Effect of winter and spring meteorological conditions on milk production of grazing dairy sheep in the Mediterranean environment

This three-year study evaluated the effects of winter and spring meteorological conditions on milk production of grazing dairy sheep in Mediterranean conditions, in order to define optimal and critical thresholds, quantify milk yield reductions due to environmental stress, and evaluate the immediate or delayed effects of meteorological factors (MF). Milk production was recorded twice a day (7:00 and 15:00) throughout the lactation period (January–June) in three flocks (FL) kept in the same experimental farm but grazed different pasture areas. The first flock (FLNA) was composed of Nera di Arbus dairy ewes managed conventionally; the second flock (FLSD) was composed of Sarda dairy ewes managed conventionally; and the third flock (FLORG) was a mixed flock of Nera di Arbus and Sarda dairy sheep raised under organic management. Daily MF and some biometeorological indices, i.e. Wind Chill Index (WCI), Temperature Humidity Index (THI) and derived indices, were evaluated by using hourly data recorded 24 h before the last milking of each day and also 1, 2 and 3 days before milking in winter and spring. Data on main MF associated with the morning and afternoon milkings were analyzed using the hourly data from 15:00 of the previous day to 6:00 of the day of milking and from 7:00 to 14:00 of the day of milking, respectively. The interaction between FL and MF was not significant in winter and spring. Milk yield was influenced by most of the MF studied, especially minimum, average and maximum air temperature in both seasons and, to a lesser extent, permanence at temperatures below 0 °C and 3 °C in winter and above 25 °C in spring. The highest milk yield was related to the following optimal ranges: 6–12 °C (Tmin), 6–15 °C (Tavg) and 12–21 °C (Tmax) in winter and 9–12 °C (Tmin), 12–18 °C (Tavg) and 15–24 °C (Tmax) in spring. In winter, daily milk yield was negatively affected by WCI and the persistency of WCI at values lower or equal to −1. In spring, milk yield decreased at average and maximum THI higher than 65 and 68, respectively, and as hours of permanence at Mild-Discomfort level and Discomfort level increased. Wind speed equal to or higher than 2.5 m/s in winter and 4 m/s in spring and maximum wind speed equal to or above 8 m/s in both seasons were detrimental to milk yield. Average wind values between 1.5 and 4 m/s had a beneficial effect in spring. Radiation above 24 MJ/m2 was detrimental to milk yield in spring, whereas rain had a negative effect only in winter. Milk yield reductions were as high as 19% for Tmax, 17% for Tavg and 15% for minimum WCI (WCImin) in winter, and 19% for Tmax, and 17% for both Tmin and maximum THI (THImax) in spring. The ewes responded immediately (0d and 1d) to almost all unfavourable conditions in winter, whereas the timing of responses was more variable during spring. A lageffect of rainfall was detected. The 0–2d period before milking was the most influencing for most relevant MF in both seasons. When comparing the morning and afternoon milkings, the dairy ewes were more sensitive to low temperatures before the afternoon milking in winter, and to higher temperatures before the morning milking in spring. In conclusion, thermal stress caused reductions in milk yield in winter and spring, emphasizing the importance of adopting proper management practices to relieve the negative effects of stressful weather conditions on milk yield of grazing dairy sheep in the Mediterranean region.