"Composites" Make Linear Trait Selection Easier

Dairy Pipeline: January 2000

Bennet Cassell
Extension Dairy Scientist, Genetics and Management
Virginia Tech
(540) 231-4762
bcassell@vt.edu

Most producers want to use linear trait information when choosing service sires. That's why it's a rare proven bull that doesn't have a type proof - they won't sell! However, not all producers are willing to use an index like TPI or Net Merit that improves lifetime economic performance of the cow, preferring to make their own assessment of the relative value of individual traits. Unfortunately, the Holstein Red Book profiles include 17 different linear type traits, and the production-somatic cell-productive life evaluations add several more traits to the information load. That's far too much detail to keep track of in a semen market that includes at least fifty to one hundred bulls that might be of interest to any given herd. There are two type indexes that were designed to simplify the selection process, the udder composite index and the feet and legs composite. Producers can look for bulls with higher evaluations for these two composites and not worry too much about problems in the major structural areas of udder and mobility. The udder composite includes six linear type traits with most emphasis on udder depth, moderate emphasis on fore and rear attachment and teat placement, and less weight on udder cleft. The feet and legs composite is a little more complex, because rear legs - side view has an intermediate optimum (too straight and too crooked are both "bad"). It combines foot angle and rear legs from side and rear in a workable manner to improve overall mobility of the cow. My preference is to select bulls on an index of overall merit and ignore the individual traits considered in that index, but the udder and feet and legs composites are useful guides if you want to look at linear data separately in sire selection.

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