J. E. Rossi and S. C. Loerch1
The Ohio State University Department of Animal Sciences
This experiment evaluated effects of different growth rates in steers fed to achieve step-wise increases in growth rate during the feeding period. Steers (n = 96; 679.6 lb) were either offered feed ad libitum (AL) throughout the feeding period or intake was restricted to achieve gains of 2.5 (prescription intake; low rate of growth; PIL) or 2.75 lb/day (prescription intake; high rate of growth; PIH) for the first 170 lb of gain; 3.0 (PIL) or 3.25 lb/day (PIH) for the next 280 lb of gain; and offered feed ad libitum for the final 127 lb of gain before slaughter (at 1,260 lb). Steers programmed to gain 0.25 lb/day more (PIH) during periods of restricted intake actually gained 0.42 and 0.34 lb/day more than PIL steers during Periods 1 and 2, respectively. Steers in both PIL and PIH treatments gained 36% more than predicted during Period 2. However, during Period 3, PIL steers gained 0.72 lb/day more than PIH steers. Feed efficiency was improved (P < 0.10) for PIH (0.230) vs. PIL steers (0.213) during Period 1, was similar (P > 0.10) for Period 2 (0.219 and 0.230 for PIL and PIH, respectively), and was improved (P < 0.05) for PIL (0.200) vs. PIH (0.165) steers during Period 3. Days fed for PIH were reduced eight days during Period 1 and five days during Period 2 compared with PIL steers. Overall, ADG was similar (P > 0.37) between treatments. Dry-matter intake per day was greatest (P < 0.05) for AL steers (19.6 lb/day), intermediate for PIH steers (18.4 lb/day), and lowest for PIL steers (17.5 lb/day). Feed efficiency tended to be improved for PIL (0.212) and PIH (0.211) steers compared with AL steers (0.198). Total intake was reduced 158 lb for PIL and 167 lb for PIH steers compared with AL steers. Total days fed were the same for AL and PIH steers and nine days greater for PIL steers. No differences (P > 0.22) were observed for carcass characteristics.
Feeding cattle to achieve step-wise increases in rate of gain during the feeding period has been shown to improve feed efficiency and reduce total feed costs compared with feeding cattle ad libitum throughout the feeding period (Knoblich et al., 1997; Loerch and Fluharty, 1998). However, restricting intake for a portion of the feeding period tends to decrease marbling scores and increase days on feed compared with offering feed ad libitum (Rossi et al., 1999a,b). Thus, it is important to identify optimum growth rates during periods of feed restriction to allow limit-fed steers to attain equal market weights as steers offered feed ad libitum in the same number of days.
Higher rates of gain during the restricted period should allow limit-fed steers to reach the same body weight as ad libitum steers without negatively affecting overall rate of gain. Increasing the degree of intake restriction generally increases the magnitude of the compensatory gain response (Graham and Searle, 1975). Therefore, programming gain to attain higher growth rates during periods of intake restriction may not produce as large of a compensatory growth response as steers programmed for a slower growth rate, resulting in similar overall rates of gain. Effects of growth rate during periods of feed restriction on carcass characteristics are also unknown. Our objectives were to determine effects of rate of gain during the feed restriction period on performance and carcass characteristics of steers fed to achieve step-wise increases in rate of gain.
Ninety-six crossbred steers (initial wt = 679 lb) were allotted to 12 pens with eight steers per pen and four pens per treatment. Steers in Treatment 1 were offered feed ad libitum throughout the experiment (AL). Steers in Treatments 2 and 3 were fed using a prescription-intake feeding strategy and programmed to gain at a high (PIH) or low (PIL) rate of gain during periods of intake restriction. Amount of feed offered to PIL and PIH steers during periods of feed-restriction were determined using NRC (1984) net energy equations for large- framed steer calves. For the first 170 lb of gain (Period 1), intake was restricted to achieve a predicted gain of 2.5 lb/day for PIL steers and 2.75 lb/day for PIH steers. For the next 280 lb of gain (Period 2), intake was restricted to achieve a predicted gain of 3.0 lb/day for PIL and 3.25 lb/day for PIH steers. Steers in both prescription-intake treatments were offered feed ad libitum for the final 127 lb of gain (Period 3) before slaughter at 1,250 lb. The diet for AL steers was formulated to contain 13% crude protein, 27 g Rumensin/ton, and 10 g Tylan/ton. Concentrations of crude protein, vitamins, minerals, Rumensin, and Tylan were increased in diets of prescription-intake steers to ensure equal grams per day intake of these nutrients as AL steers.
Steers were fed once daily beginning at 0800 hours. On a daily basis, feed refusal was weighed, recorded, and discarded. Composite feed samples were dried in a forced-air oven at 55EC, ground to pass a 1-mm screen, and analyzed for DM (Goering and Van Soest, 1970) and N by a combustion-type autoanalyzer (Leco FP-2000, Leco Corp., St. Joseph, Mich.). Feed samples were analyzed weekly for DM to adjust intake for dietary moisture content. Pens (18 x 18 ft) had concrete slatted floors and were located in an open-sided barn.
Initial and final weights were determined using the average weight from two consecutive days. Steers were weighed every 14 days, and feed intake of prescription-intake steers was increased to meet increased maintenance requirements as body weight increased. Steers were implanted with Synovex-S7 on day 0 and Synovex Plus7 on day 69 (provided courtesy of Fort Dodge Animal Health, Overland Park, Kan.). Carcass data were collected by trained university personnel following a 48-hour chill period.
Data were analyzed using GLM procedures of SAS (1996) for a completely randomized design experiment. Treatment means were compared using the PDIFF statement of SAS when protected by a significant (P < 0.10) F-value. Pen served as the experimental unit for all analyses.
Research animal care protocols followed guidelines recommended in the Guide for the Care and Use of Agricultural Animals in Agriculture Research and Teaching (Consortium, 1988).
The composition of diets is shown in Table 1. Effects of growth rate during periods of intake restriction on performance are shown in Table 2. During Period 1, average daily gain (ADG) was 1.3 and 0.9 lb/day greater (P < 0.01) for AL compared with PIL and PIH steers. Actual gains were 18% greater than predicted for PIL steers and 23% greater for PIH steers. In previous limit-fed experiments, steers generally gained very close to predicted gains during this period. However, differences in performance of PIL and PIH steers compared with AL steers was similar to previous experiments (Knoblich et al., 1997; and Rossi et al., 1999a,b). Feed efficiency was similar between AL and PIH steers but was lower (P < 0.08) for PIL steers. Total intake was 58 lb lower, and days fed were reduced by eight days during Period 1 for PIH compared with PIL steers. Average daily gain during Period 2 was 18% greater (P < 0.05) for PIH than AL steers. The ADG of PIL steers was numerically higher than that of the AL steers. Actual gains were 36% greater than predicted for both PIH and PIL steers. Thus, increasing the growth rate 0.25 lb/day for PIH compared with PIL steers did not impair the degree of compensatory growth during this period. Intake per day was 0.6 lb/day greater for PIH compared with PIL steers. Feed efficiency was greater (P < 0.01) for PIH and PIL steers compared with AL steers. Total intake during Period 2 was 57 pounds lower for PIH than PIL steers, and days fed were reduced by five days for PIH compared with PIL steers. When offered feed ad libitum (Period 3), ADG of both PIL and PIH steers was greater (P < 0.1) than that of AL steers. However, ADG was 0.72 lb/day lower (P = 0.06) for PIH compared with PIL steers, indicating that increased growth rates in Periods 1 and 2 may have negatively affected ADG in Period 3. Dry-matter intake per day was similar between PIL and PIH steers. However, feed efficiency for PIL steers was improved 36% and 21% compared with AL and PIH steers, respectively. Overall ADG was not different (P > 0.37) among treatments. Dry matter-intake per day was 2.1 and 1.2 lb/day greater (P < 0.05) for AL steers compared with PIL and PIH steers, respectively. Feed efficiency tended (p = 0.12) to be improved for PIL and PIH steers compared with AL steers. Prescription-intake steers consumed 158 (PIL) and 167 lb (PIH) less total feed compared with AL steers; however, this difference was not statistically significant (P = 0.35).
Table 1. Composition of Diets. |
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|---|---|---|---|---|---|
|
Predicted Rate of Gain, lb/daya |
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| Item | AL | 2.5 | 2.75 | 3.0 | 3.25 |
| Ingredient, % | |||||
| High moisturewhole-shelled corn | 70 | 60 | 65 | 65 | 70 |
| Corn silage | 15 | 15 | 15 | 15 | 15 |
| Ground corn | 1.15 | 2.90 | –– | 3.26 | –– |
| Soybean meal | 10.4 | 17.5 | 15.7 | 12.9 | 11.2 |
| Urea | 0.82 | 1.10 | 1.03 | 0.92 | 0.92 |
| Animal-vegetable fat | 0.40 | 0.40 | 0.40 | 0.40 | 0.40 |
| Dicalcium phosphate | 0.35 | 0.82 | 0.69 | 0.48 | 0.40 |
| Limestone | 1.30 | 1.46 | 1.40 | 1.40 | 1.37 |
| Trace mineral saltb | 0.50 | 0.65 | 0.61 | 0.55 | 0.53 |
| Rumensin, 176g/kg | 0.017 | 0.022 | 0.021 | 0.019 | 0.016 |
| Tylan, 220 g/kg | 0.013 | 0.016 | 0.015 | 0.014 | 0.013 |
| Selenium, 201 mg/kg | 0.050 | 0.063 | 0.061 | 0.055 | 0.050 |
| Vitamin A, 30,000 IU/g | 0.010 | 0.013 | 0.012 | 0.011 | 0.011 |
| Vitamin D, 3,000 IU/g | 0.010 | 0.013 | 0.012 | 0.011 | 0.011 |
| Vitamin E, 44 IU/g | 0.030 | 0.039 | 0.037 | 0.033 | 0.032 |
| Nutrient Composition | |||||
|
Crude proteinc, % |
14.08 | 18.06 | 16.91 | 5.57 | 14.80 |
|
Calcium, % |
0.60 | 0.78 | 0.73 | 0.67 | 0.64 |
|
Phosphorus, % |
0.42 | 0.54 | 0.51 | 0.46 | 0.64 |
|
Potassium, % |
0.63 | 0.75 | 0.72 | 0.67 | 0.44 |
|
NEm, Mcal/kg |
2.08 | 2.04 | 2.05 | 2.07 | 2.07 |
|
NEg, Mcal/kg |
1.42 | 1.40 | 1.40 | 1.41 | 1.42 |
| aAL = fed
to ad libitum steers throughout the trial and prescription-intake steers
during Period 3; 2.5, 2.75, 3.0 and 3.25 = fed to prescription-intake steers
when predicted gains were 2.5, 2.75, 3.0 and 3.25 lb/day, respectively.
bContained: > 93% NaCl, 0.35% Zn, 0.28% Mn, 0.175% Fe, 0.035% Cu, 0.007% I, and 0.007% Co. cCrude protein content was determined by analysis; remaining composition values were calculated. |
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Table 2. Effects of Growth Rate During Periods of Intake Restriction in Prescription Fed Steers on Performance. |
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|---|---|---|---|---|
| Predicted Rate of Gain, lb/daya | ||||
|
Period 1: |
AL | 2.5 | 2.75 | |
|
Period 2: |
AL | 3.0 | 3.25 | |
| Period 3: | AL | AL | AL | SE |
| Item | ||||
| No. of steers | 36 | 36 | 36 | – |
| Initial wt., lb | 680 | 678 | 680 | 0.73 |
| Final wt., lb | 1,255 | 1,2644 | 1,261 | 8.1 |
| Period 1 | ||||
| Gain, lb/day | 4.32b | 2.96d | 3.38c | 0.104 |
| DM intake, lb/day | 18.3b | 13.9d | 14.7c | 0.13 |
| Feed efficiency gain/feed | 0.236e | 0.213f | 0.230e | 0.0064 |
| Total gain, lb | 259b | 186c | 187c | 4.8 |
| Total intake, lb | 1099b | 874c | 816d | 14.7 |
| Days | 60b | 63c | 55d | 0.9 |
| Period 2 | ||||
| Gain, lb/day | 3.76c | 4.09bc | 4.43b | 0.138 |
| DM Intake, lb/day | 20.6b | 18.7d | 19.3c | 0.15 |
| Feed efficiency gain/feed | 0.183c | 0.219b | 0.230b | 0.0066 |
| Total gain, lb | 248 | 270 | 270 | 7.7 |
| Total intake, lb | 1357b | 1235c | 1178c | 18.3 |
| Days | 66b | 66b | 61c | 0.8 |
| Period 3 | ||||
| Gain, lb/day | 3.00g | 4.54e | 3.82f | 0.246 |
| DM intake, lb/day | 20.4c | 22.6b | 23.2b | 0.51 |
| Feed efficiency gain/feed | 0.147c | 0.200b | 0.165c | 0.0080 |
| Total gain, lb | 67c | 130b | 124b | 11.7 |
| Total intake, lb | 465f | 655ef | 759e | 81.8 |
| Days | 23 | 29 | 33 | 4.2 |
| Overall | ||||
| Gain, lb/day | 3.87 | 3.71 | 3.90 | 0.095 |
| DM intake, lb/day | 19.6b | 17.5d | 18.5c | 0.11 |
| Feed efficiency gain/feed | 0.198 | 0.212 | 0.212 | 0.0080 |
| Total intake, lb | 2921 | 2763 | 2754 | 86.8 |
| Total days | 149 | 158 | 149 | 4.3 |
| aAL = offered
feed ad libitum; 2.5, 2.75, 3.0 and 3.25 = predicted rates of gain of prescription-intake
steers during periods of feed restriction. bcdMeans in a row without a common letter differ (P < 0.05). efgMeans in a row without a common letter differ (P < 0.10). |
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Carcass characteristics are shown in Table 3. No differences (P > 0.22) among treatments were observed for carcass characteristics. However, limit-fed steers tended to be leaner as evidenced by numerically lower backfat, marbling scores, and yield grades. In contrast to other prescription-intake studies (Rossi et al., 1999a,b), restricting intake for a portion of the feeding period had no negative effects on carcass marbling scores compared with offering feed ad libitum. Furthermore, increasing the growth rate of prescription-intake steers during periods of feed restriction had minimal effects on carcass characteristics.
Table 3. Effects of Growth Rate During Periods of Intake Restriction in Prescription Fed Steers on Carcass Characteristics. |
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|---|---|---|---|---|
| Predicted Rate of Gain, lb/daya | ||||
|
Period 1: |
AL | 2.5 | 2.75 | |
|
Period 2: |
AL | 3.0 | 3.25 | |
| Period 3: | AL | AL | AL | SE |
| Item | ||||
| Dressing percentage | 61.3 | 60.4 | 60.6 | 0.49 |
| Hot carcass weight, lb | 769.4 | 763.9 | 763.6 | 6.4 |
| Backfat, in | 0.43 | 0.38 | 0.37 | 0.025 |
| Ribeye area, in2 | 12.78 | 13.42 | 13.08 | 0.336 |
| Kidney, pelvic, and heart fat, % | 3.36 | 3.46 | 3.54 | 0.010 |
| Marbling scoreb | 4.02 | 3.63 | 3.69 | 0.17 |
| Choice percentage | 75 | 72 | 75 | 6.16 |
| Yield grade | 3.09 | 2.75 | 2.85 | 0.14 |
| aAL = offered feed ad libitum; 2.5,
2.75, 3.0 and 3.25 = predicted rates of gain of prescription-intake steers
during periods of feed restriction. b2 = Select, 3 = Choice-, 4 = Choice°, 5 = Choice+. |
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Steers fed to achieve higher rates of growth during periods of feed restriction achieved equal gains, days on feed, and consumed approximately 150 lb less feed compared with steers offered feed ad libitum throughout the feeding period. Increasing the growth rate of prescription-intake steers during periods of feed restriction did not improve carcass characteristics compared with steers programmed at a lower growth rate. Increasing feed intake for prescription-intake steers to achieve a 0.25 lb/day increase in gain the first 60 days on feed did not affect subsequent compensatory gain during the next 65 days of the feeding period. However, the compensatory gain response was lower when feed was offered ad libitum during the last 30 days on feed in steers fed to gain 0.25 lb/day more during periods of intake restriction. A 22% growth restriction in Period 1 (PIH) resulted in calves that had equal gains and days fed as steers offered feed ad libitum. However, a 31% growth restriction in Period 1 (PIL) did not. Therefore, restricting the growth rate of cattle more than approximately 25% of maximum growth rate during Period 1 may decrease overall daily gains compared with a restriction to a lesser extent in period 1 or compared with offering cattle feed ad libitum throughout the feeding period.
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Rossi, J. E., Loerch, S. C., and Fluharty, F. L. 1999b. Effects of crude protein level in diets of feedlot steers during periods of compensatory growth in steers fed to achieve step-wise increases in rate of gain. The Ohio State University Ohio Agricultural Research and Development Center. Special Circular 162. pp. 38—43.
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1 For more information, contact at: The Ohio State University, Ohio Agricultural REsearch and Developement Center, 1680 Madison Avenue, Wooster, OH 44691; (330) 263-3900; email:loerch.1@osu.edu