INBREEDING AND ITS IMPACT IN THE CLOSED POPULATION OF ICELANDIC DAIRY-CATTLE

Average inbreeding coefficients were calculated for the Icelandic dair y cattle population, using pedigree records of 129 115 animals with th e most remote ancestor born in 1902 and the youngest animals born in 1 991, The average coefficient for animals born 1980 or later and with a t least both parents and one grandparent known was 1.82%, but for anim als with at least four ancestral generations known it was 2.70%. No si gnificant trend in inbreeding was detected in the period after 1980 wh en considering animals with at least four ancestral generations known. The AI bulls were inbred by 2.39% on average and a significant increa se in inbreeding of +0.08% per year was detected. The effects of inbre eding level on milk, fat and protein yields in each of the first three lactations were estimated by including inbreeding level in the multit rait animal model currently used for breeding value estimation of the breed. A large proportion (58.6%) of the cows with production records were inbred. Negative effects were detected, corresponding to a reduct ion of 0.22-0.39% of mean production per 1% increase in inbreeding. In clusion of inbreeding level in the model did not affect the ranking of animals.