Analysis of over 38,000,000 test-day records of registered
Holstein cows clearly demonstrated a significant
loss in productivity, and survival was associated with
increased levels of inbreeding. Inbreeding levels have
increased geometrically over the last 10 yr. The largest
production losses because of inbreeding occurred early
in life and at early stages of the lactation. Losses in fat
and protein were proportional to losses in milk production.
The SCS did not appear to be affected by inbreeding.
Inbreeding levels >0.10 showed rather large increases
in age at calving of up to 26 d. Similarly, lactation
length decreased by 2 to 8 d with levels of inbreeding
>0.10. Survival was reduced for all levels of inbreeding
and may represent the greatest economic loss
from inbreeding.