Complex sentence: By the 1930s the Shropshire had been dubbed in the USA as "the farm flock favorite", but in the 1940s, US breeders began producing Shropshires with more wool cover and decreased size.
Split into simpler sentences: By the 1930s the Shropshire had been dubbed in the USA as "the farm flock favorite". But in the 1940s US breeders began producing Shropshires with more wool cover and decreased size.