Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 4, 1999
Publication Date: N/A
Interpretive Summary: Interest and concern regarding inbreeding continue to grow as breeders search for ways to avoid the economic losses associated with inbreeding depression and slower progress resulting from homozygosity. The best way to do this while still making maximum genetic progress and maintaining genetic diversity involves identification of proven bulls that are least related to the cow or heifer being bred. To accomplish this a random sample of 600 females born in 1995 was chosen to represent each breed and an animal's relationship to that sample was calculated. This number, when divided by two, represents the inbreeding that would occur if that animal was bred to any random animal in the population. Thus, it is called expected future inbreeding for that animal. Breeding values were adjusted to reflect past and future inbreeding and were highly correlated with unadjusted breeding values. Adjustments for inbreeding will cause slight rerankings for animals whose relationship to past mates differs from that expected for future mates. These adjustments are proposed to avoid inbreeding in situations where animals are either not properly identified or where a mating is essentially random. Inbreeding can be further reduced by using mating programs. Proposed matings should be evaluated individually by combining sire's and dam's breeding values adjusted to zero inbreeding and then including the inbreeding depression of the individual mating. Thus, adjusted breeding values are useful in selection whereas breeding values adjusted to zero are needed in mating programs. Expected inbreeding of future progeny was distributed for all bulls beginning in February 1998 to help breeders find outcross bulls and avoid inbreeding.
Animals most related or least related to current members of their breed were identified by calculating expected inbreeding percentages for future progeny. A sample of potential mates was chosen by randomly selecting 600 females from a recent birth year (1995). Relationships among the sample were computed by the tabular method. Relationships of other animals to the sample population were computed as the mean of their parents' relationships. To-Mar Blackstar-ET and Round Oak Rag Apple Elevation were most related to the Holstein breed with expected inbreeding of 7.9 and 7.7%, respectively. Corresponding Jersey bulls were Highland Magic Duncan and Soldierboy Boomer Sooner of CJF with expected inbreeding of 10.9 and 9.5%, respectively. Highest expected inbreeding was 11.1% for Selwood Betty's Commander, 8.6% for Forest Lawn Simon Jetway, 10.1% for Dutch Mill Telestars Fayette, and 7.4% for Korncrest Pacesetter for Ayrshire, Brown Swiss, Guernsey, and Milking Shorthorn breeds, respectively. A regression on inbreeding in the genetic evaluation model removed effects of past inbreeding. Future inbreeding effects can be included for each potential mating or by adjusting breeding values for average inbreeding expected with random mating. The correlation between Holstein breeding values unadjusted and adjusted for inbreeding was .9976. Estimated genetic trend was 6% lower with future inbreeding included.