Estimates of breed additive, heterosis and epistasis genetic effects on milk production and reproductive traits from indigenous Borena and crosses with Holstein Friesian dairy cows at Holetta dairy research farm, Ethiopia

The aim of this study was to evaluate the breed additive, heterosis and recombination genetic effects on indigenous Borena and its crosses with Holstien Friesian dairy cows at Holetta dairy research farm. Overall, 19,454 pure Borena and crossbred dairy cattle performance records were used for the study. Crossbreeding parameter analysis on milk production and reproductive traits were applied for estimation. The regression analysis of SAS (2004) software was used to estimate the crossbreeding parameters (breed additive, heterosis and recombination losses). Results of this analysis revealed that additive effects were larger than heterosis effect for all milk production and reproductive traits. The breed additive genetic effects of Holstein Friesian breed relative to local Borena breed were 2674 kg, 7.1 kg and 142 days for lactation milk yield (LMY), daily milk yield (DMY) and lactation length (LL) traits, respectively. Similarly, the direct heterosis effects of crossbred dairy cows for LMY and DMY were 423kg and 1.25kg, respectively. Crossbreeding did not always positive effects on milk production traits. In the present study, 1902.3 ± 200kg of LMY, 4.2 ± 0.5kg of DMY and 91 ± 20.8 days of LL were lost due unfavorable epistatic allele's interaction (recombination loss). The breed additive genetic effects of Holstein Friesian as deviated from Borena breed for age at first service (AFS), age at first calving (AFC), calving interval (CI), days open (DO) and number of service per conception (NSC) were 373.9 ± 114.8 days, 337.1 ± 112.6 days, 105.7 ± 54.2 days, 98.5 ± 54.2 days and 0.05 ± 0.4 days, respectively. The heterosis retention of crossbred dairy cows for AFS, AFC, DO, and NSC in the present study were -117.6 ± 61.3 days, -207.9 ± 59.8 days, -4.9 ± 27.6 days and-0.2 ± 0.2 days, respectively. However, Friesian with Borena crosses were about 129.2 ± 97 days and 70.5 ± 95.2 days delayed AFS and AFC due to the recombination losses. This study recommended that improvement of management level (feed, health, etc.), andselection on Borena and their crosses should be implemented to favor the genetic base of crossbreeding parameters (additive and non-additive genetic effects.