INBREEDING LEVELS AND THEIR EFFECT ON MILK, FAT AND CALVING INTERVAL IN HOLSTEIN-FRIESIAN COWS

Abstract

The frequency and levels of inbreeding in Holstein-Friesian cows in the Fraser Valley of Britich Columbia were investigated. A random sample of the registered cows in Record of Performance (ROP) herds in 1973 showed that 9.8% of cows were inbred to some degree. The levels of inbreeding ranged from 3.12 to 15.62% and were caused by a common male in the ancestry four times more often than by a common female. There was no indication of individual artificial insemination (AI) sires causing this, nor of AI sires in general being responsible for more inbreeding than natural service sires. The high yield of the cows in the Fraser Valley raised the question of whether inbreeding was causing higher levels of inbreeding depression in production than reported earlier from lower yielding cows. One percent inbreeding in the range 0 to 12% reduced yield of 305-day lactation by 22.85 kg which is comparable with levels reported in other studies with lower production levels. No significant effect of inbreeding was found upon fat yield or calving interval.