This study emphasizes the necessity to account for the completeness of pedigrees when giving estimates for level and trend in inbreeding. Average inbreeding coefficient for the Icelandic dairy cattle population considering animals bom 1980 or later and with at least both parents and one grandparent known was 1.82%. Corresponding figure for animals with at least four ancestral generations known was 2.70%. No significant trend in inbreeding was detected in the period after 1980 when considering animals with at least four ancestral generations known. The A.I. bulls were inbred on average by 2.39% and a
 significant increase in inbreeding of +0.08 percentage units per year was detected. The effects of inbreeding level upon milk, fat and protein yields in the three first lactations separately were estimated by including inbreeding level in the multitrait animal model currently used for breeding value estimation of the breed. A large proportion of the cows with production records were inbred or 58.6%. Negative effects were detected corresponding to a reduction of 0.22-0.39% of mean production per 1% increase in inbreeding. 

A. Sigurdsson, J. V Jonmundsson

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 17. Genetics and breeding of dairy and beef cattle, swine and horses, , 140–143, 1994
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