Chemical composition of experimental diets
The chemical composition (% DMB) of nine experimental diets containing different binders at different levels for selection of suitable binder is represented in Table 2. The percentages of OM, CP, EE, CF, NFE and TA in SSCFB ranged from 89.96 to 93.57; 10.20 to 11.45; 2.15 to 2.93;20.07 to 24.95; 52.32 to 60.32 and 6.44 to 10.04, respectively. Similarly, the percentages of NDF, ADF, hemicellulose, cellulose and ADL of the experimental diets ranged from 47.52 to 52.37; 27.41 to 32.39; 19.31 to 20.55; 23.17 to 25.24 and 3.66 to 5.64, respectively. The CP content (%) of the complete diet (10.20 - 11.45%) was fixed to meet the crude protein requirements of rams (25 kg) based on the recommendation of
ICAR (2013) feeding standards. Incorporation of molasses, GM or CDS at different levels in concentrate mixtures did not affect the CP, EE, hemicelluose and cellulose content of the complete diets. The CF, TA, NDF and ADF content was lower and OM, NFE content was higher in GM incorporated diets, which could be due to higher inclusion of maize in these diets to balance for the energy and protein.
Physical and drying characteristics of sorghum stover based complete feed blocks with different binders
In the present study, CFBs with CDS as binder were not obtained at any inclusion level as it was unable to hold the feed particles together which might be due to the lower dry matter or higher moisture content in the CDS (70%) when compared to molasses (20-30%) (
Satheesh, 2016). CFBs with CDS, resulted in poor block formation and the blocks were very fragile and very weak in intactness, such that it could not be handled, stored or transported. Another possibility for the fragile CFB may be due to lower soluble sugar content in CDS when compared to the molasses. The soluble carbohydrates in CDS are 47.87% (
Satheesh, 2016) where as in molasses it is 85-90% (
Perez. 1995). Hence, due to the lower content of soluble carbohydrates and low DM content in CDS, it failed to form the compact block. According to the current study, CDS is not suitable to make complete feed blocks. The physical and drying characteristics of SSCFB with molasses and GM is presented in Table 3 and 4, respectively and overall comparison among 6 diets is detailed in Table 5.
The bulk density (kg/m
3) of SSCFB with different binders (Table 5) varied from 487.74 to 579.69kg/m
3. With molasses as binder, significantly (P<0.01) lowest bulk density was observed at 6% level compared to 8 and 10% inclusion levels and the bulk density in latter two groups was comparable. In case of CFBs with GM as binder, bulk density (kg/m
3) was comparable (P>0.05) among three levels of GM addition. Between the binders, CFBs containing 6% molasses had significantly (P<0.01) lower bulk density than the other feed blocks. However, there was no significant difference in bulk density between the M-8, M-10, GM-6, GM-8 and GM -10 feed blocks.
Samanta et al., (2003) recorded the bulk densities of CFBs with 10% molasses as 550-600 kg/m
3 corroborating with present results. These findings were also within the range given by
Hozhabri and Singhal (2006) with the wheat straw based CFBs with 10% molasses and the bulk density values were ranged from 422.48 to 550.25 kg/m
3. Current results are in agreement with
Yasir et al., (2008), who recorded the bulk densities (kg/m
3) of paddy straw, maize stover and oats straw based CFBs as 533.76, 600.52 and 489.2, respectively. These values are also within the range given by
Singh et al. (2016) where the bulk density of the rice straw and wheat straw based CFBs ranged from 484.4 kg/m
3 to 562.6 kg/m
3. The bulk density of the blocks of about 210 kg/m
3 was reported by
Chaudhary et al. (2017) for paddy straw based CFBs containing kinnow-mandarin waste, which is very low as compared to the 450 kg/ m
3 density recommended by
FAO (2012) for the straw based feed blocks.
The durability of SSCFB with different binders varied from 10.50 to 35.64 The CFB’s containing 10% GM, 8 or 10% molasses had significantly (P<0.01) higher durability compared to other feed blocks. The durability in other feed blocks
i.e prepared with 6% molasses and 6 or 8% GM was comparable. The durability of the blocks was increased with increasing level of binders in the diet. The results of the present study were in agreement with findings of
Sushmitha (2019), who observed increased (P<0.05) durability of complete feed blocks with increased level of molasses in chickpea straw based complete feeds and highest durability was observed at 10% level. In corroboration with the present results,
Edwin (2005) also reported higher durability values with inclusion of molasses at 10% level in SSCFB. In comparison to the present study, the durability values obtained by
Singh et al. (2016) with wheat and rice straw,
Sivajanani and Jeyalingawathani (2018) with rice straw and
Hozhabri and Singhal (2006) with wheat straw were higher and the values varied from 70.3 to 91.32%. During densification process, due to the application of high pressures and temperatures, solid bridges may be developed by diffusion of molecules from one particle to another at the points of contact. In this study, low durability (%) of the CFBs might be due to the poor development of solid bridges between the feed particles as temperature rise during densification was negligible
(Chaudhary et al., 2017) or may be due to the inadequate pressure created by the feed block making machine
Saleem et al., (2003). Similarly, higher durability was also recorded by
Yasir et al. (2008) with paddy straw, maize stover and oats straw based CFB as 76.83, 78.74 and 70.16%, respectively and higher durability in this study might be due to the inclusion of tree leaves at higher proportion (30%) or due to the urea treatment of test crop residues for preparation of feed blocks that lead to low resilience characteristics resulting in low PCE and high durability of straw based feed blocks. Moreover, tree leaves are rich in soluble carbohydrates and proteins that might have acted as additional binding agents. The durability of the paddy straw based complete feed blocks containing kinnow-mandarin waste as reported by
Chaudhary et al. (2017) was 17.36%.
Post compression expansion (%) of sorghum stover based complete feed blocks with molasses and guar meal as binders (Table 5) ranged from 8.52 to 22.50. The sorghum stover based complete feed blocks with 6% GM had significantly lower (P<0.01) PCE of the 8.52% followed by GM-8 feed blocks (12.50%) and there was no significant variation in the PCE of M-6, M-8, M-10 and GM-10 based complete feed blocks. Variations in PCE of complete feed blocks might be attributed to the different resilience characteristics of roughage sources and also to the moisture content of material, which determines the resiliency of the compacted briquette
(Yasir et al., 2008). Low (P<0.01) PCE in GM-6 and GM-8 feed blocks may be due to low final moisture content in the feed blocks.
Sushmitha (2019) also recorded similar range of PCE (12.81 to 19.65%) for chickpea straw based complete feed blocks prepared with molasses (5, 7.5 and 10% level) as binder. While
Singh et al. (2016) observed higher PCE (28.18 to 37.79%) for wheat and rice straw based complete feed blocks. Similarly,
Samanta et al. (2004) and
Hozhabri and Singhal (2006) also recorded higher PCE for wheat straw based complete feeds (35.4% and 45.6%, respectively) than blocks with other roughages which could be attributed to the higher capacity of wheat straw particles to attain their original shape than those of other roughage sources after the removal of pressure.
Initial moisture (%) of SSCFB with two different binders (molasses and guar meal) ranged from 11.04to 15.27 (Table 5). Significantly (P<0.01) highest initial moisture (%) was recorded with the blocks containing 10% molasses (M-10) and lowest (P<0.01) was observed at 6% guar meal (GM-6). Strength and durability of the densified products increased with increasing moisture content until an optimum is reached.
Reece (1966) found that, alfalfa hay with moisture contents of 10 to 23% produced wafers with durability of 80 to 90%. He observed that it was difficult to make wafers when the moisture content was 25% and above. At high moisture, probably due to the incompressibility of water, moisture trapped within the particles may prevent complete flattening and the release of natural binders from the particles
(Pickard et al., 1961). The moisture content in the current study was within range as prescribed by
Reece (1966) and it can be considered as an optimum for making of durable complete feed blocks.
Sushmitha (2019) reported significantly (P<0.05) higher initial moisture (%) at 10 per cent molasses with the chick pea straw based complete feed blocks and the values were ranged from 11.66 to 17.85% corroborating with the present findings.
Chaudhary et al. (2017) reported higher initial moisture (23.07%) for paddy straw based complete feed blocks containing kinnow-mandarin waste (KMW) which could be due to hygroscopic nature of KMW.
Final moisture (%) of sorghum stover based complete feed blocks with two different binders (Table 5) ranged from 6.62 to 12.00. The SSCFB with 10% molasses (M-10) as binder had significantly (P<0.01) higher final moisture (12%) than the other feed blocks
. The final moisture (%) content is relatively higher in molasses based CFBs when compared to GM based feed blocks which may be due to the hygroscopic nature of molasses. Final moisture level of the blocks achieved in the present study after 16 h drying was optimum for safe storage (6-12%). The present results are in agreement with the values reported by
Chaudhary et al. (2017) for paddy straw based complete feed blocks (12.13%). Similar results were also reported by
Sushmitha (2019) with chick pea straw based CFBS and the values were ranged from 10.20 to 10.37%.
Edwin (2005) recorded higher final moisture (%) when compared to the present study with sorghum stover blocks with molasses as binder and values were varied from 18.76 to 21.85% which could be due to the hygroscopic nature of molasses which makes it difficult to dry under humid conditions.
The binder which produced the blocks with higher bulk density and durability along with lower PCE was selected as the best binder. The bulk density and durability was higher (P<0.001) in M-8, M-10 and GM-10 feed blocks. The GM-8 blocks had higher bulk density (P<0.001) but less durable (P<0.001) than the other feed blocks. Durability and bulk density of GM-10 and M-10 blocks were comparable with M-8 feed blocks but the PCE of GM-10 and M-10 blocks was 11.61 and 10.75% higher than the M-8 blocks, respectively. As per the cost economics molasses (Rs. 6/kg) is cheaper than the guar meal (Rs.35/kg). By considering all these parameters we have selected molasses at 8% as a best binder for preparation of the feed blocks.