# Microwave Heat Treatment Induced Changes in Forage Hay Digestibility and Cell Microstructure
## 4 Discussion
### Scanning Electron Microscope Image Analysis  
Observation with SEM image confirmed that cell wall intactness was visible in orderly in the control sample irrespective of their high sun-drying texture during hay processing (Figures 1 and 2). An extensive cellular surface breakdown could be seen in the MW treated SEM images. The MW treatment might induce cell microstructures to disintegrate and initiate the loosening of intactness [10]. The central core sample showed more disruption than the top surface sample, which is likely due to the unevenness of MW heating [27]. The pixel intensity represents the primary pixel value, which helps to identify and classify differences in images based on texture, smoothness, and pattern [28]. In the present study, higher intensity variance in the MW treatment sample in comparison to the control indicates that there might be some potential destruction that occurred in the cell microstructure of the lucerne and wheat hay (Figures 1 and 2). Previous studies also supported this finding in the present study. For example, [PERSON] et al. (2006) [10] found that due to MW treatment, destruction in the microstructure of cell surface occurred in soybean grain, which eventually increased the extraction of soluble soy protein. Another study with rapeseed also reported microstructure disruption due to MW treatment [29]. However, it is important to note that the level of microstructure destruction in grain and forage hay may not be the same, as they are different from each other based on morphological and chemical structure.  
Relationships between the Minimal Microwave Energy Input for Different Hay to Achieve Maximal Dry Matter Digestibility Increase  
The current study showed a strong positive relationship between MME and baseline CP content of control hays (Figure 3b), and to the best of our knowledge, this is the first time a study reported such relationship. Hays with higher CP content generally required more input energy to achieve maximum DMD content improvement and the optimum MW energy for lucerne hay (1320 kJ kg\({}^{-1}\)) in present study is similar to the optimum energy calculated in the study conducted by [PERSON] et al. (2012) [13] (1200 kJ kg\({}^{-1}\) calculated from 0.750 kW MW power used 80 s treatment time for 0.05 kg sample). In the present study, positive changes in DMD of hays were also found to be related to the baseline CP content of hays (\(\mathbf{r}^{2}=0.57\)). A previous study also suggested that the improvement of digestibility (with vs without any processing) considerably depends on the control feed CP content and its digestibility [30]. However, changes with other baseline organic matter (e.g., ADF and NDF) were not as strong as CP content in this study. The reason is unknown for this relationship. Further research is required to understand and validate the relationship.  
It is important to note that the influences of MW heating on the material are affected by dielectric properties [9], each biological material possess different degree of dielectric properties, which ultimately affect the temperature distribution in the target material. Responses in any heated material depend on the temperature distribution, retention, and equilibrium [31; 32]. These mechanisms regulate the heat-induced changes in any materials. Therefore, the changes in the nutrient composition and their digestibility depends on the temperature distribution in the hays. Further research into the dielectric properties of the forage hays used in this study is required to understand the relationships between major nutritive value parameters (e.g., CP and DMD) and dielectric properties of the materials in order to better understand the MME required to achieve maximum change in nutritive characteristics.