INTERPRETING INDEXES OF REPRODUCTIVE EFFICIENCY

DAIRY HERD IMPROVEMENT
1988

INTERPRETING INDEXES OF REPRODUCTIVE EFFICIENCY
VARNER, M.A., & MAJESKIE, J.L.
VOLUME: NCDHIP HANDBOOK

Introduction

Reproductive efficiency is the ability of a dairy producer to get
cows bred back soon after calving, with a minimum number of
breedings per cow. Reproductive problems decrease profits by
reducing milk production and the number of replacement heifers
(Pelissier, 1982). In addition, there may be increased breeding
costs and veterinary fees. breeding records, summarized as
reproductive efficiency indexes, provide the best indication of
breeding problems. More importantly, indexes can provide clues
concerning the cause of various problems.

Indexes of reproductive efficiency also are useful for dairy
producers who use artificial insemination (A.I.) and do not have
problems getting cows pregnant. Trends in these indexes can be used
to detect problems as they develop. Often, trends in indexes
provide clues to a problem, and these trends can be more valuable
than looking at an index during a specific time period. Steps to
correct the problem can be taken before a problem becomes serious.

The index values for a herd should not be compared only to goals
contained in this fact sheet, but also to index values for the
state or county or both in which the herd is located. The goals in
this fact sheet are guidelines for optimal efficiency. Regional
differences, such as climate, may make goals more difficult to
reach for some producers. Consequently, comparing state and county
index values to herd values might provide an indication of how good
a job a particular producer is doing, when compared to herds in a
similar region of the country. State or county values usually can
be obtained from state Extension specialists or county agricultural
agents of the Cooperative Extension Service.

The breeding records necessary for calculating the indexes
discussed in this fact sheet are:

- date (month, day and year) of the most recent calving,

- date of the previous calving for second and later lactation
cows,

- reproductive status (pregnant, open and bred, but too early
to detect pregnancy),

- number of breedings for all cows, and

- first breeding date and most recent breeding date if a cow
has been bred more than once.

The Dairy Records Processing Centers (DRPC's) calculate some or all
of these data for producers, and those values can be used in
calculating the reproductive indexes. If the reproductive values
are not provided by DRPC's, an explanation of the procedure is
given for calculating the necessary data.

Glossary

Before evaluating the reproductive status of the herd, one must
become familiar with the following terminology:

Anestrous cows. Cows with ovaries that are not functioning with
regular 19- to 23-day cycles and are not observed in estrus.

Breeding interval (BI). The average number of days between
breedings in the herd.

Calving interval (CI). The number of months between the two most
recent calving dates.

Corpus luteum. An ovarian structure that develops from the
collapsed follicle following ovulation and produces progesterone.
It is the dominant ovarian structure during pregnancy and during
the luteal phase of the estrous cycle.

Days in milk at first service (DFS). The average number of days
from calving until a cow is bred for the first time.

Days Open (DO). The number of days between the most recent calving
and conception. For cows that are not pregnant, days open is the
number of days between last calving and either the present date or
date of last Dairy Herd Improvement Association (DHIA) test.

Metritis. A severe uterine infection, an inflammation of the
uterus.

Postpartum. The time after calving. For example, 60 days postpartum
means 60 days after calving.

Progesterone. A hormone, produced by the corpus luteum, that is
needed for maintenance of pregnancy. Milk can be tested for
progesterone to determine if a cow is cycling and whether she was
accurately diagnosed as being in estrus. Progesterone tests also
can be used to aid pregnancy detection and the diagnosis of cystic
ovarian disease.

Projected minimum calving interval (PMCI). A number that can be
compared to the actual Calving Interval in order to determine
trends in overall herd reproductive management. It is calculated by
adding days open to the gestation length for the most common breed
in the herd. This sum, which will be measured in days, is then
divided by 30.25 to convert it into months.

Reproductive tract disorder. A general term used to describe many
different problems or diseases of the reproductive tract, such as
uterine infection, metritis, retained placenta, cystic ovarian
disease, and others.

Services per conception (S/C). A measure of fertility in cows that
were reproductive successes and have become pregnant. S/C is
calculated by dividing the total number of breedings for pregnant
cows in the herd by the number of pregnant cows.

Indexes of Reproductive Efficiency

Days Open. DO is a measure of overall reproductive performance for
approximately the previous 12 months. Both fertility problems and
estrus detection increase DO. PMCI is calculated by adding DO to
the gestation length for a normal cow. PMCI is interpreted in a
manner similar to DO.

A small percentage of cows with a high DO usually inflates the
herd's average DO slightly. Open cows that will not be re-bred, but
are being kept solely for current milk production, can inflate DO,
especially in small herds. These cows should be excluded from DO
calculations. If DO is inflated significantly by a few problem
breeding cows that are pregnant or still being re-bred, then the
culling policy for reproductive problems in the herd should be
examined. Keeping these cows in the herd may be more costly than
can be justified by milk production or value of the calf.

Current DO, when added to the normal gestation length for a cow,
will not always be equal to CI, 1 to 2 years from now. Some cows
with reproductive problems are culled and never contribute to CI.
However, this difference usually is small, unless a significant
portion of the herd is culled for reproductive problems.

If most of the cull cows are sold for reproductive problems,
current DO plus gestation length may be larger than the actual CI.
Of course, a serious problem exists in any herd where most of the
cull cows are removed for reproductive problems. The causes of
these problems should be determined by examining the reproductive
efficiency indexes as described in this fact sheet.

To calculate DO for a herd, list for each cow the number of days
from calving to:

1. conception,

2. last breeding (for cows that are bred but not yet confirmed
pregnant), and

3. current date or date of last DHIA test (for open cows). Do
not include reproductive problem cows that will be culled this
lactation but are still in the herd because of efficient milk
production.

In calculating the average DO for the herd, add DO for each cow
meeting the previous three criteria, and divide by the total number
of cows contributing to the sum.

A guideline for interpreting DO is summarized in Table 1. For
example, a herd average of 85 days or less for DO indicates that
cows are being bred too early in lactation. Research has shown that
the level of milk production is decreased significantly in the
lactation following breedings earlier than 45 days postpartum
(Funk, Freeman and Burger, 1987). As shown in Table 1, a DO value
of over 145 days indicates a severe problem.

TABLE 1. Various levels for days open and a
short interpretation for each level

Level of days open (a) Interpretation
under 85 too low
85 to 110 optimum
111 to 120 slight problem
121 to 145 moderate problem
over 145 severe problem

(a) Herds with a seasonal calving pattern should
use the highest value in herd records for
Days Open during the last 12 months.

Calving Interval. The actual CI is an indication of reproductive
performance from 9 months to 2 years prior to the current date.
This measure only reflects reproductive successes (pregnancies),
and does not account for reproductive failures. Cows that are
culled for reproductive problems can be considered failures.

CI is figured by calculating the number of months between the most
recent calving and the previous calving for each cow in a second or
later lactation. CI cannot be calculated for first-calf heifers.
The CI's for each cow are then added together and the total is
divided by the number of cows with a second or later lactation.

CI should be interpreted according to the guidelines in Table 2.
Producers with a herd having a CI of under 11.7 months and a DO
under 85 days should breed cows later in lactation for their first
service to increase the DO from 85 to 115 days. Research indicates
that milk production of herds with a CI of under 11.9 months is
significantly less than milk production of herds with a CI of 12.0
to 12.9 months (Willett and Ehlers, 1981).

TABLE 2. Actual calving intervals and a brief
interpretation for each interval

Calving interval Interpretation
(months)
under 11.7 too low
11.8-12.9 optimum
13.0--13.4 slight problem
13.5-14.0 moderate problem
over 14.0 severe problem

Days in Milk at First Service. The average DFS for a herd is
influenced by the onset of ovarian function postpartum, the number
of unobserved estrous periods, and a management decision of when
first breeding will occur postpartum. The DFS goal, the earliest
number of days decided on by management, will vary greatly between
herds. Some cows can be bred safely as early as 40 days postpartum;
however, highest fertility levels usually are not reached until 60
days or later postpartum and milk production in early bred cows may
be reduced. Many producers should consider breeding cows at their
first estrus after 45 days postpartum, because the producers do not
observe or detect all possible heat periods. Producers may avoid
many fertility problems by having their veterinarian palpate cows
prior to 45 days postpartum to diagnose reproductive problems such
as metritis or other severe uterine infections. Breeding cows with
metritis or other reproductive disorders should be delayed until
the disorder is eliminated and the reproductive tract is healthy.

The average DFS for a herd is figured as follows:

1. Calculate the number of days from calving until first service
for all cows inseminated.

2. Calculate the average DFS for the herd by adding together the
DFS for each cow and dividing the total by the number of cows
inseminated.

After determining the earliest number of days postpartum that a cow
can be bred in a herd (DFS goal), the average DFS for a herd should
be interpreted according to the guidelines in Table 3. For example,
a herd might have a DFS goal of 60 days and DFS of 85 days.
According to Table 3, DFS minus DFS goal (85 minus 60) would equal
25 days and be classified as a herd with a moderate problem. Often,
producers have a management policy to breed first-calf heifers
later in lactation than older cows. If this policy exists, it
should be taken into account by adjusting the DFS goal
appropriately.

TABLE 3. The relationship of average DFS and DFS
goal to reproductive efficiency.

Average DFS minus Interpretation
DFS goal
under 22 days no problem
23 to 28 days moderate problem(a)
over 25 days severe problem(a)

(a) The problem may result from cows being anestrous
and/or having missed estrous periods.

The most common cause of DFS problems is unobserved estrus.
Researchers have found that less than 5 percent of cows are
anestrous at 40 days postpartum (Britt, Kittock and Harrison,
1974). Progesterone levels rise dramatically during the first
estrous cycle. If a cow is thought to be anestrous a producer can
test for progesterone levels in milk samples from cows at both 30
days and 40 days postpartum. If progesterone levels are high at
either 30 or 40-day samples, then that cow is not anestrous. The
percentage of tested cows that are anestrous should be calculated
and compared with Table 4. An alternative method to testing milk
progesterone levels is to calculate the average number of days from
calving to first observed estrus, and compare this average to the
information in Table 4. This method, however, is less reliable. If
a herd is below average for percentage of cows with first ovarian
activity, then the herd has too many anestrous cows. If the
percentage of cows with first ovarian activity indicates no
anestrous cows, then the DFS problem may have resulted from
producers missing estrus activity.

TABLE 4. Average days postpartum when two types of activity first occur in
normal cows.
Days Postpartum(a)
When 70 percent When 95 percent
Type of activity of cows in herd of cows in herd Average for
have activity have activity all cows
Ovarian activity(b) 32 days 40 days 24 days
First estrus activity(c) 50 days 63 days 38 days

(a) Days postpartum for percentages were determined from mean and standard
deviation.
(b) Days to first postpartum ovulation.
(c) Days to first observed estrus.
Table adapted from Britt, Kittock and Harrison (1974).

Herds with a greater than normal percentage cows with first estrus
activity do not have anestrous cows as a cause of DFS problems.
However, herds with a below normal percentage of cows with first
estrus activity may have problems because of anestrous cows or
unobserved estrus. Milk progesterone testing may be used to
determine the cause of excessive DFS problems.

Cows that are underfed during late lactation or during the dry
period often are thin when they calve and anestrus may occur. First
ovarian activity usually is delayed in these cows beyond the
averages shown in Table 4. If late lactation or dry cow nutrition
or both are a herd problem and most of the cows are thin when they
calve, herd-wide anestrus and excessive DFS problems often occur.

Metritis after calving is another cause of anestrus. As a
guideline, most producers treat about 20 percent or less of the
herd for uterine infections (Coleman, Thayne and Dailey, 1985).
Calving problems (dystocia) and retained placenta are common causes
of uterine infections.

Most producers assist less than 10 percent of all cows with
calving, and no more than 10 percent of cows should have retained
placenta. If the percentages of cows with uterine infection,
retained placenta, or assisted birth are greater than 20, 10 and 10
percent respectively, the dairy producer should discuss the herd
calving management program with a veterinarian to find the causes
of the problem, such as poor sanitation, nutrition, adequate heifer
size, and the artificial insemination of heifers to calving-ease
sires.

Services Per Conception. S/C for a herd is a measure of fertility
in cows that were reproductive successes and the cows became
pregnant. Breedings for cows that are going to be culled this
lactation and repeat breeder cows not yet diagnosed pregnant are
not included in this index.

Average S/C can be figured as follows:

1. Count the total number of breedings (this lactation) for
each pregnant cow.

2. Calculate the average S/C by dividing the total number of
breedings for all cows by the number of pregnant cows.

Average S/C should be interpreted according to the guidelines in
Table 5. Inaccurate estrus detection is a common cause of a high
S/C. Some cows may be inseminated even though they are not in
estrus. This problem may occur when the detection aid is triggered
accidentally or by misidentification of cows. Estrus and breeding
records that are inaccurate or incomplete also can contribute to
the problem.

Inaccuracy of estrus detection may be confirmed by milk
progesterone analysis (Varner, 1986). Improper techniques for
artificial insemination also may lead to an S/C greater than 2.0.
An examination of techniques used in artificial insemination (AI)
or an AI refresher course could be beneficial (O'Connor, 1985).

TABLE 5. The relationship between services
per conception (S/C) and fertility level

S/C Fertility level
Under 1.8 Good level
1.8-2.0 Adequate level
2.0-2.3 Moderate problem
Over 2.3 Severe problem

Interpreting Indexes of Reproductive Efficiency

Compare CI to PMCI. This comparison can indicate whether overall
reproductive efficiency during the last nine months is improving,
remaining the same, or getting worse than the herd reproductive
efficiency during the previous year. To compare DO to CI, a PMCI is
calculated. Average DO is added to the gestation length, in days,
for the most common breed in a herd (Ayrshire, 278 days; Brown
Swiss, 290 days; Guernsey, 284 days; Holstein, 279 days; and
Jersey, 279 days). This total is then divided by 30.25, which is
the average number of days in a month. For example, PMCI for a
Holstein herd averaging 123 days open would be calculated:

123 days + 279 days/30.25 days/month = 13.3 months for PMCI

Comparisons of actual CI and PMCI should be interpreted according
to the guidelines in Table 6. If the herd reproductive efficiency
is improving, herd reproductive management may not need to be
changed unless the number of missed or repeat breeders is too high.
For herds with an unchanging level of reproductive efficiency, the
effectiveness of reproductive management procedures should be
evaluated if the value for DO indicates an existing problem. If
overall reproductive efficiency for the herd has become worse
during the last nine months, the effectiveness of management
procedures for reproduction should be evaluated. Changes in culling
rate and policy for reproductive problems also can lead to
differences in CI and PMCI comparisons.

TABLE 6. The relationship of actual calving
interval (CI) and Projected minimum calving
interval (PMCI) to reproductive efficiency
level

CI and PCMI Reproductive
comparison efficiency level
CI greater than PMCI Improving
CI similar to PMCI Staying same
CI Less than PMCI Growing worse

Calculating Estrous Detection Efficiency

Estrous detection efficiency can be expressed as the percentage
of heats detected. The percentage of heats detected can be
estimated by first calculating an average breeding interval (BI)
for the herd and then comparing the BI to Table 7. BI is an
estimate of the average number of days between first breeding and
the insemination that results in pregnancy. The average BI can be
calculated using the following formula:

BI = Average DO - DFS/(S/C - 1)

Example: for a herd with a DO of 140, a DFS of 75 and an S/C of
2.6, the BI would be:

140 - 75/(2.6-1) = 41 days

When comparing the BI to Table 7, 41 days corresponds to 50 percent
of heats detected.

TABLE 7. An estimation of percentage of heats
detected based on breeding interval

Breeding interval Percentage of heats
(Days) detected
23 90
26 80
30 70
35 60
41 50
50 40
60 30

Source: Grusenmeyer, D., et al., 1983.

A guideline for interpreting the percentage of heats detected is
summarized in Table 8. Producers with severe heat detection
problems must improve their estrous detection program. Moderate
problems may be caused by not observing estrus in certain cows and
these problems may be reduced by the evaluation of individual cow
records. Anestrous cows or those with feet and leg problems may be
difficult to observe in estrus.

TABLE 8. Relationship of percentage heats
detected to estrous detection efficiency

Percentage heats Estrous detection
detected efficiency level
Under 50 Severe problem
50-65 Moderate problem
66-80 Adequate efficiency
Over 80 Excellent efficiency(a)

(a) Herds that also have a poor level of
fertility (services per conception over
2.0) should use milk progesterone analysis
to determine the accuracy of heats detected.

In some herds, there may be excellent estrous detection efficiency
but poor fertility (S/C over 2.0), suggesting a problem in accuracy
of estrous detection.

Summary

Inefficient reproduction in the herd is costly to the dairy
producer. Reproductive problems can be caused by many different
factors. Records, summarized into reproductive efficiency indexes,
are valuable tools because they can be used to identify the causes
of breeding problems. Indexes also can be used to spot developing
problems before they become serious. Profits can be increased
significantly by most producers if breeding problems are minimized.

References

Britt, J.H., R.J. Kittock and D.S. Harrison. 1974. Ovulation,
estrus, and endocrine response after GnRH in early postpartum. J.
Anim. Sci. 39:915-919.

Coleman, D.A., W.V. Thayne and R.A. Dailey. 1985. Factors affecting
reproductive performance of dairy cows. J. Dairy Sci. 68:1793-1803.

Funk, D.A., A.E. Freeman and P.J. Berger. 1987. Effect of previous
days open., previous days dry, and present days open on lactation
yield. J. Dairy Sci. 70:2366-2373.

Grusenmeyer, D., et al. 1983. Evaluating Dairy Herd Reproductive
Status Using DHI Records. Washington State University, Western
Regional Extension Publication, WREP 0067.

O'Connor, M.L. 1985. Artificial insemination technique. Dairy
Integrated Reproductive Management Manual. Edited by E.R. Jordan,
West Virginia University.

Pelissier, C.L. 1982. Identification of reproductive problems and
their economic consequences. In Proceedings of the National
Invitational Dairy Cattle Reproduction Workshop, 13-15 April,
Louisville, KY. Extension Committee on Policy (ECOP) Science and
Education Administration U.S. Department of Agriculture,
Washington, D.C.

Varner, M.A. 1986. Use of milk progesterone testing for problem
cows. Bovine Practitioner 21:165-171.

Willett, G.S. and M.H. Ehlers. 1981. If your CI is too high. Dairy
Herd Management 18(4): 18-22.