4.1. Dynamics of the Fermentation Profile
The silages presented pH values within the range considered ideal (between 3.8 and 4.2), as recommended by McDonald et al. [
1] for CS. These values indicate quality fermentation, showing that there were significant amounts of soluble carbohydrates among the TRS. Corn has elevated levels of soluble carbohydrates, the main substrate for silage fermentation, which allows the rapid dominance of lactic acid-producing bacteria, causing a drop in pH. These values corroborate those reported by Zanine et al. [
2], who used sugarcane as a forage in TRS, with the addition of babassu by-products.
Therefore, to obtain good silage, the DM content is seen as a fundamental element, since it directly affects the fermentation process, influencing the types of organic acids formed. According to Monteiro et al. [
26], the values shown as ideal are around 28 to 34%; in this way, we identified that the TRS was within the ideal range. Gusmão et al. [
27] found a similar effect when evaluating total feed silages containing elephant grass as a forage source, where an increase in DM content was observed in relation to the control treatment.
The indices presented for the interaction between lactic acid and the fermentation profile can be explained by the change in the silage fermentation profile, mainly due to its DM content below 25%.
TRSS and TRSC total feed silages showed the highest N-NH
3 means (9.14 and 8.99, respectively). The increase in these levels in TRS indicates a proteolysis process due to the greater supply of crude protein. Proteolysis is usually the result of the activities of enterobacteria and bacteria of the genus
Clostridium, which can produce substances harmful to animal health and are responsible for large losses [
1]. However, these results indicate a good fermentation profile because the silages evaluated in the present study showed values within those required by the quality standards in order to be considered good silage (8 to 11% of N-NH
3), according to Henderson [
28].
The highest losses from gases and effluents were obtained by CS. This is probably due to the lower DM content of CS at the time of ensiling (
Table 3). According to Rabelo et al. [
29], the silages that presented a higher moisture value were better compacted and had a greater disruption of the cellular structures of the plants, which resulted in greater losses of their contents and thus, greater nutrient losses and reduced nutritional values, justifying the greater production of butyric acid in CS.
The type of fermentation that occurs in silages is directly related to gas losses when homofermentative bacteria use glucose as a substrate for lactate production; thus, there is a lower gas loss, according to McDonald [
1] and consequently, greater energy use. Thus, the inclusion of these ingredients reduced the losses of gases and effluents in the TRS, attributed to the adequate fermentation profile as an increase in the DM content.
Rezende et al. [
30] reported a 21 g/kg reduction in effluent losses with the addition of 15 g/kg babassu meal to sugarcane silage. Zanine et al. [
15] highlighted a reduction of 1.26 g/kg in effluents from
Pennisetum purpureum silage with the addition of cassava chips. In the present study, the inclusion of babassu by-products was satisfactory, as it reduced the humidity inside the silo and provided less leaching of nutrients along with the effluents. An increase in DM content in silage is one of the main reasons for reducing effluent production and DM losses. The high capacity of this additive to absorb moisture and the high amount of soluble carbohydrates stimulates the rapid growth of LAB, resulting in rapid pH reduction. Furthermore, Zanine et al. [
7] reported that babassu reduced water activity and increased osmotic pressure in silage, making the environment less favourable for the growth of undesirable microorganisms.
Observing the chemical composition of silage, the contents of ashes and organic matter (OM) were close to the initial values, indicating the quality of the ensiled materials accumulated through a good sealing process for the silos. Restelatto et al. [
31], when working with CS in a total mixture using microbial additives, similar to that used in this work, did not find any variations in ash and OM.
4.2. Chemical Composition and In Vitro Digestibility
The inclusion of concentrates altered the crude protein content of the silages (
Table 6). CS had a CP content of 8.03%, similar to that found by Oliveira (8.0%) [
32] when working with CS at the milky stage. For treatments that received babassu by-products, the levels remained at 16% CP, meeting the nutritional requirements of lactating dairy cows, according to NRC [
9]. Thus, the nutritional contents of the silage were preserved, indicating the quality of fermentation and the lower protein breakdown and losses.
CS exhibited superior averages for NDFcp, both in the ensiled material and in the silage. The inclusion of babassu by-products in TRS reduced these contents, since they had a lower NDF content (66% NDF for babassu flour and 63.5% NDF for babassu cake) compared to grass (65.7% NDF). Similar results were reported by Santos et al. [
6] and Zanine et al. [
7].
According to Van Soest [
33], NDF content is directly related to DM digestibility and consequently, to DM intake by animals. Foods that have a high concentration of indigestible fibre reduce the rate of passage of digesta through the rumen, increasing the time that food remains in the digestive tract and reducing the DM intake, which compromises the performance and production of animals.
In this study, differences were observed in the NDF content before and after ensiling (
Table 3 and
Table 6), which is explained by the variations in biochemical processes that occurred in the silages. The NDF from CS increased after ensiling, which was also observed by Neumann et al. [
34]. In the TRS silages, the opposite behaviour was observed; that is, after ensiling, the NDF content was lower than in the fresh material, indicating better nutrient digestibility.
For the variable of ether extract (EE), CS (26.9 g/kg DM) only differed from that of TRSF (20.1 g/kg DM), an effect attributed to the ingredients used. Valadares Filho et al. [
35], when working with babassu cake, observed EE values between 5.51 and 4.23%.
In regards to total carbohydrates, the CS presented a higher average in relation to the TRS, an effect possibly linked to a higher NDFcp concentration and low crude protein content compared to TRS. However, in
Table 5, the crude protein content of the TRS was, on average, twice as high as that in CS, thus contributing to these differences between the silages. In an animal diet, there is a balance between NDF and NFC for good efficiency and development of ruminal microorganisms because the high availability of NFC can cause a physiological imbalance in ruminants, such as sudden changes in ruminal pH [
36].
TDN remained low in CS in relation to TRS, which can be explained by the inclusion of concentrates in the TRS, which reduced the levels of NDF. According to Cabral et al. [
37], the NDF content was inversely proportional to that of NFC and TDN; thus, when evaluating the TRS, an increase in the levels of TDN was observed. In this way, it can be inferred that the addition of concentrates in SRT promotes greater availability of nutrients for ruminal microorganisms and, consequently, the ruminants.
The lower TDN content and higher lignin (ADL) content from CS provided lower in vitro digestibility of DM.
TRS showed a longer stability than did the CS. Prolonged aerobic stability in TRS has been reported in other studies [
38]. In general, acetic acid produced through the metabolism of heterofermentative lactic acid bacteria is one of the main factors responsible for greater aerobic stability in silages [
39]. When it is present in satisfactory amounts, these compounds can inhibit the growth of yeasts, microorganisms that initiate the deterioration process [
40]. Thus, the acetic acid concentration found in this study was similar among all the TRSs, and the presence of other undissociated acids may have contributed to the greater stability of TRS. However, there is a deficit in the literature with regards to corn silages with the addition of babassu by-products associated with the fermentation profile. Studies must be carried out to explore the potential of these by-products in order to add value to the understanding of their use in the composition of animal diets.