The Level of Inbreeding and Its Effects on Milk Yield, Age at First Calving and Calf Mortality in Holstein Cattle Reared on the Agricultural Faculty Farm of Ege University


Abstract: In this study, the inbreeding coefficient of 1535 Holstein calves born on the Agricultural Faculty farm of Ege University during the period 1980-2000 was calculated, and the change of inbreeding levels over the years was investigated. Furthermore, the effects of inbreeding on first lactation 305-day milk yield, age at first calving and calf mortality were examined. The mean inbreeding level of calves born in the investigated period was 1.89%. The level of inbreeding in the herd fluctuated from 0% to 4.37% according to the birth years of calves. Furthermore, over the last 3 years of the period (1998-2000) inbreeding steadily increased. Over the years, it was estimated that a linear relationship (R^2 = 0.62) existed between the inbreeding level and the percentage of sires bred in the herd. Estimates of inbreeding depression per 1% increase in inbreeding were -16.9 kg for milk yield, and 2.8 days for age at first calving. These levels of depression, however, were not statistically significant. A significant relationship between inbreeding and calf mortality was found. While calf mortality for non-inbred calves was 8.9%, it was 17.8% for calves with an inbreeding level ? 12.5%.

Keywords: Inbreeding, milk yield, age at first calving, calf mortality, Holstein

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