Genetic and phenotypic analyses of days open and 305-day milk yield in a commercial Holstein Friesian herd

الملخص EN

A total number of 496 lactation records for 298 cows sired by 28 bulls of a commercial herd of Holstein Friesian cows raised in Egypt, belonging to Alexandria Copenhagen Company for Dairy and Meat Production, were used in the present study to analyze factors affecting 305-day milk yield (305-DMY) and days open (DO).

Data were collected during 5 years (2006-2010) and analyzed using SAS, XLSTAT and WOMBAT.

Parity had a significant (P < 0.05) effect on 305-DMY.

Season of calving significantly (P < 0.05) affected DO.

Estimates of heritability for 305-DMY and DO were 0.25 and 0.11, respectively.

The corresponding estimates of repeatability for 305-DMY and DO were 0.39 and 0.05, respectively.

These results reflect a very small contribution of additive genetic variance, and also point out that improvement in such traits could be achieved by improved management and feeding procedures.

Coefficients of phenotypic and genetic correlation between the two traits were -0.01 and 0.08, respectively.

Results indicate possibility of genetic improvement of milk production and reproduction traits by selection for 305-DMY only, due to its relatively high heritability estimate as well as its negatively favorable phenotypic and positively reasonable genetic correlation coefficients with DO.

Although genetic parameters are important tools for improving quantitative traits by selection, still there is room to improve milk production and reproduction traits of Holstein Friesian through the application of improved management procedures.