The effect of inbreeding on milk traits in Holstein cattle in the Czech Republic

Abstract. The objective of this study was to explore the effect of the level of inbreeding on the milk production (MP) and the breeding values (BV) of milk production. Data included cows calved in years 1990-2005 at farms in the Czech Republic. Inbred cows were grouped according to F_x coefficient (F_x = 1.25 %, F_x = 2.0–3.125 %, F_x = 4.0–12.5 % and F_x = total). MP and BV of inbred cows were compared with their outbred equals – half-sisters, sharing the same sire (n = 2,063), dam reached the same breeding value (±5 %) and their first calving happened in the same farm and at the same time (±2 months). The PROC GLM of SAS® with fixed effects (age at first calving, year of calving, number of lactations, first calving interval and relative breeding value of the sire and dam) was applied to all data.

In the examined groups of Fx coefficient milk production of inbred cows at the first lactation decreased of −103.02, −236.8, −472.24 and −247.65 kg of milk. Also an insignificant increase of percentage of fat was found in most of the inbred groups: −0.0025, +0.1204, −0.0064 and +0.0708, as well as percentage of protein: −0.0063, +0.0365, −0.0346 and +0.0157.

A similar tendency was also found when the milk production was represented by breeding values. Breeding value for milk in kg showed a decrease of −36.57, −43.55, −92.23 and −50.81 kg milk. Breeding value for fat percentage showed in inbred animals an increase of +0.0068, +0.0394, +0.0152 and +0.0251 %. A similar increase was also found in breeding value for protein percentage: +0.0015, +0.0216, −0.0035 and +0.0134 %. The Fx coefficient increasing by 1 % decreases milk production (regression coefficient) by 59.75 kg milk and increases fat and protein by +0.0112 % and +0.0030 %.