1 For more information, contact at: The Ohio State University, Ohio Agricultural Research and Development Center, 1680 Madison Avenue, Wooster, OH 44691; 330-263-3903.
The trial evaluated effects of dietary crude protein level during periods of compensatory growth in steers fed to achieve step-wise increases in growth rate during the feeding period. There were no differences in performance among prescription intake systems when predicted gain was 2.5 lbs./day. When predicted gain was 3.0 lbs./day, prescription intake steers gained 23% more (3.7 lbs./day) than what was predicted. No differences in average daily gain or feed efficiency were observed among prescription intake steers consuming 14% or 16% crude protein diets during this period. Overall feed intake was numerically lower for prescription intake steers despite requiring 14 more days on feed than ad libitum intake steers to reach the slaughter weight. Overall feed efficiency was not different among the five feeding systems (P > 0.57). Prescription intake steers had lower quality grades than ad libitum steers (P < 0.10), but were leaner than ad libitum steers as evidenced by lower (P < 0.10) backfat, yield grades, and carcass fat. Prescription intake steers performed similarly when consuming either a 14% or 16% crude protein diets, when predicted gain was 3.0 lbs./day. Likewise, performance of prescription intake steers was similar when consuming either a 12% or 14% crude protein diet during the ad libitum intake period. Therefore, feeding diets with crude protein levels higher than 14%, when predicted gain is 3.0 lbs./day, and 12% during the ad libitum intake period to prescription intake steers, does not appear to be necessary.
Feeding steers to achieve step-wise increases in gain during the feeding period can improve feed efficiency and reduce feed costs without negatively affecting carcass characteristics, compared to steers offered feed ad libitum throughout the feeding period (Knoblich et al., 1997). Performance of limit-fed steers during periods of compensatory growth is greater than expected based on NRC (1984) net energy gain equations (Knoblich et al., 1997; and Loerch and Fluharty, 1998). In the study by Knoblich et al. (1997), observed average daily gain was 4.2 lbs./day during a period when intake was increased to achieve a predicted gain of 3.0 lbs./day after a period of gaining 2.5 lbs./day. In addition, steers fed for increasing rates of gain during the feeding period have greater growth rates during the last 30 days on feed, compared to steers fed ad libitum throughout the feeding period. Thus, it is possible crude protein requirements would be higher during these periods of compensatory growth compared to steers fed ad libitum throughout the feeding period.
Crossbred steer calves (n = 142; average initial body weight (BW) 628 ± 3.1 lb) were allotted by weight to 16 pens with eight or nine steers per pen and three of four pens per finishing system. Five finishing systems were investigated. System 1 (S1) was ad libitum consumption of a 12% crude protein diet throughout the experiment. Steers in Systems 2, 3, 4, and 5 were initially fed to achieve a predicted gain of 2.5 lbs./day for the first 195 lbs. of gain. Intake was then increased to achieve a growth rate of 3.0 lbs./day for the next 285 lbs. of gain. Steers were then offered feed ad libitum for the final 120 lbs. of gain before slaughter (at 1,230 lbs.). During the three phases of growth (2.5 lbs./day, 3.0 lbs./day, and ad libitum), steers were fed the following CP levels: System 2 (12%, 14%, 12%); System 3 (12%, 14%, 14%); System 4 (12%, 16%, 12%); and System 5 (12%, 16%, 14%).
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 55 degrees C, ground to pass a one mm screen, and analyzed for dry matter (DM) (Van Soest et al. 1992), and nitrogen (N) by a combustion type N autoanalyzer Leco FP-2000 (Leco Corp., St. Joseph, MI). Feed samples were analyzed weekly for DM to adjust intake for dietary moisture content. Pens (18 x 18 ft.) were constructed of metal gates and cable, had concrete slatted floors, and were located in an open-sided barn.
Steers were weighed every two weeks, average daily gain (ADG) was determined, and intake was adjusted to meet maintenance requirements as body weight (BW) increased. Steers were implanted with Synovex-S® on day 0 and Revalor-S® on day 84 (provided courtesy of Fort Dodge Animal Health, Overland Park, KS, and Hoechst-Roussel Agri. Vet. Co., Overland Park, KS, respectively). Carcass data were collected by trained university personnel, from each animal following a 24-hour chill period to determine USDA quality and yield grades. Three steers from each pen were selected for carcass composition analysis. Selection was made so that the three carcasses from each treatment had an average weight of (751 ± 2.7 lbs.). Equal carcass weights were desired because carcass composition is affected by differences in carcass weight (Berg and Butterfield, 1968). The 9-10-11 rib section was removed from the right side of each carcass to determine chemical composition of the edible carcass according to procedures of Hankins and Howe (1946). Rib sections were deboned, ground three times, mixed once, and subsampled for determination of carcass fat, protein , and water.
Data were analyzed using GLM procedures of SAS (SAS, 1991) for a completely randomized design experiment. Treatment means were compared using the PDIFF statement of SAS (1991) when protected by a significant (P < 0.10) F-value. For performance data, the pen served as the experimental unit. For carcass composition, the animal served as the experimental unit.
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).
Composition of diets are shown in Table 1. Effects of the five finishing systems on feedlot performance are shown in Table 2. All five finishing systems were fed the same 12% crude protein diet when predicted gain was 2.5 lbs./day. Therefore, no differences were seen in performance between the four prescription intake treatments during this period. When fed to achieve a gain of 3.0 lbs./day, prescription intake steers gained 23% more than what was predicted. Dry matter intake was lower (P < 0.05) for all four prescription intake systems and feed efficiency was improved 14% for prescription intake steers (0.210) versus ad libitum intake steers (0.185) during this period. Crude protein (CP) levels would be expected to be higher during this period than at any other time during the feeding period for the four prescription intake treatments. Therefore, it was postulated that steers in Systems 4 and 5 may exhibit enhanced performance compared to Systems 2 and 3 during this period because of greater CP supplementation. However, the higher CP level (16%) did not improve performance, and a 14% CP diet appears to be adequate during this period. Average daily gain was not different (P > 0.25) among the five finishing systems when offered feed ad libitum (final growth phase). However, prescription intake steers consuming the 16% CP diet (Systems 4 and 5) during the previous period had numerically greater average daily gains (4.2 vs. 3.4 lbs./day) than steers consuming the 14% CP diet (Systems 2 and 3). Likewise, feed efficiency was similar among systems (P > 0.53), but tended to be improved for Systems 4 and 5 (0.181) versus Systems 2 and 3 (0.157). Daily dry matter intake was similar for System 1 and 3 steers (P > 0.05), but intake was greater (P < 0.05) for steers in Systems 2, 4 and 5 than System 1. Overall ADG was not different among treatments, but tended to be greater for System 1 steers (P = 0.13). Daily dry matter intake was lower for the prescription intake steers (P < 0.01), but overall feed efficiency was not different among treatments (P > 0.57). Overall feed intake was numerically lower for prescription intake steers despite requiring an average of 14 more days on feed than ad libitum steers.
| Table 1. Diet Composition. | |||||
|---|---|---|---|---|---|
| Predicted rate of gain, lbs./daya | |||||
| Item | 2.5(12%) | 3.0(14%) | 3.0(16%) | Ad lib(12%) | Ad lib(14%) |
| Ingredient | |||||
| High moisture whole-shelled corn | 70 | 65 | 65 | 70 | 70 |
| Corn silage | 15 | 15 | 15 | 15 | 15 |
| Ground corn | 5.49 | 6.99 | 2.14 | 6.37 | 1.57 |
| Soybean meal | 5.32 | 9.15 | 14.00 | 5.25 | 10.05 |
| Urea | 0.61 | 0.75 | 0.75 | 0.60 | 0.60 |
| Animal-vegetable fat | 0.50 | 0.43 | 0.43 | 0.40 | 0.40 |
| Dicalcium phosphate | 0.80 | 0.55 | 0.55 | 0.35 | 0.35 |
| Limestone | 0.50 | 1.45 | 1.45 | 1.40 | 1.40 |
| Trace mineral saltb | 0.63 | 0.54 | 0.54 | 0.50 | 0.50 |
| Rumensin, 176g/kg | 0.020 | 0.017 | 0.017 | 0.016 | 0.016 |
| Tylan, 220 g/kg | 0.011 | 0.011 | 0.011 | 0.010 | 0.010 |
| Selenium, 201 mg/kg | 0.063 | 0.054 | 0.054 | 0.050 | 0.050 |
| Vitamin A, 30,000 IU/g | 0.013 | 0.011 | 0.011 | 0.010 | 0.010 |
| Vitamin D, 3,000 IU/g | 0.013 | 0.011 | 0.011 | 0.010 | 0.010 |
| Vitamin E, 44 IU/g | 0.038 | 0.032 | 0.032 | 0.030 | 0.030 |
| Nutrient Composition, % | |||||
| Crude proteinc | 11.63 | 13.58 | 15.87 | 11.76 | 14.05 |
| Calcium | 0.75 | 0.69 | 0.71 | 0.62 | 0.63 |
| Phosphorus | 0.54 | 0.61 | 0.69 | 0.54 | 0.62 |
| Potassium | 0.49 | 0.46 | 0.47 | 0.41 | 0.42 |
| NEm, Mcal/kg | 2.07 | 2.07 | 2.06 | 2.08 | 2.07 |
| NEg, Mcal/kg | 1.42 | 1.41 | 1.41 | 1.43 | 1.42 |
| a 2.5 (12%) = fed to prescription intake steers when predicted gain was 2.5 lbs./day; 3.0 (14%), and 3.0 (16%) = fed to prescription intake steers when predicted gain was 3.0 lbs./day; AL(12%) = fed to ad libitum steers throughout the trial and prescription intake steers during the ad libitum growth phase; AL (14%) = fed to prescription intake steers during the ad libitum growth phase. b Contained: > 93% NaCl, 0. 35% Zn, 0.28% Mn, 0.175% Fe, 0.035% Cu, 0.007% I, and 0.007% Co. c Crude protein content was determined by analysis, remaining composition values were calculated. | |||||
|
Table 2. Effects of Crude Protein Level in Diets of Prescription Fed Steers During Periods of Compensatory Growth on Feedlot Performance. | ||||||
|---|---|---|---|---|---|---|
| Systema | ||||||
| 1 | 2 | 3 | 4 | 5 | ||
| % Crude Protein | ||||||
| Item | Period 1:12 | 12 | 12 | 12 | 12 | |
| Period 2:12 | 14 | 14 | 16 | 16 | ||
| Period 3:12 | 12 | 14 | 12 | 14 | SE | |
| No. of steers | 35 | 25 | 27 | 27 | 27 | - |
| Initial wt., lbs. | 630 | 631 | 628 | 629 | 629 | 2.5 |
| Final wt., lbs. | 1,230 | 1,229 | 1,228 | 1,239 | 1235 | 5.5 |
| Predicted gain, 2.5 lbs./day | ||||||
| Actual wt., lbs./day | 3.57b | 2.65c | 2.69c | 2.69c | 2.69c | 0.108 |
| DM intake, lbs./day | 16.54b | 12.88c | 12.90c | 12.88c | 12.88c | 0.280 |
| Feed efficiency, lbs. gain/lbs. feed | 0.215 | 0.205 | 0.209 | 0.209 | 0.209 | 0.0077 |
| Total gain, lbs. | 249b | 190c | 197c | 199c | 196c | 6.8 |
| Total feed, lbs. | 1,158b | 951c | 941c | 958c | 940c | 31.6 |
| Days | 70 | 74 | 73 | 74 | 73 | 2.0 |
| Predicted gain, 3.0 lbs./day | ||||||
| Actual gain, lbs./day | 3.57 | 3.79 | 3.62 | 3.68 | 3.70 | 0.119 |
| DM intake, lbs./day | 19.32b | 17.46c | 17.53c | 17.68c | 17.62c | 0.229 |
| Feed efficiency, lbs. gain/lbs. feed | 0.185b | 0.217c | 0.206c | 0.207c | 0.210c | 0.0063 |
| Total gain, lbs. | 250c | 287b | 285b | 286b | 288b | 10.1 |
| Total feed, lbs. | 1,351 | 1,322 | 1,385 | 1,380 | 1,374 | 43.5 |
| Days | 70b | 76bc | 79c | 78c | 78c | 2.2 |
| Ad libitum intake | ||||||
| Gain, lbs./day | 3.37 | 3.48 | 3.35 | 4.01 | 4.41 | 0.386 |
| Feed intake, lbs./day | 20.79b | 22.16cd | 21.50bd | 23.09c | 23.37c | 0.461 |
| Feed efficiency, lbs. gain/lbs. feed | 0.162 | 0.158 | 0.156 | 0.173 | 0.188 | 0.015 |
| Total gain, lbs. | 101 | 121 | 117 | 125 | 122 | 8.5 |
| Total feed, lbs. | 624 | 768 | 776 | 751 | 646 | 78.7 |
| Days | 30 | 35 | 36 | 33 | 28 | 4.1 |
| Overall performance | ||||||
| Gain, lbs./day | 3.53 | 3.24 | 3.18 | 3.31 | 3.40 | 0.099 |
| DM intake, lbs./day | 18.41b | 16.49c | 16.47c | 16.69c | 16.56c | 0.227 |
| Feed efficiency, lbs. gain/lbs. feed | 0.192 | 0.197 | 0.194 | 0.199 | 0.205 | 0.0063 |
| Total feed intake, lb. | 3,133 | 3,047 | 3,101 | 3,089 | 2,960 | 94.3 |
| Days fed | 170 | 185 | 188 | 185 | 179 | 5.5 |
| a System 1 = ad libitum consumption of a 12% crude protein diet; Systems 2, 3, 4, and 5 = prescription intake of the following crude protein levels during the three phases of growth (2.5 lbs./day, 3.0 lbs./day, and ad libitum): System 2 (12%, 14%, and 12%); System 3 (12%, 14%, and 14%); System 4 (12%, 16%, and 12%); and System 5 (12%, 16%, and 14%); SE = standard error. bcd Means within a row with unlike superscripts differ (P < 0.05). | ||||||
Carcass characteristics are shown in Table 3. No differences (P > 0.20) were observed among the five finishing systems in hot carcass weight, dressing percent, ribeye area, and kidney, pelvic, and heart fat. Percent of steers grading choice was not significantly different (P > 0.13), but was numerically lower for prescription intake steers (100% vs. 81.5%, for ad libitum and prescription intake steers, respectively). Prescription intake steers tended to be leaner than ad libitum steers as evidenced by lower backfat, quality grades, and improved yield grades (P < 0.10). Carcass water and protein percent were similar among treatments (Table 4), but carcass fat percent was greater (P < 0.10) for ad libitum than prescription intake steers.
|
Table 3. Effects of Crude Protein Level in Diets of Prescription Fed Steers During Periods of Compensatory Growth on Carcass Characteristics. | ||||||
|---|---|---|---|---|---|---|
| Systema | ||||||
| 1 | 2 | 3 | 4 | 5 | ||
| % Crude protein | ||||||
| Item | Period 1:12 | 12 | 12 | 12 | 12 | |
| Period 2:12 | 14 | 14 | 16 | 16 | ||
| Period 3:12 | 12 | 14 | 12 | 14 | SE | |
| Hot carcass weight, lb. | 757.0 | 743.5 | 747.7 | 745.1 | 744.8 | 8.36 |
| Dressing percentage | 61.5 | 60.5 | 60.9 | 60.1 | 60.3 | 0.53 |
| Ribeye area, in.2 | 12.95 | 12.74 | 12.86 | 12.84 | 13.52 | 0.236 |
| Backfat, in. | 0.44c | 0.37de | 0.43ce | 0.35d | 0.36de | 0.031 |
| Kidney, pelvic, heart fat, % | 3.17 | 3.00 | 3.19 | 2.89 | 2.81 | 0.130 |
| Quality gradeb | 4.34c | 3.82d | 3.89cd | 3.90cd | 3.54d | 0.191 |
| Yield grade | 2.97c | 2.78ce | 2.94 | 2.67de | 2.47d | 0.121 |
| Percent choice | 100 | 81 | 82 | 89 | 74 | 7.2 |
| a System 1 = ad libitum consumption of a 12% crude protein diet. Systems 2, 3, 4, and 5 = prescription intake of the following crude protein levels during the three phases of growth (2.5 lbs./day, 3.0 lbs./day, and ad libitum): System 2 (12%, 14%, and 12%); System 3 (12%, 14%, and 14%); System 4 (12%, 16%, and 12%); and System 5 (12%, 16%, and 14%); SE = standard error. b 2 = Select, 3 = Choice-, 4 = Choice o, 5 = Choice+. cde Means within a row with unlike superscripts differ (P < 0.10). | ||||||
|
Table 4. Effects of Crude Protein Level in Diets of Prescription Fed Steers During Periods of Compensatory Growth on Carcass Composition. | ||||||
|---|---|---|---|---|---|---|
| Systema | ||||||
| 1 | 2 | 3 | 4 | 5 | ||
| % Crude protein | ||||||
| Item | Period 1: 12 | 12 | 12 | 12 | 12 | |
| Period 2: 12 | 14 | 14 | 16 | 16 | ||
| Period 3: 12 | 12 | 14 | 12 | 14 | SE | |
| Water, % | 53.1 | 54.9 | 53.3 | 55.6 | 55.3 | 0.92 |
| Protein, % | 14.5 | 14.9 | 14.4 | 15.0 | 15.0 | 0.22 |
| Fat, % | 30.9b | 28.5bc | 30.8b | 27.5c | 27.7c | 1.19 |
| a System 1 = ad libitum consumption of a 12% crude protein diet. Systems 2, 3, 4, and 5 = prescription intake of the following crude protein levels during the three phases of growth (2.5 lbs./day, 3.0 lbs./day and ad libitum): System 2 (12%, 14%, and 12%); System 3 (12%, 14%, and 14%); System 4 (12%, 16%, and 12%); and System 5 (12%, 16%, and 14%); SE = standard error. bc Means within a row with unlike superscripts differ (P < 0.10). | ||||||
Feeding diets higher than 14% CP, when predicted gain is 3.0 lbs./day or 12% CP, during the ad libitum intake period did not improve performance of prescription intake steers. Thus, the CP levels fed in System 2 (12, 14, 12%) appear to be adequate for steers fed using a prescription intake feeding strategy.
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