Genotype by Environment Interaction Effect on Lactation Pattern and Milk Production Traits in an Ethiopian Dairy Cattle Population
The genotype by environment interaction (GEI) was evaluated for lactation milk yield (LY), initial milk yield (IY), peak milk yield (PY) and average milk yield per day (YD) in an Ethiopian multibreed dairy cattle population. Analyses used 4,488 lactation milk records from 1,320 cows collected at the Bako and Holetta research centers from 1979 to 2010. Breeds were Horro, Boran, Friesian crossbreds, Jersey crossbreds and Simmental crossbreds. The GEI for each trait was evaluated using estimates of cow breed group by environment (Bako and Holetta) interactions (univariate fixed models) and Spearman’s rank correlations between sire-predicted values for the same trait measured in both environments (bivariate mixed models). Friesian crossbreds had higher (P < 0.0001) least squares mean (LSM) values for LY, IY, PY and YD than Simmental and Jersey crossbreds at Holetta, whereas Friesian and Simmental crossbreds had higher (P < 0.0001) LSM values for LY, PY and YD than Jersey crossbreds at Bako. Correlations between sire rankings at Bako and Holetta were 0.86 for LY and IY and 0.87 for YD indicating that substantial re-ranking occurred across locations. Thus, multiple-trait models with phenotypic information from Bako and Holetta would be needed to accurately select the most appropriate sires for each location.