DYSTOCIA DATA AND ITS USE

DAIRY HERD IMPROVEMENT
1985

AITCHISON, T.E., & R.V. JOHNSON
VOLUME: NCDHIP HANDBOOK

For many years, dairy herd owners have been concerned with calving
difficulty (dystocia) in their herds. It has long been recognized
as a potentially serious problem in first-calf heifers. While size
of the first-calf heifer and the level of nutrition are factors
that influence the difficulty with which she gives birth, the size
and shape of the calf, as a result of the genetic influence of its
sire, also can play an important role. Difficult births to
first-calf heifers can be very costly. If assistance is needed at
calving, extra veterinary bills could accrue. However, greater
losses are probably the result of calf losses and damage to the
reproductive tract of the first-calf heifer. Severe cases could
result in the death of both the calf and the dam.

It is no wonder that some herd owners with severe calving problems
resorted to the use of beef (particularly Angus) bulls in an effort
to reduce the incidence of this problem. However, this resulted in
a great loss of genetic material to the dairy herd. The crossbred
beef calf took the place of what could have been a promising dairy
replacement heifer sired by one of the better bulls of that breed
available through artificial insemination.

Dystocia Research

Because of the serious economic problems associated with calving
difficulty, several artificial insemination (AI) organizations, and
later the National Association of Animal Breeders (NAAB), became
interested in supporting research in this area. Data used in the
research were collected from dairy owners who recorded observed
births in their herds using a 5-point scoring system. The scores
and their interpretations are:

1 = No problem
2 = Slight problem
3 = Needed assistance
4 = Considerable force needed
5 = Extreme difficulty

A similar scoring system also was used to evaluate the livability
and condition of the calf at birth. At the same time, the calf's
birth date, sex, breed and identification were recorded along with
the identity of the calf's sire and dam.

The large amounts of data that have been collected have provided
considerable information on the nature and causes of calving
difficulties and associated problems. Table 1 shows the
distribution of dystocia scores for heifers and older cows. Births
scored both 4 and 5 represent real calving problems. They account
for 11 percent of heifer calvings, but only 4 percent of calvings
of older cows.

The Iowa State research found that females are born with less
difficulty than males and that there is less calving difficulty
during summer months than during winter months. Early death loss
was twice as high in male calves as in female calves (15 percent
versus 7 percent). Calf mortality also was found to be higher in
calves of very small or very large sizes than in calves of average
sizes.

Dystocia research has found little or no genetic correlation
between milk production and calving ease. There are, however, small
negative correlations between calving ease and Predicted Difference
for Type (PDT), and between calving ease and Total Performance
Index (TPI). In other words, the bulls that rank the highest for
PDT and TPI tend to be the bulls that sire more calving
difficulties in their offspring. This is probably because these
bulls also tend to sire larger calves. There are many individual
bulls, however, who do not follow this pattern. Therefore, it
cannot be safely assumed that an individual bull with a high PDT
will automatically sire calves that have difficult births and vice
versa.

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PLEASE NOTE: THE FOLLOWING TABLE IS WIDER THAN THE SCREEN. USE THE
RIGHT ARROW KEY TO VIEW THE RIGHT SIDE OF THE TABLE. TO
PRINT THE ENTIRE TABLE YOU MUST FIRST EXPORT THE TABLE
AND USE A WORD PROCESSOR OUTSIDE THE RETRIEVAL SYSTEM.
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TABLE 1. Distribution of dystocia scores.

Heifers Second calf & late All cows
Score (N = 83,919) (N = 387,565) (N = 471,484)
---percentage---
1. No problem 64 84 80
2. Slight problem 11 6 7
3. Needed assistance 14 6 8
4. Considerable force needed 6 2 3
5. Extreme difficulty 5 2 2

Early research on calving ease found that differences in genetic
traits among sires can affect the ease or difficulty with which
their offspring are born. The heritability of calving ease (the
fraction of superiority or inferiority that a parent will transmit
to its offspring) was found to be approximately 8 percent. This is
low, but it allows an accurate ranking of sires for calving ease
when large amounts of data are available.

Sire Summaries

The research work on dystocia led to the development of procedures
to summarize and rank sires on their ability to transmit calving
ease. NAAB began ranking bulls in the Holstein breed for calving
ease in 1977. Originally, the data were analyzed and bulls ranked
on a within-stud basis. Since 1980, however, data from all AI
organizations have been combined into a national Sire Summary for
calving ease published annually in July. Before the summary date,
each participating Al organization collects data from its
cooperating herd owners and forwards the data to a computing center
where they are edited and summarized for NAAB. Some of the data are
collected through Dairy Herd Improvement (DHI) records from dairy
owners who have recorded dystocia information as part of their
reproductive records. Results of the annual summary are available
from the NAAB home office in Columbia, Missouri, or from the
respective AI organization owning the particular bull or bulls.

Published Information

In an effort to provide uniformity of information available on
calving ease, NAAB has established guidelines for publishing
calving-ease data. These guidelines indicate that the latest
available information should always be published along with an
indication of the source and date of the information. Usually the
source is the NAAB Dairy Sire Summary For Calving Ease. It is
important that this information be provided, however, so a reader
will know that the information is reliable. In addition, the NAAB
guidelines state that the following information should also be
included.

1. Number of direct comparisons. This is the number of calvings
for each sire that has direct comparison with calvings of
contemporary herdmate sires in the same herd, year and season.
Direct comparison is necessary to rank sires accu- rately. A bull
may have more calvings reported, but the number of direct
comparisons indicates how many were actually used in his summary.

2. Probability that the sire's true transmitting ability for
calving ease is above breed average. This expresses the probable
change in transmitting ability for a particular sire as more
calving reports become available. This single value takes into
account both the bull's estimated transmitting ability and how
accurately his transmitting ability is estimated. It would be
comparable to combining a bull's predicted difference for milk
(PDM) with repeatability to rate him for production. This makes it
possible to compare a bull with a high estimated transmitting
ability based on only a few reported births to a second bull that
has a lower estimate, but one that is based on more calving
reports. The sire with the higher probability is likely to be the
better choice.

3. Expected percentage of difficult first calvings. This provides
a direct estimate of the expected problem births (scores 4 and 5)
when a bull is used on breed average heifers. This relates directly
to decisions dairy owners must make in choosing bulls to breed
heifers. The expected percentage of difficult births would be
approximately 11 for an average bull, but it will vary from ex-
tremely low, 2 to 3 percent for the best bulls, to 30 to 40 percent
for the poorest bulls. Thus, losses resulting from calving
difficulty could vary significantly based on the sires selected for
virgin heifers.

TABLE 2. Examples of sires evaluated for calving ease.

Number of direct Probability of better Expected
Sire comparisons than breed average difficult births
---percentage ----
7H190 UK Sensation 1,814 99 4
21H333 Krahns Medallion 105 91 6
29H4147 Dedoco Rocket Hartley 14 71 7
21H319 Lynkholm Milkmaker 1,554 35 11
14H550 MD-Sunset-View RA Wonder 469 35 12
29H2851 S-W-D Valiant 964 26 12
7H289 Rinehart Top Notch 600 1 18
1H246 Le-Del Apollo Duster 45 7 20
3H406 Nicolk Sunshine Bold Chief 3,308 1 26

SOURCE: NAAB Dairy Sire Summary for Calving Ease, July 1982.

Examples of Sire Summary Information

Calving ease varies widely between progeny groups of sires.
Usually, there is a good variation of bulls within an AI
organization as well as among all AI sires. Some well-known AI
sires are listed in Table 2 with their calving-ease data.

Of the sires in Table 2, UK Sensation's progeny are expected to
have the least calving problems and Nicolk Sunshine Bold Chiefs the
most. Both of these sires have large numbers of progeny evaluated
so there is little chance that the estimates of their transmitting
abilities will change significantly. This is reflected in their
probabilities of being better than breed average. Since Sensation's
proof is already very highly rated, his probability also is very
high. On the other hand, Bold Chief is rated very low with large
amounts of data. His probability of eventually being better than
breed average is almost zero (1 percent). Notice that even though
Duster is rated below Top Notch, his probability of being better
than breed average is slightly better than Top Notch's chance. This
is because Duster's summary is based on fewer comparisons and thus
may not be quite as accurate as Top Notch's, which is based on 600
direct comparisons. Likewise, both RA Wonder and Valiant have the
same expected percentage of difficult births. The estimate for
Valiant's summary is probably slightly more accurate, but RA Wonder
has a higher probability of being better than breed average.

In reviewing Table 2, the bulls could probably be grouped into
three categories. The first three sires would probably be
considered as easy calving sires. The next three are average, and
the last three would be considered difficult calving sires. Thus,
if these bulls were selected as service sires, the first three
would best be chosen for use on virgin heifers or cows with a
history of calving problems. Likewise, one would avoid using the
last three bulls on those same animals. The remaining sires would
be mated with little regard for their calving-ease abilities.

Recommended Use of Sire Rankings

Although avoiding calving difficulty in a herd can greatly reduce
economic losses, it should be remembered that most income is
generated from production. Care should be taken, therefore, not to
place too much emphasis on calving-ease information. The following
guidelines will help keep this in perspective when planning a
breeding program.

1. Primary selection should be based on production or the
combination of production and type best suited to a herd's needs.

2. For open heifers, choose from among the sires you would
normally select. However, use only those bulls that will sire
calves that will be born with the least expected difficulty.

3. Avoid using difficult calving sires to breed open heifers and
problem cows.

4. Place little emphasis on calving ease for second and later
calvings.

Research on dystocia continues because of the economic importance
of this problem to the dairy industry. Although more will be known
about the problem in the years ahead, dairy producers are fortunate
that they now have a very useful sire evaluation program for
calving ease that, when used wisely, can be of great help in
improving the profitability of the dairy herd. Holstein producers
should no longer be tempted to use a beef sire to solve their
difficult calving problems. The NAAB Dairy Sire Summary for Calving
Ease makes it possible to use Holstein bulls of high genetic merit
to breed open heifers. This leaves better genetic material in the
herd, and the results are much more assured than when heifers are
bred to beef bulls or natural service Holstein bulls whose
transmitting abilities for calving ease are not known. In the
future, sire summaries for calving ease may be available in other
dairy breeds.

Herd owners can play an important part in the dystocia research by
faithfully reporting calving-ease information on all births in
their herds to their AI organizations and through their DHI
records. The accuracy of future research and future sire
evaluations depends directly on the collection of accurate
calving-ease information at the site where it will be applied--on
the dairy farm.
N

תתתתתתתתתתתתתתתתתתתתThe National Dairy Database (1992)תתתתתתתתתתתתתתתתתתתת
תתתתתתתתתתתתתתתתתתתתתתת\NDB\DAIRY\TEXT\DA100300.TXTתתתתתתתתתתתתתתתתתתתתתתת

%f TITLE;DYSTOCIA DATA AND ITS USE
%f COLLECTION;DAIRY HERD IMPROVEMENT
%f ORIGIN;Iowa
%f DATE_INCLUDED;June 1992