Effects of different feeding time and frequency on metabolic conditions and milk production in heat-stressed dairy cows.

The aim of this paper was to evaluate the effects of three different feeding management (FM) schedules on physiological markers of heat stress (HS), metabolic conditions, milk yield and quality during the hot season in dairy cows. The study involved 27 mid-lactating cows, subdivided in three homogeneous groups differing in feeding time and frequency: total mixed ration (TMR) delivered once daily in the morning (M); twice daily, half in the morning and half in the evening (ME); once daily in the evening (E). During the trial, blood samples were collected in the morning (a.m.) and in the evening (p.m.), breathing rate (BR), rectal temperature (RT), and milk yield were recorded and individual milk samples were collected. Microclimate data indicated that cows were subjected to mild-moderate HS. During the hotter days, cows receiving M treatment showed higher values of RT (38.97 °C vs 38.68 °C and 38.62 °C, in ME and E) and BR (71.44 vs 66.52 and 65.26 breaths min⁻¹, in ME and E), a.m. plasma glucose was lower in M (3.69 vs 3.83 and 3.83 mmol L⁻¹, in ME and E) and a.m. plasma urea was lower in E (4.82 vs 5.48 and 5.35 mmol L⁻¹, in M and ME). Milk yield was unaffected by FM, as well as milk composition and cheese-making properties. Only milk protein content and yield were higher in M (3.42 vs 3.36 and 3.27 g 100 mL⁻¹; and 1.11 vs 1.08 and 1.02 kg day⁻¹, for ME and E). Our results on cow physiology indicate that M seems a less suitable FM to match cow welfare during the summer season.