Chemical composition of experimental diets
The chemical compositions of feed ingredients used for the study are presented in Table 2. Accordingly, FBSY had the least DM and fiber constituents of NDF, ADF and lignin but was found to be higher in ash, CP, IVOMD and EME contents compared to the other protein source, BSG and the energy source (WB) were used to formulate the base concentrate diet. This is almost equivalent to having 45.02 and 19.46% more CP and EME while still 87.93, 88.51 and 64.78% less NDF, ADF and lignin contents, respectively for BSY over that of BSG. The present result indicated that FBSY is a promising protein source that can partially replace BSG as protein source in the diet animals.
Table 2: Chemical composition, in-vitro organic matter digestibility (g/kg DM) and ME (MJ/kg DM) of experimental feed ingredients
Item
|
DM
|
Ash
|
OM
|
CP
|
NDF
|
ADF
|
PmL
|
IVOMD
|
EME
|
FBSY
|
124.0
|
54.0
|
946.0
|
379.0
|
73.0
|
22.0
|
20.0
|
761.0
|
12.2
|
BSG
|
256.0
|
49.0
|
952.0
|
209.0
|
603.0
|
195.0
|
57.0
|
613.0
|
10.0
|
WB
|
935.0
|
52.0
|
948.0
|
140.0
|
472.0
|
113.0
|
37.0
|
692.0
|
11.1
|
BSG= brewery spent grain; FBSY= brewer’s spent yeast; WB= wheat bran; DM= dry matter; OM= organic matter; CP= crude protein; NDF= neutral detergent fiber; ADF= acid detergent fiber; PmL= permanganate lignin; IVOMD= in-vitro organic matter digestibility; EME= estimated metabolizable energy.
Sensory evaluation of brewer’s spent yeast-based silage
The extent of surface spoilage of brewer’s spent yeast-based silages that ensiled under the different incubation periods are presented in Table 3. No surface spoilage has been rated at all levels of BSY inclusion of the silage samples incubated up until the 4th week storage. However, silage deterioration as rated by slight mold growth and silage discoloration was noted for test BSY based silages in which the BSY inclusion level exceeded ≥20% and that incubated for six weeks of ED. Generally, at any given BSY level and ED, silage deterioration as witnessed by surface spoilage rating of 3, 4, and 5 was not observed. The result from the current trial further implied that it would be safe to feed BSY based silage diet to dairy cattle provided that the concentrate diet containing the yeast slurry at levels not exceeding 30% is ensiled for a storage duration of 4 weeks.
Table 3. Ratings of surface spoilage of BSY-based silage ensiled for different duration (week) and BSY inclusion level (%) (Mean daily temperature=15.40C and RH=84%)
ED (week)
|
BSY inclusion level from protein source (%)
|
0
|
10
|
20
|
30
|
2
|
0
|
0
|
0
|
0
|
4
|
0
|
0
|
0
|
0
|
6
|
0
|
0
|
1
|
2
|
Ratings: 0 = no visible spoilage; l = slight mold growth; 2 = mold growth + discoloration; 3 = mold growth, discoloration + surface collapse; 4 = mold growth, discoloration, surface collapse + slight odor; 5 = mold growth, discoloration, surface collapse + offensive odor
The combined analysis of BSY level and ED on fermentative, fungal load dynamics, and chemical composition of FBSY-based silage is presented in Table 4. Accordingly, the interaction effect was significant for silage temperature (P<0.05), pH (P<0.0001), TDML (P<0.05), yeast (P<0.01), mold (P<0.05), and TFC (P<0.01). Similarly, interactional effect for certain chemical composition parameters including silage CP (P<0.0001), NDF (P<0.01), ADF (P<0.05), IVOMD (P<0.05) and EME (P<0.05) was found to be significant. Permanganate lignin (PmL) and fresh silage DM responded (P<0.05) to the independent effects of both BSY and ED. Absolute DM (P<0.0001) responded only to main factor effect of ED while ash contents (P<0.01) were influenced by BSY inclusion level. Organic matter contents of the silages were noted to be the only nutritional parameter that didn’t respond to both main and interactional effects.
Table 4: Combined analysis of BSY level (%) and ED (week) for fermentative, fungal load dynamics and chemical composition of FBSY-based silage (Mean daily temperature=15.40C and RH=84%)
Parameters
|
Mean
|
Max
|
Min
|
Effects
|
ED (weeks)
|
BSYL (%)
|
ED*BSYL
|
Temp (0C)
|
18.05
|
18.32
|
17.74
|
P<0.0001
|
P<0.01
|
P<0.05
|
pH
|
4.16
|
4.37
|
3.90
|
P<0.0001
|
P<0.0001
|
P<0.0001
|
TDML (%)
|
5.08
|
9.99
|
0.84
|
P<0.0001
|
P<0.0001
|
P<0.0001
|
Yeast (log10 CFU/g DM)
|
5.34
|
6.51
|
3.32
|
P<0.0001
|
P<0.0001
|
P<0.01
|
Mold (log10 CFU/g DM)
|
4.89
|
5.11
|
4.68
|
P<0.0001
|
P<0.0001
|
P<0.05
|
TFC (log10 CFU/g DM)
|
11.26
|
11.71
|
10.80
|
P<0.0001
|
P<0.0001
|
P<0.01
|
DM (g/kg DM)
|
935.19
|
951.76
|
918.88
|
P<0.0001
|
NS
|
NS
|
DM* (g/kg DM)
|
386.97
|
461.08
|
333.64
|
P<0.0001
|
P<0.0001
|
NS
|
Ash (g/kg DM)
|
59.11
|
63.50
|
55.62
|
NS
|
P<0.01
|
NS
|
OM (g/kg DM)
|
939.83
|
944.38
|
932.00
|
NS
|
NS
|
NS
|
CP (g/kg DM)
|
204.54
|
224.50
|
179.90
|
P<0.01
|
P<0.0001
|
P<0.0001
|
NDF (g/kg DM)
|
552.98
|
643.10
|
494.50
|
P<0.01
|
P<0.0001
|
P<0.01
|
ADF (g/kg DM)
|
115.93
|
125.56
|
101.20
|
P<0.01
|
P<0.0001
|
P<0.05
|
PmL(g/kg DM)
|
40.52
|
49.60
|
31.00
|
P<0.01
|
P<0.0001
|
NS
|
IVOMD (g/kg DM)
|
643.08
|
689.40
|
607.42
|
NS
|
P<0.0001
|
P<0.05
|
EME (MJ/kg DM)
|
10.28
|
11.03
|
9.71
|
P<0.05
|
P<0.05
|
P<0.05
|
DM= Dry matter; *=Fresh silage DM; ED= ensiling duration; PmL= Permanganate lignin; BSYL= brewer’s spent yeast level; TDML= total dry matter loss; CFU= colony forming unit; TFC= total fungal count; Temp= temperature; OM= organic matter; CP= crude protein; NDF= neutral detergent fiber; ADF= acid detergent fiber; PmL= permanganate lignin; IVOMD= in-vitro organic matter digestibility; EME= estimated metabolizable energy.
Yeast and mold colony counts of BSY-based silages
The interaction effect of BSY level and ED on yeast, mold and TFC for FBSY-based silage is presented in Table 5. Fungal count was significantly affected (P<0.01) by the interaction effect with yeast, mold and TFC observed to have been occuring within the range of 3.32-6.51, 3.19-5.72 and 6.51-12.23 CFU/g DM, respectively. Higher (6.51 CFU/g DM) and lower (3.32 CFU/g DM) of yeast count (P<0.01) was observed at the sixth and second week of the ED and at the 30 and 0% of BSY inclusion levels, respectively. A similar trend (P<0.05) was observed for mold and TFC as with the yeast, the highest (5.72 CFU/g DM) and the lowest (3.19 CFU/g DM) values still being recorded for same level of BSY inclusion level and ED. Generally, in the present study with an increase in BSY level and ED, fungal colony count was observed to have also increased.
Table 5. Interaction effect of BSY level (%) and ED (week) on yeast, mold and TFC of fresh BSY-based silage (Mean daily temperature=15.4 0C and RH=84%)
ED (weeks)
|
BSYL (%)
|
Fungal count (log10 CFU/g DM of BSY-based silage)
|
Yeast
|
Mold
|
TFC
|
2
4
|
0
0
|
3.32f
4.68e
5.21cd
|
3.19c
3.41c
3.59c
|
6.51f
|
8.09e
|
6
|
0
|
8.81e
|
2
4
|
10
10
|
5.01de
5.45cd
5.60bc
|
4.59b
4.29b
4.71b
|
9.61d
|
9.75cd
|
6
|
10
|
10.31bcd
|
2
4
|
20
20
|
5.30cd
5.44cd
5.60bc
|
4.48b
4.39b
4.79b
|
9.78cd
|
9.83cd
|
6
|
20
|
10.39bcd
|
2
4
|
30
30
|
5.98b
6.04b
6.51a
|
4.72b
4.52b
5.72a
|
10.70b
|
10.56bc
|
6
|
30
|
12.23a
|
|
SEM
P-value
|
0.162
<0.01
|
0.167
<0.05
|
0.271
<0.01
|
BSYL= brewer’s spent yeast level; CFU= colony forming unit; ED= ensiling duration; TFC= total fungal count; SEM = standard error of mean; Means with in a column with different superscripts differ at p<0.05
Fermentative characteristics of BSY-based silage
The effect of BSY level and ED on fermentative characteristics as measured through silage temperature, pH and TDML of fresh BSY based silage are presented in Table 6. Silage temperature, pH and TDML were greatly influenced (P<0.05) by the associative factors effects of BSY level and ED. Silage temperature, in general, did not show any predictable trend both with BSY inclusion level and ED except the higher temperature that recorded at 4th weeks of the ED and that observed at all levels of BSY inclusions. On the other hand, the pH of the silage ranged between 3.90 and 4.37 with lowest silage pH value (P<0.0001) at all but 20% of BSY inclusion levels being recorded for silage samples incubated at the sixth weeks from initial dates of the ED. The total dry matter loss of silage in the present study was in the range of 0.84-9.99% with lowest and highest values (P<0.0001) at all length of the ED being recorded for silage samples the BSY inclusion level was set at nil (0%) and at the maximum levels (30%), respectively. The result from the present study revealed that TDML showed increasing trend (P<0.0001) with an increase in both BSY inclusion level and ED.
Table 6. Interaction effect of BSY level (%) and ED (week) on fermentative characteristics of fresh BSY-based silage (Mean daily temperature=15.4 0C and RH=84%)
ED (weeks)
|
BSYL (%)
|
Parameters
|
|
Temperature (0C)
|
pH
|
TDML (%)
|
|
|
|
|
|
2
4
6
|
0
0
0
|
17.76c
18.28a
17.74c
|
4.37a
4.22c
3.92e
|
0.84l
1.13j
2.96i
|
|
|
|
|
|
2
4
6
|
10
10
10
|
17.80c
18.32a
17.98bc
|
4.29b
4.27b
4.28b
|
0.95k
3.47g
6.77d
|
2
4
6
|
20
20
20
|
18.06ab
18.24a
17.98bc
|
4.02d
4.15c
3.90e
|
3.32h
6.47e
9.56c
|
2
|
30
|
18.16ab
|
4.16c
|
5.74f
|
4
|
30
|
18.24a
|
4.24b
|
9.82b
|
6
|
30
|
17.12ab
|
4.00d
|
9.99a
|
|
|
|
|
|
|
SEM
|
0.081
|
0.020
|
0.009
|
|
P-value
|
<0.05
|
<0.0001
|
<0.0001
|
BSYL= brewer’s spent yeast level; ED= ensiling duration; TDML=Total dry matter loss, SEM= standard error of mean; Means with in a column with different superscripts differ at p<0.05
Chemical composition and in-vitro organic matter digestibility of BSY-based silage
The interaction effect of BSY inclusion level and ED for some chemical composition parameters are indicated in Table 7 while for those parameters influenced by main factor effects are indicated in Table 8. Crude protein showed incremental changes (P<0.0001) with BSY inclusion level and ED compared to that recorded for the control silages. However, the trend among the intervention silage groups remained consistent only for up to 20% level of fresh BSY inclusion. In general, higher CP contents were noted when BSY was included at the rate of 20% and for silage samples incubated for an ED of ≥4 weeks. Similarly, compared to the control silage groups, fiber constituents (NDF and ADF) of the silages were substantially improved (P<0.01) with interaction effects of fresh BSY inclusion and ED. On average this was 13.1, 26.1 and 18.3% reduction in NDF and 4.0, 3.6 and 16.3% reduction in ADF over the control for BSY inclusion rate of 10, 20 and 30%, respectively. Among the intervention groups (BSY based silages), maximum average NDF reduction was indicated for 20% BSYL while this goes up to 30% BSY inclusion level for ADF constituents of the silage mass. Both IVOMD and EME contents were considerably improved (P<0.05) over the control silage (silage to which no BSY included). The average values for IVOMD were 611, 654, 667 and 640 g/kg DM while the recorded values for EME were 9.8, 10.5, 10.7 and 10.2 MJ/kg DM for the control, 10, 20 and 30% BSY inclusions levels, respectively. Comparing with control values there was close to having 6.6, 8.5 and 4.6% more IVOMD and 6.6, 8.4 and 4.5% more EME for silage made from 10, 20 and 30% inclusion rates, respectively. Even though substantial improvements were observed over the control silages, it should be noted that both IVOMD and EME values didn’t respond to interactional effects when BSY was added at the rate of 30% inclusion and incubated for the various length of ED. The result from the current study indicated that silage made with BSY inclusion levels of 20% and that were subjected to ≥4 weeks of ensiling periods proven to have markedly higher (P<0.05) IVOMD and EME values over all remaining silage treatments (exceptions are those silage materials made at 10% BSY inclusion level and that ensiled for 2 to 4 weeks).
Table 7. Interaction effect of BSY level (%) and ED (week) on chemical composition, IVOMD and EME of FBSY-based silage (Mean daily temperature=15.4 0C and RH=84%)
ED (week)
|
BSYL (%)
|
Chemical composition and IVOMD (g/kg DM) and EME (MJ/kg DM)
|
CP
|
NDF
|
ADF
|
IVOMD
|
EME
|
2
4
|
0
0
|
182.6f
179.9f
|
643.1a
602.2b
|
120.9abc
122.3ab
|
614.2c
|
9.8c
|
610.7c
|
9.8c
|
6
|
0
|
185.3f
|
638.5a
|
124.2a
|
607.4c
|
9.7c
|
2
4
|
10
10
|
210.8cd
214.5bc
|
565.4c
559.1cd
|
125.5a
114.4bc
|
661.1ab
|
10.6ab
|
659.5ab
|
10.6ab
|
6
|
10
|
207.0de
|
540.7de
|
113.3c
|
642.1bc
|
10.3bc
|
2
4
|
20
20
|
201.0e
224.5a
|
494.9g
504.9fg
|
119.0abc
117.4abc
|
624.2bc
|
10.0bc
|
689.4a
|
11.0a
|
6
|
20
|
220.1ab
|
494.5g
|
118.2abc
|
688.2a
|
11.0a
|
2
4
|
30
30
|
208.8cd
209.8cd
|
550.7cd
517.1f
|
113.0c
101.6d
|
637.7bc
|
10.0bc
|
642.2bc
|
10.3bc
|
6
|
30
|
210.1cd
|
524.5ef
|
101.2d
|
639.9bc
|
10.0bc
|
|
SEM
|
0.160
|
0.667
|
0.271
|
1.257
|
0.201
|
|
P-value
|
<0.0001
|
P<0.01
|
<0.001
|
<0.05
|
<0.05
|
DM= Dry matter; CP=Crude protein; NDF=Neutral detergent fiber; ADF= Acid detergent fiber; IVOMD= In-vitro organic matter digestibility; EME= Estimated metabolizable energy; SEM=standard error of mean; BSYL=brewer’s spent yeast level; ED= ensiling duration; Means within a column with different superscripts differ at P<0.05
Fresh silage dry matter, ash and PmL responded better to main effect factors (Table 8). Accordingly, fresh silage dry matter and PmL contents significantly decreased (P<0.0001) with incremental changes in the level of inclusion rates of BSY in the silages. Higher values (P<0.0001) for both constituents were recorded for silages with no BSY inclusions (control silages) while the least values (P<0.0001) were noted for silages prepared from higher BSY inclusions level (30%). Similarly, DM was found to have declined with ED with silage samples ensiled for 2 weeks having 7.86 % more DM over that ensiled for 6 weeks of ED (Table 8). The result from same table showed that while ash values remained consistent (P>0.05) over ED, PmL values showed lower values (P<0.01) when silage samples were only ensiled for an extended period of 6 weeks.
Table 8. The main effect of BSY level (%) and ED (week) on fresh silage DM and chemical composition of fresh BSY-based silage (Mean daily temperature=15.4 0C and RH=84%)
BSYL (%)
|
Chemical composition ( g/ kg DM)
|
DM*
|
Ash
|
PmL
|
0
|
443.8a
|
58.1b
|
48.7a
|
10
|
393.4b
|
57.1b
|
44.3b
|
20
|
365.0c
|
59.0b
|
35.7c
|
30
|
345.6d
|
62.0a
|
33.3d
|
SEM
|
0.311
|
0.082
|
0.068
|
P-value
|
<0.0001
|
<0.01
|
<0.0001
|
ED (week)
|
2
|
404.5a
|
61.7
|
41.6a
|
4
|
383.6b
|
62.7
|
41.6a
|
6
|
372.7c
|
61.0
|
38.3b
|
SEM
|
0.26
|
0.07
|
0.05
|
P-value
|
<0.0001
|
0.068
|
<0.01
|
DM*= fresh silage dry matter; PmL= permanganate lignin; SEM=standard error of mean; BSYL=brewer’s spent yeast level; ED= ensiling duration; Means within a column with different superscripts differ at P<0.05;