Estimates of genetic parameters for Boran, Friesian, and crosses of Friesian and Jersey with the Boran cattle in the tropical highlands of Ethiopia: milk production traits and cow weight

Breed additive and non-additive effects plus heritabilities and repeatabilities for milk yield per lactation (LMY), milk yield per day (DMY), lactation length (LL), annual milk yield (AMY), annual milk yield per metabolic body weight (AMYBW) and cow weight at calving (BW) were estimated for 5464 lactation records collected from purebred Boran (B), Friesian (F), and crosses of Friesian and Jersey (J) breeds with the Boran breed raised in the tropical highlands of Ethiopia. Single trait analysis was carried out by using two equivalent repeatability animal models. In the first model the genotype was fitted as a fixed group effect, while in the second model the genotype was substituted by breed additive, heterotic and recombination effects fitted as fixed covariates. Both the F and J breed additive effects, measured as a deviation from the B breed were significant (p < 0.01) for all traits, except for BW of the J. The F and J additive contributions were 2774 +/- 81 and 1473 +/- 362 kg for LMY, 7.1 +/- 0.2 and 4.8 +/- 0.8 kg for DMY, 152 +/- 7 and 146 +/- 31 days for LL, 2345 +/- 71 and 1238 +/- 319 kg for AMY, 20.6 +/- 0.9 and 18.9 +/- 4.3 kg for AMYBW, and 140 +/- 4 and -21 +/- 22 kg (p > 0.05) for BW. The heterotic contributions to the crossbred performance were also positive and significant (p < 0.01) for all traits. The F-1 heterosis expressed as a deviation from the mid-parent values were 22 and 66% for LMY, 11 and 20% for DMY, 29 and 29% for LL, 21 and 64% for AMY, 42 and 42% for AMYBW, and 2% (p < 0.05) and 11% for BW for the F x B and J x B crosses, respectively. The recombination effect estimated for the F x B crosses was negative and significant for LMY (-526 +/- 192 kg, p < 0.01), DMY (-3.0 +/- 0.4 kg, p < 0.001), AMY (-349 +/- 174 kg, p < 0.05) and BW (-68 +/- 11 kg, p < 0.001). For the J x B crosses the recombination loss was significant and negative only for DMY (-2.2 +/- 0.7 kg, p < 0.05) and BW (-33 +/- 17 kg, p < 0.05). The direct heritabilities (h(2)) estimated for LMY, DMY, LL, AMY and AMYBW were 0.24 +/- 0.04, 0.19 +/- 0.03, 0.13 +/- 0.03, 0.23 +/- 0.04 and 0.17 +/- 0.05, respectively. Based on the genetic parameters estimated, the best breeding strategy to increased milk production under highland Ethiopian conditions is to apply selection on purebred base populations (Boran and Friesian) and then crossing them to produce F-1 dairy cows. However, for breeding decision based on total dairy merit, further investigations are needed for traits such as milk quality, reproduction, longevity and survival.