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A recent topic of conversation in my inbox has been the effect of giving cows a choice over access to grazing during heat stress periods. Several monitor farmers have commented that even when the heat stress is mild their cows will only choose to be outside (at grazing or at the uncovered feed barrier) in the first part of the morning. About mid-morning they tend to move back inside seeking shade – irrespective of the quality of the housing and bedding. In the afternoon they then willingly go out to graze and stay there all night until the next morning’s milking.

The pictures below show the situation in mid-June on one of our monitor farms. I had been looking at a group of about 120 medium yielders (25 – 25 l/day) who had access to a good, airy cubicle shed (with mattresses/sawdust and a TMR) and also the a loafing paddock alongside. On 12 June at noon the shade temperature outside was 26.5’C and in the full sun was 34.4’C – so a hot day. The loafing paddock contained two or three cows but the cubicle shed was just about full with cows eating or lying down. Of particular interest were the few cows on the concrete loafing area who, to a cow, were hugging the shade of the building.

Often it will not be possible to give all groups of cows free access to shaded buildings – logistics and the field, tracks and gate positions will limit what can be done – but maybe we ought to be questioning the merits of keeping cows outside at grass on hot days and in the full sun. Interestingly workers in Florida are showing that this does not just apply to the milkers – dry cows (and their unborn calves) also benefit from having cooler conditions during the day.