A22-Unc«Bter Farming, Saturday, July 3, 1993
by Glenn A. Shirk
Extension Agent - Dairy
Herd Reproductive Summary
In my last column, I discussed
volunteer waiting periods (VWP)
and how they can be used as tar
gets for getting cows bred early
enough to achieve your desired
calving interval. I also mentioned
that if you wanted to achieve a
12.5-month calvin interval, aver
age days oepn would have to be
around 100.
If you average 2 services per
conception, days to first service
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GLENN’S
UDDERINGS
By
Glenn A. Shirk
Lancaster Extension
Dairy Agent
would have to be 21 days less, or
about 79, that is if you didn’t miss *
any heats. If your heat detection
rate is around 50-60 percent, de
duct another 8-10 days. That
brings you back to 70 days. And,
to end up with an average of 70
days to first service, you’ll have to
start breeding cows 60 days after
calving because some cows will
come into heat on the 61st day and
others won’t be in heat until the
81st day (average of 70 days) de
pending on their heat cycles.
What are your goals and how
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well are you doing? How do the
younger cows compare with the
older cows? What are the average
days between heats or between
services and how successful arc
you in detecting heats? What per
centage of your herd are repeat
breeders?
The Penna. DHIA Herd Sum
mary Report II and the Raleigh
DHIA Herd Summary Report can
help you answer these questions.
The average for Lancaster County
herds in May is shown on the Ral
eigh report in table 1.
(Table 1)
The performance of Ist lacta
tion heifers to 2nd lactation and
older cows were very similar.
Average, days to first service for
all cows was 92. This is about I
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REPRODUCTIVE SUMMARY 01* TOTAL HERD
heat period more than the 70 days
I discussed earlier in the second
paragraph: and it lengthened their
projected calving interval by
about 1 month, to an average of
13. S months.
This is the projected minimum
calving interval, based upon days
open which is currently averaging
131. If breeding problems persist,
days open will continue to in
crease and projected calving inter
vals will get longer. If you have a
seasonal-calving herd, this could
throw you out of cycle and affect
your milk base. For this reason, it
may be beneficial to have cows
calving somewhat uniformly
throughout the year. That way, as
one group of cows moves out of
the base building period due to
atßwet Qfi SERVIC !S TOR PAST 12 MONTHS
HEAT INTSAViL* “1 I'ZZL-.
1 ■ ■ H SERVICE NUMBER S*UC- RES*
ntmiu. numbsb services csurji ,!g s t
-Ist Tr-XS- *TB-
rr
»M 7 3RD + fy ~X9 205~
OTHER I 1 911 TOTAL i " ■92 I 4«|gldl
« ASOPT£ONS(PAST TEARJa 2
breeding problems, another group
slips into their spot and you will
still be able to build a base.
Why are these cows averaging
over 130 days open? If we look at
table 1, we can see that 28 percent
of the cows are not serviced for
the first time until after 100 days!
Some questions to ask are: were
heats being missed? Were these
cows not being bred intentionally,
because they lacked sufficient
flesh, they were milking too
much, or it was too hot to expect
them to conceive? Were they po
tential culls to be milked off and
sold with no intention of ever be
ing bred?
Another problem that can
stretch out days open is repeat
(Turn to Pago A 23)