Abstract

The trial aimed to compare the fatty acid profile of milk from dairy cows under Exclusive Grazing (EG), Supplemented Grazing (SG) or Full Confinement (FC) system. Sampling was performed in 2017 and 2018 on 6707 dairy cows from Querétaro, Tabasco, Colima, Veracruz and Chiapas in Mexico. Among the 84 farms included in the trial, 25.3% were in FC (1699 animals) and fed corn silage, alfalfa hay, tropical forages and commercial balanced concentrate (16% CP; 5 to 7kg/ head/day); in both extensive (EG) and Supplemented (SG) Grazing there was a mixture of tropical grasses: Cynodon niemfluensis, Muhlenbergia robusta, Brachiaria brizantha, B. decumbens and Echinochloa Polystachya. Group EG (30%, 2014 heads) was permanently grazing while SG (44.6%, 2944 heads) was also supplied with a commercial balanced feed (18% crude protein; 2 to 3kg/head/day). Average daily milk yield was significantly (P<0.05) different among groups: 16.2±2.12kg (FC), 9.5±2.72kg (SG) and 7.2±1.530kg (EG). The breeding system also affected milk fatty acid profile, particularly the ω6/ω3 ratio: increasing the amount of concentrate in the diet significantly (P<0.05) increased milk ω6 or decreased ω3 concentration, thus diminishing the beneficial effects for human health.

Keywords:Milk; Grazing; PUFA; Omega fatty acids; Omega6/Omega3 ratio