Invited Review: Summary of Steam-Flaking Corn or Sorghum Grain for Lactating Dairy Cows

Invited Review: Summary of Steam-Flaking Corn or Sorghum Grain for Lactating Dairy Cows C. B. THEURER,1 J. T. HUBER, A. DELGADO-ELORDUY2, and R. WANDERLEY Department of Animal Sciences, University of Arizona, Tucson 85721-0038

ABSTRACT Nineteen lactation trials (43 grain processing comparisons) are summarized, in addition to digestibility and postabsorptive metabolism studies. The net energy for lactation (NEL) of steam-flaked corn or sorghum grain is about 20% greater than the NEL for dry-rolled corn or sorghum. Based on lactational performance, steam-flaked sorghum grain is of equal value to steamflaked corn, and steam-flaked corn is superior to steamrolled corn. Steam-flaking of corn or sorghum compared to steam-rolling of corn or dry-rolling of corn or sorghum consistently improves milk production and milk protein yield. This result is because of a much greater proportion of dietary starch fermented in the rumen, enhanced digestibility of the smaller fraction of dietary starch reaching the small intestine, and increased total starch digestion. Steam-flaking increases cycling of urea to the gut, microbial protein flow to the small intestine, and estimated mammary uptake of amino acids. Steam-rolling compared to dry-rolling of barley or wheat did not alter total starch digestibilities in two trials, one with each grain source. Lactation studies with these processing comparisons have not been reported. Most cited studies have been with total mixed rations (TMR) and alfalfa hay as the principal forage. Additional studies are needed with lactating cows fed steam-flaked corn or sorghum in TMR containing alfalfa or corn silage. Optimal flake density of steam-processed corn or sorghum grain appears to be about 360 g/L (∼ 28 lb/bu). (Key words: steam-flaking, net energy, starch digestion, postabsorptive metabolism) Abbreviation key: DR = dry-rolled, FD = flake density, SF = steam-flaked, SR = steam-rolled. INTRODUCTION Steam-flaked (SF) corn or sorghum grain is extensively used in finishing cattle diets and has consistently

Received December 28, 1998. Accepted April 26, 1999. 1 Reprint requests. 2 Present address: Dairy Nutrition Services of Mexico, Piedras Negras No. 364, Esq. C/Tamazula Parque Industrial Lagunero, Gomez Palacio, Durango, Mexico. 1999 J Dairy Sci 82:1950–1959

improved feed efficiency of feedlot cattle through increased starch utilization (3, 17, 21, 54, 59). Until recently, SF corn or sorghum grain has not been utilized in diets of lactating cows. Currently, extensive use of these steam-processed grains occurs in dairy herds in several western states and some herds in northeastern states. Starch is a major source of energy in diets fed to high producing dairy cows. Consequently, optimal starch utilization is fundamental to improving efficiency of milk production. Altering NEL intake or NEL absorption (by increasing the extent of dietary starch digestion in the rumen) alters the concentration of milk protein and yield of milk and milk protein in lactating dairy cows (55). The most consistent increases in starch utilization and milk and milk protein yield appear to be by feeding SF corn or sorghum grain (55). Increased moisture, temperature, and pressure (which are all critical in the steam-flaking process) consistently increases in vitro enzymatic starch hydrolysis of grains (16, 36) and the proportion of starch digested in the rumen and the total starch digestibility by cattle (21, 54). These increased digestibilities are caused by disruption of the protein matrix surrounding the starch granules in the grain endosperm and disorganization of the starch granules (43). The relative value of increasing the proportion of corn or sorghum grain starch digested in the rumen versus the intestines has been recently reviewed (21, 54). The purpose of this review is to summarize the effects of SF corn or sorghum grain in TMR for high producing dairy cows. In most cited studies, the grain was SF to a flake density (FD) of about 360 g/L and is referred to as SF 28 (reflecting the FD in pounds per bushel). Nineteen lactation trials (43 grain processing comparisons) have been summarized, in addition to nine siteof-digestion studies and two postabsorptive metabolism trials. Most comparisons are between SF and steamrolled (SR) or dry-rolled (DR) grains; however, several comparisons focus on optimal FD for SF grains. GRAIN PROCESSING Steam-Rolling and Dry-Rolling Steam-rolling is a common processing method for barley, corn, and wheat used in dairy concentrates. Grains

1950

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INVITED REVIEW TABLE 1. Steam-flaked (SF) compared to steam-rolled (SR) corn improves total starch digestion and lactation performance by dairy cows.1 Item

SR2

SF3

SEM

P ≤4

Comparisons DMI, kg/d 3.5% FCM, kg/d FCM/DMI Milk, kg/d Protein, % Protein, kg/d Fat, % Fat, kg/d Starch digestion, total tract,%

6 26.5 33.6 1.28 35.8 2.99 1.07 3.11 1.12

6 26.5 34.6 1.31 38.0 3.06 1.16 2.98 1.13

... 0.4 0.3 0.02 0.4 0.02 0.01 0.03 0.01

... 0.93 0.07 0.31 0.02 0.11 0.01 0.02 0.44

87.45

95.75

2.0

0.05

1

Means of six comparisons, using 92 cows in four trials (10 wk/ trial; 6 to 8 cows/treatment), fed TMR with 35 to 41% alfalfa hay and 37 to 40% grain (10, 48, 62, 63). 2 Commercially SR corn is usually steamed for much less time (∼ 15 min) than SF corn and is flaked with less pressure through variable size rollers to a visual endpoint without a specific flake density (usually 438 to 540 g/L or 34 to 42 lb/bu). The grains in these studies were steamed longer (40 to 60 min) to raise moisture level to ∼ 18 to 20%, then flaked (carefully monitored) to 489 g/L (38 lb/bu) to “mimic” commercial products. 3 Steamed for 40 to 60 min at atmospheric pressure in vertical steam chamber to raise moisture level to ∼ 18 to 20%, then flaked through 46 × 76 cm rollers to density of ∼ 360 g/L (∼ 28 lb/bu). 4 Based on analyses of variance with processing treatments and comparisons as main effects. 5 Determined using Cr2O3 ratio technique (10, 48, 62) (P. Yu, 1998, personal communication).

are usually steamed for 15 min or less to increase grain moisture to about 15% and then crushed with various sizes of rollers to produce a thick flake without a specific FD endpoint, usually about 438 to 540 g/L for corn and sorghum (34 to 42 lb/bu as used in the industry). Quality is usually based on visual appraisal rather than steaming time, moisture content, FD, or laboratory indices. Dry-rolling is a common form of processing barley, sorghum, and wheat; dry grain is passed through large rollers (46 × 76 cm or larger) to break the grain into several pieces (similar to coarsely ground), with a bulk density for sorghum of about 450 to 644 g/L (35 to 50 lb/bu). Steam-Flaking Steam-flaking is a more extensive processing system (with careful quality control) than dry- or steam-rolling. Grain is steamed for 30 to 60 min in a vertical, stainless steel steam chamber (usually 3.1 to 9.2 m height and 91 to 183 cm diameter) to increase grain moisture to 18 to 20% and then flaked between preheated large rollers (46 cm diameter by 76 to 91 cm length or 61 cm diameter by 122 cm length) to a specific desired FD (usually 309 to 386 g/L or 24 to 30 lb/bu) (53). The rollers become hot as the steamed grain passes through, which is important

in the flaking process. The extent of processing (flaking pressure) increases as FD decreases (i.e., 309 g/L flake is more extensively processed than a 386 g/L flake). The quality of SF grain is routinely measured by FD, and by laboratory methods (enzymatic starch hydrolysis or percent starch gelatinization (53, 61). LACTATION STUDIES Steam-flaking of corn or sorghum grain with careful quality control consistently improves most lactational measurements, especially milk and milk protein yields. Responses are similar for corn and sorghum grain, except efficiency of milk production (FCM/DMI) is improved over the rolled grain controls with SF sorghum but not with SF corn. Most published lactation studies with dairy cows fed SF corn or sorghum have been conducted at the University of Arizona. Data presented in Tables 1, 2, and 3 summarize the results of 16 lactation trials (8 to 13 wk each) and include 33 direct comparisons with 450 Holstein cow observations between SF corn and SR corn (Table 1), SF sorghum grain and DR sorghum (Table 2), and SF corn and SF sorghum (Table 3). The experimental protocol was similar for the 16 trials, thus, statistical analyses for data presented in each table were by analysis of variance (27); treatments and comparisons were main effects. Individual cow DMI was measured daily using electronically controlled gates. Daily milk yield ranged from 28 to 47 kg. The TMR were formulated to meet NRC (30) requirements; TMR contained 35 to 50% alfalfa hay and 34 to 43%

TABLE 2. Steam-flaked compared to dry-rolled sorghum grain improves total starch digestion and lactation performance in dairy cows.1 Item

Dry-rolled2

Steam-flaked3

SEM

P ≤4

Comparisons DMI, kg/d Milk, kg/d Protein, % Protein, kg/d Fat, % Fat, kg/d FCM/DMI Starch digestion, total tract, %

24 25.6 35.6 2.95 1.06 3.20 1.14 1.39

24 25.1 37.4 3.02 1.14 3.03 1.14 1.46

... 0.2 0.3 0.01 0.01 0.02 0.01 0.02

... 0.23 0.01 0.01 0.01 0.01 0.90 0.01

83.75

97.15

1.0

0.01

1

Means of 24 comparisons, using 358 cows fed TMR with 35 to 50% alfalfa hay and 35 to 43% grain, in 13 trials (7 to 13 wk/trial; 5 to 12 cows/treatment) (8, 10, 19, 28, 31, 34, 40, 45, 46, 50, 51, 52, 58). 2 Dry-rolled through 46 × 76 cm rollers to coarsely ground consistency with a density of ∼644 g/L (∼50 lb/bu). 3 Steamed for 40 to 60 min at atmospheric pressure in vertical steam chamber to raise moisture level to ∼18 to 20%, then flaked through 46 × 76 cm rollers to density of ∼360 g/L (∼28 lb/bu). 4 Based on analysis of variance with treatments and comparisons as main effects. 5 Determined for 17 comparisons, using Cr2O3 ratio technique. Journal of Dairy Science Vol. 82, No. 9, 1999

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TABLE 3. Steam-flaked corn (SFC) and steam-flaked sorghum (SFS) grain are equal in lactation performance by dairy cows.1 Item

SFS2

SFC2

SEM

P ≤3

Comparisons DMI, kg/d 3.5% FCM, kg/d FCM/DMI Milk, kg/d Protein, % Protein, kg/d Fat, % Fat, kg/d Starch digestion, total tract, %

3 25.9 34.6 1.35 36.5 2.96 1.08 3.19 1.16

3 26.1 34.4 1.33 36.9 3.00 1.10 3.11 1.14

... 0.5 1.2 0.03 1.3 0.04 0.05 0.07 0.04

... 0.82 0.93 0.69 0.84 0.58 0.71 0.45 0.81

98.6

97.9

1.0

0.86

1

Means of three comparisons, using 44 cows in two trials (10 to 13 wk/trial; 6 to 8 cows/treatment) fed TMR with 34 to 41% alfalfa hay and 37 to 40% grain (10, 48). 2 Steamed for 40 to 60 min at atmospheric pressure in vertical steam chamber to raise moisture level to ∼18 to 20%, then flaked through 46 × 76 cm pre-heated rollers to density of ∼360 g/L (∼28 lb/bu). 3 Based on analysis of variance with treatments and comparisons as main effects.

grain, and usually 6 to 8% soybean meal. Lactational performance data from three other trials are included in the text. In six comparisons (4 trials; Table 1) with 92 lactating cows, SF28 (referring to FD in lb/bu) compared to SR38 corn increased total starch digestion by 9% (96 vs. 87%), milk yield by 6%, 3.5% FCM by 1.0 kg/d, milk protein content by 0.07 percentage units, and protein yield by 8%. Steam-flaking decreased percent milk fat by 4%, but not milk fat yield, DMI, or FCM/DMI. In one other study (13), feeding SF28 compared to cracked corn increased milk yield by 5%, but not FCM, milk fat or milk protein yield, when dairy cows were fed a TMR with corn silage and alfalfa silage. Additional studies are needed with cows fed SF corn in TMR containing corn silage and alfalfa haylage or silage. Perhaps lighter FD of SF corn (i.e., SF22) may be more effective than SF28 in TMR with low levels of SF grain (< 25% DM), as is often the case with diets containing silage or by-products. Chen et al. (9) found that substitution of 15% of SF22 sorghum for equal amounts of a concentrate mix containing SR corn, DR barley, and by-products increased milk yield over that with 15% of SF28. The improved performance of dairy cows fed SF corn is similar to the cow response to SF sorghum. In 24 comparisons (13 trials) with 358 lactating cows, SF28 compared to DR sorghum grain increased milk yield and efficiency by 5%, milk protein content by 0.07 percentage units, and milk protein yield by 8% (Table 2). The SF sorghum did not alter DMI nor milk fat yield, but decreased percent milk fat by 5%. The latter response of decreasing milk fat percentage, but not yield, has been consistent in both corn and sorghum studies. Journal of Dairy Science Vol. 82, No. 9, 1999

In 17 comparisons, SF sorghum increased total starch digestion by 16% compared to DR sorghum (97 vs. 84%; Table 2). Total starch digestion was positively correlated with milk yield (r2 = 0.49) and milk protein yield (r2 = 0.57), and negatively correlated with milk fat content (r2 = –0.62; data not shown). The lactational performance of cows fed roasted or SF sorghum grain was similar (19). The increase in percent milk protein by feeding SF corn or sorghum is not because of increased milk NPN. With corn, the concentration of milk urea N was lowest for SF compared to cracked corn (13). Milk urea N content was lower for SF sorghum than for DR sorghum, and conversion of dietary protein to milk protein and to casein N were also higher for SF than for DR sorghum (45, 46). Steam-flaked sorghum grain is equal to SF corn, as measured by lactational performance and starch digestibility of 44 dairy cows in three comparisons (Table 3). Means were essentially the same for DMI, efficiency (FCM/DMI), and yields of milk, protein, and fat. Cows fed diets with SF28 sorghum compared to SR38 corn produced higher milk protein content (2.99 vs. 2.92%), 6% more protein yield (1.07 vs. 1.01 kg/d), and had similar milk fat yields in four studies (10, 34, 47, 48). Although digestibility studies have been conducted with SF compared to DR barley and SR compared to DR wheat (discussed later), lactation trials to determine the value of these SF or SR grains have not been published. Efficiency (FCM/DMI), but not milk yield, was greater for cows fed SF28 sorghum grain than for cows fed DR barley or DR sorghum (46). Based on one study of lactational performance (62), optimal FD for steam-processed corn grain appears to be about SF28. Optimal FD may differ between lactation trials and digestibility trials. Optimal FD based on digestibility studies appears to be SF24 to SF30 (309 to 386 g/L; 23, 38, 62). In these studies SF24 was superior to SF30; SF25 (322 g/L) and SF30 were superior to SF20 (257 g/L); and SF28 was superior to SF24, respectively. Optimal FD for steam-processed sorghum grain based on lactational performance appears to be about SF28 to SF34 (360 to 438 g/L; 28, 45, 46). In these studies, SF31 (399 g/L) was superior to SF21 (270 g/ L); SF22 (283 g/L) and SF28 were superior to SF34; and SF22, SF28 and SF34 were about equal. Feeding lactating cows very light FD (SF21 or SF22) of sorghum grain has decreased DMI, milk or FCM yield, or efficiency (28, 45,46). These decreases in cow performance with light FD agree with decreases in DMI and daily gain by feedlot beef cattle fed SF sorghum or corn (41, 53, 59, 61, 65); optimal FD was SF28 to SF30. No lactation studies have been reported on FD effects of SF or SR barley or wheat.

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As expected from performance responses of cows fed SF versus DR corn, milk yields of cows fed SF corn are superior to yields of cows fed cracked corn in high silage diets (13), or coarsely ground corn in alfalfa-based diets (62). Only one study (62) with lactating dairy cows has been reported comparing SR corn or SF corn with different FD and ground corn with different particle sizes. Efficiency (FCM/DMI) of lactating cows fed TMR (35% alfalfa hay and 40% corn) with finely ground corn was greater than with coarsely ground, SF24, SF28, or SR38 corn (1.39 vs 1.20). This response was because of much lower DMI by cows fed the finely ground diet. The SF28 corn increased milk yield by 8% (37.1 vs. 34.4 kg/d) compared to SF24, SR, or coarsely ground corn, but not the finely ground treatment. Clearly, more studies are needed comparing SF corn with corn ground to various particle sizes in high-silage and alfalfa hay-based diets. RUMINAL AND INTESTINAL STARCH DIGESTION Improvement in lactational performance by feeding SF corn or sorghum grain is due in part to shifts in the proportion of starch digestion in the rumen and intestines of dairy cows. Feeding lactating cows TMR with SF corn or sorghum grain compared to SR corn or DR sorghum improves total starch digestibility by increasing the proportion of dietary starch digested in the rumen and by increasing the digestibility of the smaller amount of starch reaching the intestines. The amount of high quality protein (microbial protein) presented to the small intestine is also increased by feeding SF grains. Experimental protocols were similar for the trials with cows fed corn, and also similar for the trials with cows fed sorghum (Table 4). Thus, statistical analyses for data presented in Table 4 were by analyses of variance (27) with treatments and comparisons as main effects. In three digestibility trials (11, 23, 38), lactating dairy cows fed SF24 to 25 compared to DR corn digested 50% more starch in the rumen (52 vs. 35%), and increased postruminal digestibility of starch (as a percentage of that presented to the intestine) by 50% (93 vs. 61%) and total tract by 25% (97 vs. 78%; Table 4). In these studies, microbial protein flow to the duodenum averaged 18% greater for cows fed SF compared to DR corn (1.23 vs. 1.04 kg/d). Similar responses occurred with lactating cows fed sorghum grain in six comparisons (Table 4). The SF28 compared to DR sorghum grain increased ruminal starch digestibility by 40% (76 vs. 54%) and postruminal digestibility of starch as a percentage of that entering the small intestine by 20% (90 vs. 74%). The SF sorghum also improved, by 10%, both total starch digestibility (98 vs. 89%), and microbial protein flow to

TABLE 4. Steam-flaking of corn or sorghum grain increases ruminal and postruminal starch digestion and microbial protein flow to the duodenum of lactating dairy cows Item Corn4 Comparisons DMI, kg/d Starch intake, kg/d Starch digestibility, % Ruminal Post-ruminal % of intake % of entry Total Microbial protein, duodenal flow, kg/d Sorghum grain5 Comparisons DMI, kg/d Starch intake, kg/d Starch digestibility, % Ruminal Post-ruminal % of intake % of entry Total Microbial protein, duodenal flow, kg/d

Dry-rolled1

Steam-flaked2

SEM

P ≤3

3 18.4 3.4

3 18.8 3.7

... 0.7 0.2

... 0.89 0.85

35

52

1.9

0.03

42 61 77.5

44 93 96.6

3.2 5.2 1.1

0.57 0.05 0.01

0.04

0.08

1.04

1.23

6 22.1 7.0

6 22.4 7.0

... 0.2 0.1

... 0.47 0.69

54

76

0.9

0.01

36 74 88.7

23 90 97.9

1.7 3.8 1.7

0.01 0.04 0.01

0.09

0.11

2.10

2.33

1 Dry-rolled through 46 × 76 cm rollers to coarsely ground consistency with a density of ∼644 g/L (∼50 lb/bu). 2 Steamed for 40 to 60 min at atmospheric pressure in vertical steam chamber to raise moisture level to ∼18 to 20%, then flaked through above pre-heated rollers to density of ∼360 g/L (∼28 lb/bu). 3 Based on analyses of variance with treatments and comparisons as main effects. 4 Means of 3 treatment comparisons, using 12 cows (29.1 kg milk/ d) in 3 trials (11, 23, 38), fed TMR 24 to 40% steam-flaked or dryrolled corn and 40 to 45% alfalfa hay (Latin square design, 3 to 5 cows/treatment) using Cr2O3 ratio technique. 5 Means of 6 treatment comparisons, using 16 cows (26.6 kg milk/ d) in 4 trials, fed TMR noted in Table 2 (Latin square design, 4 cows/ treatment) using Cr2O3 ratio technique (7, 35, 39, 49).

the small intestine (2.33 vs. 2.10 kg/d) compared to DR grain. Five (35, 39, 49) of these six digestibility comparisons were conducted as companion studies to five lactation comparisons (34, 40, 52) reported in Table 2. Correlations were determined between digestibility variables and lactation parameters in these companion studies. Ruminal starch digestibility was positively correlated with total starch digestibility (r2 = 0.67) and milk protein content (r2 = 0.54), but not with milk yield or efficiency. In contrast, postruminal starch digestibility (percentage of starch intake) was negatively correlated with milk protein content (r2 = –0.73). Steamflaking increases starch digestibility within the intestines (as a percentage of starch entering the small intestine); the latter was highly correlated with total starch digestibility (r2 = 0.91), milk yield (r2 = 0.78), FCM yield (r2 = 0.70), FCM/DMI (r2 = 0.76), milk fat content (r2 = –0.80), and yield (r2 = 0.58) and milk protein yield (r2 = Journal of Dairy Science Vol. 82, No. 9, 1999

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–0.80). Most (90 to 95%) postruminal starch digestion in beef steers occurs in the small intestine, and steamflaking increases digestibility of the percentage of starch which is digested in this segment (53, 54, 57, 66, 67). No data was found for lactating cows fed SF grains. Ruminal starch digestibilities for corn diets were 19 to 24 percentage units lower than for sorghum diets, although postruminal digestibilities (percentage of entry) were similar within processing treatments for both grains (Table 4). Total digestibilities for DR corn were lower by 11 percentage units than for DR sorghum. These differences may be because of varying experimental conditions, rather than grain source. Total starch digestibilities for SR corn (Table 1) were similar to DR sorghum (Table 2) when determined in lactational performance studies; steam-rolling may increase total starch digestibility over dry-rolling. Yu et al. (62) reported that total starch digestibility for lactating cows fed SR corn diets was greater than that for coarsely ground corn, which was similar to DR corn (91 vs. 87%). Postruminal starch digestibilities, as a percentage of starch intake, were similar between SF and DR corn (43%); however, postruminal digestibility was lower for SF compared to DR sorghum (23 vs. 36%). These different responses do not agree with beef cattle data. With growing beef steers, postruminal digestibilities (percentage of intake) for both SF corn and SF sorghum were lower than DR corn or DR sorghum (3, 54, 57, 66, 68). We conclude that increasing the proportion of starch digested in the rumen versus postruminally benefits lactating cows by improving performance. In his review, Huntington (21) concluded that both the steer and cow will benefit more from a supply of readily fermented starch than from an increased supply of starch that escapes ruminal fermentation. Ruminal digestibility of starch was greater for SF30 and SF20 barley than for DR barley fed to lactating cows in 40% grain diets (37); however, total tract starch digestibilities were not altered by grain processing. The authors concluded that flaking barley to very light FD may have a detrimental effect on feed intake and nutrient digestion. With lactating cows fed diets containing 20% wheat, the ruminal, postruminal, and total tract starch digestibilities were not altered by feeding SR versus DR wheat (15). With diets containing 21% grain and 52% silage (corn and alfalfa), total tract digestibilities of total nonstructural carbohydrate by lactating cows were not altered when fed SF compared to cracked corn (92 vs. 89%; 13). Only about 50% of the dietary corn (SF plus corn silage) was steam-processed in this study. Steam-flaking of corn or sorghum or steam-rolling of barley or wheat did not consistently alter CP digestibility by lactating cows (10, 11, 15, 23, 31, 34, 35, 37, 38, 39, 45, 48, 49, 50, 51, 52). Although not usually Journal of Dairy Science Vol. 82, No. 9, 1999

significant, ruminal and total tract digestibilities of ADF and NDF were decreased by an average of 22% (11, 13) and 16% (10, 11, 13, 23, 38, 48, 62), respectively, for lactating cows fed SF compared to DR, coarsely cracked, or SR corn. Ruminal and total digestibilities of fiber were not consistently altered by feeding SF versus DR sorghum (8, 10, 28, 34, 40, 45, 50, 51, 52) or barley (37), or SR versus DR wheat (15). Although ruminal fiber digestibility was not significantly affected, it averaged 14% less for SF versus DR sorghum in site of digestion trials (35, 39, 49). More studies on the effect of feeding SF grains on ruminal NDF and ADF digestibilities need to be conducted to clarify the impact of steam-flaking on ruminal fiber digestibilities. We conclude that total CP and fiber digestibilities are not consistently altered by feeding SF grains. NET ENERGY LACTATION VALUES FOR STEAM-FLAKED GRAINS The NEL values for SF corn and sorghum grain are increased about 20% compared to DR and SR corn or DR sorghum. Based on the NRC (30) NEL values for DR (cracked) corn of 1.84 Mcal/kg, the estimated NEL values for SF corn of 2.17 (SF28) and 2.44 Mcal/kg (SF25 and 30; Table 5) are increased 18 and 33%, respectively. These increases are much greater than the 11% improvements for SF compared to cracked corn derived from NRC values (2.04 vs 1.84 Mcal/kg). Clearly, the NRC (30) value for SF corn greatly underestimates the estimated NEL values for SF corn (2.04 vs. 2.17 or 2.44 Mcal/kg). The NEL of SF corn (2.17 Mcal/ kg) increased by 5% over the NEL (2.07 Mcal/kg) for SR corn, which was 12% greater than the NRC (30) value (1.84 Mcal/kg) for cracked (DR) corn (10; Table 5). Similarly, the NEL values for SF (2.08 to 2.21 Mcal/ kg) compared to DR sorghum (1.84 Mcal/kg) (30) were increased by 13 to 20% (Table 5). Mean estimated NEL for SF sorghum is 2.15 Mcal/kg. There are no NEL values for flaked sorghum in the NRC (30) for dairy cattle. The benefits of steam-flaking corn or sorghum, compared to dry-rolling or cracking of the grains, may be greater for dairy (Table 5; average increase of 25 and 17% for corn and sorghum) than beef cattle (average increase of 14 and 12% for corn and sorghum) (3, 29, 64, 68). The increase in NEL values for SF corn are based on only two widely different estimates (one from lactational performance and one from digestibility of GE), and may overestimate the nutritive value of SF corn for lactating cows. The SF28 corn and SF28 sorghum NEL values of 2.17 and 2.14 Mcal/kg, respectively (Table 5) were obtained within the same trial; thus, NEL values for SF corn and SF sorghum may be similar. Plascencia

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et al. (37) reported that the metabolizable energy of SF barley was 13% greater than DR barley, based on GE digestibilities. We recommend that the NEL values listed in the next revision of the NRC (30) for dairy cattle be: for SF corn, at least 2.17 Mcal/kg of DM, unless more studies are conducted to more clearly define this value; for SF sorghum, 2.15 Mcal/kg of DM. POSTABSORPTIVE METABOLISM Net absorption of nutrients is not consistently altered by steam-flaking; however, steam-flaking alters partitioning of nutrients by gut, liver, and mammary tissues to enhance lactational performance. Feeding alfalfahay based TMR with 40% SF corn or sorghum grain compared to 40% SR corn or DR sorghum to lactating dairy cows does not consistently alter net absorption across gastrointestinal tissues (portal-drained viscera) of α-amino N, glucose, L-lactate, acetate, propionate, n-butyrate, and β-hydroxybutyrate (14, 44). Steamflaking markedly increases net cycling (transfer) of blood urea to the gut, net splanchnic (gut plus liver) output of L-lactate, and estimated net mammary uptake of α-amino N (estimate of amino acid N). Net hepatic uptake of L-lactate is markedly decreased, and net mammary uptake of propionate and β-hydroxybutyrate are increased with SF grains.

Lactating cows fed SF28 corn or sorghum grain compared to SR38 corn or DR sorghum increased net cycling (transfer) of blood urea N to the gut (portal-drained viscera) by 80% (Table 6). This marked increase is probably due to the increased amount of starch that was digested in the rumen with SF versus SR or DR grains (Table 4). Most of the blood urea N cycled from the liver to the gut is transferred across the rumen wall of steers fed high-grain diets containing SF or DR sorghum (56) or ground or cracked corn (20, 22, 42). Greater transfer of urea (synthesized by the liver) to the gut conserves loss of dietary N, because cycled urea can be utilized by rumen microorganisms to increase microbial protein synthesis and flow of high-quality protein to the small intestine (1). This explains, in part, the increased flow of microbial N to the duodenum of cows fed SF grains (Table 4). Efficiency of ruminal N metabolism may be enhanced by steam-flaking. Ruminal concentrations of ammonia N have often been lower with SF corn or sorghum compared to SR corn and DR corn or sorghum (7, 11, 13, 28, 34, 40, 49). Other researchers have reported no effect of SF corn or sorghum and SR wheat on ammonia N levels (15, 23, 38). Net mammary uptake of α-amino acid N was increased by almost 40% when cows were fed SF compared to SR or DR grains, even though steam-flaking tended to decrease by 17% the net output of α-amino

TABLE 5. Steam-flaking improves NEL of steam-flaked grains for lactating dairy cows. Grain Citation

Flake density1

Dry-rolled or cracked

Steamrolled

Steamflaked

Increase2 (%)

2.04 2.173 2.445

11 184 33

… 2.083 2.165 2.143 2.213

… 13 17 16 20

NEL, Mcal/kg DM Corn NRC (30) Chen et al. (10) Plascencia and Zinn (38) Sorghum NRC (30) Theurer et al. (60) Theurer et al. (60) Chen et al. (10) Simas et al. (51)

1.84 2.073

SR38, SF28 SF25, SF30 1.84 SF28 SF28 SF28 SF28

1 Flake density: SR38 = steam-rolled at density of 489 g/L (38 lb/bu); SF25, SF28, SF30 = steam-flaked at density of 322, 360, and 386 g/L, respectively (25, 28, and 30 lb/bu). 2 Percentage increase of estimated NEL value for steam-flaked corn or sorghum compared to the NRC (30) NEL value for cracked (dry-rolled) grain or dry-rolled sorghum. 3 Determined from lactation performance studies. Diet NEL (Mcal/kg) was estimated from maintenance requirements, BW change, daily FCM yield, and DMI, using established energy relationships (30). Diet differences were assumed to be totally attributable to the grain. Percentage increase for steam-flaked compared to steam-rolled or dry-rolled grain was determined based on calculations by Plascencia and Zinn (38). 4 Increase for estimated NEL for steam-flaked corn compared to the estimated NEL for steam-rolled corn, based on NEL differences between SF and SR diets, was 5%. 5 Determined from digestibility studies. Diet NEL values (Mcal/kg) were estimated from diet DE values using established relationships (30). Diet differences were assumed to be totally attributable to the grain. Percentage increase for steam-flaked compared to dry-rolled grain was determined based on calculations by Plascencia and Zinn (38).

Journal of Dairy Science Vol. 82, No. 9, 1999

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THEURER ET AL. TABLE 6. Steam-flaked corn or sorghum grain compared to steam-rolled corn or dry-rolled sorghum increases urea cycling to the gut and alters net nutrient uptake or output by hepatic, splanchnic, and mammary tissues of lactating dairy cows1,2 Item Urea N cycled to gut, g/d Net absorption from gut α-Amino acid N, g/d Glucose, g/d L-lactate, g/d Acetate, mol/d Propionate, mol/d n-Butyrate, mol/d β-Hydroxybutyrate, mol/d Net hepatic metabolism Urea-N synthesis, g/d α-Amino acid N uptake, g/d Glucose synthesis, g/d L-lactate uptake, g/d Acetate synthesis, mol/d n-Butyrate uptake, mol/d Propionate uptake, mol/d β-Hydroxybutyrate synthesis, mol/d Net splanchnic (gut + liver) output Urea N, g/d α-Amino acid N, g/d Glucose, g/d L-lactate, g/d Acetate, mol/d Propionate, mol/d n-Butyrate, mol/d β-Hydroxybutyrate, mol/d Net mammary uptake6 Urea N, g/d α-Amino acid N, g/d Glucose, g/d L-lactate, g/d Acetate, mol/d Propionate, mol/d n-Butyrate, mol/d β-Hydroxybutyrate, mol/d

Dry-rolled3 or steam-rolled4

Steamflaked4

SEM

P5

102

187

48

0.07

268 105 427 37.4 15.1 2.8 7.1

244 119 454 38.0 16.8 2.6 5.5

25 85 28 2.0 1.1 0.2 1.1

0.40 0.91 0.51 0.84 0.31 0.46 0.30

336 –138 2,739 –258 3.5 –2.2 –14.3 4.6

353 –163 2,938 –69 –0.1 –2.2 –16.5 4.4

68 31 236 52 4.9 0.2 1.3 1.8

0.79 0.44 0.57 0.03 0.62 0.80 0.28 0.95

226 149 2,718 195 42.6 1.3 0.7 13.3

203 123 3,037 378 41.3 2.5 0.6 10.0

44 23 217 69 5.6 0.8 0.1 2.2

0.62 0.11 0.32 0.10 0.86 0.28 0.64 0.32

–5 –61 –1,609 –68 – 11.4 –0.21 –0.05 –2.2

–9 –84 –1,726 –94 – 11.7 –0.27 –0.05 –2.7

18 5 57 13 0.5 0.02 0.01 0.2

0.64 0.01 0.16 0.19 0.58 0.09 0.91 0.03

1 Adapted from Delgado-Elorduy (14) and Sadik (44). Means for 6 cows (12 daily observations per cow) for urea N cycling, and for net absorption and mammary values; means for 4 cows (8 daily observations per cow) for liver metabolism and splanchnic output. 2 Positive means indicate net cycling, absorption, synthesis, or output; negative means indicate uptake by liver or mammary tissues. 3 Dry grain was passed through 46 × 76 cm rollers to a coarsely ground consistency with a density of ∼644 g/L (∼50 lb/bu). 4 Steamed for 40 to 60 min at atmospheric pressure in vertical steam chamber to raise moisture level to ∼18 to 20%, then flaked through above pre-heated rollers to densities of ∼360 g/L (∼28 lb/bu, steam-flaked corn or sorghum) or ∼489 g/L (∼38 lb/bu, steam-rolled corn). 5 Based on analyses of variance with grain source (trial), cows, and processing treatments as main effects. The interaction of grain source by processing treatment was significant for only one variable, net mammary uptake of glucose. 6 Estimated from measured arterio-venous differences times estimated mammary blood flow of 600 L/h (based on measured mammary blood flow [L/d] to milk yield [kg/d] ratio of 506:1 [4, 24, 25, 26]).

acid N from splanchnic tissues (Table 6). Thus, mammary uptake may not be controlled principally by availability of amino acids. This marked increase in mammary uptake of amino acid N can explain the increase in concentration and yield of milk protein by cows fed flaked grain (Tables 1 and 2). Journal of Dairy Science Vol. 82, No. 9, 1999

Steam-flaking did not consistently increase net absorption of nutrients or net hepatic metabolism, splanchnic (gut and liver) output, and mammary uptake of glucose, acetate, or n-butyrate (Table 6). Feeding SF grains increased estimated mammary uptake of propionate and B-hydroxybutyrate. Grain processing

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treatments did not alter postabsorptive metabolism of 2-methylbutyrate, iso-butyrate, or valerate (44). Net absorption of glucose was very small (0.1 kg/ d) by cows fed SF corn and sorghum, SR corn, or DR sorghum, compared to hepatic synthesis of glucose (2.8 kg/d; Table 6). Glucose is extensively utilized by bovine ruminal (18) and intestinal tissues (32, 33); thus, very little glucose is absorbed into portal blood. Net hepatic synthesis and splanchnic output of glucose were numerically increased by SF compared to SR and DR grains by 7 and 12%, respectively. Net mammary uptake of glucose was increased with SF corn, but not with SF sorghum, and daily splanchnic (gut and liver) output of glucose (3.0 kg) was double the daily milk lactose production (1.4 kg; 44). Net uptake of L-lactate by the liver was markedly lower and splanchnic output was greater for cows fed SF28 corn or sorghum versus SF38 corn or DR sorghum (Table 6). Decreased L-lactate uptake by the liver of cows fed SF corn or sorghum grain may be because of greater net absorption of propionate. The reverse relationship for relative utilization of propionate and L-lactate for hepatic gluconeogenesis in ruminants is well documented (2, 5, 6, 12). Concentrations of VFA (especially propionate) in rumen fluid are increased in cows fed SF corn or sorghum grain (7, 11, 28, 34, 38, 40, 49). Net absorption of propionate was increased by 25% in lactating cows fed SF sorghum, but not when cows were fed SF corn (44). In summary, feeding lactating dairy cows SF corn or sorghum compared to SR corn or DR sorghum consistently shifted a greater proportion of starch digestion to the rumen. This results in increased total starch digestibility, cycling of urea to the rumen, microbial protein reaching the small intestine, and estimated amino acid uptake by the mammary gland. Steam-flaking also changed postabsorptive metabolism of glucose, L-lactate, propionate, and β-hydroxybutyrate. CONCLUSIONS Steam-flaking of corn or sorghum grain compared to steam-rolling of corn or dry-rolling of sorghum improves performance by lactating dairy cows, particularly milk and milk protein yields, without decreasing milk fat yield. This occurs because of greater ruminal and total starch digestion by cows fed SF grain, resulting in greater cycling of urea to the gastro-intestinal tract and increased estimated uptake of amino acids and other nutrients by the mammary gland. Lactation studies to determine the value of steam-flaked or steam-rolled barley or wheat have not been reported. Clearly, more lactational performance studies with dairy cows need to be conducted to clarify the value of steam-flaking or

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steers fed diets containing 77% dry-rolled (DR)or steam-flaked (SF) sorghum grain. J. Anim. Sci. 68(Suppl. 1):539.(Abstr.) Theurer, C. B., O. Lozano, A. Alio, A. Delgado-Edorduy, M. Sadik, J. T. Huber, and R. A. Zinn. Steam-processed corn and sorghum grain flaked at different densities alters ruminal, small intestinal, and total tract digestibility of starch by steers. J. Anim. Sci. In press. Theurer, C. B., J. S. Oliveira, Z. Wu, J. T. Huber, R. S. Swingle, M. H. Poore, R. C. Wanderley, M. Arana, J. Sullivan, M. Denigan, and A. Al-Dehneh. 1991. Steam flaking with two dietary grain levels improves digestible starch intake and performance by lactating cows. J. Dairy Sci. 74(Suppl. 1):246.(Abstr.) Theurer, C. B., R. S. Swingle, R. C. Wanderley, R. M. Kattnig, A. Urias, and G. Ghenniwa. 1999. Sorghum grain flake density and source of roughage in feedlot cattle diets. J. Anim. Sci. 77:1066–1073. Theurer, B., Z. Wu, S. Swingle, T. Huber, R. Wanderley, M. Poore, J. Oliveira, K. Chen, C. DeCorte, G. Alhadhrami, J. Simas, and M. Pessarakli. 1991. Steam-flaking sorghum grain improves diet digestibilities and net energy lactation. J. Dairy Sci. 74(Suppl. 1):245.(Abstr.) Xiong, Y., S. J. Bartle, and R. L. Preston. 1991. Density of steamflaked sorghum grain, roughage level, and feeding regimen for feedlot steers. J. Anim. Sci. 69:1707–1718.

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62 Yu, P., J. T. Huber, F.A.P. Santos, J. M. Simas, and C. B. Theurer. 1998. Effects of ground, steam-flaked, and steam-rolled corn grains on performance of lactating cows. J. Dairy Sci. 81:777– 783. 63 Yu, P., J. T. Huber, C. B. Theurer, K. H. Chen, L. G. Nussio, and Z. Wu. 1997. Effect of steam-flaked or steam-rolled corn with or without Aspergillus oryzae in the diet on performance of dairy cows fed during hot weather. J. Dairy Sci. 80:3293– 3297. 64 Zinn, R. A. 1987. Influence of lasalocid and monensin plus tylosin on comparative feeding value of steam-flaked versus dry-rolled corn in diets for feedlot cattle. J. Anim. Sci. 65:256–266. 65 Zinn, R. A. 1990. Influence of flake density on the comparative feeding values of steam-flaked corn for feedlot cattle. J. Anim. Sci. 68:767–775. 66 Zinn, R. A. 1990. Influence of steaming time on site of digestion of flaked corn in steers. J. Anim. Sci. 68:776–781. 67 Zinn, R. A. 1991. Comparative feeding value of steam-flaked corn and sorghum in finishing diets supplemented with or without sodium bicarbonate. J. Anim. Sci. 69:905–916. 68 Zinn, R. A., C. F. Adams, and M. S. Tamayo. 1995. Interaction of feed intake level on comparative ruminal and total tract digestion of dry-rolled and steam-flaked corn. J. Anim. Sci. 73:1239– 1245.

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