Impact of age at first calving on reproduction, lactation, postpartum disorders and longevity in Holsteins under Egyptian circumstances

A retrospective study including reproductive and productive data of 1587 primiparous Holstein cows covering a period of eight years. The reproductive data ( interval to 1st service, service period, days open, number of inseminations per conception and calving interval ) and the productive data ( total milk yield, average daily milk yield and 305 day milk yield) were studied as a function of age at first calving and postpartum disorders. Furthermore, other data including life span longevity, number of parities, the cumulative productive days and the average calving interval were also studied as a function of age at first calving. Cows were classified according to the age at first calving into young age calvers (< 24 months), mid age calvers (> 24-28 months) and old age calvers (> 28 months). The obtained data were statistically analyzed, tabulated and discussed. The overall mean age at first calving was 26.68 months in Holstein cows under Egyptian circumstances. Most of first calving (90%) were recorded in cows less than 30 month of age. The results indicated that, the young age calvers tend to have prolonged interval to 1st service, days open and calving interval and the reverse was correct in old age calvers. The postpartum disorders had significantly detrimental effects on the reproductive performance among the different age groups. Young age calvers had a higher incidence of postpartum disorders than those of mid - age calvers and much higher than had the old age group. The postpartum disorders were associated with high milk production specially in mid and old age calvers which may indicate the high predisposition of superior producer cows to postpartum disorders. Life span, longevity, number of parities and the cumulative production days were found to be increased as a function of age at first calving. Meanwhile, the average calving interval of the young age calvers was longer than the other two age groups. Finally, it was recommended to avoid insemination of maiden Holstein heifers less than 17 month of age specially those having superior productive traits.