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 feedlot performance and carcass characteristics of steers fed to achieve step-wise increases in gain and provided supplemental crude protein either equal in pounds or percent to that of steers offered feed ad libitum. Performance between steers fed equal pounds or percent per day crude protein as ad libitum steers was not different when gain was 2.5 or 3.0 pounds per day. Overall average daily gain was lower for prescription intake than ad libitum intake steers (P < 0.05). Total feed intake was lower (P < 0.05) for prescription intake than ad libitum intake steers despite days on feed being greater (P < 0.05) than ad libitum steers. Dressing percent, backfat, and quality grade were less (P < 0.01) for prescription intake than ad libitum intake steers. Carcass composition was not affected by treatment (P > 0.23). Increasing the percentage of crude protein in diets of prescription intake steers to provide the same grams per day crude protein intake as ad libitum steers was not beneficial. Total dry matter intake was lower for prescription intake steers, compared to ad libitum steers despite requiring 14 more days on feed. Quality grade was lower in prescription intake steers, but prescription intake steers tended to be leaner as evidenced by lower yield grades and backfat.
Feeding steers to achieve step-wise increases in average daily gain during the feeding period has been shown to improve feed efficiency and reduce total feed costs, without negatively affecting performance or carcass characteristics compared to steers offered feed ad libitum throughout the feeding period (Knoblich et al., 1997; Loerch and Fluharty, 1998). In these studies, when intake is increased to achieve a greater growth rate, performance of steers has been much greater than predicted based on NRC (1984) Net Energy gain equations for predicting growth rate. Optimum levels of crude protein during periods of compensatory growth have not been investigated in steers fed for increasing rates of gain during the feeding period. Hill et al. (1996) observed that providing equal intake of crude protein to limit-fed steers and ad libitum fed steers improved performance when feed intake was restricted by 13%, but had no affect on performance when feed intake was restricted by 7.25%. The study's objectives were to evaluate performance and carcass characteristics of feedlot steers fed to achieve step-wise increases in average daily gain during the feeding period when provided supplemental crude protein either equal in percentage or pounds to that of steers offered feed ad libitum.
Crossbred steer calves (n = 106; average initial BW = 631 ± 3.3 lb.) were randomly allotted by weight to 12 pens with nine steers per pen and four pens per treatment.
Treatments consisted of ad libitum consumption of a 12% crude protein (CP) diet fed throughout the experiment (AL12%); prescription intake of a 12% CP diet fed throughout the experiment (PI12%); or prescription intake of a high crude protein diet (PIHCP) that provided equal pounds per day CP intake as the AL12% diet. Steers consuming the PI12% and PIHCP diets were initially fed to achieve a predicted gain of 2.5 lbs./day for the first 190 lbs. of gain. Intake was then increased to achieve a growth rate of 3.0 lbs./day for the next 295 lbs. of gain. Steers were then offered feed ad libitum for the final 115 lbs. of gain before slaughter (at 1,230 lbs.). The same diet was fed to both AL12% and PI12% steers throughout the experiment, thus during periods of intake restriction, the concentration of CP, minerals, vitamins, Rumensin®, and Tylan® (provided by Elanco, Greenfield, IN) were less for PI12% than AL12% steers. Concentration of these nutrients were increased in the diet of PIHCP steers during periods of intake restriction to ensure equal daily intake of these nutrients as AL12% 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 55 degrees C, ground to pass a one mm screen, and analyzed for dry matter (DM) (Goering and Van Soest, 1970) 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.
Initial and final weights were determined using the average weight from two consecutive days. Cattle 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 lb.). 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 total carcass fat, protein, and moisture.
Data were analyzed using GLM procedures of 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 protocols concerning animal care 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 treatment on steer performance is shown in Table 2. Steers fed prescription intake diets during the first period (2.5 lbs./day gain) gained slightly more than what was predicted. Increasing the percent CP from 11.4% for PI12%, to 14.1% for PIHCP steers, did not improve average dairy gain (ADG) or feed efficiency during this period. Therefore, providing the same pounds per day CP intake to ad libitum intake and prescription intake may not be necessary when predicted gain is 2.5 lbs./day. When fed to achieve a predicted gain of 3.0 lbs./day, steers gained 25% more than what was predicted. There were no differences (P = 0.38) among treatments in ADG during this period. However, dry matter intake (DMI) was greater (P < 0.05) for AL12% steers, resulting in improved (P < 0.05) feed efficiency for prescription intake steers. Since performance was similar between prescription intake treatments, increasing the concentration of CP in prescription intake diets to supply equal CP intake the as ad libitum steers does not enhance performance when predicted gain is 3.0 lbs./day. No differences (P > 0.67) in performance between the prescription intake treatments were observed for the ad libitum intake period. Overall ADG was lower (P < 0.05) for the two prescription intake treatments than AL12% steers, resulting in prescription intake steers requiring 14 more days on feed to achieve the slaughter weight. Daily dry matter intake was lower (P < 0.01) for prescription intake steers and averaged 88% of AL12% steers. Furthermore, overall feed intake tended to be lower (P = 0.08) for prescription intake steers despite 14 more days on feed than AL12% steers. In addition, feed efficiency tended to be improved (P = 0.104) for prescription intake versus ad libitum intake steers.
| Table 1. Diet Composition. | |||
|---|---|---|---|
| Predicted rate of gain, lbs./day1 | |||
| Item | Ad libitum | 2.5 | 3.0 |
| Ingredient | |||
| Whole shelled high-moisture corn | 70 | 70 | 70 |
| Corn silage | 15 | 15 | 15 |
| Ground corn | 6.37 | 0.80 | 4.64 |
| Soybean meal | 5.25 | 9.55 | 6.50 |
| Urea | 0.60 | 1.07 | 0.75 |
| Animal-vegetable fat | 0.40 | 0.50 | 0.43 |
| Dicalcium phosphate | 0.35 | 0.80 | 0.55 |
| Limestone | 1.40 | 1.50 | 1.45 |
| Trace mineral salt2 | 0.50 | 0.63 | 0.54 |
| Rumensin, 176g/kg | 0.016 | 0.020 | 0.017 |
| Tylan, 220g/kg | 0.010 | 0.011 | 0.011 |
| Selenium, 201mg/kg | 0.050 | 0.063 | 0.054 |
| Vitamin A, 30,000 IU/g | 0.010 | 0.013 | 0.011 |
| Vitamin D, 3,000 IU/g | 0.010 | 0.013 | 0.011 |
| Vitamin E, 44 IU/g | 0.030 | 0.038 | 0.032 |
| Nutrient composition, % | |||
| Crude protein3 | 11.74 | 14.14 | 12.55 |
| Calcium | 0.62 | 0.77 | 0.68 |
| Phosphorus | 0.54 | 0.61 | 0.56 |
| Potassium | 0.41 | 0.50 | 0.45 |
| NEm, Mcal/kg | 2.08 | 2.05 | 2.07 |
| NEg, Mcal/kg 1.43 1.40 1.42 | |||
| 1 Ad libitum diet was fed to AL12% and PI12% steers during the entire trail; 2.5 and 3.0 diets were fed to PIHCP steers when predicted gain was 2.5 lbs./day and 3.0 lbs./day, respectively. 2 Contained : > 93% NaCL, 0.35% Zn, 0.28% Mn, 0.175% Fe, 0.035% Cu, 0.007% I, and 0.007% Co. 3 Crude protein was determined by analysis; remaining composition values were calculated. | |||
|
Table 2. Effects of Supplementing Crude Protein to Prescription Fed Steers Either Equal in Pounds or Percent to That of Steers Offered Feed Ad Libitum on Feedlot Performance. | |||||
|---|---|---|---|---|---|
| Treatment a | |||||
| Item | AL12% | PI12% | PIHCP | SE | |
| No. of steers | 35 | 36 | 36 | - | |
| Initial wt., lbs. | 630 | 630 | 630 | 3.1 | |
| Final wt., lbs. | 1,230 | 1,231 | 1,234 | 6.3 | |
| Predicted gain, 2.5 lbs./day | |||||
| Actual gain, lbs./day | 3.57b | 2.60c | 2.71c | 0.049 | |
| DM intake, lbs./day | 16.54b | 12.70c | 12.92c | 0.280 | |
| Feed efficiency, lbs. gain/lbs. feed | 0.215b | 0.204c | 0.210c | 0.0021 | |
| Total gain, lbs. | 249 | 192c | 193c | 3.6 | |
| Total feed, lbs. | 1,158b | 940c | 918c | 21.0 | |
| Days | 70b | 74c | 71c | 0.6 | |
| Predicted gain, 3.0 lbs./day | |||||
| Actual gain, lbs./day | 3.57 | 3.75 | 3.75 | 0.097 | |
| DM intake, lbs./day | 19.32b | 17.57c | 17.49c | 0.216 | |
| Feed efficiency, lbs. gain/lbs. feed | 0.185b | 0.214c | 0.215c | 0.0051 | |
| Total gain, lbs. | 250c | 295b | 294b | 6.1 | |
| Total feed, lbs. | 1,351 | 1,383 | 1,374 | 21.9 | |
| Days | 70b | 79c | 79c | 0.8 | |
| Ad libitum intake | |||||
| Gain, lbs./day | 3.53 | 3.73 | 3.53 | 0.282 | |
| Feed intake, lbs./day | 20.79 | 21.65 | 21.83 | 0.587 | |
| Feed efficiency, lbs. gain/lbs. feed | 0.162 | 0.171 | 0.161 | 0.0093 | |
| Total gain, lbs. | 101 | 114 | 117 | 8.1 | |
| Total feed, lbs. | 624 | 673 | 729 | 46.4 | |
| Days | 30 | 31 | 34 | 2.8 | |
| Overall performance | |||||
| Gain, lbs./day | 3.53b | 3.26c | 3.31c | 0.053 | |
| DM intake, lbs./day | 18.41b | 16.27c | 16.52c | 0.207 | |
| Feed efficiency, lbs. gain/lbs. feed | 0.192 | 0.201 | 0.200 | 0.0030 | |
| Total intake, lbs. | 3,133d | 2,996e | 3,021e | 39.9 | |
| Days | 170b | 184c | 184c | 2.7 | |
| a AL12% and PI12% = ad libitum and prescription intake of a 12% crude protein diet, respectively; PIHCP = prescription intake of a high crude protein diet that supplied equal pounds per day crude protein intake as AL12%; SE = standard error. b, c Means within a row with unlike superscripts differ (P < 0.05). d, e Means within a row with unlike superscripts differ (P < 0.10). | |||||
Carcass characteristics are shown in Table 3. There were no differences (P > 0.09) among treatments in hot carcass weight, ribeye area, or kidney, pelvic, and heart fat. Dressing percent and 12th rib backfat was greater (P < 0.05) for AL12% than PI12% or PIHCP steers. Marbling score was reduced (P < 0.05) in both PI12% and PIHCP steers compared to AL12% steers. Therefore, prescription intake steers tended (P = 0.09) to have fewer carcasses grading choice (83%) than AL12% steers (100%). Prescription intake steers tended to have lower yield grades (P = 0.12) than AL12% steers. However, carcass composition was not affected by treatment (P > 0.23).
|
Table 3. Effects of Supplementing Crude Protein to Prescription Fed Steers Either Equal in Pounds or Percent to That of Steers Offered Feed ad Libitum on Carcass Characteristics. | |||||
|---|---|---|---|---|---|
| Treatmenta | |||||
| Item | AL12% | PI12% | PIHCP | SE | |
| Hot carcass weight, lb. | 757.0e | 745.7ef | 741.3f | 4.50 | |
| Dressing percentage | 61.5c | 60.6d | 59.9d | 0.29 | |
| Ribeye area, in.2 | 12.95 | 13.00 | 13.00 | 3.402 | |
| 12th rib backfat, in. | 0.44c | 0.38d | 0.35d | 0.020 | |
| Kidney, pelvic, heart fat, % | 3.17 | 3.03 | 3.01 | 0.104 | |
| Quality gradeb | 4.34c | 3.94d | 3.86d | 0.114 | |
| Yield grade | 2.97 | 2.74 | 2.63 | 0.106 | |
| % Choice | 100e | 86f | 83f | 5.1 | |
| a AL12% and PI12% = ad libitum and prescription intake of a 12% crude protein diet, respectively. PIHCP = prescription intake of a high crude protein diet that supplied equal pounds per day crude protein intake as AL12%; SE = standard error. b 2 = Select, 3 = Choice-, 4 = Choice o, and 5 = Choice+. c, d Means within a row with unlike superscripts differ P < 0.05. e, f Means within a row with unlike superscripts differ P < 0.10. | |||||
Providing prescription intake steers equal CP intake as ad libitum intake steers does not enhance performance or carcass characteristics. Prescription intake steers required less total feed than ad libitum intake steers to reach the slaughter weight, thus reducing feed costs. However, because prescription intake steers had lower carcass quality grades than ad libitum intake steers, the economic benefits of reduced feed costs were diminished. These results are in disagreement with the observations of Knoblich et al. (1997), in which feed costs were lower and quality grade was not different between prescription intake and ad libitum intake steers. Since performance was similar between prescription intake treatments, the same diet can be fed to both ad libitum and prescription intake steers, which should simplify the practical application of a prescription intake feeding system. Furthermore, feed costs can be reduced through lower supplemental crude protein needs.
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