Nutrient Degradability and gas production after 24 hours of incubation
Although the rations were formulated to be isocaloric and isonitrogenous, the decrease in degradability with the ascending substitution of alfalfa hay with Panicum maximum hay, this may be due to 1) the increase in CF, NDF, ADF and Ash content as substituting rate increased parallel with the decrease in OM contents (table 1), 2) the higher content of tannins and total phenols for Panicum hay compared to alfalfa hay (table 3). In this connection, Cilliers and Van der Merwe, (1993) concluded that the decrease in Panicum digestibility is associated with a decrease in N content and an increase in NDF, ADF, and ADL contents. Indeed Zhong et al. (2021) reported that dry matter degradation increased in feedstuff with low levels of lignin and NDF because high levels of lignin may resist fiber degrading microorganisms’ activity in the rumen. A similar trend was observed by Ramirez et al. (2009). Also, Yasmin et al., (2008) found that the presence of secondary metabolites or anti-nutritional factors (ANFs) in animal diets affects nutrient digestion and absorption negatively where the studied panicum maximum contained high levels of tannins (table 3). Anti-nutritional factors (ANFs) such as tannins, glucosides, flavonoids, alkaloids, terpenoids, cyanides, coumarin, nitrate, oxalate, and organic acids have different effects on animal performance. High levels of ANFs in an animal’s diet prevent the growth of microbes and fungi in the rumen, thus affecting the rate of nutrient digestion and absorption (Acamovic and Brooke 2005). The higher gas production parameters observed in the control ratio may be due to the fact that alfalfa is a legume that contains higher CP% and lower contents of both fiber fractions NDF, ADF, and Ash compared to Panicum maximum hay (Table 1). Although the rations were formulated to be isocaloric and isonitrogenous, there is a positive relationship between Dry Matter, NDF, and ADF Degradability (Table 1) and gas production. This relationship has been confirmed by Blummel et al. (1999), who reported that in-vitro gas production is an indirect measurement of positive changes in dry matter degradability. In addition, Blummel and Orskov (1993) observed a positive correlation between DM disappearance and gas production. Blummel et al. (1999) reported that gas production is closely related to SCFA production, which will be discussed later (Table 5). Concerning to effect of the spirulina supplementation levels on increased degradability, this may be due to several factors, including the high nutrient density of Spirulina and the stimulation of extracellular enzyme secretion by gut microflora (Tovar-Ramírez et al., 2002). Spirulina also contains vitamins, minerals, essential fatty acids, amino acids, and other nutrients that promote faster growth (Costa et al., 2016). Additionally, Spirulina reduces rumen protein degradation and alters bacterial community composition, leading to an increase in the efficiency of rumen microbial crude protein production in steers (Panjaitan et al., 2010). The increase in gas production with spirulina supplementation levels may be due to two reasons. Firstly, the degradability rates increase as spirulina supplementation increased (Table 4), which activate the microflora in the rumen, leading to an increment in the production of microbial protein and an increase in fiber degradability (Costa et al., 2016). Secondly, spirulina contains all essential amino acids and has a great impact on digestibility (Lafarga et al., 2020; Chia et al., 2019).
Fermentation and Calculated parameters after 24 hours
The level of ammonia in rumen liquor is an indicator of nutritional conditions, as many types of rumen micro-organisms use ammonia as a source of nitrogen. Mixing Alfalfa and Panicum maximum showed improved pH and NH3 than other treatments containing either of them alone. This may be attributed to complementarity between Alfalfa and Panicum maximum, leading to an improvement in the quality of the fodder, as confirmed by Alasa et al, (2014) when concluded that intercropping grasses (Panicum maximum) with forage legumes (lablab purpureus) improve the quality of the fodder. Additionally, there was an increase in degradability rate and gas production as substituting levels increased (Table 4). Elevated values of ammonia were associated with an increased percentage of Panicum in rations (R2 and R5). This may be attributed to an increased in CP content of the concentrate ration portion through increasing protein sources, especially Soya meal (highly degradable protein source, Table 1) to compensate for the low CP content of Panicum to get iso protein rations. This is in line with Jahan et al. (2018), who reported that many nitrogenous substances in the high concentration diet may be the possible reason for increasing NH3-N concentration. Nousiainen et al. (2009) also supported this explanation, where they found that increased concentrate protein feeding improved whole-diet digestibility in cows in a curvilinear manner because of positive effects on the ruminal environment for fiber digestion, but the magnitude of the effect was not very large. Regarding the volatile fatty acids, carbohydrates are fermented by a variety of bacteria in the rumen and transformed into volatile fatty acids (VFA) by the corresponding enzymes (Wang et al. 2020). The data showed a significant decrease in TVFA with the ascending substitution of alfalfa hay with Panicum hay. The control ratio (R1) was higher than the values for R2, R3, R4, and R5. This may be due to the low content of fiber fractions (NDF and ADF) and Ash in alfalfa hay compared to Panicum hay, with comparable contents of carbohydrates (NFC contents) in both alfalfa and Panicum hays (Table 1). Additionally, there was an increase in the degradability of DM, NDF and ADF as well as gas production (Table 4), as well as an increase in OMD, ME, and SCFA (Table 5). All these results improve the fermentation process, leading to an increment of VFA. The inclusion of 2 kg/ton spirulina resulted in a significant (P < .0001) increase in pH value and ammonia concentration, without affecting the value of TVFA concentration. These results may be due to the high nutrient density of Spirulina and the stimulation of extracellular enzyme secretion by gut microflora (Tovar-Ramírez et al., 2002). Spirulina also contains vitamins, minerals, essential fatty acids, amino acids, and other nutrients that promote faster growth (Costa et al., 2016). Similar observations were reported by Panjaitan et al., (2010) feeding Spirulina platensis as a supplement along with low CP containing guinea grass (Panicum maximum) hay improved efficiency of microbial protein production in cattle. Panjaitan et al. (2015) increased microbial protein synthesis and rumen ammonia-N in a quadratic fashion with increasing Spirulina inclusion in the diet. The differences between this study and our findings may be due to the differences in the experimental condition, ration composition and levels of supplementation as well as type of animals.
It’s clear that there is an inverse relationship between the ratio of Panicum maximum in ration, and the calculated parameters (OMD, ME and SCFA). This may be attributed to 1) decrease CP and EE contents in rations with panicum hay (table1), this observation was in line with the reported work of Blummel and Orskov (1993) reported that, there is a positive correlation between the calculated metabolizable energy from in vitro gas production together with CP and EE contents as well as ME value of conventional feeds measured in vivo. 2) Decrease OM contents and increased of CF, NDF and ADF in rations with panicum hay (table1), The low OMD and ME obtained for the level of panicum in the treatments increased might probably connected with the presence of high fiber (Blummel and Orskov, 1993) especially in treatment R5 (panicum 100%). 3) Relationship between the SCFA and gas production (table 4), similar observation was reported by Getachew et al. (2000) the SCFA estimated from in vitro gas production, has been widely used to evaluate the energy value of several classes of feed. Blummel and Orskov (1993) who suggested that gas production from different classes of feeds incubated in- vitro in buffered rumen fluid was closely related to the production of SCFA which was based on carbohydrate fermentation. The present findings indicated that all in-vitro parameters are affected by the concentration of panicum in ration. Supplementing the experimental rations with ascending levels of spirulina showed a positive relationship between the concentration of spirulina and the calculated parameters (OMD, ME and SCFA) until the highest values (40.51,7.16 and 0.64, respectively), which were produced with the highest concentration of spirulina 3 kg/ton, Table (5) and Fig. (8A, 8B, 8C). Referring to increased values of calculated ME with increasing spirulina concentration proved that Spirulina specifically 3 kg/ton has a good potential to enhance energy content of roughage feedstuffs. Moreover, as the level of SCFA, which is an indicator of the energy content of the ration, its production increased with increasing spirulina concentration in ration. This is due to the fact that Spirulina species, known as cyanobacteria, contain the essential fatty acids, linoleic acid (LA, 18:2 delta-9,12) (table 2) and gamma-linolenic acid (GLA, 18:3 delta-6,9,12) (Gupta et al., 2008), high quality proteins, carbohydrates, vitamins (B1, B2, tocopherols), minerals (sodium, potassium, calcium, magnesium, phosphorus, iron), carotenes (especially beta-carotene), chlorophyll a, phycocyanin, and some phenolic acids (Gupta et al., 2008). Consequently, rations associated with spirulina makes it possible to raise digestion rates, the energy supply and mineral elements to the microbes present in the rumen fluid, thus improve their growth and activity, and thus, increase the rates of degradability of OMD, ME and SCFA.