Multi-Breed Genetic Evaluation
Introduction
Series -- Parts 1 through 5 

Introduction:
The American Simmental Association (ASA) and the Canadian Simmental Association (CSA) will be releasing their first Multiple Breed International Cattle Evaluation (MB-ICE) with the Fall 1997 Sire Summary. The MB-ICE was the result of a two year research project conducted by the ASA, the CSA and the Animal Breeding Group at Cornell University. Compared to the current National Cattle Evaluation procedures used by the ASA and the CSA, the MB-ICE has the following features:

 1) Breed of Founder Effects - The phrase, breed of founder, is used to indicate that a random sample of animals from various breeds are not needed to evaluate breed differences. The breed of founder effects are developed by tracing pedigrees and determining the breed(s) represented in the most distant animals (founder) in each pedigree. A time trend is included in the breed of founder effects to account the genetic trend that may be present in each sampled breed. The MB-ICE system uses two sources of information to evaluate breed differences in the ASA and CSA data: 1) Estimates derived from the published crossbreeding studies in the scientific literature; and 2) the actual information in the ASA and CSA data bases. If the data contain numerous animals with any fraction of Angus breeding, the literature estimates of the difference between Angus and Simmental will have little impact on the final estimate. For other breeds that are not represented as well as Angus, Hereford, or Brahman, the literature values have a significant influence on the final estimates.

2) Heterosis Effects - Heterosis or hybrid vigor is produced when crossing parents with different breed backgrounds. For traits such as birth weight or weaning weight, heterosis provides an increase in performance that is not part of the animal's breeding value. In the MB-ICE, heterosis affects a calf's performance in two ways: direct heterosis of the calf and the maternal heterosis of the dam for weaning weight. The MB-ICE adjusts the calf's performance for the direct heterosis expressed by the calf and , in the case of weaning weight, the maternal heterosis expressed by the dam.

3) Continuous Age of Dam Effects - The MB-ICE system provides age of dam adjustments using the cow's age in months and based on her breed background and the sex of her calf. The age of dam effects will be estimated directly by the MB-ICE system so no records will be adjusted for age of dam prior to the evaluation. For crossbred cows, the age of dam effects will be weighted averages of the breeds represented in the dam.

4) Merging of data files from the ASA and CSA: The Fall 1997 Sire Summary will combine the data bases from the ASA and the CSA into a single International evaluation.

Using the MB-ICE, EPDs for birth weight, weaning weight, yearling weight, maternal milk, and maternal weaning weight will directly comparable among all animals in the ASA and CSA data bases regardless of their breed background or country of origin. The ASA and CSA provide EPDs for calving ease and maternal calving ease for purebred sires and maternal grandsires using a threshold model. The calving ease system will remain a purebred Simmental evaluation.

The current base for the separate Simmental, Simbrah, and Canadian Simmental evaluations is all purebred animals born in 1986. For the MB-ICE, the base will be set by summing to zero the estimated values for Simmental, Angus, Hereford, and Brahman genes represented in calves born in 1991. The base for the calving ease system will be defined as all purebred Simmental calves born in 1991.

Series of Articles Published in the Register

Part 1 -- Development of a Genetic Evaluation System
Part 2 -- Accounting for Breed Differences
Part 3 -- Adjusting for Heterosis
Part 4 -- Genetic & Gametic Trends
Part 5 -- The Genetic Base