Inbreeding trend and inbreeding depression in the Danish populations of Texel, Shropshire, and Oxford Down.

The objective of this study was to analyze the development of inbreeding and estimate inbreeding depression in the Danish populations of 3 major meat type sheep breeds. The pedigrees contained 29,336 Texel, 22,838 Shropshire, and 11,487 Oxford Down. The rate of inbreeding was approximately 1% per generation for all breeds, but the rate of increase in co-ancestry was somewhat lower (0.45 to 0.71), indicating that more inbreeding has been accumulating than would be expected if mating was at random. Inbreeding depression for birth weight, ADG from birth until 2 mo, and litter size was estimated for all 3 breeds using a minimum of 15,000 records per trait and breed. All traits showed depression due to inbreeding of the animal itself. For most combinations of trait and breed, there was also a significant reduction of the phenotype due to inbreeding in the dam. The size of inbreeding depression was 1.2 to 2.6% of the mean, resulting in an increase in the inbreeding coefficient of the individual of 0.10, and estimates were similar for similar increases in maternal inbreeding. The rate of inbreeding in these breeds needs to be reduced in the future to avoid a further decline in birth weight, ADG, and litter size.