MetaBoBainne Diet Study
Grass
GRS involves cows grazing primarily on pasture, relying on fresh grass as the main nutrient source. This system is low-cost, environmentally sustainable, and supports natural cow behavior. For our diet study, the GRS diet was composed of grazed pasture (95% annual average) through rotational grazing of perennial ryegrass (Lolium perenne L.) and parlor concentrates (5%).
Total Mixed Ration
TMR is a fully controlled feeding strategy where all dietary components—such as silage, hay, grains, protein sources, vitamins, and minerals—are mixed into a single ration and delivered to cows. For our diet study, the TMR concentrates had 93.9% DM, with 22% CP, 23.9% NDF, and 7.2% ash. In comparison, the parlor concentrates fed to each herd (sole concentrates for GRS herd) contained 89% DM, with lower CP at 13.3%, and higher fiber content at 30.9%
Partial Mixed Ration
PMR combines aspects of GRS and TMR, offering a partial mixed ration indoors while allowing cows to graze during part of the day. For our diet study, the PMR system involved cows grazing perennial ryegrass outside during daylight hours, whereas they were provided with a TMR diet at night. At night, cows were housed indoors and fed with the same diet as the TMR group but at half of the quantity. The PMR diet consisted of 45% grazed grass (9 kg), 22% concentrates (4.5 kg), 22% maize silage (4.5 kg), and 11% grass silage (2.25 kg).
The proportion of pasture in cow diet was demonstrated to have a significant effect on the milk metabolome. Multivariate analysis using PLS-DA revealed clear distinguishing effects between the diets, as shown here, with a clear evolution of the relationship between samples in line with the proportion of pasture. As such, GRS-derived milks are segregated clearly away from that of TMR, whereas PMR-derived milks demonstrate a similarity with both cohorts.
Variable importance in projection analysis highlighted 12 metabolites, in particular, driving this observed separation. The key metabolites for differentiation of milks from different feeding systems are represented here.
| structure | name | grass | partial mixed ration | total mixed ration |
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