Evaluation of the Fourier Frequency Spectrum Peaks of Milk Electrical Conductivity Signals as Indexes to Monitor the Dairy Goats' Health Status by On-Line Sensors

Abstract

The aim of this study is a further characterization of the electrical conductivity (EC) signal of goat milk, acquired on-line by EC sensors, to identify new indexes representative of the EC variations that can be observed during milking, when considering not healthy (NH) glands. Two foremilk gland samples from 42 Saanen goats, were collected for three consecutive weeks and for three different lactation stages (LS: 0-60 Days In Milking (DIM); 61-120 DIM; 121-180 DIM), for a total amount of 1512 samples. Bacteriological analyses and somatic cells counts (SCC) were used to define the health status of the glands. With negative bacteriological analyses and SCC < 1,000,000 cells/mL, glands were classified as healthy. When bacteriological analyses were positive or showed a SCC > 1,000,000 cells/mL, glands were classified as NH. For each milk EC signal, acquired on-line and for each gland considered, the Fourier frequency spectrum of the signal was calculated and three representative frequency peaks were identified. To evaluate data acquired a MIXED procedure was used considering the HS, LS and LS × HS as explanatory variables in the statistical model.Results showed that the studied frequency peaks had a significant relationship with the gland's health status. Results also explained how the milk EC signals' pattern change in case of NH glands. In fact, it is characterized by slower fluctuations (due to the lower frequencies of the peaks) and by an irregular trend (due to the higher amplitudes of all the main frequency peaks). Therefore, these frequency peaks could be used as new indexes to improve the performances of algorithms based on multivariate models which evaluate the health status of dairy goats through the use of gland milk EC sensors.

Keywords: Fast Fourier Transform; dairy goats; electrical conductivity; frequency peaks; mastitis; spectrum.

Figure 1

Dimensions of the EC sensor head.

Figure 2

View of prepared sensor heads. In the left picture, the positions of the conductivity meter heads and of the flow detectors, included in each experimental milking cluster, are also highlighted.

Figure 3

Block schema of the recording system. In the schema only one “analog conductivity board” and milking cluster is reported to simplify the reading of the figure.

Figure 4

Example of gauges obtained from the milk electrical conductivity (EC) signals acquired within a milking. The graphs in red show data concerning the left gland while those in blue are reported data for the right gland. In the upper graph the measured EC signals of milk acquired during a milking from each gland are reported. In same graph the milk flows recorded by the experimental milking cluster used during the trial are also shown. The following graphs report on: (1) the sequences without the signal samples related to the start and the end of milking (“A: Filtered samples of gland milk EC”); (2) the sequences where the mean value of each sequence have been subtracted to each signal sample acquired (“B: Scaled samples of gland milk EC”); (3) the spectrums obtained, applying the Fast Fourier Transform to the previous sequences of signal samples, and the three main frequency peaks identified for each Fourier frequency spectrum (“C: Signal spectrum with the main frequency peaks of the gland milk EC”).