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ANIMAL NUTRITION |
* Departments of Animal Sciences and Industry, and
and
Clinical Sciences, Kansas State University, Manhattan 66506-1600
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Abstract |
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 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONIMPLICATIONSLITERATURE CITED |
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Key Words: finishing cattle • flaked corn • grain processing
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONIMPLICATIONSLITERATURE CITED |
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), and increases DMI and gain efficiency when moisture is allowed to penetrate the grain internally (Karr, 1984).
If adequate moisture and heat are present, flake density (FD) is generally considered one of the more important quality control measures affecting the steam-flaking process (Zinn et al., 2002). Moisture has been suggested to affect the accuracy of determining FD measurements and may interact with FD to alter ruminal characteristics, digestibility, and cattle performance (Karr, 1984). The objective of these experiments was to determine the influence of moisture concentration during tempering and its potential interaction with FD on ruminal characteristics, growth performance, and digestion in cattle fed finishing diets.
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MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONIMPLICATIONSLITERATURE CITED |
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Experiment 1
Seventy-eight crossbred steers (initial BW = 415 ± 30 kg) were used in an individual feeding experiment to compare the effects of tempering moisture concentration and FD on finishing performance and carcass characteristics. For 14 d before the trial, steers were allowed ad libitum access to a common diet to minimize differences in gastrointestinal fill. On d 0, steers were weighed, implanted with 24 mg of estradiol and 120 mg of trenbolone acetate (Revalor-S; Intervet, Millsboro, DE), and assigned to partially enclosed, concrete-surfaced individual pens (1.5 x 7 m). Steers were weighed individually on scales to the nearest 0.454 kg on d 1, allocated to pens randomly, and pens were stratified to treatments so that differences and variances in initial BW among treatment groups were minimized. Shrunk (4%) initial BW on d 0 was used for calculation of performance. Steers were offered ad libitum access to diets that were fed 106 d.
Dietary treatments consisted of finishing diets containing 78% steam-flaked corn (SFC) that was tempered using 0, 6, or 12% moisture and processed to 360 or 310 g/L (SF28 and SF24, respectively) in a 3 x 2 factorial arrangement of treatments (Table 1). Tempering was accomplished by placing approximately 550 kg of corn in 6 or 12% water (wt/wt) overnight in a stationary mixer that was mixed periodically. Mixing ended when all apparent surface moisture had disappeared from the grain. The next morning, corn was transferred to a 2.7-m3 steam chest and steam conditioned for 45 min. Approximately 10 min before processing, the mill was started, and the rollers were heated by direct application of steam. Corn was processed to the respective FD by measuring the weight of the flakes beneath the rollers. Roll gaps were adjusted at the beginning of each run to achieve the desired FD, and grain flaked during the adjustment period was discarded. Corn tempered with 6 and 12% moisture was processed on alternating days so that both moisture levels could temper overnight. The 0% moisture treatment was processed the same day as the 6% moisture treatment. Within each moisture level, corn was split into equal quantities, steam conditioned, and flaked to a density of 360 or 310 g/L. Each treatment of SFC was processed every other day; however, daily samples (approximately 1,000 g) of each treatment were collected and analyzed for DM (forced-air oven set at 105°C) and starch availability as described by Sindt (2004). Particle size was measured on flake samples (ASAE, 1983) using a Ro-Tap (W. S. Tyler, Mentor, OH) and 7 sieves ranging from 9,500 to 841 µm.
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) in the formula described by Zinn and Shen (1998). Carcass measurements were obtained at Tyson Fresh Meats, Emporia, KS. Hot carcass weight and liver abscesses were recorded the day of slaughter, whereas LM area, percent KPH, and 12th-rib s.c. fat were determined after a 24-h chill. Marbling scores and USDA quality and yield grades were determined by a USDA grader after a 24-h chill.
Dry matter, starch availability, and particle size were analyzed as repeated measures using compound symmetry covariance structure of the MIXED procedure of SAS (SAS Inst., Cary, NC). Model effects included moisture, FD, day, and all 2- and 3-way interactions. The repeated measure was defined as day. Performance and carcass data were analyzed as a completely randomized design; steer was the experimental unit. Performance data and carcass data, except USDA yield grades and quality grades, were analyzed using the MIXED procedure of SAS. Model effects included moisture, FD, and all 2-way interactions. The GENMOD procedure of SAS with the binomial distribution option was used to analyze USDA yield grades and quality grades. Contrasts used to separate means included linear and quadratic effects of tempering moisture. In each experiment, treatment differences were considered significant at 
= 0.05.
Experiment 2
A digestibility experiment was conducted concurrently with Exp. 1 using 6 Jersey steers (average BW = 270 kg) to evaluate the 6 treatments from Exp. 1 in a 6 x 6 Latin square design with a 3 x 2 factorial arrangement of treatments. Diet composition is reported in Table 1
. Steers were fitted with ruminal, duodenal (double L; 6 cm posterior to pyloric sphincter), and ileal (double L; 10 cm anterior to the ileocecal junction) cannulas. The experiment consisted of six 15-d periods that included a 10-d adaptation period and a 4-d sampling period. On the last day of each period, ruminal fluid was collected for measurement of pH, VFA, and fluid passage rate. Diets were mixed daily and were offered to steers for ad libitum consumption at 0800. Steers were housed in a tie-stall barn equipped with individual bunks and water troughs. Chromic oxide (10 g) was hand-mixed daily into individual diets on d 4 through 13 as a marker for diet digestibility. On d 15, a 200-mL solution containing 3 g of CoEDTA was pulse-dosed through the ruminal cannula at 0800 for estimation of fluid passage rate. On d 11 through 14, a fixed percentage of daily orts was subsampled and composited by period. Diet samples were collected after mixing on d 10 through 13 and composited by period on an equal weight basis.
Duodenal (approximately 300 mL) and ileal (approximately 200 mL) chyme and fecal grab samples (approximately 300 g, wet basis) were collected 3 times daily on d 11 through 14. Samples were collected at 8-h intervals, with collection times advanced 2 h each day to obtain a sample at each 2-h interval in a 24-h cycle. Duodenal, ileal, and fecal samples were immediately frozen at –20°C. Samples of digesta and feces were composited for each steer at the end of each collection period. Diet, orts, and fecal samples were dried for 4 d at 55°C, air equilibrated, and then ground to pass a 1-mm screen (No. 2 Wiley mill; Arthur H. Thomas Co., Philadelphia, PA). Digesta samples were lyophilized before being ground to pass a 1-mm screen. Diet, orts, digesta, and feces were analyzed for DM (16 h at 105°C), OM (600°C for 2 h), N (N analyzer; LECO FP-2000; Leco Corp., St. Joseph, MI), Cr (Williams et al., 1962), and starch (Herrera-Saldana and Huber, 1989) using a Technicon Autoanalyzer III to measure free glucose (Gochman and Schmitz, 1972).
Approximately 500 mL of ruminal fluid was collected once daily on d 11 through 14 for isolation of ruminal microbes. Samples were blended to dislodge particle-associated bacteria and strained through 8 layers of cheesecloth before being frozen at –20°C. Collection times were advanced 6 h each day to obtain a sample at each 6-h interval in a 24-h cycle. Ruminal microbial cells were isolated from ruminal contents by differential centrifugation (Cecava et al., 1990), lyophilized, and analyzed for DM, OM, and N as described previously. Cytosine concentrations of microbial cells and duodenal samples were measured as described by Milton et al. (1996). The quantity of duodenal N of microbial origin was determined by dividing the duodenal cytosine flow by the ratio of microbial cytosine:N. Feed N flow was calculated by subtracting microbial N flow from total N flow. Organic matter truly fermented in the rumen was calculated as OM intake minus total OM reaching the duodenum, correcting for microbial OM reaching the duodenum.
Samples of ruminal fluid were collected at 0800 on d 15 and subsequently at 2, 4, 6, 8, 12, 18, and 24 h after feeding. Ruminal fluid was strained through 4 layers of cheesecloth and analyzed for pH at the time of sampling using a portable pH meter. Ruminal fluid (8 mL) was added to 2 mL of 25% (wt/vol) metaphosphoric acid and frozen for later analysis of VFA and ammonia. Approximately 20 mL of strained ruminal fluid were placed into scintillation vials and frozen for later analysis of Co. Cobalt in ruminal fluid was measured using atomic absorption spectrophotometry after samples were thawed and centrifuged at 30,000 x g for 20 min. To determine fluid passage rates, ruminal concentrations of Co were transformed to natural logarithms and regressed against time for individual steers using the REG procedure of SAS. Samples of acidified ruminal fluid were thawed, centrifuged at 30,000 x g for 20 min, and analyzed for VFA by gas chromatography (Hewlett-Packard 5890A, Palo Alto, CA; 183 x 0.635 cm column; Supelco column packing, Bellefonte, PA; with N2 as the carrier gas, a flow rate of 80 mL/min, and a column temperature of 130°C) and for NH3 (Broderick and Kang, 1980) using a Technicon Autoanalyzer III (Bran and Luebbe, Elmsford, NY).
Intake, flow, passage rates, and digestion data were analyzed using individual animal as the experimental unit with the MIXED procedure of SAS. The model included effects of moisture, FD and moisture x FD. Random effects included steer and period. Contrasts used to separate means included linear and quadratic effects of moisture concentration. Volatile fatty acids, NH3, and pH were analyzed as repeated measures using the compound symmetry covariance structure of the MIXED procedure of SAS. The model statement included effects of moisture, FD, sampling time, and all interactions. The random statement included effects of steer and period. The repeated measure was defined as the sampling time. One steer died during the second period due to complications with the ileal cannula, and another steer ate less than 1% of BW during 2 periods; thus, data consisted of 28 observations rather than the planned 36 observations.
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RESULTS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONIMPLICATIONSLITERATURE CITED |
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). Increasing the degree of processing (decreasing FD) increased starch availability (P < 0.001) and decreased (P < 0.001) the particle size of SFC. The influence of time after flaking on DM, starch availability, and particle size of SFC is presented in Table 3. Steam-flaked corn sampled the day of processing contained less DM (P < 0.001), had greater available starch (P < 0.001), and was larger in particle size (P = 0.05).
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). Steers fed diets containing SF24 consumed less DM as the moisture level increased, whereas steers fed diets containing SF28 had increased DMI as moisture level increased (moisture x FD interaction; P < 0.01). Feeding SF24 with 6% moisture resulted in fewer USDA Yield Grade 2 carcasses and more USDA Yield Grade 3 carcasses than all the other treatments, resulting in moisture x FD interactions (P < 0.05).
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). Dry matter, OM, and N intakes followed similar trends but were not statistically different among treatments. For steers fed SF28, flow of starch to the duodenum tended to be greatest when SFC contained 6% moisture; however, for steers fed SF24, duodenal starch flow tended to be least when SFC contained 6% moisture (moisture x FD interaction; P < 0.10). Microbial N reaching the duodenum tended (P < 0.10) to be greater for steers fed SF24 compared with SF28.
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The cytosine:N ratio in bacterial samples isolated from the rumen averaged 0.020; there were no differences among treatments (data not shown). Using this measure, our estimate of microbial N flows was greater than expected, which we believe was most likely a result of bacterial cell lysis leading to a loss of cell contents. To achieve an estimation closer to expected values, we recalculated our microbial N flows using a cytosine:N of 0.025 (which was the ratio obtained from the 12 bacterial samples with the greatest cytosine:N). This recalculation resulted in observations closer to those presented in previous work with SFC (Zinn 1990a,b; Theurer et al., 1999). These different methods of calculation explain the multiple rows in Table 5 for flows of true OM, microbial N, feed N, and ruminal digestibilities of OM, feed N, and microbial efficiency.
Flow of OM, starch, and N from the ileum did not differ among treatments. Small intestinal starch digestibility as a percentage of entry tended to be least when SFC contained 6% moisture (quadratic; P < 0.10). As a percentage of intake, small intestinal starch digestibility tended to be greatest for SF28 when SFC contained 6% moisture, but it tended to be least when SF24 contained 6% moisture (moisture x FD interaction; P < 0.10). Digestibilities of OM, starch, and N in the large intestine and total tract did not differ among treatments. Ruminal characteristics (Table 6) including pH, VFA, NH3, and fluid passage rate also did not differ among the treatments (P = 0.15 to 0.88).
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DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONIMPLICATIONSLITERATURE CITED |
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and Theurer et al. (1999) found that increasing the degree of processing increased the enzyme susceptibility or starch availability of SFC. Very little research has examined the effects of moisture on SFC. Zinn (1990a) found that steaming corn for 67 min compared with 47 or 34 min increased the moisture of SFC by 3 percentage units and provided a concomitant increase in starch reactivity. In the experiment by Zinn (1990a), however, it is difficult to determine whether starch reactivity was improved by moisture, heat, or a combination of both. Regardless, there were no apparent improvements in starch digestibility by steam conditioning corn for longer than 34 min.
Lund (1984) reported that a moisture:starch of at least 1.5:1 is required to optimize starch gelatinization. Even with liberal additions of moisture during steam flaking, this ratio is not achieved; however, provision of moisture to a moisture-limiting environment could still prove beneficial. Research with sorghum grain demonstrated that tempering before flaking, using moisture concentrations similar to those in our study, increased gelatinization and flake integrity by producing fewer broken flakes and fines (McDonough et al., 1997). In our study, adding moisture to corn during tempering tended to increase starch availability, but it did not increase particle size of flaked material. Particle sizes of SFC in the current study were measured on representative subsamples of each flaked product, which contained a wide distribution of particle sizes. In another experiment, we found that moisture additions during tempering improved the durability of whole flakes that initially were >9.5 mm in diameter (Sindt, 2004).
The effect of time on the properties of flaked grains has received interest because of the phenomenon of retrogradation. Although corn that had been processed the previous day was drier, particle size and starch availability both decreased with time. This would suggest that retrogradation occurs, although we did not measure the effects of retrogradation on the feeding value of SFC. Similarly, Ward and Galyean (1999) reported that flakes collected shortly after processing had greater enzymatic starch availabilities than samples collected after bin storage, but they also reported that in vitro DM disappearance with ruminal inoculum between the 2 flake treatments was similar. Furthermore, Zinn and Barrajas (1997) found that fresh and air-dried SFC had comparable starch reactivities and feeding values.
Tempering grain before processing has increased animal performance with barley (Wang et al., 2003) or rolled corn (Zinn et al., 1998). Moisture is thought to soften the kernel, allowing more starch to be exposed during processing, thereby increasing energy availability to the animal. This response to tempering of grain may be lost when corn is steam conditioned before processing. Steam conditioning corn for adequate periods of time may be all that is required to soften corn and prepare it for processing, which may explain the lack of performance responses to tempering in our study. Although it was not evaluated in our study, tempering may lower the requirements for steam and allow for shorter periods of steam conditioning. This decrease in steam conditioning time would be economically beneficial considering that the costs of generating steam far surpass the costs of adding water.
Intake of starch in Exp. 2 was decreased as SFC moisture level increased; however, DM and OM intakes did not differ with SFC moisture level. Resistant starches or retrogrades are known to be produced by feed manufacturing (Spears and Fahey, 2004). Moisture additions may have caused more amylose leaching and resistant starch formation from retrogradation, thus impeding complete recovery of starch in the diets. Nonethelelss, calculation of nonstarch OM digestibilities (OM minus starch) does not support the possibility of resistant starch formation.
Ruminal starch digestibilities were high, averaging 91%. These values were greater than those reported in a review by Huntington (1997) but were similar to values for SFC described by Zinn and Barrajas (1997) and Cooper et al. (2002). Similar to our findings, Zinn (1990b) found that microbial N flow to the duodenum increased as FD decreased; however, Theurer et al. (1999) found no change in microbial N flows as FD decreased. Ruminal starch and OM digestion were not altered by treatment in the current study. Theurer et al. (1999), but not Zinn (1990b), reported an increase in ruminal starch digestion by decreasing FD. In our study, decreasing FD resulted in an increase in microbial efficiency. This finding is in contrast to observations of Zinn (1990b) and Theurer et al. (1999), who found no improvement in microbial efficiency in response to decreasing FD of SFC.
Duodenal flow of feed N and intestinal digestion of total N were similar for all treatments. Zinn (1990b) found that decreasing FD linearly increased postruminal N digestibility and decreased N excretion. Theurer et al. (1999) reported no differences in N digestibility because of differences in FD.
Postruminal starch digestibilities were high; 
95% of duodenal starch disappeared in either the small or large intestine. As a percentage of entry, however, digestibilities were numerically greater in the large intestine than in the small intestine. This result is in contrast to that of Theurer et al. (1999), who reported starch to be approximately 3 times more digestible in the small intestine than in the large intestine.
There were very few meaningful interactions between moisture and FD in our 2 experiments. The most relevant information from these experiments was that moisture beyond that added during steam conditioning was not nutritionally beneficial. Because we could only process small quantities (approximately 700 kg) of grain, the finishing experiment was conducted with only a small number of animals. The small differences in performance may require further investigations to fully characterize these effects; however, it seems unnecessary to add moisture to SFC grain to improve DE because total tract starch digestibility approached 100% when no moisture was added. Conversely, steam conditioning is an expensive process of adding moisture to grain. Tempering may be beneficial by displacing some of the expense required for flaking mills that currently apply all moisture to grain via steam.
Because starch digestibility is essentially complete when corn is flaked to 360 g/L, there may be little incentive to process grain to lighter densities; however, we are unable to predict the performance or digestibility responses to corn flaked to densities between 360 and 310 g/L. Processing to 310 g/L might have caused excessive rates of digestion and decreased cattle performance. Thus, performance responses to corn flaked to intermediate levels of processing may exist.
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IMPLICATIONS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONIMPLICATIONSLITERATURE CITED |
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Footnotes |
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2 Present address: Nutri-Tech, Inc., 1435 Ave. N, Lyons, KS 67554.
3 Corresponding author: jdrouill{at}oznet.ksu.edu
Received for publication March 21, 2005. Accepted for publication August 28, 2005.
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LITERATURE CITED |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONIMPLICATIONSLITERATURE CITED |
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