The effect of cooling dairy cows was studied during four years (1998 –2001).
The survey included 14 farms, located in the costal part of Israel and classified into three different groups according to the intensity of cooling in summer.
Cows of group 1 (six farms, intensive cooling), were cooled in the holding and feeding area for a total of 10 cooling periods and 7.5 cumulative hours per day. Each cooling period combined cycles of sprinkling (0.5 min.) and forced ventilation (4.5 min.).
Cows of group 2 (three farms, moderate cooling), were cooled in the holding area only, and were provided a total of six cooling periods and 4.5 cumulative hours per day.
Cows of group 3 (five farms, no cooling) were not cooled at all.
Milk production (kg/d) and conception rates (%), were calculated for summer (July-September) and winter (December-February). The analysis included 125,000 milk recordings (> five recordings for each cow per lactation) and 17,000 inseminations. Average four years daily low and high temperatures (oC) were 8.4 and 19.3, and 22.0 and 31.8, for winter and summer, respectively. Theeffect of the interaction between season and cooling system was significant (P<0.001).
The ratios between summer and winter production were 98.5%, 96.2% and 93.4%, in intensive, moderate, and no cooling regimes, for primiparous cows and 98.5%, 96.1% and 90.7% for multiparous cows, respectively. Conception-rates were 55.8%, 53.5% and 53.9%, and 40.4%, 34.0% and 14.6%, for primiparous cows under the intensive, moderate, and no cooling regimes, inseminated in winter and summer, respectively (P<0.01). Conception-rates were 46.6%, 45.8% and 43.5%, and 33.8%, 34.5% and 16.7% for multiparous cows in the same groups inseminated in winter and summer, respectively (P<0.01).
The results indicate that intensive cooling significantly reduces the seasonal variations in productive and reproductive performances of dairy cows under sub-tropical conditions.