The primary advantages of reducing age at
first calving (AFC) include reducing rearing
costs as well as reducing time in which the
heifer is only a capital drain on farm resources.
The primary disadvantage of reducing
AFC is that it is frequently associated with
a reduction in first-lactation milk yield. Despite
this reduction in first-lactation milk
yield, production per year of herd life is typically
increased by reduced AFC. Furthermore,
although the first lactation yield may be influenced
by AFC, future lactations are decidedly
not. In addition, stayability and health of cows
are not influenced by reduced AFC as long as
heifers freshen at an adequate weight. Most
analyses indicate that the financial advantage
afforded from heifers that freshen at a low
AFC seems to at the least offset any milk lost
during the first lactation. Furthermore, when
the time value of money is considered in this
analysis, a reduced AFC (~22 months) seems
likely to represent a more fiscally sound management
decision. When applying these ideas
on the farm, a properly managed feeding and
breeding program should permit a firstlactation
cow to weigh ~1,210 lb after freshening
at 22 months of age. The National Research
Council recommends a postpartum
weight equal to 82% of her mature body
weight. This can be achieved with a maximal
prepubertal average daily gain (ADG) of 2
lb/day when a traditional preweaning program
is employed or 1.8 lb/day when an intensified
preweaning program is employed. Because of
the well defined link between inadequate body
weight at calving and increased mortality and
morbidity in first-lactation cows, achieving
this target post-calving body weight is of critical
importance.
