H.V. Knoblich, F.L. Fluharty, and S.C. Loerch
Department of Animal Sciences
Feeding steers at restricted intakes and then increasing daily gain by increasing feed intake using four different schedules all resulted in reduced (P < 0.05) daily feed intake and total feed intake compared with offering feed ad libitum. Furthermore, daily feed efficiency was increased (P < 0.05) by two of the feeding systems compared with offering feed ad libitum. Steers offered feed ad libitum for only the final 70 pounds of gain before slaughter had reduced (P < 0.05) 12th rib backfat; kidney, pelvic, and heart fat; and yield grade compared with cattle offered feed ad libitum either throughout the trial or for the final 270 pounds of gain before slaughter. Furthermore, there were no differences (P > 0.10) in dressing percentage, ribeye area, quality grade, or percentage of cattle grading choice due to dietary treatment. Feed savings per calf were 125, 309, 159, and 233 pounds (treatments 1, 2, 3, and 4, respectively) compared with feeding cattle ad libitum. Therefore, offering steers feed ad libitum was not the most economical or efficient use of feed resources in this experiment.
In the past few years, feeding programs that restrict the intake of cattle and limit-feeding cattle to achieve a desired rate of gain have become increasingly popular (Glimp et al., 1989; Loerch, 1990; Murphy and Loerch, 1994). With rising feed costs and narrowing or nonexistent profit margins in the cattle feeding industry, feeding programs that increase the efficiency of feed utilization for gain become even more desirable. Several factors have been suggested for the improvement in feed efficiency found with restricted feeding, or programmed gain systems, compared with what NRC (1984) equations predict (Glimp et al., 1989; Plegge, 1987). Increased digestibility of high concentrate diets, reduced visceral organ mass, increased lean and decreased fat accretion, and changes in the metabolism of animals fed restricted intakes have all been hypothesized as possible explanations for the improvements noted (Hicks et al., 1990). It seems probable that these factors working together in the animal could account for the improvements in feed efficiency. However, the mechanisms for the improvement in feed efficiency as well as those feeding programs that capitalize on the opportunity for increased efficiency have not been identified. This trial was conducted to determine the effects of programmed rates of gain on performance and carcass characteristics of feedlot steers.
One-hundred-sixty-one crossbred steer calves (average initial weight = 674 pounds) were used to determine effects of intake restriction on cattle performance and carcass characteristics. Steers were allotted by weight to eighteen pens with nine steers/pen and three or four pens per finishing system. The five finishing systems investigated are outlined in Table 1.
| Table 1. Five finishing systems of steers. | |||||
|
Treatments | |||||
| 1 | 2 | 3 | 4 | 5 | |
| (Pounds of gain) | |||||
| Predicted daily gain | |||||
| 2.5 Pounds | 70 | 170 | 170 | 120 | ad lib |
| 3.0 Pounds | 170 | 270 | 170 | 220 | ad lib |
| ad lib | 270 | 70 | 170 | 170 | ad lib |
Feed intake was restricted (using net energy equations) for treatments 1, 2, 3, and 4 to achieve the desired predicted daily gains for total pounds of gain shown. Feed was offered ad libitum to steers in treatment 5. Composition of the diets is shown in Table 2. Amount of feed offered to restricted-fed calves was determined using NRC (1984) net energy equations for large- frame steer calves. Cattle were weighed every 2 weeks, average daily gain (ADG) was determined, and intake was adjusted to meet maintenance requirements as body weight increased. Diets of restricted-fed steers were higher in concentrations of protein, minerals, and Rumensin (Elanco, Greenfield, IN) to ensure equal daily intakes of these components regardless of feed intake levels. Cattle were slaughtered when the pen average reached 1215 pounds, and carcass data were collected.
Steers were implanted with Synovex-S (Fort Dodge Animal Health, Overland Park, KS) on day 0 and Revalor (Hoechst-Roussel Agri Vet Co., Overland Park, KS) on day 84. Initial and final weights were calculated as the average of weights taken on two consecutive days at the beginning and end of the trial. Feed intake was measured daily and feed efficiency (1 pound gain/1 pound dry matter intake) was calculated. Data were analyzed statistically using the general linear model procedures of SAS (1991) for a completely randomized design.
| Table 2. Diet composition. | |||
| Predicted rate of gain (pounds/day) | |||
| Item | 2.5 | 3.0 | Ad lib |
| Ingredient | |||
| Whole shelled high moisture corn | 65 | 65 | 65 |
| Corn silage | 15 | 15 | 15 |
| Ground corn | 6.90 | 8.78 | 9.85 |
| Soybean meal | 8.91 | 7.73 | 6.78 |
| Urea | 0.77 | 0.64 | 0.60 |
| Dicalcium phosphate | 0.82 | 0.35 | 0.35 |
| Limestone | 1.43 | 1.43 | 1.43 |
| Trace mineral salt1 | 0.59 | 0.54 | 0.50 |
| Rumensin, 176 g/kg | 0.021 | 0.018 | 0.017 |
| Tylan 100, 220 g/kg | 0.006 | 0.005 | 0.005 |
| Selenium, 201 mg/kg | 0.062 | 0.054 | 0.050 |
| Vitamin A, 30,000 IU/g | 0.012 | 0.012 | 0.010 |
| Vitamin D, 3,000 IU/g | 0.012 | 0.012 | 0.010 |
| Animal-vegetable fat | 0.47 | 0.43 | 0.40 |
| Calculated composition | |||
| Crude protein, % | 14.3 | 13.5 | 13.0 |
| Calcium, % | 0.74 | 0.64 | 0.64 |
| Phosphorus, % | 0.51 | 0.41 | 0.41 |
| Potassium, % | 0.60 | 0.58 | 0.57 |
| NEm, Mcal/kg | 2.06 | 2.08 | 2.08 |
| NEg, Mcal/kg | 1.41 | 1.42 | 1.42 |
| 1Contained: > 93% NaCl, 0.35% Zn, 0.28% Mn, 0.175% Fe, 0.035% Cu, 0.007% I, and 0.007% Co. | |||
Effects of the five finishing systems on cattle performance are shown in Table 3. During period 1 (day 0 to 84), treatment 5 resulted in greater (P < 0.05) ADG, weight on day 84, and total feed intake compared with the other four treatments. There were no differences (P > 0.10) in feed efficiency due to diet in period 1. During period 2 (day 85 to finish), there were no differences (P > 0.10) in feed intake or animal performance due to diet. When averaged over the total trial, all restricted feeding schedules (treatments 1, 2, 3, and 4) led to reduced (P < 0.05) daily feed intake compared with steers offered feed ad libitum (treatment 5 ). Calves offered feed ad libitum had lower (P < 0.05) feed efficiency than calves on treatments 2 and 4; treatments 1 and 3 were intermediate. Restricting intake resulted in similar (P > 0.05) rates of gain as full feeding throughout the entire feeding period. Also, restricted intake of treatments 1, 2, 3, and 4 resulted in decreased overall feed intake compared to calves fed ad libitum. Feed savings per calf were 125, 309, 159, and 233 pounds (treatments 1, 2, 3, and 4, respectively) compared with feeding cattle ad libitum. Therefore, offering steers feed ad libitum was not the most economical or efficient use of feed resources in this experiment.
The effects of finishing system on animal performance during each period of feed intake restriction are shown in Table 4. Steers gained at a rate very close to the predicted 2.5 pounds/day throughout the first restricted feeding period. When animals were fed to gain at a rate of 3.0 pounds/day, actual daily gains were 10 to 38% greater than predicted gains for the restricted-fed treatments. Calves fed to gain 170 pounds at 2.5 pounds/day (treatments 2 and 3 ) had greater (P < 0.01) subsequent gains when intake was increased than those fed to gain 70 pounds (treatment 1) or 120 pounds (treatment 4) at a rate of 2.5 pounds/day. Feed efficiencies of calves fed to gain 3.0 pounds/day were affected (P < 0.01) by pounds of gain achieved when fed to gain at 2.5 pounds/day and pounds of gain achieved when fed to gain at 3.0 pounds/day. When all steers were switched to ad libitum feeding during the last feeding period, daily gains and feed efficiencies were not different among the five feeding systems.
The effects of the five finishing systems on carcass characteristics are shown in Table 5. There were no differences (P > 0.10) in carcass weight due to feeding system. This was a planned part of the experiment, because carcass fat percentage has been shown to be related directly to carcass weight (Berg and Butterfield, 1967; Ferrell et al., 1978; Waldman et al., 1971). Therefore, if the steers had been slaughtered at different weights, the carcass information would have been confounded by weight, and the heavier animals likely would have contained more fat. Steers offered feed ad libitum for only the final 70 pounds of gain (treatment 2) had reduced (P < 0.05) 12th rib backfat; kidney, pelvic, and heart fat; and yield grade compared with cattle offered feed ad libitum either throughout the trial or for the final 270 pounds of gain (treatments 5 and 1, respectively). Treatments 3 and 4 were intermediate. Furthermore, there were no differences (P > 0.05) in dressing percentage, ribeye area, quality grade, or percentage of cattle grading choice due to dietary treatment.
| Table 3. Effects of five finishing systems on cattle performance. | ||||||
| Finishing system treatment1 | ||||||
| Item | 1 | 2 | 3 | 4 | 5 | SE |
| Number of steers | 36 | 26 | 35 | 27 | 36 | |
| Initial weight, pounds | 673 | 672 | 672 | 671 | 673 | 1.43 |
| Day 84 weight, pounds | 927b | 914bc | 901c | 921bc | 979a | 7.05 |
| Final weight, pounds | 1220 | 1211 | 1213 | 1210 | 1219 | 5.43 |
| Period 1 (0 to day 84) | ||||||
| Gain, pounds/day | 3.02a | 2.88ab | 2.73b | 2.98a | 3.65c | 0.08 |
| Feed intake, pounds/day | 14.95a | 14.08b | 14.0b | 14.47ab | 18.08c | 0.25 |
| Feed efficiency, pound
gain/pound feed |
0.193 | 0.204 | 0.195 | 0.206 | 0.202 | 0.007 |
| Days fed | 84 | 84 | 84 | 84 | 84 | |
| Total intake, pounds | 1255a | 1183b | 1176b | 1215ab | 1519c | 21 |
| Period 2 (day 85 to finish) | ||||||
| Gain, pounds/day | 3.70 | 3.80 | 3.73 | 4.08 | 3.22 | 0.24 |
| Feed intake, pounds/day | 20.67 | 20.20 | 20.11 | 20.0 | 20.25 | 0.38 |
| Feed efficiency, pound
gain/pound feed |
0.200 | 0.188 | 0.185 | 0.204 | 0.159 | 0.017 |
| Days fed | 80 | 76 | 85 | 79 | 75 | 3.5 |
| Total intake, pounds | 1647dg | 1535dh | 1694eg | 1572df | 1512fh | 50 |
| Overall Performance | ||||||
| Gain, pounds/day | 3.34 | 3.37 | 3.22 | 3.33 | 3.45 | 0.08 |
| Feed intake, pounds/day | 17.74a | 17.00b | 17.05b | 17.20ab | 19.09c | 0.21 |
| Feed efficiency, pound
gain/pound feed |
0.189ij | 0.198i | 0.189ij | 0.194i | 0.181j | 0.004 |
| Days fed | 164 | 160 | 169 | 163 | 159 | 3.5 |
| Total intake, pounds | 2905ab | 2721c | 2871bc | 2797bc | 3030a | 53 |
| 1 Cattle were fed using net energy equations for increasing gains for varied periods of time (Treatments 1,2,3, and 4) or
were fed ad libitum throughout the trial (treatment 5); SE = standard error.
abc Means within a row with different superscripts differ (P < 0.01). defgh Means within a row with different superscripts differ (P < 0.06). | ||||||
| Table 4. Effects of finishing system on actual daily gains during each period of intake restriction. | ||||||
| Finishing system treatment1 | ||||||
| 1 | 2 | 3 | 4 | 5 | SE | |
| Predicted gain, 2.5 pounds/day | ||||||
| Actual gain, pounds/day | 2.50 | 2.56 | 2.50 | 2.56 | . . . | 0.061 |
| DM intake, pounds/day | 13.2 | 13.7 | 13.6 | 13.3 | . . . | . . . |
| Feed efficiency, pound
feed/pound gain |
0.190 | 0.187 | 0.184 | 0.192 | . . . | 0.005 |
| Total gain, pounds | 79 | 179 | 175 | 121 | . . . | . . . |
| Total feed, pounds | 416 | 956 | 950 | 632 | . . . | . . . |
| Days | 32 | 70 | 70 | 47 | . . . | . . . |
| Predicted gain, 3.0 pounds/day | ||||||
| Actual gain, pounds/day | 3.29a | 4.15b | 4.14b | 3.76c | . . . | 0.052 |
| DM intake, pounds/day | 16.0 | 18.3 | 17.2 | 16.8 | . . . | . . . |
| Feed efficiency | 0.206a | 0.227b | 0.240c | 0.224b | . . . | 0.003 |
| Total gain, pounds | 166 | 262 | 168 | 230 | . . . | . . . |
| Total feed, pounds | 806 | 1155 | 698 | 1030 | . . . | . . . |
| Days | 51 | 63 | 41 | 61 | . . . | . . . |
| Fed ad libitum | ||||||
| Actual gain, pounds/day | 3.71 | 3.66 | 3.50 | 3.60 | 3.46 | 0.23 |
| DM intake, pounds/day | 20.6 | 22.8 | 21.4 | 21.5 | 19.1 | 0.61 |
| Feed efficiency | 0.180 | 0.160 | 0.163 | 0.167 | 0.182 | 0.007 |
| Total gain, pounds | 302 | 99 | 199 | 188 | 549 | . . . |
| Total feed, pounds | 1682 | 615 | 1229 | 1125 | 3030 | . . . |
| Days | 82 | 27 | 58 | 53 | 159 | . . . |
| 1 Cattle were fed using net energy equations for increasing gains for varied periods of time depending on treatment (1, 2, 3,
and 4) or offered feed ad lib (treatment 5); SE = standard error.
abc Means within a row with different superscripts differ (P < 0.01). | ||||||
| Table 5. Effects of five finishing systems on carcass characteristics. | ||||||
| Finishing system treatment1 | ||||||
| Item | 1 | 2 | 3 | 4 | 5 | SE |
| Hot carcass weight, pounds | 739 | 729 | 728 | 729 | 738 | 5.35 |
| Dressing percentage | 60.6 | 60.2 | 60.0 | 60.3 | 60.6 | 0.46 |
| Ribeye area, inch2 | 12.33 | 12.80 | 12.85 | 12.21 | 12.58 | 0.37 |
| 12th rib backfat, inch | 0.41a | 0.30b | 0.38a | 0.37ab | 0.43a | 0.023 |
| Kidney, pelvic, and heart fat, % | 3.28c | 3.07d | 3.18cd | 3.07d | 3.28c | 0.044 |
| Quality grade2 | 3.30 | 2.97 | 3.15 | 3.23 | 3.40 | 0.22 |
| Yield grade | 3.05a | 2.54b | 2.74ab | 2.90ab | 3.02a | 0.12 |
| % Choice | 78 | 77 | 67 | 85 | 81 | 8.2 |
| 1 Cattle were fed using net energy equation for increasing gains for varied periods of time (1, 2, 3, and 4) or fed ad libitum
(treatment 5); SE = standard error.
2 2 = Select, 3 = Choice-, 4 = Choice, and 5 = Choice+. ab Means in the same row without a common letter in their superscripts differ (P < 0.05). cd Means in the same row without a common letter in their superscripts differ (P < 0.01). | ||||||
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