Abstract
Milk obtained from sheep grazing natural pastures and some forage crops may be worth a plus value as compared to milk obtained from stall-fed sheep, due to their apparently higher content of beneficial fatty acids (FAs). Fourier transformed mid-infrared (FT-MIR) analysis of FA can help distinguish milk from different areas and diverse feeding systems. The objective was to discriminate milk from sheep and milk from dairy sheep rotationally grazing Italian ryegrass or berseem clover for 2, 4, or 6 h/day. To test this hypothesis, a data-mining study was undertaken using a database of 1,230 individual milk spectra. Data were elaborated by principal component analysis (PCA) and analyzed by linear discriminant analysis (LDA) with or without the use of genetic algorithm (GA) as a variable selection tool with the primary aim to discriminate grazed forages (grass vs. legume), access time (2, 4, or 6 h/day), grazing day (first vs. last grazing day during the 7-day grazing period), and the milking time (morning vs. afternoon milking). The best-fitting discriminant models of FT-MIR spectra were able to correctly predict 100% of the samples differing for the pasture forage, 91.9% of the samples differing for grazing day, and 97.1% of the samples regarding their milking time. The access time (AT) to pasture was correctly predicted by the model in 60.3% of the samples, and the classification ability was improved to 77.0% when considering only the 2 and 6 h/day classes.
Highlights
Grazing delivers high-quality ruminant products usually at a lower cost as compared to stall feeding [1]
C12:0) and n-3 (p < 0.050), whereas the grazing day affected all variables with the exception of C12:0 (p < 0.073) and unsaturated fatty acids (UFA)
The content of short-chain fatty acids and saturated fatty acids (SFA) was higher in milk samples from sheep grazing the legumes than the grass pastures
Summary
Grazing delivers high-quality ruminant products usually at a lower cost as compared to stall feeding [1]. In Mediterranean dairy sheep production systems, diets only with pastures are rather rare because pasture availability is low, at least for part of the pasture growth cycle. Part-time grazing (PTG) i.e., a time-restricted allocation of ruminants to pasture is a widespread grazing technique in many areas of dairy sheep production. This technique has several benefits compared to 24-h grazing such as a better balancing of ruminant diet and a higher efficiency and evenness of herbage utilization, due to lower sward damages by animal trampling [3]
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