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Technical Bulletins

Effect of Processed Grain Sorghum and Expeller Soybean Meal on Performance of Lactating Cows1

Evan C. Titgemeer and John E. Shirley 2
Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506-1600

ABSTRACT

Forty-four Holstein cows were used to measure milk production responses to dry-rolled versus pelleted grain sorghum and expeller versus solvent soybeal meal in a 2 x 2 factorial arrangement of treatments. Pelleted grain sorghum was processed by grinding, increasing moisture to 31%, extruding, and drying to an exit temperature of 93 degrees C. Grain sorghum was included in the diets at 27% of dry matter, and soybean meal was the primary source of supplemental protein. Few interactions were observed between the methods of processing grain sorghum and sources of soybean meal. Pelleting of grain sorghum decreased dry matter intake 5%, but increased milk production 3%, protein yield 4%, and efficiency 7%; fat yield was unaffected. Replacement of solvent soybean meal with expeller soybean meal had little effect on intake, but increased milk production 3%, fat yield 5%, and efficiency 4%; protein yield was unaffected. Plasma concentrations of amino acids (AA) were increased by pelleted grain sorghum and by expeller soybean meal at 5 and 10 weeks after initiation of treatment, indicating that both of these treatments increased the supply of AA to the intestine. Pelleting improved the nutritive value of grain sorghum for lactating cows. Although total milk production and fat yield increased in response to expeller soybean meal, the lack of response in protein yield to this increased supply of RUP indicated that the effect was not solely due to an increased supply of AA to the intestine.
(Key words: expeller soybean meal, grain sorghum, lactating cows)
Abbreviation key: SBM = soybean meal.

Received January 8, 1996.
Accepted August 2, 1996.
1Contribution Number 96-258-J from the Kansas Agriculture Experiment Station.
2For correspondence.

INTRODUCTION

Grain sorghum is a feed resource available to many dairy producers in the Midwest that often is less expensive than other grains, such as corn. Although minimally processed grain sorghum (ground or dry-rolled) has a lower energy value than competing grains, such as corn and barley, grain sorghum has been shown to respond more dramatically to extensive processing procedures, such as steam-flaking, than other cereal grains (15). Thus, steam-flaked grain sorghum is approximately equal to corn (either steam-rolled or steam-flaked) for supporting lactation in dairy cows (5). Although steam-flaking improves the nutritive value of grain sorghum, the equipment necessary for this process requires a large initial investment. An alternative method for processing grain sorghum involves heating in a moist environment, followed by drying to a low moisture suitable for long-term storage. This process can be accomplished with an extruder and a drying oven. Little is known about the effectiveness of this processing method, but the lower initial investment required for its operation may justify its use by dairies with access to grain sorghum.

Protein supplementation of dairy cows is becoming increasingly sophisticated. Yet, in many cases, the relationship between protein intake and performance is defined poorly. Total AA supply to cows may be increased either by increasing microbial protein supply or by increasing the RUP content of diets. Processing cereal grains would be expected to increase microbial protein yield as energy availability in the rumen is increased (11). Processing soybeans under conditions in which heat is generated [i.e., expeller soybean meal (SBM)] also would increase AA supply to the dairy cow by increasing the RUP fraction (3).

The objectives of our experiments were 1) to evaluate a new processing method for grain sorghum and 2) to determine whether protein needs of dairy cows that were fed diets containing the pelleted grain sorghum and supplemented with solvent SBM would be better met if additional RUP were supplied by replacing solvent SBM with expeller SBM.

MATERIALS AND METHODS

Production and Evaluation of Pelleted Grain Sorghum

Pelleted grain sorghum products were manufactured by grinding, adding water, processing through an extruder, and drying. Grain sorghum, purchased from a commercial elevator, was ground finely (4.8-mm screen) at the Kansas State University feed mill and transported to the JET-PRO processing facility (Atchison, KS) for final processing. Water was added to the ground grain sorghum to achieve a moisture content of 31% immediately prior to processing through an extruder. The pellets then were raised to a temperature of 93 degrees C by passing them through an oven (153 degrees C) with a total passage time of 3.6 min. The resultant product was a pellet of approximately 5% moisture and with moderate stability during handling.

To determine optimal moisture during pelleting and optimal temperatures during drying, a series of products was manufactured with moisture (prior to extrusion) of 25, 28, and 31%. Pellets created at each of these moisture percentages then were dried by adjusting oven temperature and retention time such that exit temperatures were 82, 93, 104, 116 and 127 degrees C. Digestibility of these grain sorghum pellets was evaluated using an in vitro assay similar to that of Hibberd et al. (7) Samples (0.5 g) were placed in tubes with 30 ml of medium composed of three parts McDougall's buffer and one part ruminal fluid from a steer fed 60% grain sorghum, 22% alfalfa, and 16% SBM. Duplicate samples and blank tubes were incubated anaerobically at 39 degrees C for 6 and 24 h. Following incubation, samples were centrifuged at 25,000 x g for 10 min, the supernatant was decanted, and the tubes were dried at 70 degrees C.

Production and Evaluation of Expeller SBM

A series of expeller SBM products was manufactured commercially using heat inputs provided by a precooker (6 min; 52 degrees C), an expander (1 min; 93 degrees C), a continuous flow stack cooker (four stages; 15 min each), and the expeller. Four products were generated with decreasing heat inputs from the flow cooker; temperatures for the four products upon exit from the four stages of the flow cooker and the expeller were SBM 1 (113, 118, 131, 139, and 150 degrees C), SBM 2 (110, 118, 127, 135, and 146 degrees C), SBM 3 (96, 104, 113, 121, and 132 degrees C), and SBM 4 (85, 93, 102, 110, and 121 degrees C). An additional expeller SBM (SBM 5) was produced without the expander; temperatures upon exit from the four stages of the flow cooker and expeller were 110, 118, 129, 137 and 148 degrees C. Unextracted soybeans that were roasted using the precooker and flow cooker (exit temperatures of 118, 127, 135, and 143 degrees C) also were evaluated. All products were either cooled immediately or steeped at the exit temperature for 30 min. Steeping was performed by placing the product in an insulated box capable of holding about 20 kg.

Ruminal degradability of protein in samples was estimated using the inhibitor in vitro system described by Broderick (4); total AA were measured using a trinitrobenzenesulfonic acid assay (Technicon industrial method number 512-77T; Technicon Instruments Corp., Tarrytown, NY) rather than the ninhydrin assay. Use of this trinitrobenzenesulfonic acid assay has determined that concentrations of AA in protein hydrolysates of SBM are similar to those reported by Broderick (4) using the ninhydrin analysis. Tubes were not incubated (0 h) or were incubated for 2 h, and degradation rates for the potentially degraded fraction were calculated assuming first-order kinetics. The soluble fraction was estimated using solubility at 0 h. The undegradable fraction was estimated as ADIN. Estimated escape was calculated as described by Broderick (4) using a fractional passage rate from the rumen of 0.06/h.

Production Trial

Forty-eight Holstein cows (24 primiparous) averaging 95 DIM (range, 45 to 118) were allotted by age, milk production, and DIM to one of four dietary treatments. Treatments were arranged in a 2 x 2 factorial; treatments were dry-rolled versus pelleted grain sorghum and solvent versus expeller SBM.

Diets (Table 1) were formulated such that the pelleted grain sorghum was substituted directly into diets at the expense of dry-rolled grain sorghum. Expeller SBM was used as a replacement for solvent SBM. Because the expeller SBM contained a greater amount of residual fat than did the solvent SBM (8.5 vs. 1.5% of DM), diets were balanced to maintain equal concentrations of lipid by decreasing the amount of supplemental tallow.

Diets were formulated to meet or exceed the needs of 636-kg dairy cows producing 32 kg/d of 3.5% FCM for all nutrients (9). For diets containing solvent SBM, RUP was estimated at 35% of total protein. Although recommended (9) intakes of RUP (grams per day) were exceeded by this diet, the proportion of total CP accounted for as RUP was below that used to estimate RUP requirements (9). Diets containing expeller SBM were estimated to contain 40% of total protein as RUP.

Cows were fed a common diet for 2 weeks prior to initiation of the study in order to collect data for covariable adjustment of production data. Cows then were fed experimental diets for 13 weeks. Cows were maintained in tie stalls and had ad libitum access to feed that was supplied twice daily as a total mixed diet. Orts were weighed daily. Cows were milked twice daily, and samples were collected from both milkings on 1 d/wk to measure milk composition. Milk protein, fat, lactose, SNF, and SCC were determined by the DHIA Laboratory (Manhattan, KS).

Four cows were removed from the study because of health problems that did not appear to be related to treatment; 2 cows were fed the treatment including pelleted grain sorghum and solvent SBM, and 2 were fed the treatment including pelleted grain sorghum and expeller SBM. Three other cows missed observations for a portion of the trial because of temporary health problems that also did not appear to be related to treatment.

Cows were weighed and scored for body condition weekly. Condition scores were based on a five-point scale (18) ranging from 1 = very thin to 5 = excessively fat. Blood samples were collected from the coccygeal vein during wk 5, 10, and 13 to measure total AA (trinitrobenzenesulfonic acid assay) and urea (diacetyl-monoxime assay; Technicon industrial method number 339-01) concentrations in plasma.

Statistical Analyses

The in vitro assay with grain sorghum samples was analyzed as a completely randomized design with a ( 3 x 5) + 1 factorial arrangement of factorial arrangement of treatments (three moistures and five temperatures plus the dry-rolled grain sorghum control) using the general linear models procedure of SAS (13). Data from the in vitro assay to evaluate soybean protein degradability were analyzed as a completely randomized design wih a 6 x 2 factorial arrangement of treatments (six products with or without steeping) using the general linear models procedures of SAS (13).

The presence of treatment x week interactions in the production data was evaluated using the mixed procedure of SAS (13) by analyzing data as a repeated measures experiment; weekly observations were considered as the subplot. The model included age (primiparous vs multiparous) and treatment (grain sorghum processing, type of SBM, and the grain sorghum x SBM interaction) in the main plot; cow within age x grain sorghum x SBM was the main plot error term. Subplot terms included week, age x week interactions, and treatment x week interactions. Because week x treatment interactions either were not observed or, in the case of DMI, were considered innocuous, data from those analyses are not presented.

Table 1. Composition of experimental diets.1
Solvent SBM
Expeller SBM
Item
Dry-rolled
GS
Pelleted
GS
Dry-rolled
GS
Pelleted
GS
Ingredient
(% of DM)
Alfalfa
29.6
29.6
29.6
29.6
GS
    Dry-rolled
27.2
...
27.2
...
    Pelleted
...
27.2
...
27.2
SBM
    Solvent
11.4
11.4
...
...
    Expeller
...
...
12.1
12.1
Corn Silage
10.3
10.3
10.3
10.3
Whole cottonseed
8.8
8.8
8.8
8.8
Soybean bulls
6.7
6.7
6.7
6.7
Tallow
1.5
1.5
1.5
1.5
Molasses
1.0
1.0
1.0
1.0
Limestone
1.3
1.3
1.3
1.3
Dicalcium phosphate
0.8
0.8
0.8
0.8
Sodium Bicarbonate
0.8
0.8
0.8
0.8
Magnesium oxide
0.2
0.2
0.2
0.2
Trace-mineralized salt2
0.3
0.3
0.3
0.3
Mineral and vitamin mix3
0.1
0.1
0.1
0.1
Composition4
    CP
18.5
18.5
18.3
18.3
    Fat
5.8
5.8
5.8
5.8
    NDF
34.4
34.4
34.4
34.4
    Ca
1.05
1.05
1.04
1.04
    P
0.50
0.50
0.49
0.49
1 SBM = Soybean meal; GS = grain sorghum.
2 Contained >955 g/kg of NaCl, 2.4 g/kg of Mn, 2.4 g/kg of Fe, 0.5 g/kg of Mg, 0.32 g/kg of Cu, 0.32 g/kg of Zn, 0.07 g/kg of I, and 0.04 g/kg of Co.
3 Provided 8594 IU of vitamin A/kg of diet, 4125 IU of vitamin D/kg of diet, 34 IU of vitamin E/kg of diet, and 0.1 mg of Se/kg of diet.
4 Based on analyses of individual ingredients.

In order to account for several cows with only partial data across time, mean values across week for each individual cow were generated using the general linear models procedure of SAS (13) with a model including age (primiparous vs. multiparous), week, week x age interaction, and cow within age. The least squares means for each cow then were analyzed as a block design; age (primiparous vs. multiparous) was used to create two blocks. Production data collected in the pretrial period were included as covariables. Analysis by the general linear models procedure of SAS (13) used a model including age (i.e., block), the covariable, grain sorghum processing, type of SBM, and the grain sorghum x SBM interaction.

Plasma data were analyzed, and each sampling time was considered to be an independent observation. Analyses were performed using the general linear models procedure of SAS (13) with a model including age (primiparous vs. multiparous), grain sorghum processing, type of SBM, and the grain sorghum x SBM interaction.

Table 2. Invitro DM digestibility (IVDMD) of grain sorghum products generated using different moistures and drying to different exit temperatures.
Moisture
Drying Temperatures
25%
28%
31%
(%)
6-h IVDMD1
    82° C
43.6
48.6
50.3
    93° C
51.6
46.1
52.8
    104° C
49.5
46.8
53.6
    116° C
47.8
49.1
51.3
    127° C
46.5
49.1
50.2
24-h IVDMD2
    82° C
65.9
68.9
76.1
    93° C
...3
60.3
80.4
    104° C
...3
67.8
80.4
    116° C
68.8
67.8
81.4
    127° C
62.3
68.9
82.8
1 The IVDMD of dry-rolled grain sorghum at 6 h = 29.2% (SEM = 6.8; LSD = 19.4).
2 The IVDMD of dry-rolled grain sorghum at 24 h = 63.2% (SEM = 3.7; LSD = 10.6).
3 Samples spilled.

RESULTS AND DISCUSSION

Effect of Processing Characteristics on Pelleted Grain Sorghum

Table 2 shows the in vitro DM digestibilities at 6 and 24 h for products of pelleted grain sorghum generated using different moistures and drying temperatures. At 6 h, in vitro DM digestibility was not affected by either moisture or drying temperature, but treated products were more digestible than was the dry-rolled sorghum. At 24 h, the products manufactured with 31% moisture prior to pelleting were more digestible than those produced with either 25 or 28% moisture. Drying temperature did not affect in vitro DM digestibility at 24 h. Based on the results of the in vitro assay, the product generated at 31% moisture and dried with an exit temperature of 93 degrees C was selected for testing in vivo availability of nutrients for lactating cows.

Effects of Processing on Expeller SBM

Table 3 shows the results of the in vitro evaluation of various soybean products. Steeping had little effect on the products produced; therefore, only main effect means are shown. Steeping of heated soybean products generally increased the resistance of protein to microbial degradation; however, the effect of heat input is a function of both temperature and time. Many roasting operations use only a limited roasting time and, thus, benefits of steeping may be observed. For the products that were tested in our study, the heating process was fairly lengthy (over 1 h); thus, additional time might not have been necessary for completion of heat-catalyzed reactions.

As heat inputs were reduced for the expeller SBM (SBM 1, 2, 3, and 4; Table 3), rates of protein degradation increased, although this effect was significant only for SBM 4. The percentage of N that was estimated to escape ruminal degradation was significantly lower for SBM 3 and SBM 4, which had much lower exit temperatures from the expeller than did SBM 1.

Marginal declines in heat input leading to a decrease in exit temperature from 150 to 146 C had little effect on escape protein content, although ADIN unexplainably was increased. Products manufactured without the use of the expander (SBM 5) had exit temperatures, protein degradation rates, and escape protein contents that were similar to those of products manufactured with the expander when exit temperatures were similar (i.e., SBM 1 and 2). Similarly, roasted whole soybeans contained protein that had degradability estimates that were similar to those of expeller SBM when exit temperatures were similar. In general, the extent of protection of soybean proteins could be predicted from the exit temperature of the product. The generalization by Satter et al. (14) that exit temperatures should be at least 146 C to optimize escape of protein agreed with our data.

Based on the results of the in vitro assay, SBM 1 was selected as the heated soybean product to test in vivo. Although somewhat lower heat inputs generated soybean products that had escape characteristics that were similar to those of SBM 1, oil extraction was reduced, and processing characteristics were not considered to be optimal by plant operators.

Table 3. In vitro degradability of protein from heated soybean meal (SBM) products.
Product1
NPN
ADIN
Kd
Estimated RUP
(% of N)
(% of N)
(/h)
(% of N)
SBM 1 (150°C)
4.2
1.1
0.053a
51.8ab
SBM 2 (146°C)
6.9
7.6
0.073a
53.4a
SBM 3 (132°C)
7.8
2.8
0.086a
40.6c
SBM 4 (121°C)
9.4
2.0
0.185b
24.7d
SBM 5 (148°C)
8.0
0.9
0.070a
45.8abc
RWS (143°C)
7.8
3.0
0.076a
42.9bc
SEM
1.3
0.015
3.1
Not steeped
8.1
2.9
0.085
43.2
Steeped
6.6
2.8
0.096
43.1
SEM
0.8
0.009
1.8
abcd Means in the same column not bearing the same superscript differ (P< 0.05).

1 Products were created by modifying heat inputs during expeller extraction of soybeans. Exit temperature of the product is given in parentheses. Heat inputs were provided by a precooker, an expander, a continuous flow stack cooker, and the expeller. Soybean meals 1, 2, 3, and 4 had different heat inputs from the flow cooker. Soybean meal 5 was produced without the expander. Roasted whole soybeans (RWS) were roasted using the precooker and flow cooker. All products were either cooled immediately or steeped at the exit temperature for 30 min.

In Vivo Evaluation of Pelleted Grain Sorghum and Expeller SBM

Production characteristics of dairy cows fed diets containing either dry-rolled or pelleted grain sorghum and either solvent or expeller SBM are shown in Table 4. The DMI was reduced (P < 0.01) when the pelleted grain sorghum was fed. This reduction was most likely due to the higher available energy content and more rapid fermentation of the pelleted product. Milk production tended to be increased by both the pelleted grain sorghum (P = 0.08) and the expeller SBM (P = 0.14). However, fat content of the milk was reduced by the pelleted grain sorghum when fed in combination with solvent SBM; thus, production of 3.5% FCM was not affected by pelleted grain sorghum. However, FCM did tend (P = 0.07) to be greater for cows receiving expeller SBM than for those receiving solvent SBM. Because pelleted grain sorghum reduced feed intake without depressing FCM, feed efficiency was improved (P < 0.01) 7% when diets containing pelleted grain sorghum were fed. Expeller SBM improved (P = 0.03) efficiency by slightly more than 4%.

Total fat yields were increased (P = 0.08) with expeller SBM, probably from greater milk production rather than from a change in fat percentage. Surprisingly, the higher RUP content of the diets that were created by replacing solvent SBM with expeller SBM led to decreases in protein percentage in milk. However, total protein yield was not affected by protein source. Total protein yield was increased (P = 0.04) by pelleted grain sorghum.

Plasma concentrations of AA N were increased (P < 0.01) during week 5 of the study by the addition of either pelleted grain sorghum or expeller SBM to the diets (Table 5). During week 10, trends were similar for concentrations of plasma AA N, but the magnitude of difference and significance (P < 0.19) were less. In week 13, no treatment differences remained. The higher concentrations of AA in plasma of cows fed diets containing either pelleted grain sorghum or expeller SBM suggest that both of these dietary modifications increaesed AA supply to the small intestine. For expeller SBM, this reflects the higher RUP content generated by heat during processing (Table 3). Pelleting grain sorghum most likely increased intestinal AA supply by increasing ruminal fermentation to starch (Table 2) and, thereby increaseing microbial protien synthesis (11). At all three sampling times, plasma urea concentrations tended to be lowest for cows receiving the diet containing solvent SBM and pelleted grain sorghum; this diet also resulted in the lowest DMI and, therefore, the lowest total N intake.

TABLE 4. Production characteristics of dairy cows fed diets containing either dry-rolled or pelleted grain sorghum (GS)and either solvent or expeller soybean meal (SBM).
Solvent SBM
Expeller SBM
Contrast
Item
GS
GS
GS
GS
SEM
GS
SBM
GS X SBM
––––––––– P ––––––––
BW, kg 589 583 592 589 3.5 0.16 0.18 NS1
Body condition score2 2.26 2.27 2.26 2.19 0.06 NS NS NS
DMI, kg/d 26.4 24.7 25.7 24.9 0.3 <0.01 NS 0.17
Milk, kg/d 30.4 31.8 31.6 32.3 0.6 0.08 0.14 NS
3.5% FCM. kg/d 31.6 31.7 32.6 33.2 0.7 NS 0.07 NS
FCM/DMI 1.20 1.30 1.27 1.34 0.03 <0.01 0.03 NS
Fat
    %
3.80 3.44 3.66 3.72 0.07 0.03 NS <0.01
    kg/d
1.14 1.10 1.16 1.19 0.03 NS 0.08 NS
Protein
    %
3.12 3.16 3.07 3.09 0.02 NS <0.01 NS
    kg/d
0.95 1.01 0.97 0.99 0.02 0.04 NS NS
SCC, cells/µl 70 58 56 87 15 NS NS 0.14
1P > 0.2.
2Five-point scale where 1 = very thin to 5 - excessively fat (18).

General Discussion

Research with both growing and lactating cows clearly indicate that the nutritive value of grain sorghum can be significantly improved by processing. A series of papers from the University of Arizona (5, 8, 10, 12) has compared steam-flaked grain sorghum with dry-rolled grain sorghum included in diets of lactating cows at concentrations near 40% of DM. Across these studies, DMI was decreased 1%, milk production was increased 9%, FCM was increased 5%, protein yield was increased 9%, fat yield was increased 6%, and efficiency was improved 6% when the grain sorghum was steam-flaked than when it was dry-rolled. Moore et al. (8) observed that the extent of grain processing altered the response of lactating dairy cows. More extensive processing of sorghum, from a bulk density of 0.40 to 0.27 kg/L, led to greater decreases in feed intake and eliminated the improvements in production that were associated with processing the grain. However, efficiency was similar between the two densities.

TABLE 5. Plasma total AA N and urea concentrations in dairy cows fed diets containing either dry-rolled or pelleted grain sorghum (GS) and either solvent or expeller soybean meal (SBM).
Solvent SBM Expeller SBM Contrast
Item
Dry-rolled GS
Pelleted GS
Dry-rolled GS
Pelleted GS
SEM
GS
SBM
GS X SBM
Plasma AA N, nM
––––– P –––––
wk 5
2.77
2.99
3.10
3.33
0.08
<0.01
<0.01
NS1
wk 10
2.80
2.96
2.96
3.07
1.10
0.19
0.17
NS
wk13
2.96
3.03
2.99
2.92
0.10
NS
NS
NS
Plasma urea, mM
wk 5
7.47
7.11
7.64
7.74
0.24
NS
0.09
NS
wk 10
7.97
7.13
7.55
7.67
0.22
0.11
NS
0.03
wk 13
7.22
6.98
7.62
7.46
0.27
NS
0.09
NS
1P > 0.2.

In our study, pelleting the grain sorghum depressed feed intake 5%. Using the steam-flaking data from Moore et al. (8) for comparison, this depression indicated that less extensive processing might have been beneficial. The improvement in efficiency that we observed (7%) for cows fed pelleted grain sorghum was similar to that observed for steam-flaking (6%; mean from the four Arizona studies). Thus, the processing method we utilized might be as useful as steam-flaking to improve the nutritive value of gram sorghum. Clearly, further work evaluating less extensive processing is warranted.

Responses to expeller versus solvent SBM resulted from changes in both the protein and lipid composition in the diet. Estimated RUP, as a percentage of dietary DM, increased from 35 to 40% of the diet when expeller SBM replaced solvent SBM. According to NRC (9) recommendations, the concentrations of RUP supplied by all of our diets exceeded the requirements of the cow. However, positive responses to increased dietary RUP content in diets similar to those that were fed in this study have not been uncommon (2, 3, 6, 17).

As more soybean lipid was added to diets with expeller meal, the total fat content was maintained among diets by decreasing the amount of tallow. Thus, the composition of fat in the diet was less saturated for the diets containing expeller SBM. Interestingly, FCM and efficiency were increased 4% when expeller SBM replaced solvent SBM in our diets, but total protein yield was not affected by protein source, which resulted in a decrease in milk protein percentage when the expeller SBM was fed. Similar depressions in milk protein percentage were observed by Broderick (3) when expeller SBM replaced solvent SBM at concentrations similar to those used in our study. It is tempting to speculate that the source of lipid (soybean oils vs. tallow) might be responsible for the lower protein percentage that occurred when expeller SBM was fed. However, in the study of Broderick (3), in which protein percentage also declined in response to replacement of solvent SBM with expeller SBM, fat concentrations were equalized by the addition of soybean oil to the diets. Neither Tice et al. (16) nor Aldrich et al. (1) observed much of an effect of roasting whole soybeans on utilization of fatty acids, suggesting that soybean oil is an appropriate control. Thus, the cause of the decrease in milk protein percentage remains uncertain. The lack of response in protein yield might be explained if the diets containing solvent SBM supplied more than adequate amounts of AA to the cow. However, total protein yield increased in response to grain sorghum pelleting (and presumably an increased AA supply). In addition, concentrations of plasma AA indicated that the diets containing expeller SBM supplied more AA to the cows.

The lower saturation of dietary lipid in diets containing expeller SBM might have been expected to decrease the available energy supplies by inhibiting ruminal fermentation. However, FCM and efficiency were increased by expeller versus solvent SBM, indicating that energy utilization was improved for these diets. The amount of unsaturated fat (soybean oil) that was added by the expeller SBM probably was not sufficient to disrupt normal ruminal fermentation; this theory is supported by the study of Tice et al. (16) in which soybean lipid was fed to cows as whole soybeans in amounts greater than those fed in our study. thus, reasons for the increases in efficiency and fat yield in response to expeller SBM are unclear.

CONCLUSIONS

The processing method that we utilized (grinding, increasing moisture to 31%, extruding, and drying to an exit temperature of 93 degrees C) appeared to improve the nutritive value of grain sorghum for lactating cows. Efficiency was increased 7% when dry-rolled grain sorghum (27% of dietary DM) was replaced with the pelleted grain sorghum. Production by cows also was improved (efficiency increased 4%) when solvent SBM was replaced by expeller SBM. Because total milk protein yield was unaffected, this effect cannot be attributed solely to an increased supply of AA to the intestine.

REFERENCES

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2 Atwal, A. S., S. Mahadevan, M. S. Wolynetz, and Y. Yu. 1995. Increased milk production of cows in early lactation fed chemically treated soybean meal. J. Dairy Sci. 78:595.
3 Broderick, G. A. 1986. Relative value of solvent and expeller soybean meal for lactating cows. J. Dairy Sci. 69:2948.
4 Broderick, G. A. 1987. Determination of protein degradation rates using a rumen in vitro system containing inhibitors of microbial nitrogen metabolism. Br. J. Nutr. 58:463.
5 Chen, K. H., J. T. Huber, C. B. Theurer, R. S. Swingle, J. Simas, S. C. Chan, Z. Wu, and J. L. Sullivan. 1994. Effect of steam flaking of corn and sorghum grains on performance of lactating cows. J. Dairy Sci. 77:1038.
6 Cozzi, G., and C. E. Polan. 1994. Corn gluten meal or dried brewers grains as partial replacement for soybean meal in the diet of Holstein cows. J. Dairy Sci 77:825.
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