Effect of Season, Parity, Exotic Gene Level and Lactation Stage on Milk Yield and Composition of Holstein Friesian Crosses in Central Highlands of Ethiopia

The study used twelve years recorded data’s analysis for milk yield and composition of Holstein Friesian crossbred dairy cows in Holleta agricultural research center dairy farm. Data were summarized and categorized into the season, genotype (exotic blood level), Parity and lactation stages. The summarized data’s were season (219 wet, 1055 dry), genotype (1,117 for 50%, 115 for 62.5% and 42 for >75%), Parity (474 for parity-2, 356 parity-3, 270 for parity-4 and 174 for parity-5), Lactation stage (483 for early, 445 for mid and 346 for late). Analysis of means and standard errors of the mean for the parameter studied was estimated using SAS. The General Linear Model was used for analyses of variance on average monthly milk yield and composition for the effects of season, parity, genotype and stages of lactation. Season significantly affected milk yield, fat, and protein percentage composition. Higher yield and fat% composition record in the dry season and higher protein% during the wet season. Genotype significantly affected milk yield where the yield of 62.5% and >75% crossbred cows were significantly higher than that of 50% crossbred cows. The difference in parity significantly affected milk yield and protein content of milk where higher milk yield and protein content was recorded in parity five. An increasing trend observed in milk yield and protein content as dam parity advances. Mean monthly milk yield, percent of protein and total solid was varied significantly between different lactation stages where protein and Total solid percentage was significantly higher in the late stages of lactation. In overall milk, the yield was significantly affected by season, genotype, parity and stages of lactation but it is negatively correlated with the percentage of fat, protein, and total solids. Season, parity and stages of lactation significantly affected the protein content of milk whereas milk composition strongly correlated with each other.