Daytime Grazing in Mountainous Areas Increases Unsaturated Fatty Acids and Decreases Cortisol in the Milk of Holstein Dairy Cows

SIMPLE SUMMARY: The effects of grazing dairy cows in mountainous areas for 12 and 24 h compared with keeping the cows under confined settings were evaluated by examining the overall levels of fatty acids and cortisol in milk as an indicator of stress. Our findings revealed favorable changes in cows grazing for 12 h, with significantly improved milk fatty acid profile and decreased milk cortisol content. Additionally, we found no significant changes in the milk yield of 12 h grazed cows compared to the control group of confined cows, while milk fat and protein showed higher values in 12 h grazed cows. Grazing for 24 h caused a significant decrease in the milk yield compared to the two other groups. Overall, grazing for 12 h in a mountainous area is suggested to be beneficial for animal welfare, with positive improvements in milk fatty acids and lessening of stress levels without adverse effects on milk yield. ABSTRACT: The effects of grazing lactating cows in mountainous areas for 12 and 24 h compared with the confined indoor system were evaluated by examining the overall milk fatty acid and cortisol. Twenty-one dairy cows were allocated to three treatment groups: (1) control (confined management system in a free-stall barn; TMR based), (2) grazing for 12 h (12 hG; TMR plus grazing pasture), and (3) grazing for 24 h (24 hG; pasture-based feeding system). Dry matter intake was higher in the control and 12 hG groups than in the 24 hG group. The yields of total milk and the 3.5% fat-corrected milk were the lowest in the 24 hG group. Milk fat was the highest in the 24 hG group and higher in 12 hG compared with the control group. Milk protein and lactose levels were the highest in the 12 hG group. The highest somatic cell count was observed in the 24 hG group. The saturated fatty acid levels were higher in the control group compared with the 12 hG and 24 hG groups. There was no difference in overall mono-unsaturated fatty acids between 12 hG and 24 hG groups. Poly-unsaturated fatty acids were higher in the 12 hG group compared with the control and 24 hG groups. There was no difference in omega-6 (ω-6) fatty acids among the groups, and omega-3 fatty acids were higher in the 12 hG group than in the control group. Milk cortisol was the highest in the 24 hG group and higher in the control group compared with the 12 hG group. Taken together, grazing for 12 h is advisable for farms that have access to mountainous areas to improve the milk fatty acid profile and decrease the stress levels in high-yielding Holstein lactating cows.