sentences:  It is unknown what proportion of these cattle were cows, oxen or calves.While the Shetland cattle could thrive on inhospitable lands, the evolution of agricultural practices and chemicals made grass more plentiful for less hardy breeds, whose larger bulls could sire calves that would grow larger and more quickly.Increasing the size of the cattle was attractive in the aftermath of John Boyd-Orr's influential studies in the 1930s, which revealed a deficiency in the "midst of plenty" among the United Kingdom's urban proletariat, whose diet lacked meat.