Were the caterpillars small, green, about 1cm long and loads of them? If yes, then it's likely to be gooseberry sawfly larva. I know, it's not a gooseberry, but the pests attack both, but as you say are not interested in blackcurrant. They overwinter in the soil at the base of the bush, so if you can let your hens scratch around there that will help. They then crawl up the stem and start chewing the leaves from the centre of the bush outwards, so the outer leaves are the last to go. Picking them off and squishing is tedious but does work, although it's spikey. If you have any pet wasps they will clear the lot
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If that's not what they are, then picking off and squishing is easier with larger caterpillars.