## 2 Materials and Methods  
### Study of Spectral Characteristics of Feed Mix Components  
The physical phenomenon serving as a basis for the offered method consists of measuring the image reflection ability of a forage mix surface layer. At the preliminary laboratory study stage, it was necessary to determine spectral characteristics of components of feeding mixes as exemplified by a cattle feed ration. This type of ration can contain natural-origin forages (grass green mass, corn silage, alfalfa haylage) and concentrated mixed fodder (consisting of grain mash, corn, and barley as rape meal and sunflower meal). The study aimed to determine the optical properties and establish correlation spectral dependencies of the most commonly used components in cattle feed mixtures. The investigated materials included corn silage. The exploration of optical properties was carried out using a spectrofluorimeter CM 2203 (Lumex, St. Petersburg, Russia) (Figure 1), through which the most indicative ranges of photoluminescence for corn silage were determined. Based on the conducted measurements, it was revealed that the excitation of photoluminescence in corn silage occurs from 220 nm to 550 nm. The most representative range of photoluminescence for corn silage was found to be from 350 nm to 365 nm, where the strongest light signal absorption occurred. This allowed for the use of light-emitting diodes and photodiodes tuned to the corresponding frequency in the portable device prototype. Preliminary measurements from the spectrofluorimeter, which determined the most representative measurement range of 350-365 nm, shaped the concept of constructing a portable optical device. As there is a high probability of external light exposure within this range, the decision was made to eliminate external light exposure by creating a light-permeable casing with a retractable case. For the utmost representativeness of optical measurement results, the internal part containing the optical module was colored in a matte black shade to eliminate reflections. The external appearance of the portable optical device for determining the photoluminescence of agricultural feeds is depicted in Figure 2.  
Since the luminescent emission from silage has extremely low intensity, signal amplifiers are necessary for its detection alongside the photodiode. Operational amplifiers AD820 ANZ (Analog Devices, Shanghai, China) are used as amplifiers. Once the signal passes through the operational amplifier, it is processed via the microcontroller ATmega328P (Atmel Corporation, Shenzhen, China) and subsequently displayed on the LCD 2004 (Winstar Display, Taiwan, China). The laboratory analyzer is powered by batteries with a nominal capacity of 2200 mAh. Device control is carried out through the keyboard (Figure 2, position 3). The key indicator that determines the quantity of nutrients in feed is the dry matter content or its inverse value (humidity). Based on these values, farmers determine the agrotechnical deadlines for plant processing or the timing for starting feed harvesting. Additionally, it involves modeling a multi-component diet, considering the balance between total dry matter consumption and moisture level. This is especially important for livestock groups during peak lactation periods. The algorithm for determining the dry matter content using a portable optical device based on photoluminescence is presented in Figure 3.  
Figure 1: Spectrofluorimeter CM 2203 for determining the indicative ranges of photoluminescence in agricultural feed. Figure 2: Portable optical device for determining the nutritional value of corn silage through photoluminescence. 1—feed bed, 2—display, 3—interface control unit, 4—console, 5—photodiodes, 6—light-emitting diode, 7—adjusting screw. The main hypothesis of the presented study is to determine the nutritional value of agricultural feed using an optical method that does not require preliminary sample preparation. This will ensure the construction of a device for conducting measurements in the field.