The DM is an important factor for determining the nutritional content of forage before ensiling since it indicates the adequacy of wilting. A high forage DM (DM > 50%-55%) makes it difficult to achieve anaerobic conditions during the ensiling process, and silage is more susceptible to heating and mold growth (Piltz, 2016). In contrast, a high moisture content favors undesirable microorganisms, while a higher DM content impacts the compaction and reduction of the air present (Santos et al., 2006). In this study, the dry matter content of the fresh forages used for making silage ranged between 36% and 40%. However, at harvest, the dry matter content of the silage decreased to 26.5% and 32%, which is similar to the findings of recent studies showing that the ideal DM content is between 30 and 35% (McDonald et al., 1991a). The silage made of the [Brachiaria mulato (70%) + Desmodium distrortum (30%)] mixture (BD) had a greater DM content (32%) than did the silage made of Brachiaria mulato alone (B), measured at 26.5% DM.
Silage can be defined as an acidic fermentation product from ensiled materials (McDonald et al., 1991a), where pH is a good indicator of silage fermentation quality (Kung et al., 2018). Kung & Shaver, (2004a) recommended that good tropical silages have a pH of 4.3–4.7; however, this study indicated that the overall mean pH measured at silage maturity (day 48) was estimated to be 4.74 ± 0.20, which is considerable (Min = 4.41; Max = 5.00). Considerable variations were also detected, indicating a significant difference in pH between the 24 samples. Previous studies have suggested that a minimum pH of 4.4 is useful as a benchmark for good cassava peel silage (Asaolu, 1988), while silages of whole-plant corn and alfalfa were found to have a pH ranging between 3.14 and 5.43 (Kung et al., 2018). Furthermore, Ghedalia and Miron (2001) reported that the pH of silage from alfalfa spp. treated with S02 was 4.51, whereas that of silage from Brachiaria mulato and Panicum coloratum was 4.78 and 4.68, respectively. Therefore, the final pH of silage is likely affected by a series of factors, mostly including the DM of the ensiled forages, the ammonia produced during maturation and the nutritional value of the forage species (Kung et al., 2018).
Ammonia is produced during the clostridial fermentation of amino acids from ensiled forages (Charmley, 2001). In well-preserved silage, a small proportion of NH3 is produced, alongside other products such as nitrogen as part of amino acids and peptides (Harrison et al., 1994). Moreover, ammonia is a good indicator of fermentation. In this study, the ammonia concentrations in the silage from the four treatment groups ranged from 0.08–0.10%, while the ammonia content in the corn silage ranged from 5 to 7%, which falls within the normal range (Kung & Shaver, 2004a). Reports have suggested that an ammonia content less than 10% is desirable, while values greater than 15% can reduce silage intake, resulting in poor dairy cattle performance (Kung and Shaver, 2004a). In comparison, ammonia nitrogen concentrations ranging from 1.17–10.94% were reported for alfalfa silage by Sánchez-Duarte and García (2017); these values are higher than the ammonia content [NH4+ -N (%)] estimated to be between 0.02 and 0.18 g, which was recorded for the silos in this study. Additionally, the measured crude protein (CP, %) content suggested important variations among the silage samples, with an overall mean ± SD of 10.02 ± 2.61%. Considerable magnitudes were also observed, from 3.69–13.85%. Furthermore, a very significant difference was confirmed between the 24 sample values. According to our separate analysis, the ammonia and crude protein contents (%) were not correlated in the 24 silage samples analyzed in this study.
Neutral detergent fibers (NDFs) consist of hemicellulose, cellulose, and lignin from whole plants, while acid detergent fibers (ADFs) consist of cellulose and lignin. After the silage was harvested, NDF and ADF were measured for all the silos. The results of this study showed that the percentage of neutral detergent fibers (%) and the percentage of acid detergent fibers (%) were 62.92 ± 7.82 and 37.72 ± 5.78 (mean ± SD), respectively. Both parameters exhibited relatively important variations, and later, the 2 variables were found to be strongly correlated. As suggested in the results, silages made of 100% grasses (Treatment 1: Brachiaria mulato and Panicum coloratum) presented relatively greater percentages of neutral detergent fibers (%), acid detergent fibers (%), pH, total fermentation losses (g) and dry matter (DM%) than did mixtures of Brachiaria mulato (70%) + Desmodium distrortum (30%) and Panicum coloratum (70%) + Desmodium distortum (30%). In previous studies, NDF was found to range from 53.7–70.6%, while significant variations among the treatments were found for NDF and ADF in mixed silages (grass * legumes); in contrast, the sole panicum maximum silage contained 59.67% NDF and 33.83% ADF (Okukenu et al., 2021). This finding indicates a certain similarity with findings from the current studies. Furthermore, Kung and Shaver (2004b) suggested that a higher content of NDF in silage is usually an indication of the presence of soluble nutrients that are degraded during silage fermentation, which affects the nutritive value of the silage. It is believed that microbial fermentation processes occurring in the silo produce an array of end products and can change many nutritive aspects of a forage as a result of fermentation losses. Therefore, delayed silo filling, prolonged wilting periods, and/or the method of compacting can cause a reduction in fermentable sugars, hence resulting in clostridial fermentation (Mills & Kung, 2002).
During this study, dry matter loss significantly varied among the treatments during the ensiling period, which was in accordance with the findings of previous studies (Kung et al., 2000), where untreated silage was subjected to prolonged fermentation due to its buffering capacity. Indeed, Hoffman et al. (2011) reported a decrease in starch-protein ratio in high-moisture corn due to degradation caused by proteolytic activity within the extended ensiling period. In summary, the mixture of BD and PD had higher levels of nutrients than did the single grasses.