F.L. Fluharty*, K.E. McClure*, M.B. Solomon+,
D.D. Clevenger*, and G.D. Lowe*
*Department of Animal Sciences and
+Meat Science Research Laboratory,
USDA/ARS, Beltsville, MD
Seventy-two Targhee lambs were used to determine the effects of energy source (alfalfa pasture vs limit-fed 100% concentrate) and ionophore (lasalocid, Hoffman-La Roche, Nutley, NJ) addition on performance, visceral organ mass, and carcass characteristics. There were no differences (P > 0.10) in average daily gain (ADG) or feed efficiency (gain/feed) due to ionophore supplementation. However, adding an ionophore to the diet resulted in an increased (P < 0.05) dry matter intake (DMI) and fewer (P < 0.05) days on feed. Lambs grazing alfalfa had greater (P < 0.05) liver weights, as well as greater (P < 0.001) omasum, abomasum, small intestine, cecum, and large intestine weights compared with lambs fed a 100% concentrate diet. However, lambs fed concentrate had more (P < 0.05) visceral fat compared with lambs grazing alfalfa. Lambs grazing alfalfa had greater (P < 0.001) daily accretion rates of omasum, abomasum, small intestine, cecum, and large intestine compared with lambs fed concentrate. Lambs fed the 100% concentrate diet had heavier (P < 0.01) hot carcass weights, larger (P < 0.01) loin-eye areas, and greater (P < 0.001) dressing percentages compared with lambs grazing alfalfa. The greater visceral organ mass and resulting increases in energy and protein requirements by these tissues in the lambs grazing alfalfa were probably responsible for the smaller hot carcass weights, loin- eye areas, and dressing percentages compared with lambs fed 100% concentrate.
Several researchers have looked at the impact of forages and concentrates on ruminal fermentation, rate of gain, and carcass composition in ruminants. However, there is very limited information comparing the performance and composition of gain of animals fed legume-based diets to animals fed a similar amount of energy and protein by feeding a restricted amount of a 100% concentrate diet. Additionally, there is limited information available concerning the use of an ionophore (lasalocid) in growing lamb studies where the source of energy and protein has been compared.
In recent years, considerable evidence has shown that a large proportion of an animal's maintenance energy requirements can be attributed to the visceral organs, especially the liver and gastrointestinal tract, and appears to be associated with the high rates of protein synthesis in these tissues (Ferrell and Jenkins, 1985). The objectives of this experiment were to 1) determine the effects of grazing alfalfa vs limit-feeding all-concentrate diets formulated to achieve similar energy and protein intakes on performance and carcass characteristics, and 2) determine the effects of feeding an ionophore in both alfalfa and limit-fed concentrate diets on performance and carcass characteristics.
Seventy-two Targhee lambs were used to determine the effects of energy source (alfalfa pasture vs limit-fed 100% concentrate) and ionophore (lasalocid, Hoffman-La Roche, Nutley, NJ) addition on performance, visceral organ mass, and carcass characteristics. Four treatments were used, with two replicates of each treatment and eight lambs per replicate. There were two alfalfa pasture treatments (with and without lasalocid). The pasture paddocks were rotationally grazed such that there were eight paddocks per treatment group. The lambs were moved every 3 to 4 days so that each paddock had approximately 24 to 32 days to allow for regrowth between grazing periods. The lambs were fed lasalocid daily in a pelleted soybean hull carrier at the rate of 1 mg of lasalocid/kg of body weight. Soybean hulls were used as a carrier, because they are a fiber source which, unlike cereal grains, should not alter the proportion of ruminal fermentation end-products, specifically acetate and propionate. Two drylot treatment groups were restricted-fed a 100% concentrate diet so that the daily energy and protein intakes approximated the predicted intake of the pasture treatments (NRC, 1985). In order to achieve a similar protein intake, the dietary protein level of the two drylot groups were higher than normally fed (Table 1). Lambs in one of these treatment groups received lasalocid in their diet, while the other treatment group lambs did not.
At the initiation of the study, lambs were allotted to treatments based on body weight and sex. At this time, eight lambs (4 wethers and 4 ewes) were slaughtered to determine initial body composition and visceral organ mass. The remaining 64 lambs were weighed on two consecutive days to determine initial weights. Lambs were weighed every 14 days throughout the trial to adjust dry matter intake (DMI) of the restricted-fed, drylot lambs so that they would achieve the same rate of gain as the alfalfa-grazed lambs. Average daily gain (ADG), DMI and feed efficiency (gain/feed) were determined for each 14-day period, as well as for the total trial. Feed samples were collected every 7 days throughout the trial and analyzed for dry matter according to the procedures of Goering and Van Soest (1970). Monthly composites of feed were analyzed for nitrogen (N) content by macro-Kjeldahl (AOAC, 1984). Neutral detergent fiber (NDF) was determined according to the procedures of Van Soest et al. (1991).
Eight lambs from each treatment group (4 wethers and 4 ewes) were slaughtered when they averaged 100+3 pounds and were evaluated for carcass characteristics and visceral organ mass. Lambs were selected for slaughter in such a manner as to achieve equal carcass weights across treatments. Lambs were taken to a common slaughter weight, because carcass fat percentage has been shown to be related directly to carcass weight (Berg and Butterfield, 1967; Waldman et al., 1971; Ferrell et al., 1978). The lambs were transported by truck to the USDA Meat Science Laboratory where they were slaughtered. The visceral organs were removed from each lamb, flushed with water, allowed to drip dry, and weighed. Organs weighed were the heart, kidney, liver, rumen-reticulum, omasum, abomasum, small intestine, cecum, colon, and associated visceral fat.
Data were analyzed using the GLM procedure of SAS (1988) for a completely randomized, 2 X 2 factorial experiment. Performance data were analyzed using a model that included effects due to energy source, ionophore status, and the energy source by ionophore status interaction. Pen was used as the experimental unit. Visceral organ and carcass data were analyzed the same as performance data, except that animal was used as the experimental unit in the model.
| Table 1. Diet composition. | |||||
| Alfalfa | Drylot | ||||
| Item | + Lasalocid | -- Lasalocid | + Lasalocid | -- Lasalocid | |
| (%, Dry matter basis) | |||||
| Alfalfa | 99.978 | 100.000 | . . . | . . . | |
| Ground corn | . . . | . . . | 61.288 | 61.310 | |
| Soybean meal | . . . | . . . | 17.560 | 17.560 | |
| Blood meal | . . . | . . . | 8.780 | 8.780 | |
| Corn gluten meal | . . . | . . . | 8.780 | 8.780 | |
| Urea | . . . | . . . | 0.400 | 0.400 | |
| Limestone | . . . | . . . | 1.300 | 1.300 | |
| Dicalcium phosphate | . . . | . . . | 0.900 | 0.900 | |
| 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 | . . . | . . . | 0.010 | 0.010 | |
| Selenium, 201 mg Se/kg | . . . | . . . | 0.090 | 0.090 | |
| Ammonium chloride | . . . | . . . | 0.400 | 0.400 | |
| Lasalocid, 149 g/kg | 0.022 | . . . | 0.022 | 0.000 | |
| Calculated composition | |||||
| Crude protein, % | 19.70 | 19.70 | 30.01 | 30.02 | |
| Calcium, % | 1.96 | 1.96 | 0.75 | 0.75 | |
| Phosphorus, % | 0.30 | 0.30 | 0.58 | 0.58 | |
| NEm, Mcal/kg | 1.24 | 1.24 | 2.06 | 2.06 | |
| NEg, Mcal/kg | 0.68 | 0.68 | 1.41 | 1.41 | |
The main effects of diet source and ionophore status on animal performance are shown in Table 2. Because DMI could not be determined for the animals on pasture, there is no analysis for either DMI or gain/feed due to energy source. There were no differences (P > 0.10) in ADG or gain/feed due to ionophore supplementation. However, adding an ionophore to the concentrate diet resulted in an increased (P < 0.05) DMI for lambs on the drylot diet and fewer (P < 0.05) days on feed. This probably occurred due to the effects of small differences in DMI and ADG over time allowing the animals fed an ionophore to reach the predetermined end weight faster than those animals not fed an ionophore.
There were no differences (P > 0.10) in ADG between the alfalfa-grazed and concentrate- fed lambs. Similar growth rates between the alfalfa-grazed and concentrate-fed lambs were desired, because animals offered a high-concentrate diet ad libitum generally have a greater ADG than animals grazed on legumes. Increasing
ADG often results in increased rates of fat accretion. However, one of the purposes of this experiment was to determine if there were differences in tissue and organ accretion (growth) rates when vastly different feed sources were fed in such a way as to achieve similar rates of body weight gain.
The main effects of diet source and ionophore status on slaughter lamb performance and visceral organ mass are shown in Table 3. There were no differences (P > 0.10) in visceral organ mass due to ionophore addition to diets. However, lambs grazing alfalfa had greater (P < 0.05) liver weights, as well as greater (P < 0.001) omasum, abomasum, small intestine, cecum, and large intestine weights compared with lambs fed a 100% concentrate diet. However, lambs fed concentrate had more (P < 0.05) visceral fat compared with lambs grazing alfalfa. The effects of diet source and ionophore status on daily visceral organ accretion (growth) rates are shown in Table 4. Lambs fed concentrate had greater (P < 0.01) daily accretion of visceral fat compared with lambs grazing alfalfa. However, lambs grazing alfalfa had greater (P < 0.001) daily accretion rates of omasum, abomasum, small intestine, cecum, and large intestine compared with lambs fed concentrate.
The main effects of diet source and ionophore status on lamb carcass characteristics are shown in Table 5. Lambs fed the 100% concentrate diet had heavier (P < 0.01) hot carcass weights, larger (P < 0.01) loin-eye areas, and greater (P < 0.001) dressing percentages compared with lambs grazing alfalfa. Therefore, even lambs grown at the same rate can have large differences in carcass characteristics due to diet. Ferrell and Jenkins (1985) reported that a greater proportion of total protein synthesis occurred in the combined gastrointestinal tract (19 to 23%), and liver, kidney, and pancreas (16 to 17%) than occurred in striated muscle (24 to 28%). Furthermore, the metabolic activity of visceral organs is a function of both the metabolic activity and size of the organs. The maintenance energy requirements of organs change with the relative weights of the organs and are affected by the level of nutrition (Ferrell et al., 1986). The greater visceral organ mass and resulting increases in energy and protein requirements by these tissues in the lambs grazing alfalfa were probably responsible for the smaller hot carcass weights and dressing percentages compared with lambs fed 100% concentrate. Additionally, the smaller loin-eye areas in lambs grazing alfalfa compared with lambs fed 100% concentrate may be, in part, the result of increased visceral organ mass in lambs grazing alfalfa.
| Table 2. Main effects of diet source and ionophore on animal performance. | ||||||
| Diet source | Ionophore | |||||
| Item | Alfalfa | Concentrate | -- Lasalocid | + Lasalocid | SEM1 | |
| Initial weight, pounds | 48.95 | 48.73 | 48.95 | 48.95 | 0.22 | |
| DMI2, pounds/day3 | . . . | . . . | 2.28 | 2.32 | 0.00 | |
| ADG4, pound/day | 0.60 | 0.64 | 0.60 | 0.64 | 0.01 | |
| Gain/feed5, pound/pound | . . . | . . . | 0.28 | 0.28 | 0.07 | |
| Days on feed, day3 | 92.1 | 88.5 | 92.9 | 87.7 | 1.4 | |
| Final weight, pounds | 104.08 | 105.84 | 105.18 | 104.96 | 0.44 | |
| 1 SEM = Standard error of mean;
2 DMI = Dry matter intake; 3 Ionophore effect (P < 0.05); 4 ADG = Average daily gain; 5 Gain/feed = Feed efficiency. | ||||||
| Table 3. Main effects of diet source and ionophore on slaughter lamb performance and visceral organ mass. | ||||||
| Diet source | Ionophore | |||||
| Item | Alfalfa | Concentrate | -- Lasalocid | + Lasalocid | SEM1 | |
| Initial weight, pounds | 52.26 | 51.38 | 51.16 | 52.48 | 1.54 | |
| Final weight, pounds | 106.50 | 105.62 | 108.49 | 105.84 | 0.88 | |
| ADG2, pound/day | 0.65 | 0.68 | 0.65 | 0.68 | 0.02 | |
| Days on test | 84.4 | 80.5 | 85.4 | 79.5 | 2.8 | |
| Heart weight, g | 198 | 191 | 199 | 190 | 6 | |
| Liver weight, g3 | 973 | 908 | 926 | 955 | 22 | |
| Kidney weight, g | 150 | 146 | 150 | 146 | 4 | |
| Visceral fat weight, g3 | 1545 | 1767 | 1712 | 1600 | 70 | |
| Rumen/reticulum weight, g | 1025 | 1015 | 1021 | 1019 | 16 | |
| Omasum weight, g4 | 114 | 73 | 93 | 94 | 4 | |
| Abomasum weight, g4 | 279 | 184 | 231 | 231 | 9 | |
| Small intestine weight, g4 | 1150 | 754 | 934 | 970 | 27 | |
| Cecum weight, g4 | 78 | 60 | 66 | 71 | 3 | |
| Large intestine weight, g4 | 520 | 368 | 435 | 453 | 23 | |
| 1 SEM = Standard error of mean;
2ADG = Average daily gain. 3 Diet source effect (P < 0.05). 4 Diet source effect (P < 0.001). | ||||||
| Table 4. Main effects of diet source and ionophore on visceral organ accretion. | ||||||
| Diet source | Ionophore | |||||
| Item | Alfalfa | Concentrate | -- Lasalocid | + Lasalocid | SEM1 | |
| Heart, g/day | 1.04 | 1.02 | 1.07 | 0.99 | 0.10 | |
| Liver, g/day | 6.51 | 6.11 | 5.97 | 6.65 | 0.34 | |
| Kidney, g/day | 0.77 | 0.79 | 0.78 | 0.78 | 0.06 | |
| Visceral fat, g/day2 | 12.97 | 16.49 | 14.88 | 14.59 | 0.80 | |
| Rumen/reticulum, g/day | 6.37 | 6.66 | 6.40 | 6.63 | 0.24 | |
| Omasum, g/day3 | 0.91 | 0.43 | 0.65 | 0.69 | 0.06 | |
| Abomasum, g/day3 | 1.64 | 0.58 | 1.08 | 1.13 | 0.10 | |
| Small intestine, g/day3 | 4.37 | -0.27 | 1.87 | 2.23 | 0.40 | |
| Cecum, g/day3 | 0.52 | 0.32 | 0.38 | 0.46 | 0.03 | |
| Large intestine, g/day3 | 3.47 | 1.83 | 2.50 | 2.79 | 0.30 | |
| 1 SEM = Standard error of mean.
2Diet source effect (P < 0.01 ). 3Diet source effect (P < 0.001). | ||||||
| Table 5. Main effects of diet source and ionophore on lamb carcass data. | ||||||
| Diet source | Ionophore | |||||
| Item | Alfalfa | Concentrate | -- Lasalocid | + Lasalocid | SEM1 | |
| Hot carcass weight, pound9 | 51.40 | 54.13 | 52.94 | 52.59 | 0.66 | |
| Maturity2 | 1.00 | 1.06 | 1.00 | 1.06 | 0.04 | |
| Feathering3 | 10.63 | 11.13 | 11.06 | 10.69 | 0.27 | |
| Quality grade3 | 10.94 | 11.50 | 11.25 | 11.19 | 0.26 | |
| Flank firmness3 | 12.13 | 12.37 | 12.13 | 12.37 | 0.30 | |
| Lean color4 | 5.10 | 4.87 | 4.97 | 5.00 | 0.16 | |
| LEA, inches3, 9 | 1.71 | 2.13 | 1.94 | 1.90 | 0.08 | |
| Leg conformation3 | 12.00 | 11.56 | 12.00 | 11.56 | 0.23 | |
| Fat depth, inch | 0.28 | 0.31 | 0.30 | 0.28 | 0.03 | |
| Body wall thickness, inch | 0.54 | 0.63 | 0.60 | 0.57 | 0.04 | |
| % KPH fat | 2.31 | 2.78 | 2.63 | 2.47 | 0.18 | |
| Yield grade5 | 3.49 | 3.88 | 3.79 | 3.58 | 0.18 | |
| Fat firmness6 | 4.75 | 3.94 | 4.63 | 4.06 | 0.30 | |
| Fat color7 | 4.44 | 3.81 | 4.37 | 3.87 | 0.23 | |
| Fat texture9 | 4.81 | 4.06 | 4.75 | 4.13 | 0.27 | |
| Dressing %10 | 48.27 | 51.24 | 49.79 | 49.72 | 0.40 | |
| 1 SEM = Standard error of mean.
21 = A; 2 = A. 310 = C; 11 = C; 12 = C+; 13 = P. 41 = very light red; 7 = very dark purple. 51.66 - (0.05 x leg conformation score) + (0.25 x % KPH) + (6.66 x adjusted fat depth, inches). 61 = very soft; 5 = very firm. 71 = yellow/brown; 5 = white. 81 = oily; 5 = dry. 9Diet source effect (P < 0.01). 10Diet source effect (P < 0.001). | ||||||
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