Estimation of Additive and Non-Additive Effects on Milk Production and Reproduction Traits in Crossbred Dairy Cattle at Holeta Agricultural Research Center, Ethiopia

Abstract This study aimed to assess the genetic effects of breed additive, heterosis, and recombination in indigenous Boran cattle and their crossbreeds with Holstein Friesian dairy cows at the Holeta Agricultural Research Center. A total of 14,028 performance records from pure Boran and crossbred dairy cattle were utilized in the study. To perform the estimations, crossbreeding parameters for milk production and reproductive traits were analyzed. The crossbreeding parameters—breed additive, heterosis, and recombination losses—were estimated using regression analysis with SAS software (2004). The analysis results showed that additive genetic effects were greater than heterosis effects across all milk production and reproductive traits. Compared to the indigenous Boran breed, the Holstein Friesian breed exhibited additive genetic effects of 3728 ± 139.4 kg for lactation milk yield (LMY), 10.89 ± 0.3 kg for daily milk yield (DMY), and 48.95 ± 14.8 days for lactation length (LL). Likewise, the direct heterosis effects observed in crossbred dairy cows were -81.65 ± 97.98 kg for lactation milk yield (LMY), 0.44 ±0.2 kg for daily milk yield (DMY), and -18.72 ± 10.38 days for lactation length (LL). Crossbreeding did not always have positive effects on milk production traits. In this study, unfavorable interactions of epistatic alleles (recombination loss) resulted in reductions of 1440.92 ± 152.25 kg in lactation milk yield (LMY), 2.55 ± 0.33 kg in daily milk yield (DMY), and 75.15 ± 16.13 days in lactation length (LL). The breed additive genetic effects of Holstein Friesian, compared to the Boran breed, for calving interval (CI), age at first calving (AFS), and age at first calving (AFC), were 21.51± 29.19 days, 2.29 ± 3.12 months, 2.23 ± 3.12 months, respectively. In the current study, the heterosis retention values for crossbred dairy cows were 5.33 ± 19.79 days for calving interval (CI), -8.79 ±2.7 months for age at first calving (AFS), and -8.84 ± 2.7 months for age at first calving (AFC). Friesian and Boran crossbred cows showed a reduction from Boran cows of approximately 81.01± 32.71days in calving interval (CI), 2.95 ± 3.15 months for age at first service (AFS), and 2.91± 3.15 months for age at first calving (AFC) due to favorable recombination effects.