Estimates of heritability, repeatability and breeding value of some Performance traits of Holstein cows in Egypt using repeatability animal model

الملخص EN

Data collected from 1807 lactation records relevant to 735 Holstein cows, between 1995-2005 were utilized to estimate heritability, repeatability and breeding value of all lactation total milk yield (TMY), 305-day milk yield (305-DMY), peak yield (PY), lactation period (LP), first service period (FSP), days open (DO) and number of services per conception (NSC).

Also, the effects of season and year of calving, age at first calving and parity on all lactation traits were studied.

The least squares analysis indicated that the overall least squares means of TMY, 305-DMY, PY, LP, FSP, DO and NSC were 9537 kg, 8315 kg, 40.2 kg, 348.8 day, , 89.4 day, 113.1 day and 2.0 services, respectively.

Season of calving had significant effect (P< 0.01) on PY, LP, DO and NSC and significant effect (P< 0.05) on 305-DMY, but had no significant effect on TMY and FSP.

Year of calving had significant influence (P< 0.01) on all studied traits.

Age at first calving had significant effect (P< 0.01) on TMY and 305-DMY and significant effect (P< 0.05) on PY and FSP, but had no significant effect on LP, DO and NSC.

Parity had significant effect (P< 0.01) on TMY, 305-DMY, PY and LP and significant effect (P< 0.05) on DO, but had no significant effect on FSP and NSC.

Variance components, heritability, repeatability and breeding values for the studied traits were estimated using the Wombat programme fitting repeatability animal model.

Estimates of the heritability were 0.065, 0.149, 0.159, 0.029, 0.089, 0.028 and 0.006 for TMY, 305-DMY, PY, LP, FSP, DO and NSC, respectively.

The estimates of repeatability were 0.203, 0.189, 0.219, 0.114, 0.122, 0.028 and 0.018 for the same traits, respectively.

The breeding values for TMY, 305-DMY, PY, LP, FSP, DO and NSC of cows ranged between -2737 and 3285, -1698 and 1338 and -6.7 and 5.6 kg, between -45.0 and 71.1 day, -39.6 and 72.9, -37.9 and 64.8 days and between -0.14 and 0.19 service, respectively, the corresponding values for dams were between -2835 and 2979, -985 and 1875 and -7.3 and 6.0 kg, between -9.9 and 44.0, -38.4 and 86.9, -38.1 and 53.7 day and between -0.30 and 0.60 service, respectively.

The breeding values for sires were between -1057 and 659, -737 and 613 and -1.3 and 2.4 kg, between -23.6 and 18.6, -15.6 and 32.7 and - 11.2 and 13.5 day and between -0.76 and 1.16 service for the respective traits.

The results indicate that improvement of performance traits of Holstein cows could be obtained through improvement of management condition