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Critic. What U. S. dairymen need are not fancy animals but any sort of cow that gives high quantities of good milk. The two, says Critic Prentice, are not necessarily, or even often, the same. There is a false emphasis on '"type" (show-ring points) and pedigree. High milk production is an inherited capacity which cannot be told by looking at the creature. Nevertheless breeders buy cows which have "long thin tails with a good switch," buff noses, incurving horns, in the belief that such dams will infallibly transmit their milk-producing ability to their calves. To sire their herds they buy champion bulls which have convinced judges on some 25 show-ring points. The result is that unbiased experts no longer claim that cows registered, in herd books produce more milk than unregistered animals, that wise breeders sometimes pay more for unregistered cows than for their elite sisters. A survey in South Africa showed that when a dozen champion bulls were used for sires, they had daughters whose milk capacity averaged 1,000 lb. lower than the dams. Thus Mr. Prentice brings his argument down to a clear-cut issue: high milk production and butterfat percentage v. show-ring magnificence.
Scientist. Not entirely to nearsightedness and fatuity does Mr. Prentice lay the blame for confusion and low milk output. The science of genetics is no older than the 20th Century, and it has been pursued mainly with laboratory animals—fruit flies, guinea pigs, mice, paramecia. It is not surprising that the average cattleman should never have heard of sex-linkage, crossing over, multiple allelomorphism, or know that inheritance is a complex mechanism controlled by genes, invisible unit carriers of hereditary characters.
So many genes are involved in transmitting milk ability that it is far beyond mathematical analysis. But Mr. Prentice and his staff were convinced that by assiduous testing under the general laws of genetics they could find what they wanted. They found first, as others had found, that a cow inherits productive capacity from both dam and sire. They found further that, as regards quantity of milk, a cow gets seven-tenths of her inheritance from whichever parent has the higher inheritance; as regards butterfat percentage, four-tenths of her inheritance from whichever parent is higher. The dam's inheritance was obvious from her output. The problem remained how to evaluate the bull's transmitting capacity. The Prentice group chose the method of systematically comparing the yield of bulls' daughters with the yield of their dams. In such wise Mr. Prentice's geneticist-in-chief arrived at Mount Hope's crowning achievement—the Mount Hope Bull Index.
First bull index published in any trade paper, the Mount Hope formula appeared in 1928. It was in two forms. The Commercial Form, for dairymen unwilling or unable to deal with fractions, simply placed the milk ability of the progeny halfway between the inheritances of the parents. Thus if the dam's production was 8,000 lb. and the daughter's 10,000, the bull's index was 12,000. The index was of course computed on the basis of as many dam-daughter comparisons as possible.