**5. Degradability parameters of** *Erythrina edulis* **obtained** *in situ*

In situ degradability parameters of *E. edulis,* are shown in **Table 4**. The SF had highest disappearance of fast and slow fractions compared to SV (*α*, 35.6 vs. 28.6 0.57%/h; *p* = 0.003; *b,* 51.1 vs. 24.8 0.57%/h; *p* < 0.001, **Table 4**). But, the "*c*" degradation rate in SF was lower when compared to SV (0.55 vs. 0.62 0.57%/h; *p* < 0.001; **Table 4**). Despite this, SF had greater effective degradability values in all passage rates than SV 2%/h (73.1 vs. 47.4 0.57%/h; *p* < 0.001), 5%/h (62.4 vs. 42.3 0.57/h; *p* < 0.001), 6%/h (60.0 vs. 41.2 0.54%/h; *p* < 0.001) and 8%/h (56.4 vs. 39.4 0.57%/h; *p* < 0.001), respectively, as shown in **Table 4**.

In contrast, no differences in the soluble fraction "*α*" for CP between both phenological stages (35 2.03%, on average) were observed (**Table 4**). Nevertheless, the SF showed a highest insoluble but potentially "*b*" degradable fraction than SV (50.0 vs. 18.4 2.03%/h; *p* < 0.001; **Table 4**). Whereas the ED only varied at passage rate of 2% between SF vs. SV (66.4 vs. 52.3 2.0%/h; *p* = 0.011; **Table 4**).

The rumen degradability in SF was highest for all degradation parameters "*α*," "*b*," *α* + *b*, and ED. These differences might be related with lower fiber contents, which increase of total degradable fraction (*α* + *b*) [9]. Furthermore, with regard the lower ED for SV, we hypothesized that greater cell wall components especially lignin will be implicated. Naranjo [35] in leaves of *E. edulis* reported lower degradation parameter *α* (21.1 vs. 28.6%) than the obtained in this study, although with higher *b* (35.2 vs. 24.8%) and *c* (0.09 vs. 0.06/h) fractions. Differences that might be as a consequence of our greater ADF contents (51.2 vs. 32.2%). In this sense, forages with high wall cell components, have showed lower digestibly data, due to decreases the colonization of


*1* <sup>α</sup>*: Soluble fraction;* <sup>b</sup>*: Insoluble but degradable fraction; kd: The rate (%/h) of disappearance of* <sup>b</sup> *fraction. <sup>2</sup> Passage rates, according to Bhargava and Ørskov [69] for different intake level. INRA [31] with a fixed transit rate of 6%/h.*

*3 SV, leaves.*

*4 SF, sheath.*

*ab Mean value with different letter in the same columns differ (*p *< 0.05).*

#### **Table 4.**

*Disappearance of fast and slow fractions and effective degradability values of DM an CP from* Erythrina edulis.

*Nutritional Potential of* Erythrina edulis *as a Forage Alternative for Supplementation… DOI: http://dx.doi.org/10.5772/intechopen.107496*

rumen microbiota reducing its degradation [49, 66, 70]. Despite all differences above mentioned, the SF had higher DM degradability than SV and other forage sources [35, 71], which might be related to its lower NDF, ADF and ADL contents. To the best of our knowledge, there are no more reports with sheath of *E. edulis*, so our data could be proposed as referential.

In ruminants, the quantity of amino acids that reach the small intestine depends on the microbial protein synthesis and feed proteins which escape ruminal degradation. Therefore, the feed protein degradation can be affected by its nature [72–75]. Consequently, the CP content degraded in the rumen is determined by their fractional degradation and passage rates [38, 45, 76]. At present, the model of Ørskov et al. [30, 77] for describing protein degradation and escape, it is widely accepted and applied. How in other studies, the CP degradability increased with incubation time. According to Ibrahim et al. [47], the CP from lush pasture is highly soluble and rapidly and extensively degraded in the rumen. Possibly, this could explain our no differences in the *α* fraction rate between both studied stages (35%, on average). Nevertheless, the SF showed a higher insoluble but potentially degradable fraction "*b*" (50 vs. 18 2.03%/h), although with a slower CP disappearance rate than to the observed in SV, as shown in **Table 4**. Regarding the lower "*b*" fraction observed for SV, it could be explained by its chemical composition: greater fiber contents, resulting in a lower CP degradability than SF. Additionality, Bhargava and Ørskov [50] and Camero et al. [12] stated that when protein degradability is high, the release rate of microbial substrates is high, as well as the period after feeding, during which the microbial substrates are released over a short period of time. Therefore, the CP content in the rumen of both phenological stages was mainly affected by the retention time agree with Ørskov and McDonald [30]. In this study, at 24 h, the CP degradability in SF was 13% higher than SV (61 vs. 53 2.50%/h), which is opposite to the mentioned by Ma [63] that higher contents of CP had beneficial for CP degrading in the rumen. Similar trend was observed at 72 h incubation time, with clear differences between both studied stages (78 vs. 53 2.50%/h). Despite this, the passage rate of 5%, 6% and 8% per hour did not vary between leaves or sheath, because of similar degradation rate (0.36%/h, on average), with exception for at 2% passage rate (66 vs. 52 2.0%/h; **Table 4**). Based on these results, the "*b*" degradability rates should be taken in account for the ration in feeding ruminant programs. Referential values in leaves of *E. edulis* reported by Rosales [35] have shown a slight greater *α* fraction than our study (41 vs. 35%/h) but with a lower "*b*" potentially degradable fraction (38 vs. 50%) and no differences in disappearance rate (0.03%/h). Contrary to this, higher degradation parameters for "*α*," "*b*," and ED in other *Erythrina* varieties *(indica, subumbrans, variegata and berteroana)* than the obtained in *E. edulis* have been reported by Kongmanila et al. [18] and Pedraza et al. [59]. Anyhow, the chemical composition as well as degradability parameters obtained in this study, could be similar to the other multipurpose fodder trees and shrubs (e.g., *Leucaena leucocephala, Gliricidia sepium,T. tetraptera*, *L. diversifolia*, and *L. sericeus*) widely used in ruminant nutrition [13, 78, 79].

## **6. Conclusions**

The *E. edulis* showed similar CP contents to other widely sources used in diets for livestock nutrition, but the leaves showed greater wall cell contents than the sheath. As a consequence, at 72 h incubation time the leaves had lower DM and CP disappearance than the sheath. For this reason, the ED of DM in SF was higher than SV, and only differences at outflow rate of 2%/h for CP was observed. Based on these findings, it necessary to perform an *in vivo* study to determine adequate levels of inclusion in ruminant feeding. Anyhow, *E. edulis* is an interesting feed to include as a supplementation to improve low quality forages in livestock systems.
