I thought Vetrazin had been phased out. We use a garden hand sprayer to apply Crovect to our little sheep - the Tbar thingy just wasted nearly everything and it's too expensive to pour on the grass. We carefully measured how many mls to spray on or rather how many squirts equals the recommended dose, so not overdosing, but much easier to reach all parts, including the vital perineal area where maggots can hide.
We have just heard a story of someone who a few years ago sheared his sheep early because of hot weather, only for it to turn very wet and cold - he lost a couple of ewes overnight to pneumonia. It is worth crutching/dagging your sheep a few weeks prior to shearing - keeps the bums clean against flystrike but also helps at shearing as no dags in fleece roll.
Please remember that agents such as Crovect should not be used on fleece closer than 3 months before shearing for the sake of the BWMB sorters, to avoid pollution of scouring water, or for the health of handspinners and felters if you are selling to the craft market.