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This is the first of several columns about DHIA reproductive management reports,
These reports are a valuable tool for evaluating the reproductive status of your herd, but
for the data to be accurate you or your DHIA technician must enter all heat dates, all
breeding dates and the results of all pregnancy checks.
What calving interval are you striving for? That establishes your goal for days
open. If you are trying to maintain a 12. S month calving interval, average days open has
to be about 100 (12.5 months x 30.5 days per month - 281 days pregnant = 100 days
open). That means some cows will have to conceive before 100 days to compensate for
those that conceive later.
If your goal is to get cows settled by 100 days, how soon after calving should you
start preparing them? Also, what is the earliest you want to start breeding them? We
refer to this as the voluntary waiting period (vwp). You will find this figure on your
Raleigh DHIA Herd Summary, a portion of which has been reproduced in Table 1. If
you do not designate a vwp, Raleigh will automatically use 60 days.
If you want to start breeding cows 60 days after calving, preparations must start 2-
4 weeks or more prior to that time. This includes: recording heat dates, managing cows'
flesh, prostaglandin shots, repro checks, etc.
If your vwp is 60 days, the best average days to first service you can hope to attain
is about 70 days - about 10 days more than the vwp. The reason for this is some cows
will come in heat on day 61 and some 21 days later, with the average time being about 10
days, that is, if every cow came in heat and you detected all of the heats.
Table 1 shows Lancaster County's average for the month of May. Average days to
first service was 93. With a vwp of 59 days, that's 24 days greater than what they were
aiming for (93 days to first service - vwp of 59 days - 10 days to come into heat 24
days). In other words, they already missed one heat period, even before the first service!
This could have been intentional for some cows and accidental for others.
If their goal is a 12.5 month calving interval, cows must be pregnant by 100 days
after calving, but they won't be confirmed pregnant until pregnancy checked. That means
we can only have an average of 1.5 repeats or missed heats after the vwp (100 days open
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Table 1 SUMMARY OF CURRENT BREEDING HERD
TOTAL COWS IN
- vwp of 59 days -10 days to come into heat/21 days per heat cycle = 1.5 heat periods).
On the Penna. DHIA reports, the average days to first service appears at the
bottom of the Reproduction Management Report,
Table 1 is a summary of the breeding herd only the cows you are trying to get
bred and confirmed pregnant. For the Lancaster herds, this was an average of 22 cows,
In the table, the breeding herd is divided into two groups: 1.) those awaiting first service.
which includes cows that were pregnancy checked and confirmed not pregnant, and 2.)
cows that have been bred but not yet pregnancy checked.
Of the 22 cows in the breeding herd, 8 were awaiting first service after calving or
after having been confirmed not pregnant. Four of these are still within the normal 59-
100 day period for first services. The other half (4 cows) already passed the normal
period, and are starting to stretch the calving interval beyond 12.5 months. ■
Of the 22 cow breeding herd, 15 were serviced but not yet pregnancy checked.
One was bred early, before 59 day vwp. Five were last bred in the normal 59-100 day
period. Three were last bred 100-130 days after calving, and six were open more than
130 days at time of last breeding. In other words, 9 of the 15 last services (60%) were
beyond the desired time! At 130 days, they are already at a 13.5 month calving interval
(130 days + 281 days pregnant/30.5 days per month = 13.5 months). If repeats and
missed heals continue to lengthen the days to last breeding, calving interval will also
continue to increase.
Let's come back to the question asked earlier, what calving interval should you
strive for? A better question to ask is what should average days open be? Calving
intervals indicate what has already happened, and you can't do anything to change it.
Days open let you see trends as they develop, while you still have time to do something
about them. They determine projected calving intervals,
If our goal is to have a projected calving interval of 12.5 months, our average
Lancaster County DHTA herd is in trouble; their projected calving interval averages 13.5
months. Maybe your calving interval should be greater than 12.5 months, but be careful
not to relax your calving interval so it matches your management level. Goals should
challenge you, but they should also be reasonable,
One way to make your calving interval and days open look better is to cull your
problem cows. They can get expensive especially if they are not worth much, or they are
Lancaster Farming, Saturday, Juna 19. 1993-A35
COWS WITH NO SERVICE
OATES OR OIAG OPEN
(Turn to Page A 37)
DAYS OPEN AT LAST SERVICE