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The objective of this study was to estimate the value of pregnancy for dairy cows. Effects of the stage of gestation, stage of lactation, lactation number, milk yield, milk price, replacement heifer cost, probability of pregnancy, probability of involuntary culling, and breeding decisions were studied. A bioeconomic model was used, and breeding and replacement decisions were optimized. A general Holstein herd in the United States was modeled. The average value of a new pregnancy was $278. The value of a new pregnancy increased with days in milk early in lactation but typically decreased later in lactation. Relatively high-producing cows and first-lactation cows reached greater values, and their values peaked later in lactation. The average cost of a pregnancy loss (abortion) was $555. The cost of a pregnancy loss typically increased with gestation length. Sensitivity analyses showed that an increased probability of pregnancy, an increased persistency of milk yield, and a smaller replacement heifer cost greatly reduced the average value of a pregnancy. The value of a new pregnancy was negative for relatively high-producing first-lactation cows when persistency of lactation and the probability of pregnancy were increased. Breeding was delayed when the value of pregnancy was negative. Changes in milk price, absolute milk yield, and probability of involuntary culling had less effect on the value of pregnancy. The value of pregnancy and optimal breeding decisions for individual cows were greatly dependent on the predicted daily milk yield for the remaining period of lactation. An improved understanding of the value of pregnancy may support decision making in reproductive management when resources are limited.
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J. Dairy Sci. 89:3876–3885
© American Dairy Science Association, 2006.
Economic Value of Pregnancy in Dairy Cattle
1
A. De Vries
Department of Animal Sciences, University of Florida, Gainesville 32611
ABSTRACT
The objective of this study was to estimate the value
of pregnancy for dairy cows. Effects of the stage of gesta-
tion, stage of lactation, lactation number, milk yield,
milk price, replacement heifer cost, probability of preg-
nancy, probability of involuntary culling, and breeding
decisions were studied. A bioeconomic model was used,
and breeding and replacement decisions were opti-
mized. A general Holstein herd in the United States
was modeled. The average value of a new pregnancy
was $278. The value of a new pregnancy increased with
days in milk early in lactation but typically decreased
later in lactation. Relatively high-producing cows and
first-lactation cows reached greater values, and their
values peaked later in lactation. The average cost of
a pregnancy loss (abortion) was $555. The cost of a
pregnancy loss typically increased with gestation
length. Sensitivity analyses showed that an increased
probability of pregnancy, an increased persistency of
milk yield, and a smaller replacement heifer cost
greatly reduced the average value of a pregnancy. The
value of a new pregnancy was negative for relatively
high-producing first-lactation cows when persistency of
lactation and the probability of pregnancy were in-
creased. Breeding was delayed when the value of preg-
nancy was negative. Changes in milk price, absolute
milk yield, and probability of involuntary culling had
less effect on the value of pregnancy. The value of preg-
nancy and optimal breeding decisions for individual
cows were greatly dependent on the predicted daily
milk yield for the remaining period of lactation. An
improved understanding of the value of pregnancy may
support decision making in reproductive management
when resources are limited.
Key words: economics, pregnancy, reproduction,
abortion
Received January 9, 2006.
Accepted May 11, 2006.
E-mail: devries@ufl.edu
1
This project was supported by the Initiative for Future Agriculture
and Food Systems, Grant no. 2001-52101-11318, from the USDA
Cooperative State Research, Education, and Extension Service.
3876
INTRODUCTION
The profitability of dairy farms depends greatly on
the reproductive efficiency of dairy cows (Britt, 1985;
Plaizier et al., 1997; Meadows et al., 2005). Numerous
studies have documented that additional days in which
cows are not pregnant beyond the optimal time post-
calving are costly (Holmann et al., 1984, Groenendaal et
al., 2004; Meadows et al., 2005). The value of pregnancy
depends on the stage of lactation (Groenendaal et al.,
2004). Other factors also may influence the value of
pregnancy, such as the lactation number, milk yield,
persistency of lactation, prices, and breeding and re-
placement decisions. Studies are lacking that systemat-
ically analyze how the value of pregnancy depends on
these factors.
The value of a pregnancy for an individual cow can
be defined as the difference in discounted future cash
flows when she is pregnant compared with when she
is not pregnant. The value of a new pregnancy has been
reported to average approximately $200 (Eicker and
Fetrow, 2003). In programmed AI breeding protocols,
Stevenson (2001) estimated that the value of a new
pregnancy was between $253 and $274, excluding the
additional cost of the programmed AI breeding protocol
compared with traditional breeding based on detected
estrus. He showed that the value of pregnancy in-
creased with lower estrus detection efficiency.
Per case, the cost of pregnancy loss (abortion) has
been estimated at $640 (Thurmond and Picanso, 1990)
and from $600 to $800 (Eicker and Fetrow, 2003). Pfeif-
fer et al. (1997) estimated the cost of an abortion caused
by Neospora caninum infections at NZ$975 in New
Zealand ($624). Peter (2000) documented a cost of $600
to $1,000 per midterm abortion. Weersink et al. (2002)
estimated the cost of an abortion, including reproduc-
tive loss and reduced milk yield at CAN$1,476 in Can-
ada ($1,286). Several of these estimates were intended
as illustrations of special cases and were not herd or
group averages. Furthermore, the methods used to ob-
tain these values were not fully described or could be im-
proved.
The hypothesis of this study was that the value of
pregnancy varies greatly for individual cows, depending
on the performance of the cow and that of the herd, the
lactation number, the stage of lactation, the stage of
VALUE OF PREGNANCY 3877
gestation, prices, and breeding and replacement deci-
sions. A systematic analysis of the value of pregnancy
for individual cows may help dairy producers focus their
resources on those nonpregnant cows that are economi-
cally the most important group to get pregnant. Fur-
thermore, a systematic analysis should provide esti-
mates of the cost of abortion for different groups of cows
(e.g., by stage of gestation).
The objective of this study was to estimate the value
of pregnancy for cows that differed in lactation number,
stage of lactation, and milk yield. The effects of various
replacement heifer costs, prices of milk, levels of herd
performance (probability of pregnancy, probability of
involuntary culling, 305-d milk yield, persistency of lac-
tation), and breeding decisions (length of breeding pe-
riod) were evaluated. Both the value of establishing a
new pregnancy and the cost of pregnancy loss were
studied.
MATERIALS AND METHODS
Methodology
A dairy cow breeding and replacement model devel-
oped and described by De Vries (2004) was used, with
a number of modifications, as described in the following
paragraphs. In brief, the objective of that model was to
maximize profit per slot per year with the current cow
and subsequent replacement heifers through optimal
breeding and replacement decisions. The model con-
sisted of 3 modules: 1) a bioeconomic module to enter
and calculate cow performance data and prices; 2) an
optimization module based on dynamic programming
to determine the optimal breeding and replacement de-
cisions for individual cows; and 3) a herd performance
module based on Markov chains to calculate summary
results for subgroups of cows or for the entire herd. The
model used monthly time steps (30.4 d). The model by
De Vries (2004) was similar to earlier models (DeLo-
renzo et al., 1992; Dekkers et al., 1998). Notation of the
model components described in the following para-
graphs is similar to those used by De Vries (2004),
except that seasonality in cow performance and prices
was excluded in the present study.
Cows were categorized by a combination of milk yield
(i, with i = 1 to 15, where i = 1 was the smallest milk
yield and i = 15 was the largest milk yield), lactation
number (k, with k = 1 to 12), month in lactation (mo,
with mo = 1 to 24), and reproductive status (n, where
n = 0 was a nonpregnant cow and n = 1 to 9 was the
month of gestation for pregnant cows). Nonfeasible cat-
egories, for example where mo = 1 and n = 2, were
excluded. Furthermore, CV
i,k,mo,n,t
was the discounted
future cash flow given optimal breeding and replace-
ment decisions for the individual cow and her future
Journal of Dairy Science Vol. 89 No. 10, 2006
replacement in month t until the end of the planning
horizon. It follows that the value of pregnancy during
month n of gestation was calculated as VP
i,k,mo,n,t
=
CV
i,k,mo,n,t
CV
i,k,mo,0,t
. For example, VP
i,k,mo,5,t
was the
value of the pregnancy at the start of the fifth month
of gestation. The value of the pregnancy is equivalent
to the cost of pregnancy loss if the cow should abort.
The value of pregnancy is equivalent to the difference
in retention payoff (RPO) of 2 cows that are categorized
similarly but that differ in that 1 cow is not pregnant
(n = 0) and the other cow is pregnant (n 1) and both
RPO are greater than $0. The RPO is the discounted
future cash flow from trying to keep the cow until the
optimal time to cull her and her future replacement
heifers (KEEP
i,k,mo,n,t
), minus the discounted future
cash flow from immediately culling the cow and her
future replacement heifers (CULL
i,k,mo,n,t
; van Aren-
donk, 1984). Thus, RPO
i,k,mo,n,t
= KEEP
i,k,mo,n,t
CULL
i,k,mo,n,t
. Furthermore, CV
i,k,mo,n,t
=
max(KEEP
i,k,mo,n,t
, CULL
i,k,mo,n,t
). If the RPO is greater
than $0, then the optimal decision is to keep the cow
at least 1 more month. If the RPO is less than $0, then
the optimal decision is to immediately cull the cow, and
usually immediately fill the slot with a replacement
heifer. If both the nonpregnant and the pregnant cow
have an RPO of less than $0, then the value of preg-
nancy equals $0 because the model assumes that the
cull price is independent of pregnancy status and both
cows would be replaced at the same time by identical
replacement heifers. Thus, their discounted future cash
flows are identical.
A few modifications were made to the optimization
module described by De Vries (2004). First, the proba-
bility of abortion per month of gestation was included.
If a cow aborted, it was assumed that she continued as
an identical nonpregnant cow in the same lactation.
Furthermore, the probability of establishing a preg-
nancy per month was calculated as PR + (1 PR) × PR
× 9.4/21, where PR (pregnancy rate) was the probability
of getting pregnant in a 21-d estrous cycle. The number
of breedings per month for an eligible, nonpregnant cow
was SR + (1 PR) × SR × 9.4/21, where SR (service
rate) was the probability of breeding in a 21-d estrous
cycle. The SR equals the probability of estrus detection
in a 21-d estrous cycle when breeding is based on detec-
tion of estrus alone. Therefore, PR = SR × probability
of conception. These changes more accurately represent
the probability of occurrence of breeding and pregnancy
per month compared with the formulation in De Vries
(2004). The consequences at realistic levels of PR and
SR are minor.
Finally, a positive association was included between
days not pregnant during a previous lactation and 305-
d milk yield during the current lactation, using the
DE VRIES3878
multiplication factors from Funk et al. (1987). These
factors ranged from 98% when the cow was 61 d not
pregnant to 105% when the cow was 456 d not pregnant.
The distribution of transition probabilities to the milk
yields during the first month of the next lactation (van
Arendonk, 1985), based on a 60% repeatability of the
305-d total milk yield (van Arendonk, 1986), was shifted
slightly to obtain the adjusted 305-d total milk yields.
Breeding and replacement decisions in this study
were optimal unless specified otherwise. The supply of
replacement heifers was unlimited. The value of a new
pregnancy was calculated for every nonpregnant cow
that was eligible for breeding. Cows were eligible for
breeding after 61 DIM until the end of the 15th month
in lactation (d 456), unless the cow was culled earlier.
Results were calculated for herds in steady state, as
determined by the herd performance module. Average
results for subgroups of cows were obtained by weighing
the probability that a cow was in a category in that
subgroup multiplied by the value of pregnancy for that
category (De Vries, 2004). For example, the herd aver-
age value of a new pregnancy was the weighted value of
pregnancy of nonpregnant cows at various milk yields,
lactations, and DIM.
Default Input Values
Input values for the bioeconomic module were chosen
to represent a general Holstein dairy herd in the United
States. Unless specified otherwise, input values were
the same as in De Vries (2004).
Milk Yield. Milk yield by month of lactation for non-
pregnant cows per lactation was predicted by the dipha-
sic logistic function, defined as
y
DIM
=
2
i=1
a
i
b
i
{1 tanh
2
[b
i
(DIM c
i
)]},
where y
DIM
= milk yield at DIM and a
i
, b
i
, and c
i
are
parameters for phase i; tanh is the hyperbolic tangent
function; a
i
b
i
is the peak yield for phase i; and c
i
is DIM
at the peak yield for phase i (Grossman and Koops,
1988). This function was able to provide accurate esti-
mates of milk yields for standard and extended lacta-
tions in other studies (Vargas et al., 2000). The 6 param-
eters of the diphasic logistic function were estimated
from average peak yield, DIM at the peak yield, and
2X 305-d mature equivalent (ME) milk yields for the
first, second, and third and greater lactations based on
2.2 million records completed in 2003. These averages
were provided by the USDA Animal Improvement Pro-
grams Laboratory (AIPL) in Beltsville, Maryland. Ac-
tual 2X 305-d milk yields during the first and second
lactations were assumed to be 83.3 and 90.9% of the
Journal of Dairy Science Vol. 89 No. 10, 2006
ME yield (Norman et al., 1995). Because average peak
yields and DIM at peak yield obtained from the AIPL
were based on various milking frequencies but the 305-
d ME yield was for 2X only, 305-d milk yields were
estimated by adding 1,000 kg to the actual 2X 305-d
milk yields, based on Erdman and Varner (1995). The
Solver function in Microsoft Excel was used to minimize
the difference between the actual and predicted 305-d
milk yields given the following 4 constraints. Predicted
DIM at the peak milk yield, predicted peak milk yield,
and predicted 305-d milk yield were constrained to be
within 20% of the actual averages obtained from the
AIPL. In addition, the ratio of predicted daily yields at
280 and 60 DIM was constrained to be within 20% of
0.75, 0.59, and 0.57 for cows in their first, second, and
third and greater lactations (Canadian Dairy Network,
2004), respectively. No feasible solutions could be found
if the constraints were not satisfied. Meadows et al.
(2005) used the same approach to estimate lactation
curves for herds located in Ohio. Persistency of milk
production in the current study was measured as the
linear decline in predicted milk yield per day between
DIM at peak milk yield and d 305. The results of fitting
the diphasic logistic functions are shown in Table 1.
Milk yields predicted by the diphasic logistic func-
tions represented the lactation curves at the average
milk yield (i = 8) during the 3 lactations. Other milk
yields in the same lactation and month of lactation were
a percentage of the average amount, with the smallest
amount (i = 1) equal to 69.7% and the largest amount
(i = 15) equal to 130.3% of the average milk yield (van
Arendonk, 1985; De Vries, 2004).
Pregnancy reduced milk production by 5, 10, and 15%
in mo 5, 6, and 7 of gestation (De Vries, 2004). Cows
were not lactating in mo 8 and 9 of gestation.
Reproduction. The probability of being inseminated
during a 21-d estrous cycle (SR), and the probability of
conception at 61 DIM were both set at 40% (Groenen-
daal et al., 2004). Thus, PR at 61 DIM was 16%. The
probability of conception declined after 61 DIM by 2.6%
per month, based on De Vries (2004).
The probability of abortion by month of gestation (n =
2 to 8) was set at 3.5, 2.5, 1.5, 0.5, 0.25, 0.1, and 0.1%,
respectively (data adapted from Santos et al., 2004).
Consequently, the total probability of abortion after the
first month if the cow was not culled was 8.2%. The
probability of fetal loss during the first month of preg-
nancy was set at 0% because the probability of concep-
tion was defined as the probability that the cow was
pregnant 1 mo after breeding.
Involuntary Culling. The probability of involun-
tary culling per month of lactation was set at 70% of the
values reported in De Vries (2004) for the southeastern
United States. This adjustment was made to obtain
VALUE OF PREGNANCY 3879
Table 1. Parameters describing the diphasic logistic function as a model for lactation curves for nonpregnant
cows
1
Lactation no.
Parameter 1 2 3
Phase 1, a
1
11,111.9 7,573.9 7,928.5
Phase 1, b
1
0.00221 0.00379 0.00392
Phase 1, c
1
84.84 55.72 55.12
Phase 2, a
2
4,532.4 4,609.8 4,707.0
Phase 2, b
2
0.00262 0.00317 0.00321
Phase 2, c
2
124.15 92.57 91.69
Actual peak yield, kg/d 36.3 44.5 45.4
Predicted peak yield, kg/d 36.4 43.2 46.0
Actual DIM at peak yield 126 79 74
Predicted DIM at peak yield 101 65 64
Actual 305-d yield, kg 10,501 11,175 11,794
Predicted 305-d yield, kg 10,501 11,175 11,794
Predicted persistency, kg/d 0.036 0.085 0.095
Predicted yield d 280:yield d 60 0.85 0.59 0.57
1
Diphasic logistic function: y
DIM
=
2
i=1
a
i
b
i
{1 tanh
2
[b
i
(DIM c
i
)]} where y
DIM
is yield (kg) at DIM, a
i
, b
i
,
and c
i
are parameters for phase i (Grossman and Koops, 1988). Actual data source: Cole and Tooker, the
USDA Animal Improvement Programs Laboratory (Beltsville, MD), personal communication.
overall culling rates that were in better agreement with
national averages reported for the dairy industry.
Prices. Milk price was set at $0.31/kg. The replace-
ment heifer cost was set at $1,600 per head and the
calf price at $200. The replacement heifer cost was
greater than the typical cost to raise a heifer and
smaller than the typical cost to purchase a heifer in
2005 (Meadows et al., 2005).
Cull prices for voluntarily culled cows were set at
$0.74/kg of BW (Meadows et al., 2005). Additional costs
because of involuntary culling were set at $0. Instead,
cull prices for involuntarily culled cows were set at 50%
of the cull price of voluntarily culled cows. Feed cost
per kilogram of DMI was set at $0.20 for lactating cows
and $0.15 for dry cows (Groenendaal et al., 2004). Other
variable costs were set at $1/cow per d. Future cash
flows were discounted monthly at an 8% annual dis-
count rate and were converted to their equivalent an-
nual annuity values in the herd performance module
(Keown et al., 2002).
Sensitivity Analyses
Sensitivity analyses were performed to evaluate the
effects of changes in the input values on the value of
pregnancy. Daily milk yield, milk price, replacement
heifer cost, and probability of involuntary culling were
multiplied by 1.2 or 0.8 to obtain 20% changes in these
input values. The probability of conception at 61 DIM
was set at 43.8 or 35.8% to obtain 20% changes in the
probability of pregnancy (PR) if breeding was optimal.
The last DIM when breeding was allowed was reduced
to 365 d (12 mo) or 274 d (9 mo). Persistencies of lacta-
Journal of Dairy Science Vol. 89 No. 10, 2006
tion were increased or decreased by 0.025 kg/d. De-
creased persistencies (steeper curves) were therefore
0.061, 0.110, and 0.120 kg/d for first, second, and
third and greater lactations; increased persistencies
(flatter curves) were 0.011, 0.060, and 0.070 kg/d,
respectively. Parameters of the diphasic logistic func-
tion were reestimated with the following constraints.
Total 305-d total milk yield and milk yield at 1 DIM
were constrained to be the same as for the default in-
puts. Persistency was constrained to be exactly 0.025
kg/d smaller or greater than the default persistencies.
Peak milk yield and DIM at peak milk yield were al-
lowed to vary. Lactation curves for cows in their first
and third and greater lactations having different persis-
tencies are shown in Figure 1.
Figure 1. Lactation curves for first (1, thick lines) and third and
greater (3+, thin lines) lactations with average persistency (lactation
1, ——; lactation 3+, ——), smaller persistency (lactation 1, ––; lacta-
tion 3+, - - -), and greater persistency (lactation 1, ---, lactation
3+, –).
DE VRIES3880
Table 2. Steady-state herd statistics for the default inputs
Herd statistic Value
Milk sales, $/cow per yr 3,544
Cow sales, $/cow per yr 128
Calf sales, $/cow per yr 209
Total revenue, $/cow per yr 3,881
Feed cost, $/cow per yr 1,572
Heifer purchase cost, $/cow per yr 602
Breeding cost, $/cow per yr 33
Other costs, $/cow per yr 1,320
Total costs, $/cow per yr 3,527
Profit, $/cow per yr 354
DIM 223
Milk yield, kg/cow per yr 11,431
Days to conception 137
Pregnancy rate, % 15
Annual cull rate, % 36
Salvage value, $/cow 354
Value of new pregnancy, $ 278
Cost of pregnancy loss, $ 555
RESULTS
Default Assumptions
Major herd statistics for the default inputs are pre-
sented in Table 2. Milk sales were 91% of total sales.
Feed costs were 45% of the total cost. Replacement costs
(replacement heifer cost minus cow sales) were $474/
cow per yr. Revenues minus feed costs were $5.40/d.
Profit was $3.10 per 100 kg of milk. Breeding cost per
pregnancy was $40. Average days to first service was
86 and average days to last breeding was 337. Five
percent of breeding opportunities were delayed. The
average value of a new pregnancy was $278. The aver-
age cost of a pregnancy loss was $555.
An example of the value of pregnancy for cows in
their first lactation with average lactation curves is
shown in Figure 2. With conception at 61 DIM, the
value of pregnancy increased from $81 during the first
month of pregnancy to $841 during the last month of
pregnancy. In this example, the value of pregnancy was
equal to the difference between the RPO of the pregnant
and nonpregnant cow, because both RPO were greater
than $0 during the first 11 mo after calving. The RPO
of the nonpregnant cow decreased from $993 in the first
month after calving to less than $0 after 13 mo in milk,
indicating that the cow should then be culled. The RPO
of the pregnant cow varied from $1,015 for a new preg-
nancy to $956 in the last month of pregnancy. The
reduction in RPO during midgestation was caused by
the remaining risk of involuntary culling and abortion
before the pregnancy was completed.
Value of a New Pregnancy. The results in Table 3
show the differences in total discounted future revenues
and costs that determine the value of a new pregnancy
for 12 cows categorized by lactation number, stage of
Journal of Dairy Science Vol. 89 No. 10, 2006
Figure 2. Retention payoffs (RPO) for a nonpregnant cow () and
a cow that became pregnant on d 61 after calving () by day after
calving. Cows are in their first lactation with average lactation curves.
Value of pregnancy is equal to the difference between the RPO of the
pregnant and nonpregnant cow on the same days after calving be-
cause both RPO are greater than $0.
lactation at conception, and relative milk yield. For
example, a cow in her first lactation with 80% the milk
yield of the average lactation curve that conceived at
61 DIM, and her replacement heifers, had $106 less in
milk sales, $133 less in replacement costs, $31 less in
feed costs, $27 less in breeding costs, and $1 less in
other costs than an identical nonpregnant cow. Calf
sales were $34 greater than for nonpregnant cows. Total
revenues were reduced by $72 and total costs were re-
duced by $192. Therefore, the value of the new preg-
nancy was $120.
Several interactions were observed. Early in first lac-
tation, the value of a new pregnancy decreased when
relative milk yield increased. The low-producing cow
(80% of average) had less opportunity to get pregnant
before she was culled; therefore, her replacement cost
was greater. At 120% milk yield, the $14 value implied
that delayed breeding was more profitable. Breeding
was always delayed when the value of a new pregnancy
was negative. Later in lactation, the value of a new
pregnancy was greater for higher-producing cows. Dur-
ing second lactation at 61 DIM, the value of a new
pregnancy at average milk yield was greater than at
lesser (80%) or greater (120%) milk yields. At 243 DIM,
the value of pregnancy was $0 for the low-producing
cow because the optimal decision for that cow was to
be culled, independent of pregnancy status. In the other
cases, the value of a new pregnancy was greater for
higher-producing cows.
Changes in the value of a new pregnancy by the stage
of lactation and relative milk yield are shown in Figures
3 (first lactation) and 4 (second lactation). The value of
a new pregnancy was observed to be smaller during
early and late lactation. The value decreased more rap-
idly for cows in their second lactation. The value for
high-producing cows peaked later in lactation.
VALUE OF PREGNANCY 3881
Table 3. Value of a new pregnancy explained by differences in the sums of discounted future revenues and costs of a newly pregnant cow
compared with an identical nonpregnant cow
Differences in sums of discounted future
revenues and costs (pregnant nonpregnant), $
RPO, Value
Lactation DIM at Milk RPO, not of new Milk Calf Replacement Feed Breeding Other
no. conception yield,
1
% pregnant
2
pregnant
3
pregnancy
4
sales sales cost
5
cost cost costs
1 61 80 394 274 120 106 34 133 31 27 1
1 61 100 1,015 933 81 859 6 16 27 6
1 61 120 1,652 1,666 14 101 64 34 38 27 8
1 243 80 146 7 146 1,070 110 1,050 201 24 51
1 243 100 712 299 413 26 7 348 9 28 13
1 243 120 1,317 817 500 253 26 238 53 29 7
2 61 80 429 258 171 150 15 235 38 25 8
2 61 100 1,035 811 224 54 36 104 3 26 1
2 61 120 1,659 1,452 208 98 48 38 1 27 3
2 243 80 42 42 0 0 0 0 0 0 0
2 243 100 304 23 281 524 73 744 71 25 38
2 243 120 798 247 551 86 25 479 38 26 23
1
Relative to average lactation curves.
2
RPO = Retention payoff ($) in pregnant cows.
3
RPO = Retention payoff ($) in nonpregnant cows.
4
Value of new pregnancy ($) = sum of differences in milk sales + calf sales replacement costs feed costs breeding costs other costs.
The sum of the differences may not add up to equal the value of the new pregnancy because of rounding.
5
Replacement cost = replacement heifer cost cow sales.
Cost of Pregnancy Loss. The cost of pregnancy loss
after the first month of gestation (Table 4) was typically
greater than the value of a new pregnancy (Table 3),
except in the rare case in which the pregnant cow should
be culled. This was occasionally the case for low-produc-
ing older cows. The cost of pregnancy loss was then $0
because the cull price was assumed to be independent
of pregnancy. The results in Table 4 show the cost of
pregnancy loss at 1, 4, and 7 mo of gestation by relative
milk yield, lactation number, and stage of lactation (61
or 243 DIM) at conception. Costs ranged from $0 to
$1,373.
Several interactions were observed. The cost of preg-
nancy loss increased by the stage of lactation at concep-
tion and by the stage of gestation. Costs were typically
Figure 3. Value of a new pregnancy during first lactation by days
after calving and relative milk yield (80%, ; 100%, ; 120%, )
compared with an average lactation curve.
Journal of Dairy Science Vol. 89 No. 10, 2006
greater for the high-producing cow except when the loss
occurred early in first lactation. First-lactation cows
had lower costs early in lactation but greater costs later
in lactation than older cows.
Sensitivity Analyses
Realistic changes in the inputs could have significant
effects on herd statistics, as shown in Table 5. As ex-
pected, increased daily milk yield, greater persistency,
increased milk price, decreased replacement heifer cost,
a greater probability of pregnancy, more opportunity to
breed cows, and a decreased probability of involuntary
culling were associated with increased profit per cow
per year. Changes in the annual cull rate, the value of
Figure 4. Value of a new pregnancy during second lactation by
days after calving and relative milk yield (80%, ; 100%, ; 120%,
) compared with an average lactation curve.
DE VRIES3882
Table 4. Cost of pregnancy loss after 1, 4, or 7 mo of gestation by relative milk yield, lactation number,
and DIM at conception
61 DIM at conception 243 DIM at conception
Relative
Month of gestation Month of gestation
milk Lactation
yield,
1
% no. 1 4 7 1 4 7
80 1 152 281 418 160 295 576
80 2 207 282 414 0 119 565
80 3 230 278 404 0 0 391
100 1 110 279 578 489 739 962
100 2 285 525 756 310 517 933
100 3 336 562 726 121 298 711
120 1 3 136 490 599 993 1,373
120 2 272 579 984 649 937 1,324
120 3 361 694 1,023 487 669 1,055
1
Relative to average lactation curves.
a new pregnancy, and the cost of pregnancy loss were
not clearly associated with changes in profit per cow per
year. A greater value of a new pregnancy was always
associated with a greater cost of pregnancy loss. A
greater value of pregnancy was associated with in-
creased daily milk yield, reduced persistency of lacta-
tion, increased milk price, increased replacement heifer
cost, decreased probability of pregnancy, less opportu-
nity to breed cows, and decreased probability of involun-
Table 5. Effect of changes in the inputs on selected herd statistics, including the value of a new pregnancy
and the cost of pregnancy loss
Herd statistic
Milk yield, Annual Profit, Value Cost of
kg/cow Days to cull kg/cow of new pregnancy
Input per yr conception rate, % per yr pregnancy, $ loss, $
Daily milk yield
1
+20% 13,840 133 39 908 280 565
20% 9,019 141 33 193 271 536
Persistency
2
+0.025 kg/d 11,602 163 33 414 227 488
0.025 kg/d 11,442 129 38 337 314 603
Milk price
$0.372/kg 11,552 133 40 1,067 280 565
$0.248/kg 11,230 142 32 348 269 531
Heifer cost
$1,920 11,233 143 32 242 332 674
$1,280 11,672 128 44 484 216 420
Probability of pregnancy
3
19.2% 11,437 131 33 393 235 529
12.8% 11,408 145 40 302 331 589
Last DIM to breed
4
365 11,445 134 37 351 282 560
274 11,479 125 39 334 310 594
Prob. of involuntary culling
5
+20% 11,423 137 38 323 268 540
20% 11,431 137 34 387 289 573
1
Relative to default lactation curves.
2
Defined as the linear decline in milk yield per day between DIM at peak yield and 305 DIM.
3
Probability of pregnancy at the end of 61 DIM if breeding is optimal.
4
Last DIM when breeding is allowed.
5
Probability of involuntary culling relative to the default probability of involuntary culling.
Journal of Dairy Science Vol. 89 No. 10, 2006
tary culling. Major determinants of the value of preg-
nancy were persistency of lactation, replacement heifer
cost, and probability of pregnancy. The value of preg-
nancy was smaller when cows were given more opportu-
nity to become pregnant before culling, or when replace-
ment costs were reduced.
Figure 5 shows the value of a new pregnancy during
first and second lactation by the stage of lactation, per-
sistency of lactation, and probability of pregnancy. Per-
VALUE OF PREGNANCY 3883
Figure 5. Value of a new pregnancy during first and second lacta-
tion by days after calving. Compared with the default inputs, persis-
tency of lactation was greater (G, +0.025 kg/d) or smaller (S, 0.025
kg/d) and the probability of pregnancy was greater (g, 19.2%) or
smaller (s, 12.8%). Lactation 1: Gg, ; Gs, ; Sg, ;Ss. Lactation
2: Gg, ; Gs, ; Sg, ; Ss, ).
sistency was greater (+0.025 kg/d) or smaller (0.025
kg/d) compared with the default situation, as in Table
5. The probability of pregnancy was set at 19.2 or 12.8%.
In the first lactation, the value of a new pregnancy
increased nearly linearly by days after calving to the
last opportunity to get pregnant (end of mo 15 after
calving), when both persistency and the probability of
pregnancy were greater than in the default situation.
Early in lactation, the value of pregnancy was negative
or smaller than in all other situations. In all other situa-
tions, the value of pregnancy peaked between the fifth
and eighth month after calving. The value of pregnancy
decreased thereafter because cows were culled at
greater milk yields. The value of pregnancy was $0 for
second-lactation cows after 13 mo in milk because both
the nonpregnant and the newly pregnant cow should
be culled.
DISCUSSION
In this study the value of pregnancy was systemati-
cally estimated by lactation number, stage of lactation,
stage of gestation, milk yield, milk price, replacement
heifer cost, persistency of lactation, probability of preg-
nancy, probability of involuntary culling, and duration
of breeding period. The results depended on cow perfor-
mance, prices, and breeding and replacement decisions.
No single complete description of a general herd is
available in the literature. Therefore, default inputs in
the model were necessarily based on various sources
that may be different in location and time. Default in-
puts were chosen such that the resulting herd statistics
(Table 2) were comparable with statistics published in
several dairy farm financial surveys (Knoblauch et al.,
Journal of Dairy Science Vol. 89 No. 10, 2006
2005; Moore Stephens Wurth Frazer and Torbet, 2005;
Giesy et al., 2006). Although these surveys show re-
gional differences, they also show large variations
among dairy farms within regions.
The shape of the lactation curve was a major determi-
nant of the value of pregnancy. Data describing recent
lactation curve characteristics of large groups of cows
(regions or nationally) were not found. Therefore, lacta-
tion curves used in this study were fitted on observed
averages for peak yield, DIM at peak milk yield, and
2X 305-d ME yield obtained from the AIPL based on
more than 2 million records from across the United
States. A reasonably close fit was obtained (Table 1).
The major difference was that predicted DIM at peak
yield was earlier than actually reported but later than
that used by others (Dekkers et al., 1998; Groenendaal
et al., 2004; Meadows et al., 2005). Predicted persistenc-
ies of lactation in this study were between the persis-
tencies used in those studies that varied widely.
The goal for use of estimated lactation curves in the
current study was to predict future milk yields in the
remainder of the lactation for nonpregnant cows,
whereas most published lactation curves are plots of
average milk yield per DIM. Average milk yields ob-
served in practice are affected by management, culling,
and pregnancy, and are therefore biased predictors of
future milk yields for cows earlier in lactation. Further-
more, predicted future milk yields during the remain-
der of the lactation should be updated as new informa-
tion becomes available to make economically optimal
breeding and replacement decisions later in lactation.
This requires predictions of milk yields in lactations
that will extend past the historical 305 DIM (Grossman
and Koops, 2003).
The average value of a new pregnancy for the default
inputs ($278) was similar to the value used by Steven-
son (2001) and somewhat greater than the value re-
ported by Eicker and Fetrow (2003). The default aver-
age cost of pregnancy loss ($555) was smaller than pre-
viously reported ($600 to $1,286). These differences
were caused by differences in predicted cow perfor-
mance, prices, and breeding and replacement decisions.
When the pregnancy was lost by abortion, the future
performance of the cow in the current and (possibly)
future lactations was assumed to be similar to that of
the nonpregnant cow. The effect of abortion on future
performance was not considered in this study, but af-
fects future cash flow predictions. There is evidence,
for example, that aborted cows are 5 times more likely
to abort subsequently than are cows that never aborted
(Peter, 2000). Abortion also has been associated with
losses in milk yield (Pfeiffer et al., 1997; Weersink et
al., 2002). A cow with compromised future performance
as a result of abortion is more likely to be culled. The
DE VRIES3884
cost of pregnancy loss would be greater than reported
in this study if these effects were included.
The value of a new pregnancy typically increased
greatly when cows were given less time to get pregnant
before they were culled or when replacement costs were
greater. Consequently, cows with more persistent lacta-
tion curves had much smaller average values for new
pregnancies. The importance of lactation persistency
on economically optimal breeding and replacement de-
cisions was previously documented (Dekkers et al.,
1998; Vargas et al., 2000). The economic value of a new
pregnancy was negative early in first lactation when
these cows were more persistent, had a greater proba-
bility of pregnancy, and were relatively high producing.
The negative value of a pregnancy implied that breed-
ing should be delayed past the voluntary waiting period
of 60 d used in this study. The finding that breeding
should be delayed for such cows also has been reported
by others (Dekkers et al., 1998; Rajala-Schultz et al.,
2000).
Groenendaal et al. (2004) showed that the cost per
extra nonpregnant day was smaller for relatively high-
producing cows. Furthermore, costs per extra nonpreg-
nant day were smaller and increased more slowly for
first-lactation cows compared with older cows in that
study. Those trends are similar to those for the value
of pregnancy in the current study. Groenendaal et al.
(2004) set the cost per nonpregnant day to $0 when it
was optimal not to breed a relatively low-producing
cow. In contrast, the optimal decision to delay breeding
(and thus a negative cost per nonpregnant day) was
sometimes associated with a positive value for preg-
nancy (not shown) in the current study. Delayed breed-
ing increases the number of nonpregnant days by ap-
proximately 1 mo, whereas the average time to conceive
after the start of the breeding period is typically longer.
Therefore, the associated discounted future cash flows
are different. The positive value of a new pregnancy
therefore does not necessarily imply that a cow should
be bred. Further investigation should clarify this rela-
tionship.
The variation in milk yield between cows within lac-
tation was modeled as a percentage of the average lacta-
tion curve. Consequently, high-producing cows were
slightly less persistent than the average-producing cow.
In practice, persistencies of lactation also vary among
cows of the same lactation that produce the same
amount of milk in 305 d. Optimal breeding and replace-
ment decisions, and consequently the value of preg-
nancy, depend on the prediction of the persistency of
lactation for individual cows early in the lactation. Fur-
ther investigation that includes prediction of individual
lactation curves seems warranted.
Journal of Dairy Science Vol. 89 No. 10, 2006
Later in lactation, the average value of a new preg-
nancy typically was reduced because more newly preg-
nant cows were culled, especially those with relatively
low milk yields, as well as identical nonpregnant cows.
The difference in their future cash flow predictions was
$0. Low-producing cows that would become pregnant
in a later lactation were assumed to be milked for an-
other 7 mo before dry off. The repeatability of 305-d
total milk yields among lactations was 60% (van Aren-
donk, 1986). The optimization module therefore calcu-
lated that replacing these cows with average heifers
would increase future cash flows. Early dry off for low-
producing pregnant cows was not considered, but this
might be economically advantageous. The value of preg-
nancy depended more on the relative milk yield of a
cow compared with that of a replacement heifer than
on the absolute milk yield.
CONCLUSIONS
The average value of a new pregnancy was $278 and
the average cost of pregnancy loss by abortion was $555
in a simulated herd based generally on Holstein cow
performance and prices in the United States. The value
of a new pregnancy increased with DIM early in lacta-
tion but typically decreased later in lactation. First-
lactation cows and relatively high-producing cows
reached greater values and peaked later in lactation.
The cost of pregnancy loss typically increased with the
length of gestation. Increased persistency of lactation,
increased probability of pregnancy, and decreased re-
placement heifer cost greatly decreased the average
value of pregnancy. Changes in the milk price, milk
yield, and probability of involuntary culling had smaller
effects. The value of pregnancy for individual cows de-
pends greatly on the prediction of milk yield during the
remainder of the lactation. An improved understanding
of the value of pregnancy for individual cows may assist
in decision making in reproductive management.
ACKNOWLEDGMENTS
The milk yield data provided by J. B. Cole and M.
E. Tooker, the USDA Animal Improvement Programs
Laboratory (Beltsville, MD) is greatly appreciated.
Comments from K. C. Bachman and 3 anonymous re-
viewers have improved the clarity of this paper.
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