The Impact Level of Milk Production on Some Reproductive and Lifetime Milk Yield in Friesian Cows in Egyptian Farms

The database obtained from the 2891multiparous records were collected from  1686 records for Sakha and 1205 records for and El-Karada station Affiliated to the Ministry of Agriculture and Land Reclamation in Egypt in the period from 1990 to 2019. To study the effect level of milk production on productive traits Daily milk yield (DMY), total milk yield (TMY), Lifetime milk yield (LTMY), lactation period (LP) and dry period (DP) and reproductive traits calving interval (CI) and days open (DO). The independent fixed effects were a month, year of calving, farm, and parity for all studied traits. The data were analyzed using the general linear models of the SAS program and the genetic parameters were estimated using the multiple-trait animal model. The overall least square means for (DMY, TMY, LTMY, DP, CI and DO) increase with increasing level of milk production except, for the lactation period shortened with an increase in the level of production. The phenotypic correlation is more positive in the higher level of milk production, while the genetic correlation is more positive and pronounced in the medium level of milk production. Estimates of the heritability of productive and reproductive traits differ for each of the different levels of production. The heritability estimates of the productive traits of the high-yielding group increased and decreased in the low-production group, while the h² of reproductive traits increased in the low-production group. Estimates of the high heritability indicated in the high production groups, in particular, Lifetime milk yield indicate that a reasonable genetic improvement of these traits may be possible through selection.