Effects of heat stress and diet on milk production and feed and energy intake of Sarda ewes

Ten Sarda dairy ewes (5th-6thmonth of lactation; 1995 ± 353 g/d of milk yield) were divided into
two isoproductive groups and fed two different diets (high and low fiber) from May 20thto June 18th2003, to evaluate
diet effects on milk yield and intake. In addition, the relationships between meteorological conditions, measured
during that unusually hot period, and milk yield and quality, dry matter intake, NDF or NDL were determined,
to study animal responses to heat stress. Diet did not have any significant effect on the evaluated parameters.
Milk yield was reduced by 20% (0.39 kg/d per head) as minimum temperatures changed from 9-12 °C to 18-21
°C. Similar milk yield reduction was observed as mean temperature-humidity index (THI) went from 60-65 to 72-
75. As wind speed increased from 1.5-2.5 m/s to 2.5-4 m/s, milk yield increased by 10%. Milk composition was not
affected by heat stress throughout the experiment except for milk somatic cell count, which was increased by high
temperatures. Dry matter, fibre and net energy intake varied significantly during the trial, with consistent and
marked decreases as heat load increased.