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Effect of corn particle size with moderate amounts of wet distillers grains in finishing diets on starch digestibility and steer performance
The Professional Animal Scientist 31 (2015):535–542; http://dx.doi.org/10.15232/pas.2015-01387 ©2015 American Registry of Professional Animal Scientists
E fmoderate fect of corn particle size with amounts of wet distillers grains in finishing diets on starch digestibility and steer performance
E. L. Lundy,* PAS, B. E. Doran,† E. E. Vermeer,‡ PAS, D. D. Loy,* PAS, and S. L. Hansen*1 *Department of Animal Science, Iowa State University, Ames 50011; †Iowa State University Extension and Outreach, Orange City 51041; and ‡Midwest PMS, Merrill, IA 51038
ABSTRACT Five hundred yearling steers (370 ± 30.0 kg, SD) were used to determine the effect of corn particle size in diets containing 35% wet distillers grains plus solubles (WDGS) on steer performance, carcass characteristics, and apparent total-tract starch digestibility (TTSD). Treatments included 45% cracked corn (CON; 2,350 μm) or finely ground corn (FIN; 500 μm) with 35% WDGS and were replicated in 4 pens per treatment with 60 or 64 steers per pen. Fecal samples were collected on d 71 and 72 (F-1) and d 102 and 103 (F-2). Final BW and HCW were heavier (P ≤ 0.01) for steers finished on CON compared with steers finished on FIN. Whereas G:F was not different (P = 0.22) between treatments, DMI and ADG were greater (P ≤ 0.01) for CON-fed steers than FIN-fed steers. Liver abscess scores were not influenced (P ≥ 0.39) by treatment. Liver abscess scores tended (P = 0.10) to influence ADG over the experiment, with steers
1 Corresponding author: slhansen@iastate. edu
having severe liver abscess scores gaining less compared with steers with no or mild liver abscess scores. A treatment × time effect (P < 0.01) was observed for TTSD. Whereas TTSD of steers fed CON decreased over time (90.28 and 85.74% for F-1 and F-2, respectively), TTSD of steers finished on FIN did not differ across the 2 sampling dates (97.95 and 97.55% for F-1 and F-2, respectively). Apparent starch digestibility was improved for steers fed finely ground corn with 35% WDGS; however, cattle performance was less compared with steers fed cracked corn with 35% WDGS. Key words: cattle, corn particle size, distillers grains, liver abscess, starch digestibility
INTRODUCTION Expansion of the ethanol industry has led to a steady supply of highquality coproducts, including wet distillers grains plus solubles (WDGS) and wet corn gluten feed (WCGF). These coproducts have proven to be beneficial replacements for corn in finishing diets through improved ADG
and feed efficiency (Klopfenstein et al., 2008). Because corn starch is the primary substrate of alcohol fermentation, both WDGS and WCGF have relatively low concentrations of starch. As a result, coproducts from both the dry and wet milling industries appear to moderate the risk of acidosis in finishing diets (Stock et al., 2000). Decreasing corn particle size through grain processing is an effective way to increase starch utilization and thus improve performance of the ruminant animal (Owens et al., 1986; Huntington, 1997). However, grinding corn too finely often results in rapid rumen fermentation leading to acidosis. Persistent acidosis often results in decreased animal performance and liver abscesses, causing an economic loss to producers (Brown and Lawrence, 2010). Adding coproducts at the expense of corn often decreases dietary starch concentrations; therefore, decreasing grain particle size may allow for more complete starch digestion of what starch is present in the diet, potentially improving cattle performance. Research has shown that more extensive
536 grain processing when feeding WCGF improves feed efficiency by 10.5% (Macken et al., 2006) to 12.5% (Scott et al., 2003). However, decreasing corn particle size in diets containing WDGS has given more variable results. Corrigan et al. (2009) noted up to 8% improvement in feed efficiency when assessed across multiple WDGS inclusions, whereas Vander Pol et al. (2008) observed a 7% decrease in feed efficiency with decreased particle size in diets containing 30% WDGS. Therefore, the objective of this experiment was to determine whether feeding moderate levels of WDGS would decrease the acidosis risk associated with further grain processing and allow fine grinding of corn to improve starch utilization and, thus, cattle performance.
MATERIALS AND METHODS Animals and Experimental Design Procedures and protocols were approved by the Iowa State University Institutional Animal Care and Use Committee (9-13-7630-B). Six hundred crossbred steers were purchased from a single source and
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transported to a commercial feedlot (Mogler Stock Farms, Alvord, IA). Upon arrival, steers were housed in a concrete open lot and fed a series of 4 transition diets over 17 d to ensure all steers were prepared for a concentrate-based diet. Five days before the start of the experiment, steers were vaccinated with Bovi-Shield GOLD One Shot (Zoetis, New York, NY), Ultrabac CD (Zoetis), and Somubac (Zoetis) and implanted with Synovex Choice (Zoetis). Steers were treated for internal and external parasites with Dectomax Injectable (Zoetis) and ProMectin B Pour-on (Vedco Inc., St. Joseph, MO). Body weights were also measured on d −5, and 500 steers (370 ± 30.0 kg, SD) were selected to be used in the experiment, blocked by BW, and randomly assigned to 1 of 2 diets: cracked (2,350 μm) corn–based control diet (CON) or finely ground (500 μm) corn diet (FIN), with both treatments containing 35% WDGS (DM basis; Table 1). Diets were formulated to meet or exceed animal requirements (NRC, 2000). At the initiation of the experiment, individual BW were collected before feeding. Steers were given a unique visual and electronic ID and sorted into
Table 1. Ingredient and nutrient composition of diets1 (%, DM basis) Item
CON
FIN
Ingredient Cracked corn2 Finely ground corn2 Wet distillers grains plus solubles3 Corn silage Corn stalks Liquid supplement4 Analyzed composition5 CP NDF Starch Ether extract
45.0 — 35.2 10.0 6.5 3.3 18.1 29.6 36.9 5.1
— 45.0 35.2 10.0 6.5 3.3 18.2 26.8 35.2 4.9
CON = cracked corn diet; FIN = finely ground corn diet. Cracked corn, 2,350 μm; finely ground corn, 500 μm. 3 Composite analysis: 35.5% CP, 8.7% ether extract, and 0.62% S (DM basis). 4 Liquid supplement includes 12.7% Ca, 5.7% salt, 1.6% K, 0.02% P, and 95,000 IU/ kg of vitamin A, and monensin sodium provided at 700 mg/kg (DM basis). 5 Diets were analyzed by Dairyland Laboratories Inc. (Arcadia, WI). 1 2
their respective pens within a slotted confinement facility with rubber mats. Each treatment was replicated in 4 pens with 60 or 64 steers per pen, split equally across treatments, to maintain a similar pen density of 2.0 m2 per steer. On d 72, interim BW were measured, and steers were reimplanted with Revalor 200 (Merck Animal Health, Millsboro, DE). On d 106, steers were started on ractopamine hydrochloride (Optaflexx, Elanco Animal Health, Greenfield, IN) and fed at a rate of 300 mg per steer per day for the last 21 or 22 d of the experiment. Steers were slaughtered by pen BW blocks on d 127 or 128 at a commercial abattoir (Tyson Foods Inc., Dakota City, NE). Throughout the experiment, 5 steers were removed because of illness, injury, or death, for reasons unrelated to treatment (2 CON and 3 FIN), and data were excluded from analysis. It was assumed that steers were consuming the pen average DMI up until the day of removal or death.
Corn Particle Size Both sources of corn were processed through a double pair roller mill (Model 12 × 52 Dual Ind, RMS, Harrisburg, SD) at the feedlot. To achieve a 500-μm finely ground corn, the top roller was adjusted to 0.02 cm, and the bottom roller was closed. For the cracked corn, the top rollers were set to minimally process 100% of corn kernels, and the bottom rollers were opened for full flow through. Batches of each corn source were processed back to back to provide uniformity of corn source. After processing, both cracked corn and finely ground corn were stored in bunkers under a covered roof until they were fed. Samples of both sources of corn were taken 4 times throughout the duration of experiment for determination of corn particle size, which was determined using the method described by American Society of Agricultural and Biological Engineers (ANSI/ASAE, 2008, method ANSI/ ASAE S319.4). Samples were shaken
Corn particle size, wet distillers grains, and starch digestion
through a corn sieve (Tyler Equivalent Mesh, W.S. Tyler Industrial Group, Mentor, OH) using 5 screens (US Sieve # 8, 12, 20, 30, and 40 for cracked corn and 20, 30, 40, 50, and 100 for finely ground corn). Particle size was determined by dividing the weight of sample retained on each sieve by the total sample weight (asfed basis) run through the series of sieves multiplied by the micrometer opening value given for each sieve (ANSI/ASAE, 2008). For each source of corn, the particle size of each sampling day was averaged and equivalent to 2,350 μm for cracked corn and 500 μm for the finely ground corn.
Sample Collection and Analytical Procedures Steers were fed their respective diets twice daily for ad libitum intake using a clean bunk management protocol (Pritchard and Bruns, 2003). Bunks were visually assessed each morning before feeding, and feed delivery was adjusted daily based on the amount of feed remaining. Daily feed delivery was recorded for each pen, and pen average DMI was calculated. Average daily gain and G:F were determined using pen total DMI and total BW gain of steers in the pen over the duration of the experiment. On d 71 and 72 and d 102 and 103, fecal collections were taken for apparent total starch digestibility calculation. On each collection day, a pen composite of 8 fresh samples, approximately 30 g per sample (wet basis), was collected randomly from the pen surface. Pen composites from each of the 4 d were sent to Dairyland Laboratories Inc. (Arcadia, WI) for wet chemistry analysis of CP (AOAC International, 1995, method 990.03) and fecal starch (Hall, 2009). Samples of each TMR were also collected on d 71 and 102 and sent to Dairyland Laboratories Inc. for analysis of CP and starch using the same methods. Apparent total-tract starch digestibility was estimated using the equation described by Zinn et al. (2007): starch digestion (expressed as a percentage of intake)
is equivalent to 100{1 − [(0.938 − 0.497 × FN + 0.0853 × FN2) × FS ÷ DS]}, where FN is fecal nitrogen concentration (% DM), FS is fecal starch concentration (% DM), and DS is dietary starch concentration (% DM). Starch digestion was averaged for each pen over the 2 consecutive days of collection (F-1 for d 71 and 72 and F-2 for d 102 and 103). Individual camera carcass data were provided by Tyson Foods Inc. Carcass data collected included HCW, marbling score, 12th-rib backfat thickness, LM area, liver abscess scores (LAS), YG, and QG. Liver abscess scores were facilitated by representatives from Elanco Animal Health, who were masked to treatments, using the Elanco Liver Check System on a 0, A, and A+ scale. Livers free of abscesses were classified as a LAS of 0. Mild abscesses, up to 4 small abscesses less than 2.54 cm in diameter, were classified as LAS of A. Larger or more severe abscesses, with active areas of inflammation on the liver or when portions of the liver were attached to the diaphragm, were classified as a LAS of A+. A 4% pencil shrink was applied to initial BW, and final BW was calculated from HCW using the average DP of the cattle in this experiment, 62.4%.
Statistical Analysis Data were analyzed by ANOVA in SAS 9.3 (SAS Institute Inc., Cary, NC) as a complete block design with pen as the experimental unit (n = 4 per treatment). The model included the fixed effects of treatment and block. Performance, carcass characteristics, and starch digestibility data were analyzed using the MIXED procedure of SAS. Treatment distributions of YG, QG, and LAS data were determined using PROC GLIMMIX of SAS. The effect of LAS on individual steer ADG and carcass characteristics were also tested using PROC Mixed with steer as the experimental unit (n = 495 steers). Data were tested for normalcy and homogeneity of variance using the Shapiro-Wilks test. Only HCW data were found
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to require transformation, and the square root function was used, and back-transformed data are presented. Significance was declared at P ≤ 0.05, and tendencies were declared from P = 0.06 to 0.10. Means are reported are least squares means ± SEM.
RESULTS AND DISCUSSION Performance and carcass results are presented in Table 2. Although initial BW and interim BW (d 72) were not different (P ≥ 0.16) between treatment groups, final BW was heavier (P ≤ 0.01) for steers finished on CON compared with FIN. Dry matter intake and ADG were greater (P ≤ 0.01) for steers finished on CON compared with those finished on FIN. However, G:F was not different (P = 0.22) between treatment groups. Vander Pol et al. (2008) also showed that fine ground corn (FGC) in a diet with 30% WDGS had negative effects on performance compared with a more traditional dry-rolled corn (DRC) diet with 30% WDGS, as demonstrated by a 17% decrease in ADG, 10% decrease in DMI, and 7% decrease in G:F over cattle fed diets of DRC and 30% WDGS. In a university report of the same experiment published earlier, Vander Pol et al. (2006) reported an increase in dietary roughage after 107 d on feed, suggesting that steers being fed FGC experienced apparent acidosis, although it was not explicitly stated by the authors. It seems that the probable acidosis may partially explain why cattle performance was less in the work by Vander Pol et al. (2008) compared with the current experiment. Average HCW of CON-fed cattle was heavier (P = 0.01) than steers fed FIN. Longissimus muscle area, backfat thickness, and YG were not different (P ≥ 0.38) because of treatment. However, marbling scores of FIN cattle were less (P = 0.04) compared with cattle fed CON. Although distributions of USDA QG of average Choice and higher and Low Choice were not affected by treatment (P ≥ 0.17), the percentage of cattle grading Select tended to be greater (P = 0.07)
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Table 2. Influence of corn particle size1 on steer performance and carcass characteristics Item Growth performance2 Initial BW (kg) Interim BW3 (kg) Final BW (kg) DMI (kg/d) ADG (kg/d) G:F Carcass characteristics HCW (kg) LM area (cm2) Marbling score4 Backfat thickness (cm) YG
CON
FIN
SEM
P-value
368 500 624 11.76 2.01 0.161 390 86.6 434 1.23 3.2
371 494 605 11.07 1.84 0.156 378 85.8 417 1.20 3.1
1.54 3.44 1.79 0.10 0.03 0.003 1.58 1.20 4.63 0.05 0.09
0.20 0.16 <0.01 <0.01 <0.01 0.22 0.01 0.56 0.04 0.56 0.38
CON = cracked corn diet; FIN = finely ground corn diet; n = 4 pens per treatment. A 4% pencil shrink was applied to all live BW. Final BW were calculated from HCW using a common DP of 62.4%, which was used in calculation of DMI, ADG, and G:F over the duration of the experiment. 3 Interim BW were collected on d 72. 4 Marbling score: 300 = slight, 400 = small, and 500 = modest. 1 2
for cattle finished on FIN (Table 3). Lighter carcasses and decreased QG indicate that steers fed FIN treatment may not have reached the desired degree of finish by slaughter. Yield grade distributions were not different (P ≥ 0.20) by treatment. In this ex-
periment, distribution of LAS was not influenced (P ≥ 0.39) by treatment. Because the liver is a vital organ required for essential life function, damage to the liver could result in decreased functionality and, ultimately, decreased animal growth and
Table 3. Influence of corn particle size in steer diets1 on distribution of quality and yield grades and liver abscess scores Item QG (%) Average Choice and higher Low Choice Select YG (%) 1 2 3 4/5 Liver abscess score2 (%) 0 A A+
CON
FIN
SEM
P-value
16.3 51.9 28.9 2.0 33.0 55.4 8.6
10.8 45.6 41.1 3.5 38.3 48.1 8.9
2.21 3.20 3.14 1.34 3.07 3.20 1.80
0.17 0.28 0.07 0.37 0.31 0.20 0.90
91.3 6.0 2.4
88.8 6.8 4.0
1.90 1.56 1.11
0.42 0.74 0.39
CON = cracked corn diet; FIN = finely ground corn diet; n = 4 pens per treatment. Liver abscess score: 0 = no abscesses; A = 1 or 2 small abscesses; A+ = 1 or more large abscesses.
1 2
performance. Previous research has shown that severe liver abscesses result in up to a 15% decrease in ADG (Brink et al., 1990). Similarly in this experiment, there was a tendency (P = 0.10) for LAS to influence ADG over the duration of the experiment (Table 4); steers with a LAS of A+ gained less BW compared with steers having a LAS of 0 or A. Interestingly, during period 1 (d 0–72), LAS did not affect ADG (P = 0.30). However, during period 2 (d 73–127 or 128), the ADG of steers that had a LAS of A+ was approximately 0.4 kg less than steers with LAS of 0 or A, indicating that negative performance associated with severe LAS occurs later in the feeding period. Other research has shown similar results where no difference in performance existed between steers with no LAS or mild LAS, but steers with severe LAS experienced a decrease in performance up to 16.6% loss of BW gain (Brink et al., 1990) or 0.22 kg/d decrease in BW gain (Rezac et al., 2014). In addition to LAS effect on ADG, the effect of LAS on carcass characteristics was also evaluated (Table 5). Cattle with severe LAS (A+) had approximately 19 kg lighter HCW (P = 0.05) compared with cattle with no LAS or mild LAS. In addition, cattle with severe abscesses (LAS of A+) had decreased (P = 0.03) LM area compared with their counterparts. Liver abscess score had no effect (P ≥ 0.33) on backfat thickness, marbling score, QG, or YG. Although only 10% of the cattle in this experiment had liver abscesses, the severity of decreased performance of cattle with an A+ LAS could affect efficiency of cattle and producer profitability. Thus, additional research is warranted to better understand development of liver abscesses and influence on cattle growth performance. Prevalence of liver abscesses in the industry ranges from approximately 10 to 20% of cattle on feed consuming steam-flaked corn diets (Brown and Lawrence, 2010; Rezac et al., 2014) with tylosin (Tylan, Elanco Animal Health). When antimicrobials were not fed, occurrence of LAS was
Corn particle size, wet distillers grains, and starch digestion
Table 4. Influence of liver abscess score on average daily gain of steers Liver abscess score1 ADG (kg/d) Periods 1 and 2 Period 12 Period 23
0
A
1.81 1.84 1.77a
A+
1.84 1.91 1.76a
x
1.68 1.91 1.40b
x
y
SEM
P-value
0.061 0.054 0.090
0.10 0.30 <0.01
Means within a row without a common superscript differ (P ≤ 0.05). Means within a row without a common superscript tend to differ (P ≤ 0.10). 1 Liver abscess score: 0 = no abscesses, n = 445 steers; A = 1 or 2 small abscesses, n = 33 steers; A+ = 1 or more large abscesses, n = 17 steers. 2 Day 0 to 72 of the experiment. 3 Day 73 to 127 or 128 of the experiment. a,b x,y
reported to be as high as 32% in DRC diets (Brink et al., 1990) and 43% in steam-flaked corn diets (Brown and Lawrence, 2010). Although tylosin was not fed in this experiment, only 10% of steers had LAS, indicating that acidosis was not a major issue in this experiment. However, research has shown steers with severe LAS typically have a 0.5-kg reduction in DMI (Brink et al., 1990; Nagaraja and Chengappa, 1998), which is consistent with decreased DMI of steers fed FIN compared with CON. During the first 21 d on feed, DMI varied between the 2 treatment groups. This is likely due to the FIN cattle experi-
encing subacute acidosis while making the transition to FGC from cracked corn. Steers on FIN experienced a decrease of approximately 1.1 kg in daily DMI from d 10 to 20 and continued to have an average DMI that was 0.3 kg less than CON-fed steers for the remainder of the experiment (Figure 1). Although visible signs of acidosis were not observed during the experiment, measurement of rumen pH throughout the experiment, especially the first 21 d, may have been an informative indicator of increased risk of rumenitis, which occurs before liver abscess development. Corrigan et al. (2009) found that the addition
Table 5. Influence of liver abscess score on carcass characteristics Liver abscess score1 Item HCW2 (kg) LM area (cm2) Backfat thickness (cm) Marbling score3 QG4 YG
0
A
A+
SEM
P-value
383.7a 83.55a 1.22 426 1.79 3.1
386.2a 85.16a 1.17 422 1.81 3.0
365.8b 78.84b 1.22 409 1.63 3.3
7.29 1.232 0.051 11.1 0.110 0.10
0.05 0.03 0.76 0.61 0.62 0.33
Means within a row without a common superscript differ (P ≤ 0.05). Liver abscess score: 0 = no abscesses, n = 445 steers; A = 1 or 2 small abscesses, n = 33 steers; A+ = 1 or more large abscesses, n = 17 steers. 2 Data transformed using square root function. Means and SE values reported were back transformed. 3 Marbling score: 300 = slight; 400 = small; 500 = modest. 4 1 = Select, 2 = Low Choice, 3 = average and High Choice, and 4 = Prime. a,b 1
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of 40% WDGS (DM basis) to diets based on DRC, high-moisture corn, or steam-flaked corn did not affect rumen pH; however, Siverson et al. (2014) reported that feeding 30% WCGF (DM basis) in diets based on DRC or whole shelled corn aided in moderation of rumen pH and increased starch digestibility in growing diets, potentially due to differences in intestinal and ruminal digestion. Wet corn gluten feed generally contains less starch and has greater digestible fiber compared with WDGS (Stock et al., 2000), which may contribute to the variation in rumen pH results between the 2 studies. Increased starch availability through grain processing often improves cattle performance (Huntington, 1997), and starch digestibility can be predicted based on fecal starch concentration (R2 = 0.96; Zinn et al., 2007). In this experiment, fine grinding of corn decreased fecal starch concentrations and improved apparent total-tract starch digestibility. A treatment × time effect (P ≤ 0.01; Figure 2) was observed for fecal starch concentrations, where steers fed CON diets had increased concentrations (14.34 and 17.58% fecal starch for F-1 and F-2, respectively) over the 2 sampling dates compared with steers fed FIN diets, which had consistently lesser concentrations (2.95 and 3.20% fecal starch concentrations for F-1 and F-2, respectively). Although starch concentrations of the diets varied by less than 2% (Table 1), a treatment × time interaction (P ≤ 0.01; Figure 3) was also observed for apparent totaltract starch digestibility of steers. Starch digestibility of steers fed CON diets decreased over time (90.28 and 85.74% for F-1 and F-2, respectively). However, apparent total-tract starch digestibility of steers fed FIN diets did not differ across sampling days (97.95 and 97.55% for F-1 and F-2, respectively). Consistent with increased fecal starch concentrations of CON, Barajas and Zinn (1998) noted an increase in fecal starch concentrations ranging from 20.3 to 28.5% over an 8-wk period in cattle fed a 75% DRC
540 diet. Decreased starch digestibility as days on feed increased could be attributed to changes in microbial population, site of starch digestion, or DMI. Particle size of the grain plays a large role in retention time within the rumen (Owens et al., 1986). Although retention time was probably greater for CON, a greater portion of the starch most likely reached the small intestine, which does not have as extensive of digestion capacity in comparison to the rumen (Owens et al., 1986). Although increased DMI would be thought to lead to more rapid passage rate and less utilization of starch, intakes in the present experiment were consistent between the 2 sampling dates for CON-fed steers. It is unclear why fecal starch concentrations decreased over time in the CON-fed steers. Scott et al. (2003) observed a 1.8% decrease in fecal starch concentrations when 32% WCGF replaced DRC in the diet. Fecal starch concentrations in FGC diets with moderate inclusions of WCGF ranged from 7.1% (Scott et al., 2003) to 11.8% (Macken et al., 2006) and were greater than fecal starch concentrations of FIN-fed steers in current experiment, which averaged 3.1% over the duration of the experiment. Vander Pol et al. (2008) found fecal starch concentrations in DRC diets with 30% WDGS to be consistent with FGC diets containing 30% WDGS (12.0 and 13.4% for DRC and FGC, respectively). The lack of difference in fecal starch concentrations found by Vander Pol et al. (2008) compared with the present experiment could have been attributed to the amount of effective dietary fiber used in the 2 studies. In the present experiment, roughage concentration was 11.5%, which could have slowed passage rate, thus allowing for increased starch digestibility, compared with diets containing 5.6% roughage as fed by Vander Pol et al. (2008). Although fecal starch concentrations have been more extensively reviewed, apparent total-tract starch digestibility of DRC diets has not been reported to the same extent. Others have
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Figure 1. Dry matter intake by steers fed cracked corn (CON; indicated by solid line) or finely ground corn (FIN; indicated by dashed line) in diets containing 35% wet distillers grains (DM basis) over the duration of the experiment.
observed apparent total-tract starch digestibility of DRC diets to range from 91 to 96% (Cooper et al., 2002; Owens and Soderlund, 2006; Corrigan et al., 2009). Variation in fecal starch concentrations and apparent total-tract starch digestibility among previous studies could be attributed to the variation of corn particle size used in the studies. In a recent survey of feedlots in the Midwest using
DRC as the primary energy source, the average fecal starch concentration of 34 feedlots was 18.9%, ranging from 7.0 to 36.6%. The range of corn particle size reported varied from 1,165 to 6,823 μm with an average size of 4,201 μm (Schwandt et al., 2014). The CON diet used in the present experiment was 2,350 μm, which may help explain why the fecal starch concentrations of cattle
Figure 2. Fecal starch concentration by steers fed cracked corn (CON) or finely ground corn (FIN) with 35% wet distillers grains (DM basis). Each bar (CON = dark bar; FIN = light bar) represents fecal starch concentration taken at 2 time points: F-1 (average concentration of d 71 and 72) and F-2 (average concentration of d 102 and 103). Error bars indicate pooled SEM of 0.809. a–cMeans without a common letter differ (P ≤ 0.05). Treatment × time, P ≤ 0.01.
Corn particle size, wet distillers grains, and starch digestion
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AOAC International. 1995. Official Methods of Analysis. 16th ed. AOAC Int., Arlington, VA. Barajas, R., and R. A. Zinn. 1998. The feeding value of dry-rolled corn and steam-flaked corn in finishing diets for feedlot cattle: Influence of protein supplementation. J. Anim. Sci. 76:1744–1752. Brink, D. R., S. R. Lowry, R. A. Stock, and J. C. Parrott. 1990. Severity of liver abscess and efficiency of feed utilization of feedlot cattle. J. Anim. Sci. 68:1201–1207. Brown, T. R., and T. E. Lawrence. 2010. Association of liver abnormalities with carcass grading performance and value. J. Anim. Sci. 88:4037–4043. http://dx.doi.org/10.2527/ jas.2010-3219.
Figure 3. Apparent total-tract starch digestibility of steers fed cracked corn (CON) or finely ground corn (FIN) with 35% wet distillers grains (DM basis). Each bar (CON = dark bar; FIN = light bar) represents total-tract starch digestibility calculated at 2 time points: F-1 (average digestibility of d 71 and 72) and F-2 (average digestibility of d 102 and 103). Error bars indicate pooled SEM of 0.856. a–cMeans without a common letter differ (P ≤ 0.05). Treatment × time, P ≤ 0.01.
in the present experiment were less than reported by others. When fecal starch concentrations are greater than 5%, it is often attributed to less than optimal starch digestibility due to insufficient grain processing (Owens and Soderlund, 2006), supporting that starch digestibility of FIN-fed steers was more favorable than steers fed CON. However, improved starch digestibility did not translate into improved performance of steers fed FIN. Further research is needed to evaluate the optimum particle size of corn in diets with moderate amounts of WDGS. As ethanol plants in the dry milling industry continue to extract more value, primarily corn oil and fiber, from distillers grains (Lundy and Loy, 2014), distillers grains may become more similar in nutrient value to coproducts from the wet milling industry. Therefore, additional research should be conducted with the next generation of WDGS to determine the optimum inclusion of WDGS in finely ground corn diets to enhance cattle performance.
not improve feed efficiency and actually hindered DMI and ADG in this experiment compared with cracked corn when included in finishing diets with 35% WDGS. Although indicators of acidosis such as LAS were not different between CON or FIN treatments, the decrease in DMI outweighed the increase in starch digestibility and, therefore, limited cattle performance.
IMPLICATIONS
ANSI/ASAE. 2008. Method of Determining and Expressing Fineness of Feed Materials by Sieving. American National Standards Institute/American Society of Agricultural Engineers S319.4. Am. Soc. Agric. Biol. Eng., St. Joseph, MI.
Although research with finely ground corn and WCGF has been successful, fine grinding of corn did
ACKNOWLEDGMENTS The authors thank Brian, Howard, and Ross Mogler of Mogler Stock Farms (Alvord, IA) for the opportunity to conduct this research on their farm. In addition, the authors thank representatives of Elanco Animal Health for collection of liver-abscessscore data, Zoetis for product donation, and the Iowa Beef Center (Ames, IA) for providing financial support to conduct this research.
LITERATURE CITED
Cooper, R. J., C. T. Milton, T. J. Klopfenstein, T. L. Scott, C. B. Wilson, and R. A. Mass. 2002. Effect of corn processing on starch digestion and bacterial crude protein flow in finishing cattle. J. Anim. Sci. 80:797–804. Corrigan, M. E., G. E. Erickson, T. J. Klopfenstein, M. K. Luebbe, K. J. Vander Pol, N. F. Meyer, C. D. Buckner, S. J. Vanness, and K. J. Hanford. 2009. Effect of corn processing method and corn wet distillers grains plus solubles inclusion level in finishing steers. J. Anim. Sci. 87:3351–3362. http://dx.doi. org/10.2527/jas.2009-1836. Hall, M. B. 2009. Determination of starch, including maltooligosaccharides, in animal feeds: Comparison of methods and a method recommended for AOAC collaborative study. J. AOAC Int. 92:42–49. Huntington, G. B. 1997. Starch utilization by ruminants: From basics to the bunk. J. Anim. Sci. 75:852–867. Klopfenstein, T. J., G. E. Erickson, and V. R. Bremer. 2008. BOARD-INVITED REVIEW: Use of distillers grains by-products in the beef cattle feeding industry. J. Anim. Sci. 86:1223–1231. http://dx.doi.org/10.2527/ jas.2007-0550. Lundy, E. L., and D. Loy. 2014. Ethanol Coproducts for Beef Cattle: Changing Distillers Grains. Iowa Beef Center, Iowa State University Extension and Outreach Factsheet IBCR 200B. Iowa State Univ., Ames. Macken, C. N., G. E. Erickson, T. J. Klopfenstein, and R. A. Stock. 2006. Effects of corn processing method and protein concentration in finishing diets containing wet corn gluten feed on cattle performance. Prof. Anim. Sci. 22:14–22. Nagaraja, T. G., and M. M. Chengappa. 1998. Liver abscesses in feedlot cattle: A review. J. Anim. Sci. 76:287–298. NRC. 2000. Nutrient Requirements of Beef Cattle. 7th rev. ed. Natl. Acad. Press, Washington, DC. Owens, F. N., and S. Soderlund. 2006. Ruminal and postruminal starch digestion
542 by cattle. Accessed Dec. 11, 2014. http:// www.beefextension.com/proceedings/cattle_ grains06/06-17.pdf. Owens, F. N., R. A. Zinn, and Y. K. Kim. 1986. Limits to starch digestion in ruminant small intestine. J. Anim. Sci. 63:1634–1648. Pritchard, R. H., and K. W. Bruns. 2003. Controlling variation in feed intake through bunk management. J. Anim. Sci. 81:E133– E138. Rezac, D. J., D. U. Thomson, S. J. Bartle, J. B. Osterstock, F. L. Prouty, and C. D. Reinhardt. 2014. Prevalence, severity, and relationships of lung lesions, liver abnormalities, and rumen health scores measured at slaughter in beef cattle. J. Anim. Sci. 92:2595–2602. http://dx.doi.org/10.2527/jas.2013-7222. Schwandt, E., D. Thomson, C. Reinhardt, and S. Bartle. 2014. A survey of dry-rolled corn particle size and fecal starch in U.S.
Lundy et al. Midwestern feedlots. J. Anim. Sci. 92 (ESuppl. 2):593. (Abstr.) Scott, T. L., C. T. Milton, G. E. Erickson, T. J. Klopfenstein, and R. A. Stock. 2003. Corn processing method in finishing diets containing wet corn gluten feed. J. Anim. Sci. 81:3182–3190. Siverson, A. V., E. C. Titgemeyer, S. P. Montgomery, B. E. Oleen, G. W. Preedy, and D. A. Blasi. 2014. Effects of corn processing and dietary wet corn gluten feed inclusion on performance and digestion of newly received growing cattle. J. Anim. Sci. 92:1604–1612. http://dx.doi.org/10.2527/jas.2013-6839. Stock, R. A., J. M. Lewis, T. J. Klopfenstein, and C. T. Milton. 2000. Review of new information on the use of wet and dry milling feed by-products in feedlot diets. J. Anim. Sci. 77:1–12.
Vander Pol, K. J., G. E. Erickson, M. A. Greenquist, T. J. Klopfenstein, and T. Robb. 2006. Effect of corn processing in finishing diets containing wet distillers grains on feedlot performance and carcass characteristics of finishing steers. Pages 48–50 in 2006 Nebraska Beef Cattle Reports. Paper 119. Univ. Nebraska, Lincoln. Vander Pol, K. J., M. A. Greenquist, G. E. Erickson, T. J. Klopfenstein, and T. Robb. 2008. Effect of corn processing in finishing diets containing wet distillers grains on feedlot performance and carcass characteristics of finishing steers. Prof. Anim. Sci. 24:439–444. Zinn, R. A., A. Barreras, L. Corona, F. N. Owens, and R. A. Ware. 2007. Starch digestion by feedlot cattle: Predictions from analysis of feed and fecal starch and nitrogen. J. Anim. Sci. 85:1727–1730. http://dx.doi. org/10.2527/jas.2006-556.
E fmoderate fect of corn particle size with amounts of wet distillers grains in finishing diets on starch digestibility and steer performance
E. L. Lundy,* PAS, B. E. Doran,† E. E. Vermeer,‡ PAS, D. D. Loy,* PAS, and S. L. Hansen*1 *Department of Animal Science, Iowa State University, Ames 50011; †Iowa State University Extension and Outreach, Orange City 51041; and ‡Midwest PMS, Merrill, IA 51038
ABSTRACT Five hundred yearling steers (370 ± 30.0 kg, SD) were used to determine the effect of corn particle size in diets containing 35% wet distillers grains plus solubles (WDGS) on steer performance, carcass characteristics, and apparent total-tract starch digestibility (TTSD). Treatments included 45% cracked corn (CON; 2,350 μm) or finely ground corn (FIN; 500 μm) with 35% WDGS and were replicated in 4 pens per treatment with 60 or 64 steers per pen. Fecal samples were collected on d 71 and 72 (F-1) and d 102 and 103 (F-2). Final BW and HCW were heavier (P ≤ 0.01) for steers finished on CON compared with steers finished on FIN. Whereas G:F was not different (P = 0.22) between treatments, DMI and ADG were greater (P ≤ 0.01) for CON-fed steers than FIN-fed steers. Liver abscess scores were not influenced (P ≥ 0.39) by treatment. Liver abscess scores tended (P = 0.10) to influence ADG over the experiment, with steers
1 Corresponding author: slhansen@iastate. edu
having severe liver abscess scores gaining less compared with steers with no or mild liver abscess scores. A treatment × time effect (P < 0.01) was observed for TTSD. Whereas TTSD of steers fed CON decreased over time (90.28 and 85.74% for F-1 and F-2, respectively), TTSD of steers finished on FIN did not differ across the 2 sampling dates (97.95 and 97.55% for F-1 and F-2, respectively). Apparent starch digestibility was improved for steers fed finely ground corn with 35% WDGS; however, cattle performance was less compared with steers fed cracked corn with 35% WDGS. Key words: cattle, corn particle size, distillers grains, liver abscess, starch digestibility
INTRODUCTION Expansion of the ethanol industry has led to a steady supply of highquality coproducts, including wet distillers grains plus solubles (WDGS) and wet corn gluten feed (WCGF). These coproducts have proven to be beneficial replacements for corn in finishing diets through improved ADG
and feed efficiency (Klopfenstein et al., 2008). Because corn starch is the primary substrate of alcohol fermentation, both WDGS and WCGF have relatively low concentrations of starch. As a result, coproducts from both the dry and wet milling industries appear to moderate the risk of acidosis in finishing diets (Stock et al., 2000). Decreasing corn particle size through grain processing is an effective way to increase starch utilization and thus improve performance of the ruminant animal (Owens et al., 1986; Huntington, 1997). However, grinding corn too finely often results in rapid rumen fermentation leading to acidosis. Persistent acidosis often results in decreased animal performance and liver abscesses, causing an economic loss to producers (Brown and Lawrence, 2010). Adding coproducts at the expense of corn often decreases dietary starch concentrations; therefore, decreasing grain particle size may allow for more complete starch digestion of what starch is present in the diet, potentially improving cattle performance. Research has shown that more extensive
536 grain processing when feeding WCGF improves feed efficiency by 10.5% (Macken et al., 2006) to 12.5% (Scott et al., 2003). However, decreasing corn particle size in diets containing WDGS has given more variable results. Corrigan et al. (2009) noted up to 8% improvement in feed efficiency when assessed across multiple WDGS inclusions, whereas Vander Pol et al. (2008) observed a 7% decrease in feed efficiency with decreased particle size in diets containing 30% WDGS. Therefore, the objective of this experiment was to determine whether feeding moderate levels of WDGS would decrease the acidosis risk associated with further grain processing and allow fine grinding of corn to improve starch utilization and, thus, cattle performance.
MATERIALS AND METHODS Animals and Experimental Design Procedures and protocols were approved by the Iowa State University Institutional Animal Care and Use Committee (9-13-7630-B). Six hundred crossbred steers were purchased from a single source and
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transported to a commercial feedlot (Mogler Stock Farms, Alvord, IA). Upon arrival, steers were housed in a concrete open lot and fed a series of 4 transition diets over 17 d to ensure all steers were prepared for a concentrate-based diet. Five days before the start of the experiment, steers were vaccinated with Bovi-Shield GOLD One Shot (Zoetis, New York, NY), Ultrabac CD (Zoetis), and Somubac (Zoetis) and implanted with Synovex Choice (Zoetis). Steers were treated for internal and external parasites with Dectomax Injectable (Zoetis) and ProMectin B Pour-on (Vedco Inc., St. Joseph, MO). Body weights were also measured on d −5, and 500 steers (370 ± 30.0 kg, SD) were selected to be used in the experiment, blocked by BW, and randomly assigned to 1 of 2 diets: cracked (2,350 μm) corn–based control diet (CON) or finely ground (500 μm) corn diet (FIN), with both treatments containing 35% WDGS (DM basis; Table 1). Diets were formulated to meet or exceed animal requirements (NRC, 2000). At the initiation of the experiment, individual BW were collected before feeding. Steers were given a unique visual and electronic ID and sorted into
Table 1. Ingredient and nutrient composition of diets1 (%, DM basis) Item
CON
FIN
Ingredient Cracked corn2 Finely ground corn2 Wet distillers grains plus solubles3 Corn silage Corn stalks Liquid supplement4 Analyzed composition5 CP NDF Starch Ether extract
45.0 — 35.2 10.0 6.5 3.3 18.1 29.6 36.9 5.1
— 45.0 35.2 10.0 6.5 3.3 18.2 26.8 35.2 4.9
CON = cracked corn diet; FIN = finely ground corn diet. Cracked corn, 2,350 μm; finely ground corn, 500 μm. 3 Composite analysis: 35.5% CP, 8.7% ether extract, and 0.62% S (DM basis). 4 Liquid supplement includes 12.7% Ca, 5.7% salt, 1.6% K, 0.02% P, and 95,000 IU/ kg of vitamin A, and monensin sodium provided at 700 mg/kg (DM basis). 5 Diets were analyzed by Dairyland Laboratories Inc. (Arcadia, WI). 1 2
their respective pens within a slotted confinement facility with rubber mats. Each treatment was replicated in 4 pens with 60 or 64 steers per pen, split equally across treatments, to maintain a similar pen density of 2.0 m2 per steer. On d 72, interim BW were measured, and steers were reimplanted with Revalor 200 (Merck Animal Health, Millsboro, DE). On d 106, steers were started on ractopamine hydrochloride (Optaflexx, Elanco Animal Health, Greenfield, IN) and fed at a rate of 300 mg per steer per day for the last 21 or 22 d of the experiment. Steers were slaughtered by pen BW blocks on d 127 or 128 at a commercial abattoir (Tyson Foods Inc., Dakota City, NE). Throughout the experiment, 5 steers were removed because of illness, injury, or death, for reasons unrelated to treatment (2 CON and 3 FIN), and data were excluded from analysis. It was assumed that steers were consuming the pen average DMI up until the day of removal or death.
Corn Particle Size Both sources of corn were processed through a double pair roller mill (Model 12 × 52 Dual Ind, RMS, Harrisburg, SD) at the feedlot. To achieve a 500-μm finely ground corn, the top roller was adjusted to 0.02 cm, and the bottom roller was closed. For the cracked corn, the top rollers were set to minimally process 100% of corn kernels, and the bottom rollers were opened for full flow through. Batches of each corn source were processed back to back to provide uniformity of corn source. After processing, both cracked corn and finely ground corn were stored in bunkers under a covered roof until they were fed. Samples of both sources of corn were taken 4 times throughout the duration of experiment for determination of corn particle size, which was determined using the method described by American Society of Agricultural and Biological Engineers (ANSI/ASAE, 2008, method ANSI/ ASAE S319.4). Samples were shaken
Corn particle size, wet distillers grains, and starch digestion
through a corn sieve (Tyler Equivalent Mesh, W.S. Tyler Industrial Group, Mentor, OH) using 5 screens (US Sieve # 8, 12, 20, 30, and 40 for cracked corn and 20, 30, 40, 50, and 100 for finely ground corn). Particle size was determined by dividing the weight of sample retained on each sieve by the total sample weight (asfed basis) run through the series of sieves multiplied by the micrometer opening value given for each sieve (ANSI/ASAE, 2008). For each source of corn, the particle size of each sampling day was averaged and equivalent to 2,350 μm for cracked corn and 500 μm for the finely ground corn.
Sample Collection and Analytical Procedures Steers were fed their respective diets twice daily for ad libitum intake using a clean bunk management protocol (Pritchard and Bruns, 2003). Bunks were visually assessed each morning before feeding, and feed delivery was adjusted daily based on the amount of feed remaining. Daily feed delivery was recorded for each pen, and pen average DMI was calculated. Average daily gain and G:F were determined using pen total DMI and total BW gain of steers in the pen over the duration of the experiment. On d 71 and 72 and d 102 and 103, fecal collections were taken for apparent total starch digestibility calculation. On each collection day, a pen composite of 8 fresh samples, approximately 30 g per sample (wet basis), was collected randomly from the pen surface. Pen composites from each of the 4 d were sent to Dairyland Laboratories Inc. (Arcadia, WI) for wet chemistry analysis of CP (AOAC International, 1995, method 990.03) and fecal starch (Hall, 2009). Samples of each TMR were also collected on d 71 and 102 and sent to Dairyland Laboratories Inc. for analysis of CP and starch using the same methods. Apparent total-tract starch digestibility was estimated using the equation described by Zinn et al. (2007): starch digestion (expressed as a percentage of intake)
is equivalent to 100{1 − [(0.938 − 0.497 × FN + 0.0853 × FN2) × FS ÷ DS]}, where FN is fecal nitrogen concentration (% DM), FS is fecal starch concentration (% DM), and DS is dietary starch concentration (% DM). Starch digestion was averaged for each pen over the 2 consecutive days of collection (F-1 for d 71 and 72 and F-2 for d 102 and 103). Individual camera carcass data were provided by Tyson Foods Inc. Carcass data collected included HCW, marbling score, 12th-rib backfat thickness, LM area, liver abscess scores (LAS), YG, and QG. Liver abscess scores were facilitated by representatives from Elanco Animal Health, who were masked to treatments, using the Elanco Liver Check System on a 0, A, and A+ scale. Livers free of abscesses were classified as a LAS of 0. Mild abscesses, up to 4 small abscesses less than 2.54 cm in diameter, were classified as LAS of A. Larger or more severe abscesses, with active areas of inflammation on the liver or when portions of the liver were attached to the diaphragm, were classified as a LAS of A+. A 4% pencil shrink was applied to initial BW, and final BW was calculated from HCW using the average DP of the cattle in this experiment, 62.4%.
Statistical Analysis Data were analyzed by ANOVA in SAS 9.3 (SAS Institute Inc., Cary, NC) as a complete block design with pen as the experimental unit (n = 4 per treatment). The model included the fixed effects of treatment and block. Performance, carcass characteristics, and starch digestibility data were analyzed using the MIXED procedure of SAS. Treatment distributions of YG, QG, and LAS data were determined using PROC GLIMMIX of SAS. The effect of LAS on individual steer ADG and carcass characteristics were also tested using PROC Mixed with steer as the experimental unit (n = 495 steers). Data were tested for normalcy and homogeneity of variance using the Shapiro-Wilks test. Only HCW data were found
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to require transformation, and the square root function was used, and back-transformed data are presented. Significance was declared at P ≤ 0.05, and tendencies were declared from P = 0.06 to 0.10. Means are reported are least squares means ± SEM.
RESULTS AND DISCUSSION Performance and carcass results are presented in Table 2. Although initial BW and interim BW (d 72) were not different (P ≥ 0.16) between treatment groups, final BW was heavier (P ≤ 0.01) for steers finished on CON compared with FIN. Dry matter intake and ADG were greater (P ≤ 0.01) for steers finished on CON compared with those finished on FIN. However, G:F was not different (P = 0.22) between treatment groups. Vander Pol et al. (2008) also showed that fine ground corn (FGC) in a diet with 30% WDGS had negative effects on performance compared with a more traditional dry-rolled corn (DRC) diet with 30% WDGS, as demonstrated by a 17% decrease in ADG, 10% decrease in DMI, and 7% decrease in G:F over cattle fed diets of DRC and 30% WDGS. In a university report of the same experiment published earlier, Vander Pol et al. (2006) reported an increase in dietary roughage after 107 d on feed, suggesting that steers being fed FGC experienced apparent acidosis, although it was not explicitly stated by the authors. It seems that the probable acidosis may partially explain why cattle performance was less in the work by Vander Pol et al. (2008) compared with the current experiment. Average HCW of CON-fed cattle was heavier (P = 0.01) than steers fed FIN. Longissimus muscle area, backfat thickness, and YG were not different (P ≥ 0.38) because of treatment. However, marbling scores of FIN cattle were less (P = 0.04) compared with cattle fed CON. Although distributions of USDA QG of average Choice and higher and Low Choice were not affected by treatment (P ≥ 0.17), the percentage of cattle grading Select tended to be greater (P = 0.07)
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Table 2. Influence of corn particle size1 on steer performance and carcass characteristics Item Growth performance2 Initial BW (kg) Interim BW3 (kg) Final BW (kg) DMI (kg/d) ADG (kg/d) G:F Carcass characteristics HCW (kg) LM area (cm2) Marbling score4 Backfat thickness (cm) YG
CON
FIN
SEM
P-value
368 500 624 11.76 2.01 0.161 390 86.6 434 1.23 3.2
371 494 605 11.07 1.84 0.156 378 85.8 417 1.20 3.1
1.54 3.44 1.79 0.10 0.03 0.003 1.58 1.20 4.63 0.05 0.09
0.20 0.16 <0.01 <0.01 <0.01 0.22 0.01 0.56 0.04 0.56 0.38
CON = cracked corn diet; FIN = finely ground corn diet; n = 4 pens per treatment. A 4% pencil shrink was applied to all live BW. Final BW were calculated from HCW using a common DP of 62.4%, which was used in calculation of DMI, ADG, and G:F over the duration of the experiment. 3 Interim BW were collected on d 72. 4 Marbling score: 300 = slight, 400 = small, and 500 = modest. 1 2
for cattle finished on FIN (Table 3). Lighter carcasses and decreased QG indicate that steers fed FIN treatment may not have reached the desired degree of finish by slaughter. Yield grade distributions were not different (P ≥ 0.20) by treatment. In this ex-
periment, distribution of LAS was not influenced (P ≥ 0.39) by treatment. Because the liver is a vital organ required for essential life function, damage to the liver could result in decreased functionality and, ultimately, decreased animal growth and
Table 3. Influence of corn particle size in steer diets1 on distribution of quality and yield grades and liver abscess scores Item QG (%) Average Choice and higher Low Choice Select YG (%) 1 2 3 4/5 Liver abscess score2 (%) 0 A A+
CON
FIN
SEM
P-value
16.3 51.9 28.9 2.0 33.0 55.4 8.6
10.8 45.6 41.1 3.5 38.3 48.1 8.9
2.21 3.20 3.14 1.34 3.07 3.20 1.80
0.17 0.28 0.07 0.37 0.31 0.20 0.90
91.3 6.0 2.4
88.8 6.8 4.0
1.90 1.56 1.11
0.42 0.74 0.39
CON = cracked corn diet; FIN = finely ground corn diet; n = 4 pens per treatment. Liver abscess score: 0 = no abscesses; A = 1 or 2 small abscesses; A+ = 1 or more large abscesses.
1 2
performance. Previous research has shown that severe liver abscesses result in up to a 15% decrease in ADG (Brink et al., 1990). Similarly in this experiment, there was a tendency (P = 0.10) for LAS to influence ADG over the duration of the experiment (Table 4); steers with a LAS of A+ gained less BW compared with steers having a LAS of 0 or A. Interestingly, during period 1 (d 0–72), LAS did not affect ADG (P = 0.30). However, during period 2 (d 73–127 or 128), the ADG of steers that had a LAS of A+ was approximately 0.4 kg less than steers with LAS of 0 or A, indicating that negative performance associated with severe LAS occurs later in the feeding period. Other research has shown similar results where no difference in performance existed between steers with no LAS or mild LAS, but steers with severe LAS experienced a decrease in performance up to 16.6% loss of BW gain (Brink et al., 1990) or 0.22 kg/d decrease in BW gain (Rezac et al., 2014). In addition to LAS effect on ADG, the effect of LAS on carcass characteristics was also evaluated (Table 5). Cattle with severe LAS (A+) had approximately 19 kg lighter HCW (P = 0.05) compared with cattle with no LAS or mild LAS. In addition, cattle with severe abscesses (LAS of A+) had decreased (P = 0.03) LM area compared with their counterparts. Liver abscess score had no effect (P ≥ 0.33) on backfat thickness, marbling score, QG, or YG. Although only 10% of the cattle in this experiment had liver abscesses, the severity of decreased performance of cattle with an A+ LAS could affect efficiency of cattle and producer profitability. Thus, additional research is warranted to better understand development of liver abscesses and influence on cattle growth performance. Prevalence of liver abscesses in the industry ranges from approximately 10 to 20% of cattle on feed consuming steam-flaked corn diets (Brown and Lawrence, 2010; Rezac et al., 2014) with tylosin (Tylan, Elanco Animal Health). When antimicrobials were not fed, occurrence of LAS was
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Table 4. Influence of liver abscess score on average daily gain of steers Liver abscess score1 ADG (kg/d) Periods 1 and 2 Period 12 Period 23
0
A
1.81 1.84 1.77a
A+
1.84 1.91 1.76a
x
1.68 1.91 1.40b
x
y
SEM
P-value
0.061 0.054 0.090
0.10 0.30 <0.01
Means within a row without a common superscript differ (P ≤ 0.05). Means within a row without a common superscript tend to differ (P ≤ 0.10). 1 Liver abscess score: 0 = no abscesses, n = 445 steers; A = 1 or 2 small abscesses, n = 33 steers; A+ = 1 or more large abscesses, n = 17 steers. 2 Day 0 to 72 of the experiment. 3 Day 73 to 127 or 128 of the experiment. a,b x,y
reported to be as high as 32% in DRC diets (Brink et al., 1990) and 43% in steam-flaked corn diets (Brown and Lawrence, 2010). Although tylosin was not fed in this experiment, only 10% of steers had LAS, indicating that acidosis was not a major issue in this experiment. However, research has shown steers with severe LAS typically have a 0.5-kg reduction in DMI (Brink et al., 1990; Nagaraja and Chengappa, 1998), which is consistent with decreased DMI of steers fed FIN compared with CON. During the first 21 d on feed, DMI varied between the 2 treatment groups. This is likely due to the FIN cattle experi-
encing subacute acidosis while making the transition to FGC from cracked corn. Steers on FIN experienced a decrease of approximately 1.1 kg in daily DMI from d 10 to 20 and continued to have an average DMI that was 0.3 kg less than CON-fed steers for the remainder of the experiment (Figure 1). Although visible signs of acidosis were not observed during the experiment, measurement of rumen pH throughout the experiment, especially the first 21 d, may have been an informative indicator of increased risk of rumenitis, which occurs before liver abscess development. Corrigan et al. (2009) found that the addition
Table 5. Influence of liver abscess score on carcass characteristics Liver abscess score1 Item HCW2 (kg) LM area (cm2) Backfat thickness (cm) Marbling score3 QG4 YG
0
A
A+
SEM
P-value
383.7a 83.55a 1.22 426 1.79 3.1
386.2a 85.16a 1.17 422 1.81 3.0
365.8b 78.84b 1.22 409 1.63 3.3
7.29 1.232 0.051 11.1 0.110 0.10
0.05 0.03 0.76 0.61 0.62 0.33
Means within a row without a common superscript differ (P ≤ 0.05). Liver abscess score: 0 = no abscesses, n = 445 steers; A = 1 or 2 small abscesses, n = 33 steers; A+ = 1 or more large abscesses, n = 17 steers. 2 Data transformed using square root function. Means and SE values reported were back transformed. 3 Marbling score: 300 = slight; 400 = small; 500 = modest. 4 1 = Select, 2 = Low Choice, 3 = average and High Choice, and 4 = Prime. a,b 1
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of 40% WDGS (DM basis) to diets based on DRC, high-moisture corn, or steam-flaked corn did not affect rumen pH; however, Siverson et al. (2014) reported that feeding 30% WCGF (DM basis) in diets based on DRC or whole shelled corn aided in moderation of rumen pH and increased starch digestibility in growing diets, potentially due to differences in intestinal and ruminal digestion. Wet corn gluten feed generally contains less starch and has greater digestible fiber compared with WDGS (Stock et al., 2000), which may contribute to the variation in rumen pH results between the 2 studies. Increased starch availability through grain processing often improves cattle performance (Huntington, 1997), and starch digestibility can be predicted based on fecal starch concentration (R2 = 0.96; Zinn et al., 2007). In this experiment, fine grinding of corn decreased fecal starch concentrations and improved apparent total-tract starch digestibility. A treatment × time effect (P ≤ 0.01; Figure 2) was observed for fecal starch concentrations, where steers fed CON diets had increased concentrations (14.34 and 17.58% fecal starch for F-1 and F-2, respectively) over the 2 sampling dates compared with steers fed FIN diets, which had consistently lesser concentrations (2.95 and 3.20% fecal starch concentrations for F-1 and F-2, respectively). Although starch concentrations of the diets varied by less than 2% (Table 1), a treatment × time interaction (P ≤ 0.01; Figure 3) was also observed for apparent totaltract starch digestibility of steers. Starch digestibility of steers fed CON diets decreased over time (90.28 and 85.74% for F-1 and F-2, respectively). However, apparent total-tract starch digestibility of steers fed FIN diets did not differ across sampling days (97.95 and 97.55% for F-1 and F-2, respectively). Consistent with increased fecal starch concentrations of CON, Barajas and Zinn (1998) noted an increase in fecal starch concentrations ranging from 20.3 to 28.5% over an 8-wk period in cattle fed a 75% DRC
540 diet. Decreased starch digestibility as days on feed increased could be attributed to changes in microbial population, site of starch digestion, or DMI. Particle size of the grain plays a large role in retention time within the rumen (Owens et al., 1986). Although retention time was probably greater for CON, a greater portion of the starch most likely reached the small intestine, which does not have as extensive of digestion capacity in comparison to the rumen (Owens et al., 1986). Although increased DMI would be thought to lead to more rapid passage rate and less utilization of starch, intakes in the present experiment were consistent between the 2 sampling dates for CON-fed steers. It is unclear why fecal starch concentrations decreased over time in the CON-fed steers. Scott et al. (2003) observed a 1.8% decrease in fecal starch concentrations when 32% WCGF replaced DRC in the diet. Fecal starch concentrations in FGC diets with moderate inclusions of WCGF ranged from 7.1% (Scott et al., 2003) to 11.8% (Macken et al., 2006) and were greater than fecal starch concentrations of FIN-fed steers in current experiment, which averaged 3.1% over the duration of the experiment. Vander Pol et al. (2008) found fecal starch concentrations in DRC diets with 30% WDGS to be consistent with FGC diets containing 30% WDGS (12.0 and 13.4% for DRC and FGC, respectively). The lack of difference in fecal starch concentrations found by Vander Pol et al. (2008) compared with the present experiment could have been attributed to the amount of effective dietary fiber used in the 2 studies. In the present experiment, roughage concentration was 11.5%, which could have slowed passage rate, thus allowing for increased starch digestibility, compared with diets containing 5.6% roughage as fed by Vander Pol et al. (2008). Although fecal starch concentrations have been more extensively reviewed, apparent total-tract starch digestibility of DRC diets has not been reported to the same extent. Others have
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Figure 1. Dry matter intake by steers fed cracked corn (CON; indicated by solid line) or finely ground corn (FIN; indicated by dashed line) in diets containing 35% wet distillers grains (DM basis) over the duration of the experiment.
observed apparent total-tract starch digestibility of DRC diets to range from 91 to 96% (Cooper et al., 2002; Owens and Soderlund, 2006; Corrigan et al., 2009). Variation in fecal starch concentrations and apparent total-tract starch digestibility among previous studies could be attributed to the variation of corn particle size used in the studies. In a recent survey of feedlots in the Midwest using
DRC as the primary energy source, the average fecal starch concentration of 34 feedlots was 18.9%, ranging from 7.0 to 36.6%. The range of corn particle size reported varied from 1,165 to 6,823 μm with an average size of 4,201 μm (Schwandt et al., 2014). The CON diet used in the present experiment was 2,350 μm, which may help explain why the fecal starch concentrations of cattle
Figure 2. Fecal starch concentration by steers fed cracked corn (CON) or finely ground corn (FIN) with 35% wet distillers grains (DM basis). Each bar (CON = dark bar; FIN = light bar) represents fecal starch concentration taken at 2 time points: F-1 (average concentration of d 71 and 72) and F-2 (average concentration of d 102 and 103). Error bars indicate pooled SEM of 0.809. a–cMeans without a common letter differ (P ≤ 0.05). Treatment × time, P ≤ 0.01.
Corn particle size, wet distillers grains, and starch digestion
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AOAC International. 1995. Official Methods of Analysis. 16th ed. AOAC Int., Arlington, VA. Barajas, R., and R. A. Zinn. 1998. The feeding value of dry-rolled corn and steam-flaked corn in finishing diets for feedlot cattle: Influence of protein supplementation. J. Anim. Sci. 76:1744–1752. Brink, D. R., S. R. Lowry, R. A. Stock, and J. C. Parrott. 1990. Severity of liver abscess and efficiency of feed utilization of feedlot cattle. J. Anim. Sci. 68:1201–1207. Brown, T. R., and T. E. Lawrence. 2010. Association of liver abnormalities with carcass grading performance and value. J. Anim. Sci. 88:4037–4043. http://dx.doi.org/10.2527/ jas.2010-3219.
Figure 3. Apparent total-tract starch digestibility of steers fed cracked corn (CON) or finely ground corn (FIN) with 35% wet distillers grains (DM basis). Each bar (CON = dark bar; FIN = light bar) represents total-tract starch digestibility calculated at 2 time points: F-1 (average digestibility of d 71 and 72) and F-2 (average digestibility of d 102 and 103). Error bars indicate pooled SEM of 0.856. a–cMeans without a common letter differ (P ≤ 0.05). Treatment × time, P ≤ 0.01.
in the present experiment were less than reported by others. When fecal starch concentrations are greater than 5%, it is often attributed to less than optimal starch digestibility due to insufficient grain processing (Owens and Soderlund, 2006), supporting that starch digestibility of FIN-fed steers was more favorable than steers fed CON. However, improved starch digestibility did not translate into improved performance of steers fed FIN. Further research is needed to evaluate the optimum particle size of corn in diets with moderate amounts of WDGS. As ethanol plants in the dry milling industry continue to extract more value, primarily corn oil and fiber, from distillers grains (Lundy and Loy, 2014), distillers grains may become more similar in nutrient value to coproducts from the wet milling industry. Therefore, additional research should be conducted with the next generation of WDGS to determine the optimum inclusion of WDGS in finely ground corn diets to enhance cattle performance.
not improve feed efficiency and actually hindered DMI and ADG in this experiment compared with cracked corn when included in finishing diets with 35% WDGS. Although indicators of acidosis such as LAS were not different between CON or FIN treatments, the decrease in DMI outweighed the increase in starch digestibility and, therefore, limited cattle performance.
IMPLICATIONS
ANSI/ASAE. 2008. Method of Determining and Expressing Fineness of Feed Materials by Sieving. American National Standards Institute/American Society of Agricultural Engineers S319.4. Am. Soc. Agric. Biol. Eng., St. Joseph, MI.
Although research with finely ground corn and WCGF has been successful, fine grinding of corn did
ACKNOWLEDGMENTS The authors thank Brian, Howard, and Ross Mogler of Mogler Stock Farms (Alvord, IA) for the opportunity to conduct this research on their farm. In addition, the authors thank representatives of Elanco Animal Health for collection of liver-abscessscore data, Zoetis for product donation, and the Iowa Beef Center (Ames, IA) for providing financial support to conduct this research.
LITERATURE CITED
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