Performance of autumn- and spring-calving Holstein dairy cows confined indoors or managed with pasture and supplementation under various housing conditions.

Dairy cows' productive performance is influenced by various factors, including nutrition, housing comfort, and weather conditions during grazing. In classic confinement systems, animal comfort is typically ensured through ventilation and sprinkling features. However, in mixed feeding systems, controlling environmental conditions at the supplementation site is less common. The present 2-yr study evaluated 2 lactations and 2 calving seasons (autumn and spring) with 3 treatments that combined 2 housing systems (compost barn [CB] or outdoor soil-bedded pens with shade structures [OD]) and 2 feeding strategies with varying proportions of grazing (TMR with no grazing and one-session grazing supplemented with mixed ration [GRZ]). The treatments resulted in the following combinations: (1) CB-confined cows fed a TMR ad libitum (CB-TMR); (2) CB housing with GRZ (CB-GRZ); and (3) OD housing with GRZ (OD-GRZ). Data collected included milk production and composition, feed intake, BCS, BW, and cyclicity. The confined system resulted in higher milk and milk solids production per cow than the mixed feeding systems, with differences being more pronounced in the spring- than in the autumn-calved cows. However, contrary to our hypotheses, the differing environmental exposure in the 2 mixed feeding systems did not affect overall performance, although under certain exposure conditions, the CB outperformed and better protected against heat stress than the OD during several weeks of the trial. In OD-GRZ, milk solids production per cow was greater in autumn- than in spring-calving season, whereas solids production in CB-TMR and CB-GRZ did not differ between autumn- and spring-calving cows. Total DMI and feed efficiency, as well as the amount of concentrate per unit of milk, were higher for the confined system than the mixed feeding systems, with no effect of calving season or environmental exposure level between the 2 mixed feeding systems. Confined cows maintained higher body reserves throughout the trial, with no effects of environmental exposure in the mixed feeding systems. The OD-GRZ had the highest operating profit and return on assets, followed by CB-GRZ and CB-TMR. In conclusion, in the mixed feeding system, performance was not affected by housing conditions at the supplementation site, whereas profitability was higher for OD-GRZ. Regardless of calving season, confined cows produced more milk than mixed feeding cows, with differences being more pronounced in spring-calving compared with autumn-calving cows.