Fecal Matter Applications
Introduction
Analysis of feces in different types of animals has long been used for multiple types of tests and research. As a sampling method for wild animals, it offers the advantages of being non-invasive and the elimination of blood and tissue samples, which is impractical for many animals in the field. Determination of many diseases and the presence of parasites is done for all types of animals, including pets. Advances in molecular biology technology have broadened the scope of the types of applications that fecal analysis can be used for in animals. These include population survey, genetics, and minimum viability, material and energy flow of wild animals, and home range. In terms of chemical and physical parameters, food composition and digestive dynamics can be analyzed from fecal composition. Numerous tests exist for determining both the physical and chemical composition of animal feed and feces. Analysis that determines the digestibility of animals by comparing nutritional parameters in both feed and feces is especially useful in determining the composition of Total Mixed Rations (TMR) for farm animals. While effective, these tests are often expensive and time-consuming while requiring the use of toxic chemicals and solvents. They are not suited for large-scale analysis and can only test a single parameter at a time.
NIR spectroscopy offers the advantages of being fast and non-invasive while requiring little to no sample preparation. While this method does require the creation of chemometric models that correlate NIR spectra to the parameters of interest, once the models are created the advantages are vast. Large amounts of samples can be tested in a quick manner and multiple parameters of interest can be determined from a single reading. An examination and review of applications using NIR spectroscopy in the animal feed industry is presented here. Reviewed topics include the use of the technique to determine chemical and nutritional parameters in animal feces for the determination of animal digestibility.
Analytes
- Dry Matter
- Crude Protein
- Starch
- Ash
- Acid Detergent Fiber
- Acid Detergent Lignin
- Neutral Detergent Fiber Components (aNDFom, uNDF240, IVNDFD240)
- Moisture
- Crude Fat
- Crude Fiber
- Nitrogen
- Digestible Energy
- Digestibility Components (Dry Matter, Organic Matter, Energy, Nitrogen Content)
- Total-Tract Apparent Digestibility
Scientific References and Statistics
Near Infrared Reflectance Spectroscopy to Predict Fecal Indigestible Neutral Detergent Fiber for Dairy Cows
Neutral detergent fiber (NDF) is the most common measure of fiber used for animal feed analysis. It represents most of the structural components in plant cells, such as lignin, hemicellulose, and cellulose. The concentration in NDF in feed is negatively correlated with energy concentration. Ruminal digestion of NDF is linked to the part of NDF that is indigestible and the rate at which the potentially digestible NDF is fermented. Indigestible NDF (iNDF) has been reported to be a reliable digestibility marker in controlled animal experiments. The term undigested NDF (uNDF) was created to improve the accuracy of the standard terminology used to describe fiber fermentation dynamics. It can be estimated from long-term (240 hours) in vitro fermentation. uNDF240 refers to this procedure and represents the fiber fraction that affects physical effectiveness, digestion, passage rates, and gut fill of forages. Measuring these digestibility parameters in feed and forage and then comparing fecal NDF parameters gives valuable information on the proportion of potentially digestible NDF really digested in vivo. Traditional methods for determining digestibility parameters in feed, forage, and fecal matter are both expensive and time-consuming (especially in the case of uNDF240). Such analysis often requires the use of hazardous chemicals and is only able to determine one parameter of interest at a time. NIR spectroscopy has been extensively analyzed and used as an accurate alternative method for determining digestibility parameters. It offers the advantages of being fast, accurate, and non-invasive as well as requiring minimal sample preparation and the ability to determine multiple parameters of interest from a single measurement. In this study, NIR spectroscopy was used to correlate NIR spectra to various NDF parameters as well as other standard quality measurements in fecal samples of dairy cows. Specifically, the goal of the study was to construct calibrations for fecal uNDF240 in dairy cows to aid nutritionists in the adaptation of the cow response to forage quality. While many studies have been conducted that use NIR spectroscopy to determine digestibility parameters, this is the first to specifically correlate fecal uNDF240 to NIR spectra.
A total of one thousand two hundred and eighty-one fecal samples were collected from dairy cows for the study. Three hundred and one of these samples were selected for NIR spectra collection and standard testing for parameters of interest. Four separate feeding trials were conducted for sample collection to incorporate as much variability as possible in the parameters of interest. Differences in the trials included the forage fed to the cows and cow lactation level. A portion of each sample was used to conduct reference tests for the following parameters of interest: Dry Matter (DM), Crude Protein (CP), Starch, Ash, Acid Detergent Fiber (ADF), Acid Detergent Lignin (ADL), and three specific NDF parameters. aNDFom is amylase and sodium sulfite-treated NDF corrected for ash residue. uNDF240 is undigested NDF estimated via 240h in vitro fermentation. IVNDFD240 is in vitro aNDFom digestibility after 240h of incubation. The remaining portion of each sample was packed into a spinning cup holder for NIR spectra collection. Samples were scanned using an NIR spectrometer from 400 nm to 2498 nm at 2 nm intervals. Various pre-treatment algorithms were applied to the NIR spectra before chemometric analysis. Calibration models were constructed that correlate the NIR spectra to the parameters of interest. Results are shown below.
| DM | R2 = 0.77 | SECV = 1.11 |
| CP | R2 = 0.93 | SECV = 1.08 |
| Starch | R2 = 0.66 | SECV = 0.55 |
| Ash | R2 = 0.91 | SECV = 0.98 |
| aNDFom | R2 = 0.92 | SECV = 1.89 |
| ADF | R2 = 0.91 | SECV = 2.07 |
| ADL | R2 = 0.93 | SECV = 2.05 |
| uNDF240 | R2 = 0.92 | SECV = 2.24 |
| IVNDFD240 | R2 = 0.90 | SECV = 3.43 |
SECV stands for Standard Error of Cross-Validation and references the percent error that can be expected by using the models in a predictive capacity. Units for all parameters are expressed as % DM. It must be noted that all reference tests were not performed on every sample and the range of values for the different parameters varied. However, reference tests were performed on at least two-hundred and forty-nine samples for all digestive parameters. The R2 correlation coefficient was above 0.90 for all digestibility parameters, proving the feasibility of the method. The results of this study and advantages presented by NIR spectroscopy in analyzing the three NDF parameters present enormous potential. The traditional reference methods for determining these parameters are especially complex and time-consuming. Ultimately, the important conclusion from this study is that uNDF240 is a physical entity that is composed of various chemical entities that can be accurately predicted using NIR spectroscopy. It is an excellent marker for tracing real digestibility in dairy cows from the diet to the feces and using NIR spectroscopy for this purpose has the potential to be a game-changer in the feed and dairy industries.
Application of FT-NIR Spectroscopy for Evaluation of Feeds Digestibility by Analysis of Feces Chemical Composition
Over past decades with the emergence of new analytical methods and software advances, the determination of feed and forage nutritional value for farm animals has received more attention from nutritionists. Likewise, technological advances in computers and the development of multivariate statistical analysis have allowed spectroscopic methods to develop as an alternative to traditional reference methods for determining chemical and physical parameters of interest. Numerous studies have proven the feasibility of using NIR spectroscopy as a method for determining the nutritional value of feed and forage. While not as widespread, another application of NIR spectroscopy is to monitor the products of nutrient digestion and fermentation through fecal analysis. The potential exists to use NIR spectroscopy as a method for optimizing animal feed from the raw material analysis through feed formulation and digestibility determination after feeding. Traditional methods for determining parameters of interest in both animal feed and feces are expensive and time-consuming while requiring extensive sample preparation and the use of toxic chemicals. Most traditional methods can only determine a single parameter of interest per test as well. NIR spectroscopy offers the advantages of being fast and non-invasive while requiring minimal sample preparation. While the process of creating calibration models that correlate NIR spectra to physical and chemical parameters of interest can be extensive, once models are constructed they can predict multiple parameters from a single spectrum measurement. In this study, NIR spectroscopy was used for assessing the digestibility of feed determined from the chemical composition of pig feces.
The parameters analyzed in this study are moisture, crude protein, crude fat, and crude fiber. Over sixty samples of pig feces were procured from a farm for the study. Before NIR spectra were collected, traditional methods were used to determine reference values for the parameters of interest. Moisture values were determined by drying the sample to a constant weight at 103°C. Crude fat was determined by extraction of the sample in a Soxhlet apparatus. Crude protein was determined by the Kjeldahl method. Crude fiber was determined by intermediate filtration. A FT-NIR spectrometer was used for NIR spectra collection. Samples were scanned from 12,400 cm-1 to 3,600 cm-1 using 16 cm-1 resolution. Each sample was scanned three times and the scans were averaged into a single spectrum. Various pre-treatment algorithms were applied to the NIR spectra before chemometric analysis. Calibration models were created using the NIR spectra and reference values to correlate the spectra to the parameters of interest. Results are shown below.
| Moisture | Range – 65.9% to 84.1% | R2 = 0.98 | RMSEP = 0.67 |
| Crude Protein | Range – 3.8% to 10.27% | R2 = 0.90 | RMSEP = 0.48 |
| Crude Fat | Range – 1.34% to 3.77% | R2 = 0.82 | RMSEP = 0.31 |
| Crude Fiber | Range – 3.14% to 5.71% | R2 = 0.81 | RMSEP = 0.42 |
The results of this study were excellent and proved the feasibility of the method. The models were validated by removing five of the samples from the calibration models, creating new models without those five samples, and using the new models to predict reference values for the five removed samples. This method is known as cross-validation and predicted values for moisture, crude protein, crude fat, and crude fiber compared well with values determined by traditional methods. Further study using this method could be used to expand the number of physicochemical parameters, such as amino acids, starch, total sugars, and energy and digestibility parameters in pig feces. The possibility also exists of using FT-NIR spectroscopy for determining the quality of organic fertilizers that are made from animal feces.
Predicting Feed Digestibility from NIRS Analysis of Pig Faeces
Animal feed often requires careful management and balance due to increasing costs and the scarcity of raw materials. The feed formulation process optimizes the cost while providing sufficient nutritional intake to animals. However, while diets are optimized for nutritional value and cost, the actual digestive capabilities of animals depend on several factors. These can include age and genetic background. Feces represent the end product of the digestive process and can contain information on both the animal feed itself and the digestibility of the animal. An easy measurement of digestibility with minimal cost and animal disturbance could provide the basis for experimental designs on a large number of animals, especially when comparing genetics and the digestive capabilities of animals. NIR spectroscopy is well-suited for such an experiment. It offers the advantages of being fast and non-invasive while requiring little or no sample preparation. Successful studies have been conducted analyzing the digestibility of broilers using excrement and NIR spectroscopy. In this study, various feed digestibility parameters in pigs were measured in feces to determine if NIR spectroscopy is a suitable method for analyzing digestion capabilities. The study was designed and conducted using a specific feed fed to pigs that varied in genetic background and age. Thus, the feed effect is absent and any differences in feces only come from the digestive process.
A total of two hundred digestibility collections were carried out on twenty castrated male pigs for the experiment. They were of the same breed but bred from four different boars. After a week long adaptation period to the diet and living area, feces were collected during weekdays for ten consecutive weeks. Pigs were fed pellets twice a day containing a high fiber diet (NDF = 21.4% DM) to maximize potential digestibility differences. Feed samples were also kept and analyzed over the course of the experiment. At the end of each week, each of the five feces sampled collected per pig over the course of the week were pooled, homogenized, freeze-dried, and ground for chemical analysis. Gross energy, total nitrogen, and minerals were measured in both the feed and feces, allowing for the calculation of the following digestibility coefficients: Dry Matter (dDM), Organic Matter (dOM), Energy (dE), and Nitrogen Content (dN). Total Nitrogen (N) and Apparent Digestible Energy Contents (ADE) were expressed relatively to DM. A portion of each ground feces sample was set aside and scanned using an NIR spectrometer from 400 nm to 2500 nm in 2 nm increments. For each sample, two portions were scanned in the sampling cup and these two NIR spectra were averaged into a single spectrum. Various pre-processing algorithms were applied to the NIR spectra before chemometric analysis. Partial Least Squares (PLS) calibration models were created to correlate the NIR spectra to the digestibility parameters of interest. Results are shown below.
| Nitrogen (%DM) | R2 = 0.88 | SEC = 0.08 |
| Digestible Energy (kJ/kg DM) | R2 = 0.77 | SEC = 167 |
| Digestibility Coefficients (%): | ||
| dDM | R2 = 0.64 | SEC = 0.97 |
| dOM | R2 = 0.80 | SEC = 0.79 |
| dN | R2 = 0.82 | SEC = 1.04 |
| dE | R2 = 0.77 | SEC = 0.87 |
This study showed decent correlation and results from the calibration models, especially considering the limitations of the sample set. While nitrogen is not directly correlated with digestibility, it is important to note that the results for nitrogen shown here are comparable with other studies using pig, poultry, and rabbit feces to measure nitrogen. This comparison validates the experiment, sample collection, and reference data used in the study. The correlation for dOM, dN, and dE can be considered adequate for screening purposes. While the correlation for dDM is smaller, the actual error can be considered low relative to the small variation in the reference values. The important conclusion to note from this study is the digestibility of animals can be measured using NIR spectroscopy. An expansion of this work could use different feeds of varying nutritional value and then compare the differences between determination of nutritional content in feed and feed digestibility in animals using NIR spectroscopy.
Predicting feed digestibility from NIRS analysis of pig faeces – PubMed (nih.gov)
The Use of Visible/Near-Infrared Spectroscopy to Predict Fibre Fractions, Fibre-Bound Nitrogen and Total-Tract Apparent Nutrients Digestibility in Beef Cattle Diets and Faeces
Beef cattle diet can be assessed in vivo by evaluating animal growth, body conditions, and fecal characteristics. It can also be assessed in vitro by chemical and nutritional analysis of Total Mixed Ration (TMR) and fecal analysis. Fecal analysis is the best way to analyze animal digestibility. Such analysis includes observing color, consistency, undigested physical residues, pH, and particle size distribution. Fiber fractions are particularly important because they relate to dry matter intake, rumination behavior, nutrient digestibility, and passage rate. Fiber fractions bind less digestible fractions of nitrogen and include undigested neutral detergent fiber (uNDF). Combined analysis of uNDF in both feed and feces is a good determinant of Total-Tract Apparent Digestibility (ttaD) of several nutrients, which allows for the estimation of nutrient utilization when feed intake and fecal output are not provided. While such analysis has been proven to be valid in numerous studies using traditional methods, these methods are time consuming and expensive. They are also inadequate for large scale testing. NIR spectroscopy offers the advantage of being fast and non-invasive while being able to measure large amounts of samples with little or no sample preparation. In this study, a comparison between using NIR spectroscopy to measure fiber content as well as fiber bound Nitrogen and ttaD using uNDF as a marker in both feed and fecal samples of beef cattle was analyzed.
A total of one hundred seventy-two pools of fecal samples were collected over one year from five farms located in a specific region of Italy for the study. All samples were collected twenty-four hours after feeding. One hundred sixty-four corresponding feed samples were selected as well. Both the fecal and feed samples were dried, ground, and split into two portions. One portion was used for chemical analysis and the other for scanning with an NIR spectrometer. Numerous nutritional, chemical, and digestibility parameters were measured using standard methods of analysis for both the fecal and feed samples. The remaining portions of the feed and fecal matter were scanned using a NIR spectrometer from 400 nm to 2500 nm in 0.5 nm increments. Thirty-two scans were collected per reading and averaged into one spectrum per sample. Various pre-processing algorithms were applied to the spectral data before chemometric analysis.
Most of the numerous parameters analyzed in this study were unable to be adequately predicted using NIR spectroscopy. Good correlation and accurate predictions were made for Acid Detergent Fiber (ADF), Nitrogen, and Ash in the TMR samples, while only ADF showed good correlation and accurate predictions in the fecal samples. For both the feed and fecal samples, ttaD showed an R2 correlation coefficient lower than 0.66, a result not considered good enough for any kind of accurate analysis. Further detailed examination of the results would be necessary to determine the reasons for the poor results, as many of the examined nutritional and digestibility parameters have been accurately predicted using NIR spectroscopy in other studies. Possible explanations include reference error and low variability among the parameters of interest. Despite the poor results in this study, the benefits of using NIR spectroscopy for the type of analysis studied here are vast and warrant further study to see if such analysis can be used to determine ttaD in feed and fecal samples from beef cattle.