Effects of Source of Energy on Performance, Ultrasonic, Carcass, and Economic Characteristics of Early-Weaned Heifers

INTRODUCTION

The ability to produce pounds of high-quality beef while minimizing input costs is an ongoing challenge for beef producers. Quality may be reduced if high by-products are fed. With more corn likely going to ethanol production, corn by-products will be produced in large quantities. Although corn by-products have more protein, they contain less starch content when compared with corn. Improvements in intramuscular fat (Schoonmaker et al., 2003; Schoonmaker et al., 2004) and marbling score (Myers et al., 1999a; Shike 2005) have been shown when high-grain diets were utilized in accelerated finishing programs such as early weaning. This improvement is likely due to the increase in blood glucose through starch fermentation, because Smith and Crouse (1984) found that glucose was the preferred substrate for intramuscular fat. Strategic feeding of corn and corn by-products to early-weaned heifers could increase the amount of high-quality beef produced and increase profitability. The objectives of this study were to evaluate the effects of source of energy on performance, ultrasonic, carcass, and economic characteristics of early-weaned heifers during the final finishing period after the heifers were fed a high-concentrate diet to initiate marbling.

MATERIALS AND METHODS

One hundred ninety-two Angus × Simmental heifer calves (BW = 253 ± 2 kg) were used to evaluate the effects of source of energy on performance, ultrasonic, carcass, and economic characteristics of early-weaned heifers. Heifers used in this trial were managed according to the guidelines recommended in the Guide for the Care and Use of Agricultural Animals in Agriculture Research and Teaching (Consortium, 1988). All experimental procedures followed those approved by the University of Illinois Laboratory Animal Care Advisory Committee.

Heifers were weaned at an average age of 77 d and allowed ad libitum access to a high-concentrate creep feed (Table 1) for 146 d to initiate marbling. This reflects the nutrition of the calves before starting the trial. During the creep feeding period, heifers were in a dry lot for 21 d and then placed on pasture for 125 d. Pasture consisted of 90% endophyte-infected tall fescue (Festuca arundinacea) and a 10% mixture of legumes. At the end of the 146-d creep feeding period, heifers were randomly allotted to 1 of 4 dietary treatments (Table 2). Treatments investigated were 1) high starch (HS); 2) intermediate starch (IS); 3) low starch (LS); and 4) pasture (PAST). Heifers allotted to PAST treatment were randomly allotted to 8 pastures (6 head/pasture) for the growing period. Heifers allotted to the PAST treatment grazed a paddock that consisted of 90% endophyte-infected tall fescue (Festuca arundinacea) and a 10% mixture of grass and legumes. At the end of the growing period, PAST heifers were placed on the IS treatment for the remainder of the trial. This allowed us to compare these heifers with the IS treatment. The other 3 treatments, HS, IS, and LS, were tested with linear and quadratic contrasts. The calculated levels of starch were 63, 41, and 12% for the HS, IS and LS, respectively. While in the feedlot, heifer was the experimental unit because individual feed intake was recorded using the GrowSafe automated feeding system (GrowSafe Systems Ltd., Airdrie, Alberta, Canada). Heifers were vaccinated 4 wk before early weaning with Ultrabac 7/Somubac (Smith Kline Beecham, West Chester, PA), Cattlemaster 4 + VL5 (Pfizer, Exton, PA), and One Shot Ultra 7 (Pfizer). At the time of early weaning heifers were vaccinated with Vision 7 Somnus with Spur (Intervet, Inc., Millsboro, DE), Express 5-PHM (Boehringer Ingelheim Pharmaceuticals Inc., Ridgefield, CT), and Leptoferm-5 (Pfizer). Three and one-half months after early weaning, half of the heifers were vaccinated with Vista 5 L5 SQ (Intervet, Inc.) and Once PMH (Bayer Animal Health, Shawnee Mission, KS), and half the heifers were vaccinated with Leptoferm-5 and Express 5-PHM. Heifers were implanted at the end of the growing period with Component TE-H (140 mg progesterone, 14 mg estradiol, and 29 mg tylosin tartate; Vetlife, Overland Park, KS).

The experimental growing period was 73 d and the finishing period was 103 d for the HS, IS, and LS heifers and 131 d for the PAST heifers. Full weights were taken on 2 consecutive days at the initiation of trial and after the growing period to calculate growing phase performance. Final weights were calculated from hot carcass weight (HCW) using a standard dressing percentage of 62%. Finishing phase performance and overall performance were calculated. Individual daily DMI was recorded using the GrowSafe automated feeding system. Intakes were not measured during the growing period for PAST heifers because they were on pasture, and as a result, feed efficiency was not calculated for the growing or overall period. Ultrasonic measurements were taken for marbling score, 12th rib fat thickness, and ribeye at the initiation of trial and after the 73 d growing period using an Aloka SSD-500 V ultrasound machine fitted with a 3.5-MegaHz probe (Aloka Co. Ltd., Wallingford, CT). Marbling image analysis was performed according to Brethour (1994). The image of the ribeye was traced for area using software provided by the Cattle Performance Enhancement Company (Oakley, KS). Fat thickness was also used to establish harvest date. A target fat thickness of 1.25 cm was used to harvest heifers at 173 d on trial for HS, IS, and LS heifers and 204 d on trial for PAST heifers. Rate of marbling for the growing period was calculated by subtracting the ultrasonic scan after the growing period from the ultrasonic scan at the initiation of the trial and dividing by 73 d on feed (DOF). Rate of marbling for the finishing period was calculated by subtracting harvest marbling score from ultrasonic scan after the growing period and then dividing by 103 (DOF) for the HS, IS, and LS heifers or by dividing by 131 (DOF) for the PAST heifers. Rate of marbling for the combined period was calculated by subtracting harvest marbling score form ultrasonic initial scan and then dividing by 176 (DOF) for the HS, IS, and LS heifers or by dividing by 204 (DOF) for the PAST heifers. Rate of marbling per centimeter of back fat was not calculated during the 73-d growing period because PAST heifers lost back fat. However, during the finishing period the rate of marbling per centimeter of back fat was calculated by subtracting harvest marbling score from ultrasonic scan after the growing period and dividing by harvest back fat subtracted from ultrasonic scan after the growing period and multiplying by 100.

Heifers were transported via commercial trucking to Tyson, Inc. (Joslin, IL) and harvested. University of Illinois trained personnel measured carcass characteristics. Measurements were taken for HCW on day of harvest. Following a 24-h chill at -40C, LM, 12th to 13th rib fat thickness, KPH, and marbling score were determined. Chromatography paper was used to make an image of the longissimus dorsi (LD); the image was later traced and a grid was used to determine ribeye area. University of Illinois measurements were used to determine QG and calculate YG. The YG was calculated using the following equation: 2.5 + (2.5 × inches of BF) + (0.20 × % KPH) + (0.0038 × lbs of HCW) - (0.32 × LD in square inches) (Taylor, 1994).

Five-year (2002 to 2006) average price data for feedstuffs, dressed beef price, feeder heifer price (medium and large ones), and grid premiums and discounts were collected and used to standardize conditions across treatments. Corn price was collected from annual commodity (NASS, 2007). Price for corn silage was calculated based on corn price using the following equation: (6.5 × price/bushel of corn + $5.00/total harvest and storage cost)/35% DM. By-product prices were collected from the Missouri Dairymen's By-Product Feed Page (University of Missouri, 2007). Diet costs for treatments are shown in Table 3. The PAST heifers were charged $0.45/d for a grazing fee. Purchase price was calculated by using initial weight times the following prices (from 2002 to 2006): $116.99/45.4 kg at 204 to 226 kg; $111.84/45.4 kg at 227 to 249 kg; $106.58/45.4 kg at 250 to 271 kg; and $101.63/45.4 kg at 272 to 295 kg (USDA, 2007c). Average dressed heifer price (2002 to 2006) was $129.31/45.4 kg (USDA, 2007a). Average premiums and discounts (2002 to 2006; USDA, 2007b) were assessed to the base price and are shown in Table 4. Input costs included purchase price, feed costs, processing charge (medical, veterinary, and labor; $25/head), yardage ($0.30head/d), interest (8% annual percentage rate), and for PAST heifers a grazing fee ($32.85/head). Final carcass value was calculated for each heifer using actual HCW and specific premiums and discounts. Profit was calculated by subtracting final carcass value from total costs endured during the trial.

Performance, ultrasonic, carcass, and economic data were analyzed using the GLM (non-categorical data) and GENMOD (categorical data) procedures of SAS (SAS Inst Inc., Cary, NC). Because individual intakes were recorded, heifer was the experimental unit used for performance, ultrasonic, economic, and carcass data. Both linear and quadratic terms were evaluated for performance, ultrasonic, economic, and carcass parameters for starch levels. A single degree of freedom orthogonal contrast was used (IS vs. PAST) because the 2 groups were fed the same finishing diets. The independent variable used in the model was treatment.

RESULTS AND DISCUSSION

Performance data are shown in Table 5. Initial weight did not differ (P > 0.53) among treatments. During the growing period, gain increased linearly (P < 0.01) as level of starch decreased. In addition, IS heifers gained 1.21 kg/d more (P < 0.01) than PAST heifers during the growing period. Consequently, IS heifers weighed 87 kg more (P < 0.01) after the growing period than PAST heifers. Intake increased linearly (P < 0.01) as level of starch decreased. Additionally, a quadratic (P = 0.08) trend was observed for intake, where LS heifers ate the most feed. Feed efficiency decreased curvilinearly (P < 0.01) as level of starch decreased, with the IS heifers being the most efficient. Similar to the growing period, gain during the finishing period increased curvilinearly (P < 0.01) as level of starch decreased because HS heifers gained the slowest. During the finishing period, PAST heifers experienced compensatory gain, and gained 0.26 kg/d more (P < 0.01) than IS heifers. Intake during the finishing period resulted in the same response as observed during the growing period; as level of starch decreased, intake increased linearly (P < 0.01). In agreement with faster gains, PAST heifers consumed 0.99 kg/d more (P < 0.01) feed than IS heifers (8.96 vs 7.97 kg/d). Feed efficiency was not linearly (P =0.17) different among the HS, IS, and LS heifers. However, a quadratic (P = 0.04) response was observed for feed efficiency, where IS heifers were the most efficient. In addition, PAST heifers were 5% more (P = 0.03) efficient than IS heifers.

When the growing and finishing periods were combined, there was a curvilinear (linear, P < 0.01 and quadratic, P = 0.01) response for overall gain, where HS heifers gained the slowest. Farlin (1981) and Firkins et al. (1985) reported greater gains when steers were fed wet distillers grains compared with steers fed corn. Ham et al. (1994) also reported an improvement in gain when steers were fed dry distillers grains compared with steers fed dry-rolled corn. Green et al., (1987) reported similar gains when dry corn gluten feed replaced dry-rolled corn. Furthermore, overall intake increased linearly (P < 0.01) as starch level decreased. Increased intakes have been shown in other studies (Trenkle, 1986; Kampman and Loerch, 1989; Ham et al., 1994, 1995). Greater intake with decreasing starch level is likely because of less negative feed interactions (Highfill et al., 1987). Often when feeding high-grain diets, rumen pH is between 5.5 and 6.5 (Owens and Goetsch, 1988) and intakes become more irregular (Fulton et al., 1979). Heifers fed greater levels of starch were more likely experiencing longer periods of subacute acidosis than heifers fed lower levels of starch. Krehbiel et al. (1995) concluded that when wet corn gluten feed replaced dry-rolled corn, the incidence of acidosis is likely shorter. As a result, the increase in gains as starch level decreased may be due to more consistent appetites, particularly for cattle on a finishing diet for a long time as in this study. There was no difference (linear, P = 0.54) for overall feed efficiency among the HS, IS, and LS heifers. However, there was a quadratic (P < 0.01) effect for feed efficiency, where IS heifers were the most efficient. Even though PAST heifers gained faster during the finishing period, IS heifers gained 0.28 kg/a faster (P < 0.01) than PAST heifers for overall gain. Myers et al. (1999b) reported a similar overall improvement in gain (0.17kg/d) in steers fed concentrate ad libitum compared with steers allowed an 82-d growing period on pasture. Because of faster gains as level of starch decreased, final weights linearly (P < 0.01) increased. There was no difference (P = 0.12) between the IS and PAST heifers for final weight because the PAST heifers were fed longer.

Ultrasonic data are shown in Table 6. At initial scan there were no differences (P = 0.14) for marbling score, ribeye area, ribye area/100 kg of live weight, or 12th-rib backfat between the HS, IS, and LS heifers. In addition, there were no differences (P = 0.27) between the IS and PAST heifers for marbling score, ribeye area/100 kg of live weight, or 12th-rib backfat. For ultrasonic scan, after the growing period, there was linear (P < 0.01) increase in 12th-rib backfat as starch level decreased. Additionally, there was a quadratic (P = 0.06) trend for 12th-rib backfat, where LS heifers had the most 12thrib backfat. The IS heifers had 0.38 cm more (P < 0.01) 12th-rib backfat than PAST heifers at the end of the growing period. In addition, there was a linear (P = 0.01) increase in ribeye area and ribeye area/100 kg of live weight as the starch level decreased. Furthermore, IS heifers had 13.2 cm^sup 2^ larger (P < 0.01) ribeye areas than PAST heifers after the growing period. However, ribeye area/100 kg of live weight did not differ (P = 0.43) between the IS and PAST heifers. The improvements in ribeye area for IS heifers probably reflect gain differences. The IS heifers gained faster than PAST heifers during the growing phase.

Marbling score after the growing period did not differ (P = 0.33) between the HS, IS, and LS heifers. Although there was no difference for marbling score after the growing period, there was a linear (P = 0.09) trend for rate of marbling per day. As level of starch increased, rate of marbling per day tended (P = 0.07) to increase. This increase may be due to an increase in blood glucose through starch fermentation, as Smith and Crouse (1984) found that glucose is the preferred substrate for intramuscular fat. Schoonmaker et al. (2003) and Schoonmaker et al., (2004) using early-weaned steers 119 d of age found an improvement for ultrasonic intramuscular fat after a 100- or 153-d growing period when steers were fed an ad libitum concentrate diet compared with an ad libitum fiber diet. Schoonmaker et al. (2004) also found that adipocyte hyperplasia was affected by source of energy. In the present trial, heifers averaged 223 d of age when trial initiated and 296 d of age when the growing period was completed. Diets were fed ad libitum, so greater rates of marbling per day as starch level increased are likely due to the source of energy because intakes and gains increased as starch level decreased. The IS heifers had a 57-unit improvement (P < 0.01) for marbling score than PAST heifers after the growing period. Consequently, IS heifers deposited 0.52 more (P < 0.01) units of marbling per day than PAST heifers. During the finishing period, rate of marbling per day tended to increase linearly (P = 0.07) as level of starch decreased. This probably is not due to level of starch, but is a reflection of the increased ADG for the lower starch diets. Prior (1983) established that total energy intake was more important than energy density of diet for increases in adipocyte hypertrophy. Heifers fed lower levels of starch had greater gains during the finishing period, likely when adipocyte hyperplasia had ceased. Greater rates of marbling per day during the finishing period could be attributed to faster gains and greater intakes as starch level decreased. Also, IS heifers deposited 0.37 more (P < 0.01) units of marbling per day than PAST heifers during the finishing period despite the PAST heifers gaining faster. This suggests that the slow rate of gain on fescue pasture reduced the ability of the heifers to marble in the feedlot. During the finishing period, there was no difference (P = 0.68) for marbling score/1 cm of 12th-rib backfat between the HS, IS, and LS heifers. However, IS heifers deposited 13.5 more (P < 0.01) units of marbling score/1 cm of 12th-rib backfat than PAST heifers during the finishing period. Overall rate of marbling per day was not different (P = 0.41) between the HS, IS, and LS heifers. However, IS deposited 0.37 more (P < 0.01) units of marbling per day than PAST heifers during the combined trial.

Carcass data are shown in Table 7. The HCW increased linearly (P < 0.01) as level of starch decreased. Heifers fed lower levels of starch gained faster during the 176-d trial, and increase HCW are likely reflective of the gain response. There was a curvilinear (linear, P < 0.01 and quadratic, P = 0.04) response for the percentage of carcasses =272 kg, where HS heifers had the greatest percentage of light weight carcasses. Schoonmaker et al. (2002) and Barker-Neef et al. (2001) both reported lighter carcass weights when early-weaned (105 d of age) steers were compared with normal-weaned (205 d of age) steers. Consequently, at harvest, early-weaned steers were on a high concentrate diet longer (271 vs. 166 d) than normal-weaned steers. In the present study, all heifers were fed a concentrate creep for 146 d before the start of the trial, and thus HS heifers were fed a high concentrate diet for 322 d. Heifers fed lower levels of starch during the 176 d trial likely benefited from the added fiber in the rations, which may have reduced subacute acidosis for these long-fed heifers. In contrast to Schoonmaker et al. (2002) and Barker-Neef et al. (2001), Myers et al. (1999a) reported heavier carcass weights when early-weaned steers (168 d of age) were compared with normal-weaned steers (222 d of age). Early-weaned steers were fed a high-concentrate diet from early weaning to normal weaning and until harvest. Although heifers used hy Schoonmaker et al. (2002) and Barker-Neef et al. (2001) were of similar breed makeup as Myers et al. (1999a), steers were used in their study. In addition, as starch level increased, gain and intake decreased, which may be due to irregular intakes and subacute acidosis, thus causing a reduction in HCW. As level of starch decreased, 12th-rib backfat tended to increase linearly (P = 0.06). Ribeye area did not differ (linear, P = 0.13) between the HS, IS, and LS heifers. However, a quadratic (P = 0.05) response was observed for ribeye area, where IS heifers had the largest ribeye areas. Ribeye area/100 kg of HCW decreased linearly (P < 0.01) as level of starch decreased. Heifers fed greater levels of starch had lighter HCW, so when ribeye area was expressed per 100 kg of HCW, heifers fed greater levels of starch demonstrated improvements. There were no differences (P > 0.12) for HCW, 12th-rib backfat, ribeye area, or ribeye area/100 kg of HCW, and consequently, calculated YG between the IS and PAST heifers. In addition, there was no difference (P = 0.24) for the percentage of carcasses =272 kg between the IS and PAST heifers. There were also no differences (P = 0.14) for the percentage of YG 1, 2, 3, or 4 between the IS and PAST heifers. Percentage of KPH increased linearly (P < 0.01) as level of starch decreased. Additionally, IS heifers had a greater (P < 0.01) percentage of KPH than PAST heifers (2.8 vs. 2.4%). Calculated YG increased linearly (P = 0.02) as starch level decreased. Percentage of YG 2 increased linearly (P = 0.03) as level of starch increased. On the other hand, percentage of YG 3 decreased linearly (P < 0.01) as level of starch increased. The differences in YG distribution reflect more 12th-rib backfat as the level of starch decreased. There were no differences (P = 0.20) for the percentage of YG 1 or 4 between HS, IS, and LS heifers. There was no difference (P > 0.45) for marbling score between the HS, IS, and LS heifers. No marbling score differences are in an agreement with numerous trials when replacing either dry-rolled or high-moisture corn with wet or dry distillers grains or corn gluten feed (Firkins et al. 1985, Trenkle 1986; Kampman and Loerch 1989). However, IS heifers had 57 units more (P < 0.01) marbling score than PAST heifers. As a result, IS heifers had a greater (70.2 vs. 40.4, P < 0.01) percentage of heifers grading average choice or higher, a greater (91.5 vs. 76.6, P = 0.03) percentage of heifers grading low choice or greater, and a lower (8.5 vs. 23.4, P = 0.03) percentage of heifers grading select than the PAST heifers. This contrasts with the results of Myers et al. (1999b), who found no differences for marbling score or the percentage of steers grading low choice or greater when steers fed ad libitum concentrate were compared with steers allowed an 82-d growing period on pasture. However, in their study pasture steers were supplemented with corn, where in the present trial PAST heifers were not supplemented during the 73-d growing period. There was no difference (P = 0.58) for the percentage of heifers grading low prime or greater between the IS and PAST heifers. The percentage of heifers grading select, low choice, or greater and low prime or greater did not differ (P > 0.26) between the HS, IS, and LS heifers. However a quadratic (P = 0.06) trend was observed for heifers grading average choice or greater, where IS heifers had the greatest percentage heifers grading average choice or greater.

Economic data are shown in Table 8. There was no difference (P > 0.89) for purchase price between the HS, IS, and LS heifers or between the IS and PAST heifers (P = 0.54). Feed cost increased linearly (P < 0.01) as level of starch decreased. This can be explained partially by diet cost per kilogram, which increased linearly (P < 0.01) as starch level decreased, and by the fact that heifers fed lower levels of starch had greater intakes. As a result, as starch level decreased, interest cost and total cost increased linearly (P < 0.01). The IS heifers had $19.01 greater (P < 0.01) feed costs than PAST heifers. Because IS heifers were on feed longer than PAST heifers (176 vs. 131 d), they consequently had a $13.50 greater (P < 0.01) yardage charge and a $1.51 greater (P < 0.01) interest cost than PAST heifers. However, total cost was not different (P = 0.71) between the IS and PAST heifers because PAST heifers were assessed a grazing charge. There tended to be a linear (P = 0.08) increase in price ($/45.4 kg) as level of starch increased. As level of starch increased, the percentage of carcasses =272 kg increased; consequently, carcass value increased linearly (P < 0.01) as level of starch decreased. As level of starch decreased, profitability increased linearly (P < 0.01). Although total cost was less as level of starch increased, the lighter HCW were not recoverable. Additionally, a quadratic (P = 0.02) response was observed for profit, where the IS were worth the most per head and the HS heifers were worth the least. The IS heifers were the most profitable because they were intermediate for feed cost and had the greatest percentage of carcasses grading average choice or greater. The IS heifers had a $2.19/45.4 kg greater (P = 0.06) price paid for carcass than PAST heifers and had an improved percentage of heifers grading low choice and average choice or greater. Thus, IS heifers had a $37.99/head greater (P < 0.01) carcass value than PAST heifers. This difference can also be attributed to numerically heavier HCW for IS heifers compared with PAST heifers. Furthermore, IS heifers were $41.30/head more profitable than PAST heifers. Also, IS heifers had lower (0.84 vs. 0.87) cost of gain than PAST heifers. There was a curvilinear (linear, P < 0.01 and quadratic, P - 0.04) response for cost of gain, where LS heifers had the most expensive cost per kilogram of gain. This can be explained by greater intakes and feed costs as starch decreased.

IMPLICATIONS

Heifers fed IS gained faster, were younger at harvest, had greater marbling scores, had a greater percentage of heifers grading low choice or greater, and had increased profitability when compared with PAST heifers. Despite faster gains during the finishing period, PAST heifers deposited marbling at a slower rate per day than IS heifers. Heifers fed diets with a greater percentage of by-products ate more feed, gained faster, increased YG, had fewer lightweight carcasses, had greater carcass values, and similar marbling scores, which resulted in more profit than heifers fed the high grain diets. This study implies that when using long-fed (322 d) heifers in an accelerated finishing program, by-products can be effectively fed during the final (176 d) finishing period with no reduction in QG.

© 2008 American Registry of Professional Animal Scientists Provided by ProQuest LLC. All Rights Reserved.