paddock. After lambs were moved to a new paddock, 50 non-gestating, non-lactating ewes were immediately moved where the lambs had been to glean stubble to a height of 2 inches. Ewes remained on the paddocks for not more than 1 day. Alfalfa in each paddock had 23 to 25 days rest before lambs returned to graze.
Linear and subjective measurements were made on all carcass right halves. Halves were separated at the 12th to 13th rib for measuring ribeye area and fat over the rib. The foresaddle was frozen for grinding later at USDA, Beltsville, MD. The hindsaddle was separated into leg, loin, and flank. Leg and loin separation was at the 7th (last) lumbar vertebra, with the last lumbar left on the leg. The leg and loin were each physically separated into lean, fat, and bone. Lean was ground three times through a 0.25 inch plate and a 1.8 ounce sample saved for intramuscular fat determination. Fat was recorded as subcutaneous, seam, or mesenteric. Leg components and flank were combined and frozen for later grinding and analysis. Loin components were frozen separately. Animals were blocked by sex, and the data were analyzed by the GLM procedure of SAS (1988).
| Table 1. Composition of concentrate diets.1 | ||
| Item | Diet 1
Fed during Phase 1 |
Diet 2
Fed during Phase 2 |
| ( %, Dry matter basis) | ||
| Whole shelled corn | 70.000 | 70.000 |
| Ground corn | 15.641 | 19.041 |
| Soybean meal | 5.700 | 4.000 |
| Blood meal | 2.850 | 2.000 |
| Corn gluten meal | 2.850 | 2.000 |
| Urea | 0.400 | 0.400 |
| Limestone | 1.300 | 1.300 |
| Dicalcium phosphate | 0.250 | 0.250 |
| Trace mineral salt | 0.450 | 0.450 |
| Vitamin A,
30,000 IU/g |
0.010 | 0.010 |
| Vitamin D,
3,000 IU/g |
0.010 | 0.010 |
| Vitamin E, 44 IU/g | 0.030 | 0.030 |
| Selenium, 201 ppm | 0.090 | 0.090 |
| Ammonium chloride | 0.400 | 0.400 |
| Lasalocid, 67.5 g/pound | 0.019 | 0.019 |
| Calculated composition | ||
| Crude protein, % | 17.025 | 15.155 |
| Calcium, % | 0.545 | 0.536 |
| Phosphorus, % | 0.411 | 0.404 |
| NEm, Mcal/kg2 | 2.082 | 2.083 |
| NEg, Mcal/kg3 | 1.432 | 1.433 |
| 1 Diets were a blend of 70% whole shelled corn and
30% pelleted supplement.
2 Net energy available for maintenance. 3 Net energy available for gain. | ||
| Table 2. Performance of intermediate and end slaughter lambs. | ||||||
| Treatments1 | ||||||
| Item | DL | DLTBA | DLALF | ALF | SEM2 | P value |
| (pounds) | ||||||
| Initial body weight | 50.3 | 49.2 | 51.0 | 45.1 | 1.57 | 0.86 |
| Intermediate body weight | 83.8 | 77.1 | 82.2 | 79.1 | 2.46 | 0.23 |
| End body weight | 107.2 | 108.9 | 109.5 | 108.0 | 0.68 | 0.12 |
| Average daily gain
Phase 1 |
0.80 | 0.72 | 0.81 | 0.70 | 0.85 | 0.34 |
| Phase 2 | 0.76b | 0.91a | 0.44c | 0.56c | 0.04 | < 0.001 |
| Overall | 0.79a | 0.82a | 0.58b | 0.62b | 0.03 | < 0.001 |
| 1Treatments were as follows: DL = drylot (concentrate); DLTBA = DL with lambs implanted with trenbolone
acetate:estradiol benzoate when average BW was 79.2 pounds; DLALF = DL with lambs moved to alfalfa
grazing when average BW was 79.2 pounds; ALF = alfalfa grazing throughout.
2 Standard error of the mean. abcWithin a row, means without a common superscript differ. | ||||||
| Table 3. Bone, lean, and fat gain in leg and loin of intermediate lambs (Phase 1). | |||||||||
| Tissue gain in leg and loin | |||||||||
| Treatments1 | |||||||||
| Leg | Loin | ||||||||
| Item | DL | ALF | SEM2 | P value | DL | ALF | SEM | P value | |
| (pounds) | (pounds) | ||||||||
| Bone | 0.50 | 0.55 | 0.03 | 0.39 | 0.14 | 0.15 | 0.03 | 0.99 | |
| Lean | 1.68 | 1.58 | 0.13 | 0.59 | 0.38 | 0.30 | 0.04 | 0.24 | |
| Fat | 0.60a | 0.34b | 0.05 | 0.006 | 0.28a | 0.14b | 0.01 | 0.003 | |
| 1 Treatments were as follows: DL = drylot (concentrate); ALF = alfalfa grazing.
2 Standard error of the mean. ab Within a row, means without a common superscript differ. | |||||||||
| Table 4. Bone, lean, and fat gain in leg and loin of end slaughter lambs. | |||||||||||||
| Tissue gain in leg and loin | |||||||||||||
| Treatments1 | |||||||||||||
| Leg | Loin | ||||||||||||
| Item | DL | DLTBA | DLALF | ALF | SEM2 | P value | DL | DLTBA | DLALF | ALF | SEM | P value | |
| Phase 2 | (pounds) | (pounds) | |||||||||||
| Bone | 0.14 | 0.28 | 0.29 | 0.14 | 0.07 | 0.23 | 0.07 | 0.14 | 0.14 | 0.15 | 0.03 | 0.24 | |
| Lean | 0.99 | 1.41 | 1.54 | 1.37 | 0.19 | 0.24 | 0.36b | 0.53a | 0.33b | 0.33y | 0.04 | 0.004 | |
| Fat | 0.45 | 0.41 | 0.38 | 0.67 | 0.09 | 0.13 | 0.41 | 0.42 | 0.26 | 0.36 | 0.06 | 0.24 | |
| Overall | |||||||||||||
| Bone | 0.67 | 0.71 | 0.78 | 0.67 | 0.07 | 0.67 | 0.22 | 0.27 | 0.28 | 0.29 | 0.03 | 0.47 | |
| Lean | 2.72 | 2.87 | 3.16 | 2.92 | 0.15 | 0.24 | 0.76ab | 0.87a | 0.70b | 0.63b | 0.05 | 0.01 | |
| Fat | 1.06 | 0.95 | 0.97 | 1.01 | 0.09 | 0.83 | 0.71 | 0.68 | 0.55 | 0.50 | 0.06 | 0.07 | |
| 1 Treatments were as follows: DL = drylot (concentrate); DLTBA = DL with lambs implanted with trenbolone acetate:estradiol benzoate when
average BW was 79.2 pounds; DLALF = DL with lambs moved to alfalfa grazing when average BW was 79.2 pounds; ALF = alfalfa grazing.
2 Standard error of the mean. ab Within a row, means without a common superscript differ. | |||||||||||||
Results reported here are lamb ADG and bone, lean, and fat gain in the leg and loin, which are considered representative of the carcass hindsaddle.
Lamb Performance. During Phase 2 and overall, live ADG of lambs grazing alfalfa were not different (P > 0.05), regardless of whether they were fed concentrate or grazed on alfalfa during Phase 1 (Table 2). However, during Phase 2, lambs which were continued in drylot and fed concentrate DL had ADG higher (P = 0.001) than those grazing alfalfa. Furthermore, lambs implanted with TBA:EB (DLTBA) had higher ADG than DL-fed lambs. The same trend in performance continued when Phase 1 and Phase 2 were combined (overall), except implants during Phase 2 did not improve overall performance compared with DL-fed lambs without implants.
Lamb Hindsaddle Tissue Accretion. Bone, lean, and fat gain in the hindsaddle (leg and loin) of the intermediate lambs which were fed either the DL diet or grazed ALF during Phase 1 are reported in Table 3.
Fat gain in carcasses of lambs fed the DL diet was more than for ALF-grazed lambs in both leg (P = 0.006) and loin (P = 0.0003). Bone and lean gain were not different (P > 0.05) between treatments for either leg or loin.
During Phase 2, lean gain in the loin of implanted lamb carcasses was more (P = 0.004) than for the other treatments (Table 4). There were no differences (P > 0.05) in any of the other measured tissue gains during Phase 2. When Phase 1 and Phase 2 were combined (overall), lean gain in the loin of carcasses of DLTBA lambs was more (P = 0.01) than for DLALF and ALF lambs and similar to DL lambs.
Accretion of fat in both the leg and loin was greater for lambs fed concentrate in drylot than for lambs grazed on alfalfa before they reached the intermediate weight, as mentioned earlier.
Earlier research from this laboratory supports the idea that fat accretion is high in the loin. In the present experiment, lean accretion in the loin was influenced by dietary and hormonal treatments.
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.
McClure, K.E., M.B. 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.
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.