The cost of raising dairy replacement heifers prior to calving can range from $2.25 to $3.00 per 100 lb of milk sold. In other words this cost represents about 20 percent of the cost to produce milk (Luening et al. 1987). Conlin and Linn included the salvage value of a cull cow and determined the cost to be between $0.77 and $1.95 per 100 lb of milk sold. Independent of how you calculate the cost to raise dairy replacement heifers, they represent a major expense in producing milk. There are many factors that can reduce replacement heifer rearing cost. Major emphasis has been on growth and development of heifers to reduce age-at-first-calving (AFC). It is well recognized that there is a significant cost ($1.17 to $3.00) for each day beyond 24 months that calving is delayed (Luening et al., 1987). This cost is equivalent to the cost per day open beyond 15 months for virgin heifers.
Growth and development of replacement heifers is only a small piece of the profitability puzzle. Reproductive efficiency in virgin heifers is a major factor that farm management can control to become more profitable. The cost of reproductive inefficiency is a hidden cost in the way we traditionally look at heifer raising budgets. It is hidden in the feed, labor, equipment, and facility costs. There is no offsetting income from milk sales for extended days open in virgin heifers, it is all cost. Because of these factors, more can be done to improve dairy farm profitability by focusing on reproductive efficiency in virgin heifers than focusing on reproductive efficiency in lactating cows .
Age at first calving (AFC) is really a measure of reproductive efficiency rather than growth. It is similar to using calving intervals with lactating cows. The problem is that age at first calving is very highly correlated with growth because growth (body size) is used to determine the voluntary wait period (VWP) or time-to-begin-breeding of replacement heifers. Furthermore, age-at-puberty is a function of growth. Figure 1 illustrates this simple relationship. The solid growth line represents the phase that has significant impacts on age at first calving. The dotted lines indicate those phases that have little influence on age at first calving. The only time that growth has a significant impact on age at first calving is in determining the length of the voluntary wait period or how soon to breed the replacement heifers. Sometimes this period is extended to compensate for poor growth during the last two phases. Once breeding begins, growth has very little impact on age at first calving. The fact that heifers must conceive is often overlooked in evaluating the causes of excessive age at first calving.
Table 1. Distribution of AFC, body weight, and total cost per day open beyond 15 months per 100 heifers raised.1
|
AFC
(months) |
HDR2 = 50 per cent
VWP3 = 13 months
CR4 = 65 percent
BWB5 = 830 pounds |
|
|
% of heifers |
BW6 |
Cost7 |
|
22-23 |
65 |
1219 |
$0.00 |
|
24-25 |
22 |
1268 |
$772.20 |
|
26-27 |
6 |
1308 |
$631.80 |
|
28-29 |
3 |
1340 |
$526.50 |
|
30-31 |
2 |
1350 |
$491.40 |
|
32-33 |
2 |
1355 |
$631.80 |
|
34-35 |
0 |
|
$0.00 |
|
> 36 |
0 |
|
$0.00 |
|
Avg AFC= 23.6 months |
|
Avg BW6 = 1228 pounds |
|
Total Cost = $3053.70 |
1 Assumes "ideal" growth, and a cost per day open = $1.17.
2 HDR = Heat Detection Rate.
3 VWP = Voluntary Wait Period
4 CR = Conception Rate
5 BWB = Body Weight when Breeding begins
6 BW = Body Weight after calving.
7 Cost = cost of total days open beyond 15 months for % of 100 heifers calving at respective age.
Reproductive efficiency is the primary determinant of the distribution of age at first calving. Tables 1,2, and 3 illustrate the impact different reproductive efficiencies have on the distribution of age at first calving and the cost of the resulting heifers. Comparing Table 1 with Table 2 there is a difference of $2527.20 per 100 heifers. This difference is due to a change in heat detection rate (HDR) and nothing more.
Table 2. Distribution of AFC, body weight, and total cost per day open beyond 15 months per 100 heifers raised.1
|
AFC
(months) |
HDR2 = 30 per cent
VWP3 = 13 months
CR4 = 65 percent
BWB5 = 830 pounds |
|
|
% of heifers |
BW6 |
Cost7 |
|
22-23 |
49 |
1221 |
$0.00 |
|
24-25 |
25 |
1269 |
$877.50 |
|
26-27 |
12 |
1309 |
$1263.60 |
|
28-29 |
7 |
1342 |
$1228.50 |
|
30-31 |
3 |
1368 |
$737.10 |
|
32-33 |
2 |
1388 |
$631.80 |
|
34-35 |
1 |
1405 |
$386.10 |
|
> 36 |
1 |
1415 |
$456.30 |
|
Avg AFC= 24.9 months |
|
Avg BW6 = 1263 pounds |
|
Total Cost = $5580.90 |
1 Assumes "ideal" growth, and a cost per day open = $1.17.
2 HDR = Heat Detection Rate.
3 VWP = Voluntary Wait Period
4 CR = Conception Rate
5 BWB = Body Weight when Breeding begins
6 BW = Body Weight after calving.
7 Cost = cost of total days open beyond 15 months for % of 100 heifers calving at respective age.
In Tables 1, 2, and 3 it is assumed that the producer will continue to breed the heifers until they are all pregnant. If this is not the case, then there will be an increase cost associated with culled heifers. This additional cost would be equivalent to the heifer’s salvage value subtracted from the cost to raise her. In Table 2, if we assume that the producer stops breeding heifers at the end of 24 months of age and culls those that are not pregnant, then 2 heifers would be culled. If it cost $1100.00 to raise the heifer and salvage value was $600.00, then there would be an additional cost of $500 per heifer ($1000.00 cost for the 2 heifers) culled for reproductive inefficiency. The difference between Table 1 and Table 2 would now be $3527.20 per 100 heifers.
As reproductive efficiency gets worse, not only does the cost escalate due to increased total days open but the number of reproductive culls also increases. Table 3 illustrates what happens when conception rate (CR) falls to 50 percent and HDR is only 30 percent. Comparing Table 3 with Table 1 the difference in losses would be $5265.00 per 100 heifers. This does not include the losses from reproductive culls.
For a variety of reasons, many milk producers like their heifers to be older and bigger when they breed them. Usually this is because they think “bigger is better” or because of poor growth post-conception. They make up for this inefficiency by waiting until heifers are bigger and/or older to be bred. Table 4 illustrates what happens to the distribution of age at first calving and the cost.
Table 3. Distribution of AFC, body weight, and total cost per day open beyond 15 months per 100 heifers raised.1
|
AFC
(months) |
HDR2 = 30 per cent
VWP3 = 13 months
CR4 = 50 percent
BWB5 = 830 pounds |
|
|
% of heifers |
BW6 |
Cost7 |
|
22-23 |
39 |
1222 |
$0.00 |
|
24-25 |
24 |
1270 |
$842.40 |
|
26-27 |
15 |
1310 |
$1579.50 |
|
28-29 |
9 |
1342 |
$1579.50 |
|
30-31 |
5 |
1368 |
$1228.50 |
|
32-33 |
3 |
1389 |
$947.70 |
|
34-35 |
2 |
1405 |
$772.20 |
|
> 36 |
3 |
1418 |
$1368.90 |
|
Avg AGE AT FIRST CALVING= 25.6 months |
|
Avg BW6 = 1276 pounds |
|
Total Cost = $8318.70 |
1 Assumes "ideal" growth, and a cost per day open = $1.17.
2 HDR = Heat Detection Rate.
3 VWP = Voluntary Wait Period
4 CR = Conception Rate
5 BWB = Body Weight when Breeding begins
6 BW = Body Weight after calving.
7 Cost = cost of total days open beyond 15 months for % of 100 heifers calving at respective age.
Comparing different breeding policies and HDR (Table 4 and Table 1), the losses associated with an extended breeding policy and lower HDR were $7757.10 per 100 heifers raised. If the cost of reproductive culls were included the cost would be even higher.
The differences in losses between the different scenarios presented in Tables 1,2,3, and 4 could be interpreted as the potential savings due to better reproductive efficiency. To estimate the actual savings, the cost of improving reproductive efficiency and any related management changes would have to be included.
Table 4. Distribution of AFC, body weight, and total cost per day open beyond 15 months per 100 heifers raised.1
|
AFC
(months) |
HDR2 = 30 per cent
VWP3 = 15 months
CR4 = 65 percent
BWB5 = 930 pounds |
|
|
% of heifers |
BW6 |
Cost7 |
|
22-23 |
0 |
|
$0.00 |
|
24-25 |
49 |
1269 |
$772.20 |
|
26-27 |
25 |
1309 |
$631.80 |
|
28-29 |
12 |
1342 |
$526.50 |
|
30-31 |
7 |
1368 |
$491.40 |
|
32-33 |
3 |
1388 |
$631.80 |
|
34-35 |
2 |
1405 |
$0.00 |
|
> 36 |
2 |
1418 |
$0.00 |
|
Avg AFC= 26.9 months |
|
Avg BW6 = 1304 pounds |
|
Total Cost = $10810.80 |
1 Assumes "ideal" growth, and a cost per day open = $1.17.
2 HDR = Heat Detection Rate.
3 VWP = Voluntary Wait Period
4 CR = Conception Rate
5 BWB = Body Weight when Breeding begins
6 BW = Body Weight after calving.
7 Cost = cost of total days open beyond 15 months for % of 100 heifers calving at respective age.
To evaluate the effect of reproductive efficiency on age at first calving, HDR and CR were used to calculate the expected age at first calving (Table 5). It was assumed that breeding began at 13 months of age and any heifer nonpregnant at 21 months of age was culled. In this example, age at first calving only varied from 22.7 months to 25.9 months. That may not seem like a big difference considering the tremendous range in reproductive efficiency. The reason for the lower than expected range in age at first calving is reproductive culls. Table 6 gives the reproductive cull rates for each reproductive efficiency scenario. Table 6 clearly shows that poor reproductive efficiency may be camouflaged by culling. If there had been no culling, the range in age at first calving values in Table 5 would be much greater.
Table 6. Reproductive cull rate for various reproductive efficiencies in virgin heifers1.
|
Conception Rate |
Heat Detection Rate |
|
|
20 |
35 |
50 |
65 |
80 |
|
20 |
59 |
39 |
25 |
16 |
10 |
|
35 |
39 |
18 |
8 |
3 |
1 |
|
50 |
25 |
8 |
2 |
1 |
0 |
|
65 |
16 |
3 |
1 |
0 |
0 |
|
80 |
10 |
1 |
0 |
0 |
0 |
1 Assumes that breeding begins at 13 months of age and all heifers not pregnant by 21 months of age are culled
Table 5. AFC for various reproductive efficiencies 1.
|
Conception Rate |
Heat Detection Rate |
|
|
20 |
35 |
50 |
65 |
80 |
|
20 |
25.9 |
25.7 |
25.4 |
25.1 |
24.8 |
|
35 |
25.7 |
25.2 |
24.7 |
24.3 |
23.9 |
|
50 |
25.4 |
24.7 |
24.1 |
23.6 |
23.3 |
|
65 |
25.1 |
24.3 |
23.6 |
23.2 |
22.9 |
|
80 |
24.8 |
23.9 |
23.3 |
22.9 |
22.7 |
1Assumes that breeding begins at 13 months of age and all heifers not pregnant by 21 months of age are culled.
Reproductive efficiency must be monitored before it can be improved. The only regularly available and consistently reliable number is services per conception or conception rate. These values aren’t enough to know what is going on. Most of the data needed to effectively monitor reproductive efficiency in heifers is available. However, one very important date may be difficult to find. That date is the day the producer decides the heifer is ready to be bred. This date is very important in calculating reproductive efficiency. It isn’t real difficult to obtain at the time it occurs because on many dairies it corresponds to a pen change. That being the case, all that would need to be recorded is which calves got moved into the breeding pen on a particular day.
Recording the birth date, the date the producer decides to begin breeding a heifer, every breeding date, and the calving date, most reproductive indices can be calculated. Pregnancy confirmation, date of observed estrus, and sire identification also provide useful information.
The following reproductive indices along with how they are calculated are suggested for monitoring reproductive efficiency in heifers. The standard for many of these measures will depend on the growth strategy implemented on the farm. Therefore no standard is given for those measures. Standards are provided for measures that are independent of growth strategy.
Projected Minimum Average AFC. This measure is the average projected age of all heifers that have been bred and not calved or are currently in the breeding pool but not bred. Projected minimum age at first calving can be calculated as follows, then averaged and expressed in months.
= ((last breeding date1 - birth date) + 280) / 30.4 days
1or current date + 10 days for heifers in the breeding pool but not bred
Past Year Average AFC. This measure is the average age of all heifers that have calved in the last 12 months. Age at first calving is calculated as follows, then averaged and expressed in months.
= (calving date - birth date) / 30.4 days
Projected Minimum Average Heifer Days Open. This measure is the average number of projected days open between the time when breeding begins and last breeding. A value of less than 45 days would be excellent and less than 70 days would be good. Heifer days open can be calculated as follows and then averaged for all heifers currently in the breeding pool and pregnant heifers.
= last breeding date1 - date of begin breeding
1or current date + 10 days for heifers in the breeding pool but not bred
Average Age At Last Breeding. This measure is the average age of all heifers that have been bred at least once. Age at last breeding can be calculated as follows, then averaged and expressed in months.
= (last breeding date - birth date) / 30.4 days
Heat Detection Rate (HDR). This measure is the percent of possible heats that are detected. A value of 50 percent or higher is good. The calculation below assumes that all heifers are bred when observed in estrus. Only heifers currently or previously in the breeding pool are used. HDR is calculated as follows:
= (no. of services per heifer bred) / ((last breeding date - date of begin breeding) / 21) + 1)
Services Per Pregnancy. This measure is the average number of services it takes to get a heifer pregnant. A pregnant heifer can be defined as 65 day non -returns, confirmed by palpation, or both. Confirmed-by-palpation is the preferred definition of pregnancy. A value of 1.4 or lower is excellent and less than 1.6 is good. Services per pregnancy for the desired time interval is calculated as follows:
= total no. of services / total no. of heifers that conceive
Conception Rate (CR). This measure is the percent of heifers that conceive to each service. It is the inverse of services per pregnancy. A value of 70 percent or higher is excellent and higher than 60 percent is good. CR for the desired time interval is calculated as follows:
= (total no. of heifers that conceive / total no. of services) * 100
Heifer Reproductive Cull Rate. This measure is a running average for the last 12 months. A value of less than 5 percent is good. It is calculated as follows; where the average number of heifers in the herd is an average of the 12 previous monthly inventory counts and the number culled is the total number culled in the last 12 months.
= total no. culled / average inventory
Percent Pregnant By Bull. This measure is the percent of pregnancies in the previous 12 months that were the result of natural service. Sire identification is important for this measure to have any real meaning. It is calculated as follows:
= no. of pregnancies by natural service / total no. of pregnancies
Reproductive efficiency is a major determinant of age at first calving and is very important for profitable heifer raising. Improving virgin heifer reproductive efficiency can have a major impact on dairy farm profitability. To do this requires implementing a monitoring system as well as employing various strategies to improve reproductive efficiency.
References:
Conlin, B.J. and J.G. Linn. 1993. Contract Raising of Dairy Replacements: Concepts and Considerations. Minnesota Extension Service Dairy Update. Issue 116.
Luening, R.A., R.M. Klemme, and W.T. Howard. 1987. Wisconsin Farm Enterprise Budgets: Dairy Cows and Replacements. Bulletin A2731. University of Wisconsin-Extension.
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