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In Vitro Digestibility and Preference by Sheep for Silages Made from Whole-Plant Soybeans1
The Professional Animal Scientist 11 :81-87
InPreference Vitro Digestibility and by Sheep for Silages Made from Whole-Plant Soybeansl K. P. COFFEy2, PAS, G. V. GRANADE3, and J. L. MOYER2 Kansas State University - Southeast Agricultural Research Center, Parsons, KS 67357 University of Georgia, Georgia Experiment Station, Griffin, GA 30223
Abstract
digestibility higher at 24, 48, and 72 h from R2 than R4 and R6 silages (p<.05). Maturity group IV ('Stafford') vs Com silage was preferred (p< .05) to any group V ('Bay') soybean forages were of the soybean silages. Consumption of harvested and ensiled at either full R6 silage was greater (p<.05) than that bloom (R2), full pod (R4), or full seed of R2 and R4 in 1988 and of R4 in (R6) growth stages, with or without a. 1989. Silage consumption was corresilage inoculant and offered to sheep In a lated positively (p<.05) with forage DM consumption experiment having a content; DM yield; molar percentage of balanced incomplete block design. Silage isovaleric and valerie acids; and lactic samples were collected at the time of acid, ethanol, and acid-detergent lignin feeding for in vitro total DM digestibility contents and negatively with acetic, determination. Three sheep were propionic, isobutyric, butyric, and total adapted to ensiled R6 Bay silage, then volatile fatty acid concentrations; molar individually offered a selection of four percentage of propionic and isobutyric different silages (soybean silage combinaacids; pH; and N, Ca, and P contents. tions or com silage) daily for 13 d. Delaying ensiling of whole-plant soyQuantity of each silage was limited to beans until the R6 growth stage some50% of the total daily silage consumpwhat compromises digestibility of the tion. In 1988, the indigestible fraction forage but provides a silage of higher was higher and digestibility at 18, 24, acceptance by sheep. and 72 h was lower from R4 Stafford than from the other cultivar and growth (Key Words: Soybean, Silage, Forage stage combinations (p<.05). In 1989, Quality, Growth Stage, Animal the indigestible fraction was lower and Preference, Intake.)
Introduction 1 Contribution No. 95-159-1 from the Kansas Agricultural Experiment Station, Manhattan, KS 66506.
2Kansas State University. 3University of Georgia. Reviewed by D. C. Anderson and L.
I. Bush.
Although soybeans [Glycine max (L.) Merr.] are grown primarily for
seed production in the United States, adverse weather conditions may cause reduced seed yields or quality. The market price of lower quality soybean seeds often is reduced
severely, forcing the soybean producer to seek alternatives for the crop. Previous research evaluating alternative uses for soybeans has centered upon using whole-plant soybeans as a hay crop (10, 14, 16). Soybeans have been intercropped with corn (3, 6) or sorghum (I, 7, 11) to improve the protein content of a subsequent silage crop, but evaluation of soybeans alone as a silage crop has been limited. In a previous study (5), we evaluated the quality and fermentation characteristics of silages of two different cultivars harvested at three growth stages and ensiled directly or treated with a silage inoculant. The objective~ of . this experiment were to determme m vitro digestibility and preference by sheep of silages from these same treatments.
Materials and Methods Forty-eight four-row plots, 9.1-m in length having a .76-m row spacing, were established in 1988 and . 1989 on separate areas of Parsons SlIt loam soil. Plots were arranged in four blocks of 12 plots each in a randomized complete block design (17) . Half of the plots were seeded to a maturity group IV soybean cultivar ('Stafford'), whereas the remaining plots were seeded to a maturity group
82
Coffey et ai.
TABLE 1. Schedule for offering of silages to sheepa. Bucket no. Day 1988 1 2
3 4
5 6
7 8 9 10
11 12
13
1
2
3
4
B61 B6NI B21 S2NI B4NI B41 B61 S61 S4NI S21 CORN S41 S6NI
S2NI S21 B6NI CORN S61 S61 S41 B41 B21 S6NI B2NI S4NI B4NI
B2NI B4NI S6NI S41 B61 CORN B21 S2NI S21 B61 S4NI B6NI B41
S6NI B2NI CORN B4NI B21 S21 B41 B6NI S2NI S41 S61 B61 S4NI
1989 ..JLI"II
..IV •
C,cl
B2f'-~1
I1A I
B61 B21 S6NI S61 B6NI B61 B21 S41 B6NI S2NI S2NI S41
S4NI B41 S41 S6NI S21 B41 B4NI B4NI S4NI B61 S21 S4NI
S21 S6NI B6NI B4NI B21 B6NI 'CORN B41 S2NI S41 S6NI CORN
B2NI S4NI B2NI B61 S61 CORN B2NI S21 B4NI B21 CORN S61
(,'''1'Ir.1I
2
3 4
5 6
7 8
9 10 11 12
13
U""T'
aSilage treatment codes are as follows: Cultivar: B = Bay, S = Stafford; Growth stage: 2 = R2, 4 = R4, 6 = R6; Inoculant: I = inoculant, NI = no inoculant.
~
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _
I
~
adaptation period was used as a basis to limit the offering of each silage to no more than 50% of the total daily OM consumption. This was done to ensure that distinctions were made between silages of lower palatability. Sheep had ad libitum access to fresh water and a commercial sheep mineral throughout the feeding study. Fresh silage samples were collected at the time of feeding, dried at SOCC, and ground (1 mm) for in vitro digestibility analyses after allowing a minimum of 72 h for equilibration to atmospheric moisture. Sample OM was determined by drying overnight at 105°C. In vitro OM digestibilities were determined at 6, 12, 18, 24, 48, and 72 h of incubation by the procedures of Van Soest et al. (18) modified by adding Termamyl 120 amylase (12) during the subsequent neutral-detergent fiber procedure. Rumen inoculum was obtained from a ruminally fistulated steer maintained on alfalfa hay. Digestibility data were analyzed within an incubation time using General Linear Models (GLM) procedures (15) for a split-plot design experiment. Year, replicate, and their interaction were included in the model as the whole-plot effects. Year and replicate effects were tested using their interaction as the error term. Subplot effects were cultivar; growth ~~~~ocu~n~ill~~mdfure~
way interactions among cultivar, V soybean cultivar ('Bay'). The growth stage, and inoculant; and all Three or four of the experimental interactions with year. Because silos were opened on the day of center two rows from two plots of feeding during a 13-d consumption each cultivar from each block were interactions of cultivar, growth stage, study using sheep. During each year, or inoculant with year were detected, harvested with a forage chopper at either R2, R4, or R6 growth stages (5, three wethers were housed individu- the analysis was conducted within 8). Forage from one of each pair of ally in pens with concrete floors year using GLM procedures (IS) for a plots of each cultivar from each bedded with wheat straw. The sheep 2 x 3 x 2 factorial arrangement of a replicate was inoculated with .03 g/kg were offered NI R6 Bay silage for 10 d randomized complete block design. Biomate LP/PC® (Chr. Hansen's Lab., to adapt them to silage. Dry matter The model consisted of effects of Milwaukee, WI) to pwvide 100,000 intake was monitored during this cultivar, growth stage, inoculant, and all interactions. Differences among cfu of Lactobacillus plantarum and time. Following the adaptation treatment means were determined Pediococcus cerevisiae/g of forage (I), period, four different silages were whereas the forage from the other using a protected t test (17). Paraoffered to each sheep daily for 13 d plot was not inoculated (NI). in a balanced incomplete block meters for digestion kinetics were All forages were packed into 19-L design (4) . Corn silage was included estimated using the Marquardt plastic containers lined with three as a positive control and constituted option of the NUN procedure (IS) to plastiC trash can liners and allowed to the 13th treatment (Table 1). Dry fit digestibility data to a nonlinear ferment for a minimum of 60 d. matter consumption during the model (13) . Initial parameters for the
83
Whole-Plant Soybean Silages for Sheep
TABLE 2. In vitro digestibility (%) with time and digestion klnetics a of silages made from whole-plant soybeans. Year, incubation time, and kinetics R2
Bay
Inoculant
Stafford
R4
R6
R2
R4
R6
SE
NI
SE
1988 6b 12 c 18d 24d 48 c 72 d
55.8 61.5 65.7 hi 66.8 ij 69.7 69.9 hi
51.1 60.1 64.1 i 65.9i 65.9 67.2i
55.6 62.3 66.4 hi 67.9 hi j 70.4 70.0 hi
57.7 62.5 68.6 h 69.9 h 70.7 70.6 h
52.0 56.3 59.9i 63.0 k 64.2 63.4i
54.8 63.8 67.9 h 69.1 hi 71.5 72.5 h
1.59 1.16 1.13 .83 1.12 1.08
56.2 61.3 65.9 67.4 69.2 69.6
53.8 60.8 65.0 66.8 68.2 68.3
.93 .69 .63 .48 .65 .63
f/,% fic, % k, h-' lag, h
17.9 29.7 ii .096 2.9
17.0 32.6 i .095 2.7
17.2 30.3 ii .119 4.2
19.1 29.0 ij .114 2.1
16.0 36.3 h .154 4.8
19.6 27.6i .104 4.1
.85 1.06 .020 1.03
18.1 30.4 .100 2.7
17.5 31.4 .127 4.3
.49 .61 .0117 .061
6e 12t 18t 24 c9 48 c9 72 c
62.2 69.3 73.9 76.4 78.6 79.4
57.6 63.4 69.4 71.0 74.2 75.1
59.0 63.1 68.0 69.9 72.0 73.7
63.3 69.8 74.7 76.3 79.2 78.3
58.4 67.0 70.2 73.0 75.3 76.3
60.7 65.8 70.5 73.0 75.8 77.0
1.23 1.09 .69 .75 .77 .87
59.7 65.6 70.8 73.2 75.8 76.3
53.8 67.2 71.4 73.3 76.0 77.0
.93 .63 .40 .43 .44 .50
fd' % fic, % k, h-' lag b, h
15.9 20.3 .094 8.0
15.6 25.1 .095 7.7
15.9 26.4 .068 4.0
14.0 21.4 .117 9.0
15.8 23.6 .091 5.9
17.2 23.0 .096 6.3
.89 .91 .0173 1.33
15.7 23.6 .095 7.6
15.8 23.0 .093 6.1
.52 .53 .0101 .77
1989
aDigestion kinetics are presented as follows: fd = potentially digestible fraction; fi stant; lag =digestion lag time. bDifferences among growth stages were detected (P<.10). cDifferences among growth stages were detected (P<.05). dCultivar x growth stage interaction was detected (P<.05). eGrowth stage x inoculant interaction was detected (P<.05). tCultivar x growth stage x inoculant interaction was detected (P<.05). 9Differences among cultivars were detected (P<.05). h-kMeans within a row with no common superscript differ (P<.05).
NLIN calculations were determined on each sample by regression of the natural logarithm of the potentially digestible organic matter remaining against incubation time (D. R. Mertens, personal communication, USDA, ARS, U.S. Dairy Forage Research Center, Madison, WI) to reduce the number of iterations necessary for procedure NLIN to converge and to improve the accuracy of the estimated initial parameters. Consumption data were analyzed as a split-plot in time with effects of
=indigestible fraction; k = digestion rate con-
year, treatment, and their interaction in the model. In this model, 13 treatments consisted of silages offered from 1 of 12 combinations of cultivar, growth stage, and inoculant or corn silage. Because year x treatment interactions were detected, the analysis was conducted within year as a one-way analysis of variance (IS), and differences among treatments were tested using a protected t test (17). Consumption data also were analyzed as a 2 x 3 x 2 factorial arrangement of treatments with corn silage data excluded. Correlations
between consumption and various yield and quality measurements (5) were determined using the CORR procedure (15).
Results and Discussion Interactions of year with other treatments were detected (P<.OS) for most parameters measured. Therefore, digestibility and consumption data were analyzed and reported within year. In 1988, digestibility at 12 and 48h of incubation was lower (P<.OS) from silages harvested at R4
84
Coffey et ai.
TABLE 3. Comparison of consumption by sheep of ensiled whole-plant soybean treatments, with (I) or without (NI) inoculant, and corn silage. Bay Year and consumption
R2
R4
Stafford R6
R2
R4
Corn silage
R6
SE
1988
gld % of offer % of OM intake
I NI I NI I NI
217 cd 206d 44.4 d 46.3 d 15.3 c 13,5 c
323 c 309 cd 57.9 bcd 56.4 bcd 20.7 c 2UC
579 b 525 b 72.4 b 66.9 bc 38.0 b 34,6 b
223 cd 256cd 50.4 cd 55.9 bcd 15.8c 18,1 c
233 cd 25Fd 44.4 d 44.8 d 14.2c 18.1 c
509 b 513 b 72.9 b 69.6 b 30.1b 33 .0 b
836a
285 bcd 322 b 58.2bc 69.5 b 23.2bcd
171 de 172 de 35.9 de 34.6 e 15.3 cd lS.scd
329 b 339 b 58.2 bc 56.8 bcd 27.5 b 27.6 b
267 bcde 291 bc 60.2b 66.1b 23.1 bcd
153 e 375 b 189 cde 363 b 34.6 e 69.5 b 39.7 cde 63.3 b 13.2b 31.7 b "'"'0 '''In L.O.'£'15.8 cd
660a
38.8
99.6a
6.10
51.9 a
3.02
1989
gld % of offer % of OM intake
I NI I NI I NI
,","'7..,h
L.I
.t-
..,.., nhr
L.'>.O--
41.2
92.9 a
7.46
52.1 a
3.59
a-dMeans within an item with no common superscript differ (P<.05).
than from silages harvested at R2 or R6 (Table 2). A cultivar x growth stage interaction was detected (P< .OS) for digestibilities at 18, 24, and 72 h of incubation and for the in vitro indigestible fraction of the silages. Ensiled R4 Stafford soybeans had lower (P<.OS) digestibility at 18, 24, and 72 h and the greatest (P<.OS)
indigestible fraction compared with the other cultivar x growth stage combinations. Digestibility at 18, 24, and 72 h of incubation and the indigestible fractions of Bay soybeans did not differ (P>.10) across growth stages. Silages harvested at R4 had lower potentially digestible fractions than did those harvested at R2 or R6,
but digestion rate did not differ among .the various silage combinations. Digestion lag tended to be shorter (P<.lO) for I silages compared with NI silages. In 1989, a three-way interaction was detected (P<.OS) at 12 and 18 h of incubation (Table 2) . At these times, NI R2 Bay silages were more
TABLE 4. Comparison of consumption by sheep of ensiled whole-plant soybean treatments in a factorial arrangement model. Cultivar Year and consumption
Bay
Growth stage R4
Stafford
SE
360 58.5 23.9 b
331 54.0 20.9 c
15.1 1.79 .83
225 d 47.7 14.0d
279 c 531 b 47.9 73.1 17.3c 35.9 b
18.5 2.23 1.04
269 51.4 22.3
273 54.2 22.1
17.9 2.94 1.34
291 b 62.5 b 24.3 c
17F 352 b 32.2c 63.7 b 12.7d 29.7 b
21.9 3.60 1.64
R2
R6
Inoculant SE
NI
SE
343 58.1 23.2
347 54.4 21.6
15.1 1.80 .84
263 54.3 22.7
279 51.4 21.8
17.9 2.88 1.31
1988
gld % of offera %of OM intake 1989
gld % of offer % of OM intake
aCultivar x growth stage (P<.05). b-dMeans within a row and main effect with no common superscript differ (P< .05).
Whole-Plant Soybean Silages faT Sheep
85
and petioles, with the most rapid rate of decline in IVOMO of stems occurring after the R4 growth stage. In this experiment, no differences were detected in the potentially digestible Dry matter consumption fraction among growth stages at harvest, but the indigestible fraction %ofDM tended to be highest at the R4 Yield and Amount offered % of DM intake growth stage. At approximately the quality R4 growth stage, yield of leaves and constituent r P r P r P stems may begin to decline, whereas the yield of pod substantially inOM % of preensiled forage .7113 .0001 .3654 .0003 .5287 .0001 creases through the R7 growth stage OM yield .4814 .0001 .1920 .0609 .4564 .0001 Fresh yield .0854 .4090 -.0475 .6459 .1851 .0710 (14). Because the IVOMO of pods may exceed that of stems by as much Concentration in OM of as 25 percentage units at the R6 Acetic -.3959 .0001 - .1246 .2289 -.2769 .0066 growth stage, the contribution of the -.4214 .0001 -.2986 .0033 -.3673 Propionic .0003 pod and seed material at R6 to the Isobutyric -.2955 .0037 -.2537 .0131 -.2955 .0036 overall digestibility of the whole -.2529 .0134 -.1390 .1791 -.2561 Butyric .0122 plant would help to increase it above Isovaleric .2382 .0201 .1694 .1007 .1696 .1004 that at R4 . Valeric .0191 .8543 .0684 .5101 .0531 .6097 Consumption was expressed as Total VFA .4333 .0001 .1766 .0869 -.3393 .0008 actual quantity consumed (grams per Molar proportion of total VFA of day), as a percentage of the OM .2505 .2022 Acetic .1751 .0897 .1191 .0494 offered, and as a percentage of total Propionic -.4303 .0001 -.3272 .0012 -.3848 .0001 OM intake. Although many similari-.2728 .0075 -.2413 .0185 -.2845 .0052 Isobutyric ties existed in the relative responses, Butyric -.1745 .0908 - .1057 .3080 -.2068 .0443 some distinctions were observed . Isovaleric .3017 .0030 .2058 .0454 .2341 .0224 Because equal quantities of fresh Valeric .2272 .0268 .2001 .0518 .2188 .0331 material were offered daily from each of the deSignated plots, silages pH - .5342 .0001 -.3793 .0001 - .5277 .0001 having a greater OM concentration Concentration in OM of would be offered proportionally at a Lactic acid .6438 .0001 .3628 .0003 .5017 .0001 higher OM level than silages having - .1601 Ammonia .1192 -.1417 .1686 -.3377 .0008 lower moisture content. Although Ethanol .2622 .0103 .1300 .2092 .3017 .0030 some overlap obviously existed, we Nitrogen -.4809 .0001 -.1676 .1026 -.3117 .0020 interpret OM consumption expressed NOF .1675 .1028 - .0367 .7230 -.0359 .7286 as total grams consumed as the AOF .1152 .2639 - .0501 .6282 - .1027 .3193 amount of silage sheep were willing AOL .2867 .0046 -.0059 .9549 .1617 .1155 to ingest when other silages were - .2112 .0388 - .1690 .0998 -.2828 Calcium .0052 Phosphorus - .2172 .0335 -.1886 .0658 - .2145 .0359 present; consumption expressed as a percentage of OM offered might best indicate the relative palatability or gestible fraction than R4 or R6 silages. acceptability of the silage; and (P<.05) digestible than all other Bay silages as well as I R4 Stafford silages Ensiled R2 soybeans tended (P<.10) to consumption expressed as a percentand I and NI R6 Stafford silages. have a longer digestion lag than R6 age of daily OM intake should more Ensiled R2 Stafford soybeans were silages. No differences among culticlosely distinguish preferences more digestible at 12 and 18 h of var, growth stage, or inoculant among the different silages. incubation than I R4 Stafford silages treatment were detected (P<.05) in Consumption of greater than 90% and than I and NI R6 Stafford silages the potentially digestible fraction or of the corn silage offered compared at 18 h . Digestibility was higher digestion rate of 1989 silages. Gupta with a maximum of 73% consump(P<.05) for 1989 Stafford soybeans et al. (9) reported a linear decline in tion of anyone soybean silage than for Bay after 24 and 48 h of in IVOMO of leaves and a quadratic offered indicated that sheep preferred vitro incubation. Ensiled R2 soydecline in IVOMO of stems as soycorn silage to any of the soybean beans were more digestible (P<.05) at bean maturity advanced. Munoz et silages offered (Table 3). Corn silage 24, 48, and 72 h of in vitro incubaal. (14) also reported a quadratic consumption averaged 52% of total tion and had a lower (P<.05) indidecline in IVOMO of soybean stems OM intake on the days when it was
TABLE 5. Selected correlation coefficients of yield and quality constituents with dry matter consumption by sheep.
86
o
offered. This approximated our goal of limiting consumption of any silage to no more than 50% of daily OM intake. In 1988, total daily OM consumption (grams per day) of R6 silages (Bay and Stafford I and NI) was greater than consumption of any of the R2 or R4 silages (Table 3). Acceptability (percentage of OM offered) was greater (P<.05) for R6 Bay than R2 Bay silages and for R6 Stafford than I R2 and R4 and NI R4 Stafford silages. Sheep preferred (percentage of OM intake; P<.05) R6 silages to those from R2 or R4 soybeans. In 1989, total daily consumptions (grams per day) of R6 silages and NI R2 Bay silages were greater (P<.05) than that of R4 silages. Acceptability (percentage of OM offer) of R4 silages was consistently lower (P<.05) than that of R2 or R6 silages, but no differences in consumption as a percentage of OM offered were observed between cultivars or between R2 and R6 silages. Silage preference (percentage of total OM intake) was greater (P<.05) for R6 than for R4 silages but did not differ (P>.10) between R2 and R6 silages. When the analysis was conducted as the factorial treatment arrangement excluding corn silage data, a cultivar x growth stage interaction was detected (P<.05) for consumption as a percentage of OM offered in 1988 (Table 4). No other interactions were detected (P<.OS) in either year. Quantity of silage consumed (grams per day) increased (P<.05) with increasing growth stage in 1988 but did not differ (P<.OS) by cultivar or inoculant. Acceptability (percentage of offer) was greater (P<.05) for R6 Bay (73.5%) and Stafford (72.6%) silages in 1988 than for either R2 Bay or Stafford (46.9 and 48.6%, respectively) or R4 Bay or Stafford (55.0 and 40.9%, respectively) silages. Furthermore, R4 Stafford silages were apparently the least palatable to sheep as illustrated by their lower (P<.05) proportional consumption (percentage of OM offered) . Preference (percentage of OM intake) by sheep
Coffey et ai.
for Bay silages was 14.4% greater (P<.05) than that for Stafford silages in 1988 and preference increased with advancing growth stage in 1988. No differences in consumption between cultivars or inoculant treatments were detected (P>.1O) in 1989. Total daily consumption (grams), acceptability (percentage of OM offered), and preference (percentage of OM intake) were lower for R4 than R2 and R6 silages. No differences were detected between total consumption (grams per day) or acceptability (percentage of OM offer) of R2 and R6 silages but preference (percentage of OM intake) was greatest for R6 silages in 1989. In order to help determine factors that influenced silage consumption, acceptability, and preference by sheep, correlation coefficients were determined between these factors and selected yield and quality measurements (Table 5). A number of factors affected the quantity, acceptability, and preference for particular silages when other silages were present. Silage consumption (grams per day, percentage of OM offered, and percentage of OM intake) was correlated strongly (P<.Ol) and positively with OM percentage of the preensiled forage. Consumption amount (grams per day) and preference (percentage of OM intake) also were correlated highly (P< .Ol) with OM yield. Consumption amount, acceptability, and preference were correlated positively (P< .05) with molar concentration (micromoles per 100 mol) of isovaleric acid and concentration (percentage of OM) of lactic acid. Consumption and preference were correlated positively (P<.05) with ethanol concentration and molar concentration of valeric acid. Consumption, acceptability, and preference were correlated negatively (P<.05) with propionic and isobutyric acid concentrations (micromoles per gram of OM), molar concentrations, and silage pH. Additionally, consumption and preference were correlated negatively with acetic and butyric acid concentrations and total VFA, N, Ca, and P
concentrations. Buchanan-Smith (2) evaluated factors affecting palatability of silages with sham-fed lambs. In that experiment, intake increased linearly with increasing levels of a combination of lactic and acetic acids up to 53 g/kg OM of lactic acid and 35 g/kg acetic acid, but decreased linearly as acetic acid alone was increased from 0 to 88 g/kg OM. In the present experiment, lactate concentrations ranged from 3.8 (NI R2 Stafford) to SO (I R6 Bay) g/kg OM, and acetic acid concentrations rariged from 25 (NI R6 Stafford) to 76 (I R2 Bay) g/kg OM (5). The technique of offering sheep different silages to test for preference appears to have been effective in distinguishing acceptability and preference, as well as predicting consumption of silages differing in quality. Our initial concern was that the sheep might start eating in one bucket and avoid sampling others. This was not the case, however. At each feeding, the sheep were observed to either smell or take a bite from each bucket. After sampling each bucket, the sheep then would proceed to ingest from one bucket. The exception to this was on the days when corn silage was offered. On those days, the sheep only sampled buckets until corn silage was located and then ingested from that bucket without sampling the remaining buckets. Therefore, although some bias is apparently interposed with this technique, we feel it is an effective method to evaluate acceptability of silages differing in quality. Expressing consumption data in the different ways may seem somewhat repetitive, but in actuality, some differences existed depending on the way the data was expressed. Expressing consumption as a percentage of OM offered represents the proportion of a particular silage the sheep were willing to consume. Sheep particularly preferred corn silage in both years, but in 1989, they only consumed 93% of that offered. The orts were primarily coarse pieces of cob. With the soybean silage, the orts of R6 silages were primarily coarse
87
Whole-Plant Soybean Silages for Sheep
pieces of heavier stem material whereas the orts of R4 silages were a mixture of leaf and stem material. In an actual feeding situation, these R6 stems would probably be rejected just as corn cob pieces are sometimes rejected in corn silage feeding situations. Therefore, this measurement represents relative acceptability of the different silages. Expressing the data as a percentage of daily DM intake is more of a measure of relative preference of one silage compared with the others present. Because silage quantities were limited to approximately 50% of the total daily DM intake and each silage treatment was offered in combination with each other silage treatment, sheep were forced to consume from more than one silage, but were allowed adequate selectivity by offering them a total of approximately 200% of their daily DM consumption. With adequate silage available for selectivity, silage consumption expressed as a percentage of total dry matter intake more closely represents silage preference relative to other silages present. Certain observations of physical appearance and odor of silages were noted. Ensiled whole-plant soybeans harvested at R2 and R4 appeared much darker than growing soybeans, ranging in color somewhere between a dark green and black. Both R2 and R4 silages also had various degrees of mold on the very top of the experimental silos when they were opened. These silages also displayed a somewhat displeasing odor. Conversely, R6 silages rarely had mold formation, retained a color similar to the freshly harvested forage, and had a pleasant odor. Munoz et al. (14) recommended that soybeans be harvested for hay at the R6 growth stage to optimize yield and quality. Yields were dramatically higher at the R6 than at the R2 growth stage in this experiment, but quality tended to decline with advancing growth stage (5). However, R6 silages were at least as acceptable to sheep but usually more acceptable than silages from earlier
harvested soybeans. Furthermore, Hubbell et al. (10) concluded that whole-plant soybeans harvested for hay at R2 and R5 were similar in feeding value when offered as the sole source of forage in diets for lactating dairy cows. Because the objective of most soybean producers is to produce seed rather than forage for ruminants, the decision of whether or not to ensile the forage would need to be delayed as much as possible. Considering the quality and acceptability of silages made from soybeans harvested at the R6 growth stage, delaying forage harvest until that growth stage should maximize both yield and acceptance of the silage compared with harvesting the soybeans at an earlier growth stage.
Acknowledgments The authors wish to express their gratitude to Chr. Hansen's Lab. for providing silage inoculant; to Bob Middleton, Charlie Middleton, Larry Ellis, Terry Green, and Joyce Erikson for assistance with planting and harvesting operations; and to Glenda Newkirk for laboratory analyses. The authors also wish to express their gratitude to D. R. Mertens for providing the SAS® statements used to calculate initial parameters for the nonlinear model to determine in vitro digestion kinetics.
3. Christosov, A. 1972. Influence of the plant density in post-harvest maize-soybean mixed crops upon the yield and feed value of silage. Plant Sci. 9:136. 4. Cochran, W. G., and G. M. Cox. 1957. Experimental Designs (2nd Ed.). John Wiley & Sons, New York, NY. 5. Coffey, K. P., G. V. Granade, andJ. 1. Moyer. 1995. Nutrient content of silages made from whole-plant soybeans. Prof. Anim. Sci. 11:74. 6. Daniel, P., and P. Romer. 1988. The influence of the admixture of Andean lupin silage (Lupinus mutabilis 1.) and soybean silage (Glycine soja (1.) Sieb. et ZUCc.) to crude protein content, feeding value and quality of maize silages. Landwirtsch. Forsch. 41:131. 7. Elmore, R. w., andJ. A. Jackobs. 1986. Yield and nitrogen yield of sorghum intercropped with nodulating and nonnodulating soybeans. Agron. J. 78:780. 8. Fehr, W. R., C. E. Caviness, D. T. Burmood, andJ. S. Pennington. 1971. Stage of development descriptions for soybeans, Glycine max (1.) Merr. Crop ScI. 11:929. 9. Gupta, B. S., D. E. Johnson, F. C. Hinds, and H. C. Minor. 1973. Forage potential of soybean straw. Agron. J. 65:538. 10. Hubbell, D., J. M. Rakes, O. T. Stallcup, 1. B. Daniels, and K. E. Harrison. 1988. Soybean hays made from plants in bloom and pod stage in diets of lactating cows. Nutr. Rep. Int. 37:537. 11. Jaster, E. H., C. R. Staples, G. C. McCoy, and C. 1. Davis. 1984. Evaluation of wet corn gluten feed, oatJage, sorghum-soybean silage, and alfalfa haylage for dairy heifers. J. Dairy Sci. 67:1976. 12. Jeraci, J. 1., T. Hernandez, J. B. Robertson, and P. J. Van Soest. 1988. New and improved procedure for neutral-detergent fiber. J. Anim. Sci. 66(Suppl. 1):351 (Abs.). 13. Mertens, D. R., and J. R. Loften. 1980. The effect of starch on forage fiber digestion kinetics in vitro. J. Dairy Sci. 67:1437. 14. Munoz, A. E., E. C. Holt, and R. W. Weaver. 1983. Yield and quality of soybean hay as influenced by stage of growth and plant density. Agron. J. 75:147. 15. SAS Institute. 1988. SAS/STAT® User's Guide. SAS Institute Inc., Cary, NC.
literature Cited 1. Baxter, H. D., M. J. Montgomery, and J. R. Owen. 1984. Comparison of soybean-grain sorghum silage with corn silage for lactating cows. J. Dairy Sci. 67:86. 2. Buchanan-Smith, J. G. 1990. An investigation into palatability as a factor responsible for reduced intake of silage by sheep. Anim. Prod. 50:253.
16. Shroyer, J. P., W. H. Fick, and G. 1. Posler. 1987. Yield and quality of soybean hay as influenced by drought stress. Appl. Agric. Res. 2:301. 17. Snedecor, G. W./ and W. G. Cochran, 1980. Statistical Methods (7th Ed.). The Iowa State Vniv. Press, Ames, IA. 18. Van So est, P. J., R. H. Wine, and 1. A. Moore. 1966. Estimation of the true digestibility of forages by the in vitro digestion of cell walls. In: Proc. 10th Int. Grassl. Congo July 716, 1966. A.G.G.L. Hill (Ed.). P 438. Univ. of Helsinki, Valtioneuvoston Kirjapaino, Helsinki, Finland.
InPreference Vitro Digestibility and by Sheep for Silages Made from Whole-Plant Soybeansl K. P. COFFEy2, PAS, G. V. GRANADE3, and J. L. MOYER2 Kansas State University - Southeast Agricultural Research Center, Parsons, KS 67357 University of Georgia, Georgia Experiment Station, Griffin, GA 30223
Abstract
digestibility higher at 24, 48, and 72 h from R2 than R4 and R6 silages (p<.05). Maturity group IV ('Stafford') vs Com silage was preferred (p< .05) to any group V ('Bay') soybean forages were of the soybean silages. Consumption of harvested and ensiled at either full R6 silage was greater (p<.05) than that bloom (R2), full pod (R4), or full seed of R2 and R4 in 1988 and of R4 in (R6) growth stages, with or without a. 1989. Silage consumption was corresilage inoculant and offered to sheep In a lated positively (p<.05) with forage DM consumption experiment having a content; DM yield; molar percentage of balanced incomplete block design. Silage isovaleric and valerie acids; and lactic samples were collected at the time of acid, ethanol, and acid-detergent lignin feeding for in vitro total DM digestibility contents and negatively with acetic, determination. Three sheep were propionic, isobutyric, butyric, and total adapted to ensiled R6 Bay silage, then volatile fatty acid concentrations; molar individually offered a selection of four percentage of propionic and isobutyric different silages (soybean silage combinaacids; pH; and N, Ca, and P contents. tions or com silage) daily for 13 d. Delaying ensiling of whole-plant soyQuantity of each silage was limited to beans until the R6 growth stage some50% of the total daily silage consumpwhat compromises digestibility of the tion. In 1988, the indigestible fraction forage but provides a silage of higher was higher and digestibility at 18, 24, acceptance by sheep. and 72 h was lower from R4 Stafford than from the other cultivar and growth (Key Words: Soybean, Silage, Forage stage combinations (p<.05). In 1989, Quality, Growth Stage, Animal the indigestible fraction was lower and Preference, Intake.)
Introduction 1 Contribution No. 95-159-1 from the Kansas Agricultural Experiment Station, Manhattan, KS 66506.
2Kansas State University. 3University of Georgia. Reviewed by D. C. Anderson and L.
I. Bush.
Although soybeans [Glycine max (L.) Merr.] are grown primarily for
seed production in the United States, adverse weather conditions may cause reduced seed yields or quality. The market price of lower quality soybean seeds often is reduced
severely, forcing the soybean producer to seek alternatives for the crop. Previous research evaluating alternative uses for soybeans has centered upon using whole-plant soybeans as a hay crop (10, 14, 16). Soybeans have been intercropped with corn (3, 6) or sorghum (I, 7, 11) to improve the protein content of a subsequent silage crop, but evaluation of soybeans alone as a silage crop has been limited. In a previous study (5), we evaluated the quality and fermentation characteristics of silages of two different cultivars harvested at three growth stages and ensiled directly or treated with a silage inoculant. The objective~ of . this experiment were to determme m vitro digestibility and preference by sheep of silages from these same treatments.
Materials and Methods Forty-eight four-row plots, 9.1-m in length having a .76-m row spacing, were established in 1988 and . 1989 on separate areas of Parsons SlIt loam soil. Plots were arranged in four blocks of 12 plots each in a randomized complete block design (17) . Half of the plots were seeded to a maturity group IV soybean cultivar ('Stafford'), whereas the remaining plots were seeded to a maturity group
82
Coffey et ai.
TABLE 1. Schedule for offering of silages to sheepa. Bucket no. Day 1988 1 2
3 4
5 6
7 8 9 10
11 12
13
1
2
3
4
B61 B6NI B21 S2NI B4NI B41 B61 S61 S4NI S21 CORN S41 S6NI
S2NI S21 B6NI CORN S61 S61 S41 B41 B21 S6NI B2NI S4NI B4NI
B2NI B4NI S6NI S41 B61 CORN B21 S2NI S21 B61 S4NI B6NI B41
S6NI B2NI CORN B4NI B21 S21 B41 B6NI S2NI S41 S61 B61 S4NI
1989 ..JLI"II
..IV •
C,cl
B2f'-~1
I1A I
B61 B21 S6NI S61 B6NI B61 B21 S41 B6NI S2NI S2NI S41
S4NI B41 S41 S6NI S21 B41 B4NI B4NI S4NI B61 S21 S4NI
S21 S6NI B6NI B4NI B21 B6NI 'CORN B41 S2NI S41 S6NI CORN
B2NI S4NI B2NI B61 S61 CORN B2NI S21 B4NI B21 CORN S61
(,'''1'Ir.1I
2
3 4
5 6
7 8
9 10 11 12
13
U""T'
aSilage treatment codes are as follows: Cultivar: B = Bay, S = Stafford; Growth stage: 2 = R2, 4 = R4, 6 = R6; Inoculant: I = inoculant, NI = no inoculant.
~
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _
I
~
adaptation period was used as a basis to limit the offering of each silage to no more than 50% of the total daily OM consumption. This was done to ensure that distinctions were made between silages of lower palatability. Sheep had ad libitum access to fresh water and a commercial sheep mineral throughout the feeding study. Fresh silage samples were collected at the time of feeding, dried at SOCC, and ground (1 mm) for in vitro digestibility analyses after allowing a minimum of 72 h for equilibration to atmospheric moisture. Sample OM was determined by drying overnight at 105°C. In vitro OM digestibilities were determined at 6, 12, 18, 24, 48, and 72 h of incubation by the procedures of Van Soest et al. (18) modified by adding Termamyl 120 amylase (12) during the subsequent neutral-detergent fiber procedure. Rumen inoculum was obtained from a ruminally fistulated steer maintained on alfalfa hay. Digestibility data were analyzed within an incubation time using General Linear Models (GLM) procedures (15) for a split-plot design experiment. Year, replicate, and their interaction were included in the model as the whole-plot effects. Year and replicate effects were tested using their interaction as the error term. Subplot effects were cultivar; growth ~~~~ocu~n~ill~~mdfure~
way interactions among cultivar, V soybean cultivar ('Bay'). The growth stage, and inoculant; and all Three or four of the experimental interactions with year. Because silos were opened on the day of center two rows from two plots of feeding during a 13-d consumption each cultivar from each block were interactions of cultivar, growth stage, study using sheep. During each year, or inoculant with year were detected, harvested with a forage chopper at either R2, R4, or R6 growth stages (5, three wethers were housed individu- the analysis was conducted within 8). Forage from one of each pair of ally in pens with concrete floors year using GLM procedures (IS) for a plots of each cultivar from each bedded with wheat straw. The sheep 2 x 3 x 2 factorial arrangement of a replicate was inoculated with .03 g/kg were offered NI R6 Bay silage for 10 d randomized complete block design. Biomate LP/PC® (Chr. Hansen's Lab., to adapt them to silage. Dry matter The model consisted of effects of Milwaukee, WI) to pwvide 100,000 intake was monitored during this cultivar, growth stage, inoculant, and all interactions. Differences among cfu of Lactobacillus plantarum and time. Following the adaptation treatment means were determined Pediococcus cerevisiae/g of forage (I), period, four different silages were whereas the forage from the other using a protected t test (17). Paraoffered to each sheep daily for 13 d plot was not inoculated (NI). in a balanced incomplete block meters for digestion kinetics were All forages were packed into 19-L design (4) . Corn silage was included estimated using the Marquardt plastic containers lined with three as a positive control and constituted option of the NUN procedure (IS) to plastiC trash can liners and allowed to the 13th treatment (Table 1). Dry fit digestibility data to a nonlinear ferment for a minimum of 60 d. matter consumption during the model (13) . Initial parameters for the
83
Whole-Plant Soybean Silages for Sheep
TABLE 2. In vitro digestibility (%) with time and digestion klnetics a of silages made from whole-plant soybeans. Year, incubation time, and kinetics R2
Bay
Inoculant
Stafford
R4
R6
R2
R4
R6
SE
NI
SE
1988 6b 12 c 18d 24d 48 c 72 d
55.8 61.5 65.7 hi 66.8 ij 69.7 69.9 hi
51.1 60.1 64.1 i 65.9i 65.9 67.2i
55.6 62.3 66.4 hi 67.9 hi j 70.4 70.0 hi
57.7 62.5 68.6 h 69.9 h 70.7 70.6 h
52.0 56.3 59.9i 63.0 k 64.2 63.4i
54.8 63.8 67.9 h 69.1 hi 71.5 72.5 h
1.59 1.16 1.13 .83 1.12 1.08
56.2 61.3 65.9 67.4 69.2 69.6
53.8 60.8 65.0 66.8 68.2 68.3
.93 .69 .63 .48 .65 .63
f/,% fic, % k, h-' lag, h
17.9 29.7 ii .096 2.9
17.0 32.6 i .095 2.7
17.2 30.3 ii .119 4.2
19.1 29.0 ij .114 2.1
16.0 36.3 h .154 4.8
19.6 27.6i .104 4.1
.85 1.06 .020 1.03
18.1 30.4 .100 2.7
17.5 31.4 .127 4.3
.49 .61 .0117 .061
6e 12t 18t 24 c9 48 c9 72 c
62.2 69.3 73.9 76.4 78.6 79.4
57.6 63.4 69.4 71.0 74.2 75.1
59.0 63.1 68.0 69.9 72.0 73.7
63.3 69.8 74.7 76.3 79.2 78.3
58.4 67.0 70.2 73.0 75.3 76.3
60.7 65.8 70.5 73.0 75.8 77.0
1.23 1.09 .69 .75 .77 .87
59.7 65.6 70.8 73.2 75.8 76.3
53.8 67.2 71.4 73.3 76.0 77.0
.93 .63 .40 .43 .44 .50
fd' % fic, % k, h-' lag b, h
15.9 20.3 .094 8.0
15.6 25.1 .095 7.7
15.9 26.4 .068 4.0
14.0 21.4 .117 9.0
15.8 23.6 .091 5.9
17.2 23.0 .096 6.3
.89 .91 .0173 1.33
15.7 23.6 .095 7.6
15.8 23.0 .093 6.1
.52 .53 .0101 .77
1989
aDigestion kinetics are presented as follows: fd = potentially digestible fraction; fi stant; lag =digestion lag time. bDifferences among growth stages were detected (P<.10). cDifferences among growth stages were detected (P<.05). dCultivar x growth stage interaction was detected (P<.05). eGrowth stage x inoculant interaction was detected (P<.05). tCultivar x growth stage x inoculant interaction was detected (P<.05). 9Differences among cultivars were detected (P<.05). h-kMeans within a row with no common superscript differ (P<.05).
NLIN calculations were determined on each sample by regression of the natural logarithm of the potentially digestible organic matter remaining against incubation time (D. R. Mertens, personal communication, USDA, ARS, U.S. Dairy Forage Research Center, Madison, WI) to reduce the number of iterations necessary for procedure NLIN to converge and to improve the accuracy of the estimated initial parameters. Consumption data were analyzed as a split-plot in time with effects of
=indigestible fraction; k = digestion rate con-
year, treatment, and their interaction in the model. In this model, 13 treatments consisted of silages offered from 1 of 12 combinations of cultivar, growth stage, and inoculant or corn silage. Because year x treatment interactions were detected, the analysis was conducted within year as a one-way analysis of variance (IS), and differences among treatments were tested using a protected t test (17). Consumption data also were analyzed as a 2 x 3 x 2 factorial arrangement of treatments with corn silage data excluded. Correlations
between consumption and various yield and quality measurements (5) were determined using the CORR procedure (15).
Results and Discussion Interactions of year with other treatments were detected (P<.OS) for most parameters measured. Therefore, digestibility and consumption data were analyzed and reported within year. In 1988, digestibility at 12 and 48h of incubation was lower (P<.OS) from silages harvested at R4
84
Coffey et ai.
TABLE 3. Comparison of consumption by sheep of ensiled whole-plant soybean treatments, with (I) or without (NI) inoculant, and corn silage. Bay Year and consumption
R2
R4
Stafford R6
R2
R4
Corn silage
R6
SE
1988
gld % of offer % of OM intake
I NI I NI I NI
217 cd 206d 44.4 d 46.3 d 15.3 c 13,5 c
323 c 309 cd 57.9 bcd 56.4 bcd 20.7 c 2UC
579 b 525 b 72.4 b 66.9 bc 38.0 b 34,6 b
223 cd 256cd 50.4 cd 55.9 bcd 15.8c 18,1 c
233 cd 25Fd 44.4 d 44.8 d 14.2c 18.1 c
509 b 513 b 72.9 b 69.6 b 30.1b 33 .0 b
836a
285 bcd 322 b 58.2bc 69.5 b 23.2bcd
171 de 172 de 35.9 de 34.6 e 15.3 cd lS.scd
329 b 339 b 58.2 bc 56.8 bcd 27.5 b 27.6 b
267 bcde 291 bc 60.2b 66.1b 23.1 bcd
153 e 375 b 189 cde 363 b 34.6 e 69.5 b 39.7 cde 63.3 b 13.2b 31.7 b "'"'0 '''In L.O.'£'15.8 cd
660a
38.8
99.6a
6.10
51.9 a
3.02
1989
gld % of offer % of OM intake
I NI I NI I NI
,","'7..,h
L.I
.t-
..,.., nhr
L.'>.O--
41.2
92.9 a
7.46
52.1 a
3.59
a-dMeans within an item with no common superscript differ (P<.05).
than from silages harvested at R2 or R6 (Table 2). A cultivar x growth stage interaction was detected (P< .OS) for digestibilities at 18, 24, and 72 h of incubation and for the in vitro indigestible fraction of the silages. Ensiled R4 Stafford soybeans had lower (P<.OS) digestibility at 18, 24, and 72 h and the greatest (P<.OS)
indigestible fraction compared with the other cultivar x growth stage combinations. Digestibility at 18, 24, and 72 h of incubation and the indigestible fractions of Bay soybeans did not differ (P>.10) across growth stages. Silages harvested at R4 had lower potentially digestible fractions than did those harvested at R2 or R6,
but digestion rate did not differ among .the various silage combinations. Digestion lag tended to be shorter (P<.lO) for I silages compared with NI silages. In 1989, a three-way interaction was detected (P<.OS) at 12 and 18 h of incubation (Table 2) . At these times, NI R2 Bay silages were more
TABLE 4. Comparison of consumption by sheep of ensiled whole-plant soybean treatments in a factorial arrangement model. Cultivar Year and consumption
Bay
Growth stage R4
Stafford
SE
360 58.5 23.9 b
331 54.0 20.9 c
15.1 1.79 .83
225 d 47.7 14.0d
279 c 531 b 47.9 73.1 17.3c 35.9 b
18.5 2.23 1.04
269 51.4 22.3
273 54.2 22.1
17.9 2.94 1.34
291 b 62.5 b 24.3 c
17F 352 b 32.2c 63.7 b 12.7d 29.7 b
21.9 3.60 1.64
R2
R6
Inoculant SE
NI
SE
343 58.1 23.2
347 54.4 21.6
15.1 1.80 .84
263 54.3 22.7
279 51.4 21.8
17.9 2.88 1.31
1988
gld % of offera %of OM intake 1989
gld % of offer % of OM intake
aCultivar x growth stage (P<.05). b-dMeans within a row and main effect with no common superscript differ (P< .05).
Whole-Plant Soybean Silages faT Sheep
85
and petioles, with the most rapid rate of decline in IVOMO of stems occurring after the R4 growth stage. In this experiment, no differences were detected in the potentially digestible Dry matter consumption fraction among growth stages at harvest, but the indigestible fraction %ofDM tended to be highest at the R4 Yield and Amount offered % of DM intake growth stage. At approximately the quality R4 growth stage, yield of leaves and constituent r P r P r P stems may begin to decline, whereas the yield of pod substantially inOM % of preensiled forage .7113 .0001 .3654 .0003 .5287 .0001 creases through the R7 growth stage OM yield .4814 .0001 .1920 .0609 .4564 .0001 Fresh yield .0854 .4090 -.0475 .6459 .1851 .0710 (14). Because the IVOMO of pods may exceed that of stems by as much Concentration in OM of as 25 percentage units at the R6 Acetic -.3959 .0001 - .1246 .2289 -.2769 .0066 growth stage, the contribution of the -.4214 .0001 -.2986 .0033 -.3673 Propionic .0003 pod and seed material at R6 to the Isobutyric -.2955 .0037 -.2537 .0131 -.2955 .0036 overall digestibility of the whole -.2529 .0134 -.1390 .1791 -.2561 Butyric .0122 plant would help to increase it above Isovaleric .2382 .0201 .1694 .1007 .1696 .1004 that at R4 . Valeric .0191 .8543 .0684 .5101 .0531 .6097 Consumption was expressed as Total VFA .4333 .0001 .1766 .0869 -.3393 .0008 actual quantity consumed (grams per Molar proportion of total VFA of day), as a percentage of the OM .2505 .2022 Acetic .1751 .0897 .1191 .0494 offered, and as a percentage of total Propionic -.4303 .0001 -.3272 .0012 -.3848 .0001 OM intake. Although many similari-.2728 .0075 -.2413 .0185 -.2845 .0052 Isobutyric ties existed in the relative responses, Butyric -.1745 .0908 - .1057 .3080 -.2068 .0443 some distinctions were observed . Isovaleric .3017 .0030 .2058 .0454 .2341 .0224 Because equal quantities of fresh Valeric .2272 .0268 .2001 .0518 .2188 .0331 material were offered daily from each of the deSignated plots, silages pH - .5342 .0001 -.3793 .0001 - .5277 .0001 having a greater OM concentration Concentration in OM of would be offered proportionally at a Lactic acid .6438 .0001 .3628 .0003 .5017 .0001 higher OM level than silages having - .1601 Ammonia .1192 -.1417 .1686 -.3377 .0008 lower moisture content. Although Ethanol .2622 .0103 .1300 .2092 .3017 .0030 some overlap obviously existed, we Nitrogen -.4809 .0001 -.1676 .1026 -.3117 .0020 interpret OM consumption expressed NOF .1675 .1028 - .0367 .7230 -.0359 .7286 as total grams consumed as the AOF .1152 .2639 - .0501 .6282 - .1027 .3193 amount of silage sheep were willing AOL .2867 .0046 -.0059 .9549 .1617 .1155 to ingest when other silages were - .2112 .0388 - .1690 .0998 -.2828 Calcium .0052 Phosphorus - .2172 .0335 -.1886 .0658 - .2145 .0359 present; consumption expressed as a percentage of OM offered might best indicate the relative palatability or gestible fraction than R4 or R6 silages. acceptability of the silage; and (P<.05) digestible than all other Bay silages as well as I R4 Stafford silages Ensiled R2 soybeans tended (P<.10) to consumption expressed as a percentand I and NI R6 Stafford silages. have a longer digestion lag than R6 age of daily OM intake should more Ensiled R2 Stafford soybeans were silages. No differences among culticlosely distinguish preferences more digestible at 12 and 18 h of var, growth stage, or inoculant among the different silages. incubation than I R4 Stafford silages treatment were detected (P<.05) in Consumption of greater than 90% and than I and NI R6 Stafford silages the potentially digestible fraction or of the corn silage offered compared at 18 h . Digestibility was higher digestion rate of 1989 silages. Gupta with a maximum of 73% consump(P<.05) for 1989 Stafford soybeans et al. (9) reported a linear decline in tion of anyone soybean silage than for Bay after 24 and 48 h of in IVOMO of leaves and a quadratic offered indicated that sheep preferred vitro incubation. Ensiled R2 soydecline in IVOMO of stems as soycorn silage to any of the soybean beans were more digestible (P<.05) at bean maturity advanced. Munoz et silages offered (Table 3). Corn silage 24, 48, and 72 h of in vitro incubaal. (14) also reported a quadratic consumption averaged 52% of total tion and had a lower (P<.05) indidecline in IVOMO of soybean stems OM intake on the days when it was
TABLE 5. Selected correlation coefficients of yield and quality constituents with dry matter consumption by sheep.
86
o
offered. This approximated our goal of limiting consumption of any silage to no more than 50% of daily OM intake. In 1988, total daily OM consumption (grams per day) of R6 silages (Bay and Stafford I and NI) was greater than consumption of any of the R2 or R4 silages (Table 3). Acceptability (percentage of OM offered) was greater (P<.05) for R6 Bay than R2 Bay silages and for R6 Stafford than I R2 and R4 and NI R4 Stafford silages. Sheep preferred (percentage of OM intake; P<.05) R6 silages to those from R2 or R4 soybeans. In 1989, total daily consumptions (grams per day) of R6 silages and NI R2 Bay silages were greater (P<.05) than that of R4 silages. Acceptability (percentage of OM offer) of R4 silages was consistently lower (P<.05) than that of R2 or R6 silages, but no differences in consumption as a percentage of OM offered were observed between cultivars or between R2 and R6 silages. Silage preference (percentage of total OM intake) was greater (P<.05) for R6 than for R4 silages but did not differ (P>.10) between R2 and R6 silages. When the analysis was conducted as the factorial treatment arrangement excluding corn silage data, a cultivar x growth stage interaction was detected (P<.05) for consumption as a percentage of OM offered in 1988 (Table 4). No other interactions were detected (P<.OS) in either year. Quantity of silage consumed (grams per day) increased (P<.05) with increasing growth stage in 1988 but did not differ (P<.OS) by cultivar or inoculant. Acceptability (percentage of offer) was greater (P<.05) for R6 Bay (73.5%) and Stafford (72.6%) silages in 1988 than for either R2 Bay or Stafford (46.9 and 48.6%, respectively) or R4 Bay or Stafford (55.0 and 40.9%, respectively) silages. Furthermore, R4 Stafford silages were apparently the least palatable to sheep as illustrated by their lower (P<.05) proportional consumption (percentage of OM offered) . Preference (percentage of OM intake) by sheep
Coffey et ai.
for Bay silages was 14.4% greater (P<.05) than that for Stafford silages in 1988 and preference increased with advancing growth stage in 1988. No differences in consumption between cultivars or inoculant treatments were detected (P>.1O) in 1989. Total daily consumption (grams), acceptability (percentage of OM offered), and preference (percentage of OM intake) were lower for R4 than R2 and R6 silages. No differences were detected between total consumption (grams per day) or acceptability (percentage of OM offer) of R2 and R6 silages but preference (percentage of OM intake) was greatest for R6 silages in 1989. In order to help determine factors that influenced silage consumption, acceptability, and preference by sheep, correlation coefficients were determined between these factors and selected yield and quality measurements (Table 5). A number of factors affected the quantity, acceptability, and preference for particular silages when other silages were present. Silage consumption (grams per day, percentage of OM offered, and percentage of OM intake) was correlated strongly (P<.Ol) and positively with OM percentage of the preensiled forage. Consumption amount (grams per day) and preference (percentage of OM intake) also were correlated highly (P< .Ol) with OM yield. Consumption amount, acceptability, and preference were correlated positively (P< .05) with molar concentration (micromoles per 100 mol) of isovaleric acid and concentration (percentage of OM) of lactic acid. Consumption and preference were correlated positively (P<.05) with ethanol concentration and molar concentration of valeric acid. Consumption, acceptability, and preference were correlated negatively (P<.05) with propionic and isobutyric acid concentrations (micromoles per gram of OM), molar concentrations, and silage pH. Additionally, consumption and preference were correlated negatively with acetic and butyric acid concentrations and total VFA, N, Ca, and P
concentrations. Buchanan-Smith (2) evaluated factors affecting palatability of silages with sham-fed lambs. In that experiment, intake increased linearly with increasing levels of a combination of lactic and acetic acids up to 53 g/kg OM of lactic acid and 35 g/kg acetic acid, but decreased linearly as acetic acid alone was increased from 0 to 88 g/kg OM. In the present experiment, lactate concentrations ranged from 3.8 (NI R2 Stafford) to SO (I R6 Bay) g/kg OM, and acetic acid concentrations rariged from 25 (NI R6 Stafford) to 76 (I R2 Bay) g/kg OM (5). The technique of offering sheep different silages to test for preference appears to have been effective in distinguishing acceptability and preference, as well as predicting consumption of silages differing in quality. Our initial concern was that the sheep might start eating in one bucket and avoid sampling others. This was not the case, however. At each feeding, the sheep were observed to either smell or take a bite from each bucket. After sampling each bucket, the sheep then would proceed to ingest from one bucket. The exception to this was on the days when corn silage was offered. On those days, the sheep only sampled buckets until corn silage was located and then ingested from that bucket without sampling the remaining buckets. Therefore, although some bias is apparently interposed with this technique, we feel it is an effective method to evaluate acceptability of silages differing in quality. Expressing consumption data in the different ways may seem somewhat repetitive, but in actuality, some differences existed depending on the way the data was expressed. Expressing consumption as a percentage of OM offered represents the proportion of a particular silage the sheep were willing to consume. Sheep particularly preferred corn silage in both years, but in 1989, they only consumed 93% of that offered. The orts were primarily coarse pieces of cob. With the soybean silage, the orts of R6 silages were primarily coarse
87
Whole-Plant Soybean Silages for Sheep
pieces of heavier stem material whereas the orts of R4 silages were a mixture of leaf and stem material. In an actual feeding situation, these R6 stems would probably be rejected just as corn cob pieces are sometimes rejected in corn silage feeding situations. Therefore, this measurement represents relative acceptability of the different silages. Expressing the data as a percentage of daily DM intake is more of a measure of relative preference of one silage compared with the others present. Because silage quantities were limited to approximately 50% of the total daily DM intake and each silage treatment was offered in combination with each other silage treatment, sheep were forced to consume from more than one silage, but were allowed adequate selectivity by offering them a total of approximately 200% of their daily DM consumption. With adequate silage available for selectivity, silage consumption expressed as a percentage of total dry matter intake more closely represents silage preference relative to other silages present. Certain observations of physical appearance and odor of silages were noted. Ensiled whole-plant soybeans harvested at R2 and R4 appeared much darker than growing soybeans, ranging in color somewhere between a dark green and black. Both R2 and R4 silages also had various degrees of mold on the very top of the experimental silos when they were opened. These silages also displayed a somewhat displeasing odor. Conversely, R6 silages rarely had mold formation, retained a color similar to the freshly harvested forage, and had a pleasant odor. Munoz et al. (14) recommended that soybeans be harvested for hay at the R6 growth stage to optimize yield and quality. Yields were dramatically higher at the R6 than at the R2 growth stage in this experiment, but quality tended to decline with advancing growth stage (5). However, R6 silages were at least as acceptable to sheep but usually more acceptable than silages from earlier
harvested soybeans. Furthermore, Hubbell et al. (10) concluded that whole-plant soybeans harvested for hay at R2 and R5 were similar in feeding value when offered as the sole source of forage in diets for lactating dairy cows. Because the objective of most soybean producers is to produce seed rather than forage for ruminants, the decision of whether or not to ensile the forage would need to be delayed as much as possible. Considering the quality and acceptability of silages made from soybeans harvested at the R6 growth stage, delaying forage harvest until that growth stage should maximize both yield and acceptance of the silage compared with harvesting the soybeans at an earlier growth stage.
Acknowledgments The authors wish to express their gratitude to Chr. Hansen's Lab. for providing silage inoculant; to Bob Middleton, Charlie Middleton, Larry Ellis, Terry Green, and Joyce Erikson for assistance with planting and harvesting operations; and to Glenda Newkirk for laboratory analyses. The authors also wish to express their gratitude to D. R. Mertens for providing the SAS® statements used to calculate initial parameters for the nonlinear model to determine in vitro digestion kinetics.
3. Christosov, A. 1972. Influence of the plant density in post-harvest maize-soybean mixed crops upon the yield and feed value of silage. Plant Sci. 9:136. 4. Cochran, W. G., and G. M. Cox. 1957. Experimental Designs (2nd Ed.). John Wiley & Sons, New York, NY. 5. Coffey, K. P., G. V. Granade, andJ. 1. Moyer. 1995. Nutrient content of silages made from whole-plant soybeans. Prof. Anim. Sci. 11:74. 6. Daniel, P., and P. Romer. 1988. The influence of the admixture of Andean lupin silage (Lupinus mutabilis 1.) and soybean silage (Glycine soja (1.) Sieb. et ZUCc.) to crude protein content, feeding value and quality of maize silages. Landwirtsch. Forsch. 41:131. 7. Elmore, R. w., andJ. A. Jackobs. 1986. Yield and nitrogen yield of sorghum intercropped with nodulating and nonnodulating soybeans. Agron. J. 78:780. 8. Fehr, W. R., C. E. Caviness, D. T. Burmood, andJ. S. Pennington. 1971. Stage of development descriptions for soybeans, Glycine max (1.) Merr. Crop ScI. 11:929. 9. Gupta, B. S., D. E. Johnson, F. C. Hinds, and H. C. Minor. 1973. Forage potential of soybean straw. Agron. J. 65:538. 10. Hubbell, D., J. M. Rakes, O. T. Stallcup, 1. B. Daniels, and K. E. Harrison. 1988. Soybean hays made from plants in bloom and pod stage in diets of lactating cows. Nutr. Rep. Int. 37:537. 11. Jaster, E. H., C. R. Staples, G. C. McCoy, and C. 1. Davis. 1984. Evaluation of wet corn gluten feed, oatJage, sorghum-soybean silage, and alfalfa haylage for dairy heifers. J. Dairy Sci. 67:1976. 12. Jeraci, J. 1., T. Hernandez, J. B. Robertson, and P. J. Van Soest. 1988. New and improved procedure for neutral-detergent fiber. J. Anim. Sci. 66(Suppl. 1):351 (Abs.). 13. Mertens, D. R., and J. R. Loften. 1980. The effect of starch on forage fiber digestion kinetics in vitro. J. Dairy Sci. 67:1437. 14. Munoz, A. E., E. C. Holt, and R. W. Weaver. 1983. Yield and quality of soybean hay as influenced by stage of growth and plant density. Agron. J. 75:147. 15. SAS Institute. 1988. SAS/STAT® User's Guide. SAS Institute Inc., Cary, NC.
literature Cited 1. Baxter, H. D., M. J. Montgomery, and J. R. Owen. 1984. Comparison of soybean-grain sorghum silage with corn silage for lactating cows. J. Dairy Sci. 67:86. 2. Buchanan-Smith, J. G. 1990. An investigation into palatability as a factor responsible for reduced intake of silage by sheep. Anim. Prod. 50:253.
16. Shroyer, J. P., W. H. Fick, and G. 1. Posler. 1987. Yield and quality of soybean hay as influenced by drought stress. Appl. Agric. Res. 2:301. 17. Snedecor, G. W./ and W. G. Cochran, 1980. Statistical Methods (7th Ed.). The Iowa State Vniv. Press, Ames, IA. 18. Van So est, P. J., R. H. Wine, and 1. A. Moore. 1966. Estimation of the true digestibility of forages by the in vitro digestion of cell walls. In: Proc. 10th Int. Grassl. Congo July 716, 1966. A.G.G.L. Hill (Ed.). P 438. Univ. of Helsinki, Valtioneuvoston Kirjapaino, Helsinki, Finland.