I think there's also a vast range of what it means to "Work cattle".
There's bringing them up from the range land, crowding them into pens with no shade while they wait in a mass group hours for their turn through the chute where they will be weighed, tagged, vaccinated, etc.... and squirting some fly control on them when they are in a trailer. Or, in my little bitty small case, opening the gate from the field holding 20 cattle into my green grass and shaded catch arena where they are ushered back out in groups of 3-4 to spend 5 minutes in the chute while I do this or that to them. Even the chute is in the shade and the animals are docile - not range - so the process isn't really working them up.
THAT said - in this particular case, I would be more concerned about catching, loading, and hauling these heavy breds with these temps then getting some fly control on them there after.