A study of the opportunities for usage of short lactations data for bull breeding value estimation
2008
Gergovska, Zh., Thracian University, Stara Zagora (Bulgaria) | Jprdanova, L., Thracian University, Stara Zagora (Bulgaria) | Kalev, R., Regional Centre of Scientific Applied Service, Targovishche (Bulgaria)
This study included a total of 1207 lactations of 796 cows from 6 herds, daughters of 54 bulls. Only lactations with available 10 monthly test days were used in the calculations. The age of the cows was from the first to the seventh lactation. The lactations were divided into 30-day periods from calving to 240 lactation days. The milk production for each period was adjusted to 305 days via a function of productivity for short lactations. After receiving the predicted production values, the BLUP estimates of the bulls - sires of the included cows, were calculated. The correlation coefficients between the sire estimates indicated that a high correspondence in the breeding values (rp 0.80) could be obtained when the adjusted lactations have 90-120 days or more. Shorter lactations had correlations lower than 0.70. The lowest correlations (rp = 0.60) concerned the 30-day lactations. Higher correlations between the sire ranks were reached for the predicted 150-180 days’ lactations (rs=0,80). Shorter lactations had lower rank correlations than the phenotypic ones (rs 0,60).
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