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.