Cattle breeds were first sorted between dairy and beef types, and then evolved into breeds by regional segregation and closed population mate selection. Recognition that the geophysical environment was the primary determinant of which gene combinations were successful, breeds all developed their identity as bundles of traits that adapted them to their formative environment. Physical qualities were the basis of heritable characteristics. Bloodlines emphasized individual aspects of total breed expression.
In North America, we work exclusively with animals imported from their native regions, adapted here to the world’s first specialized dairy industry to develop economically. We began to weigh milk and keep records of yields, tested for butter content, formed breed associations to publish records and promote the heavier milkers as breeding cows. The AI industry began in 1940 to spread these concepts, under their promotion of the herd health and human safety aspects of AI over keeping bulls on the farm.
For all our modern breeds, the leading cattle of the 1960s (more widely disseminated as a result of the new process of freezing semen) are known to be the progenitors of today’s cattle. We exchanged the formative purebred bloodlines for the dominating AI sire lines (Ayrshire—Bettys Commander; Brown Swiss—Stretch; Guernsey—Royal Nance and May Rose Prince; Jersey— Secret Signal Observer; Holstein—Ivanhoe, Arlinda Chief and Elevation.) Dairy extension and AI worked together to spread the “genetic value” gospel replacing all prior methods of pedigree screening, trait selection and compensatory mating. All those efforts read us to Genomics as the culmination of what has been a “single trait” focus on composite trait index ranking.
The most profitable herds still utilize all the tools
It is just this simple.
You milk a physical cow that consumes physical volumes of feed, water and air, in a physically defined environment. You must have a multi-functional and adaptable cow physique. The most reliable and consistent method to produce uniformly functional cow physiques is “aAa Breeding Guide” (also known as Weeks’ Analysis after its discoverer Bill Weeks).
You face an economically competitive environment in commercial milk production and within what is known from statistical evaluation of the dairy macro-environment, genetic trait values will approximate the more currently successful sire lines. This is the function of PTA values, and the latest realization is that (rather than depend on the ranking indexes used for genetic marketing) you should determine the traits most needed in your current herd and focus your sire selection around those specific traits. Do not assume that your herd will need these same traits forever; re-evaluate each new generation to detect if (a) prior selection solved the old problems, (b) a new selection focus addresses any new problems.
Given that the mature cow that remains functional is your highest milk producer and will give you the most calves, longevity in the maternal line of sires you select cannot be overemphasized. It is known by biologists that the best way to a long life is long-life parents; the best way to a healthy life is healthy parent lifetimes; the most profitable dairy herds are based on reproduction as precursor to production.
No cow gets old who is not fertile, no cow stays in the herd who is not competitive in productivity. The heritability of maternal pedigree selection for multi-generational “longevity” exceeds the heritability of all the “fitness” traits (which are better used to screen out less fertile, shorter herdlife sires).
Above all, avoid popular “one size fits all” simplifications of the breeding process. The ever-feared “inbreeding depression” is always a consequence of “single trait” [single index] selection.