Dairy cow
Updated: May 7, 2021
By Sarah Potts

Many dairy producers grew up during a time when all heifer calves born on the farm were retained and reared as replacement candidates. However, improvements in pre-weaned calf management, heifer nutrition, and reproductive management have enabled dairy producers to maintain herd size while raising fewer replacements. Reducing the number of replacements reared, whether on-farm or off-site, represents significant cost savings. Additionally, by reducing the number of heifers reared on-farm, more attention and resources can be directed toward the calves that are retained to ensure superior performance.  

How many replacements are needed?

The number of heifers that need to be retained on the dairy depends on several factors, which will vary from farm to farm.

  1. Herd size.
    This number includes the number of milking cows and the number of dry cows.
     
  2. Age at first calving.
    The national average for age at first calving is 25 months (USDA, 2014). Studies show that Holsteins that calve for the first time between 22 and 24 months of age are the most profitable (Heinrichs et al., 2017). Heifers should be approximately 65% of mature weight at breeding and 85% of mature weight post-calving so management adjustments may be required if a producer wants to reduce a 25-month to a 23-month age at first calving. For example, if the average mature cow in a herd weighs 1400 lb, a calf that weighs 190 lbs at weaning (2 months of age) must achieve an average growth rate of ~1.97 lb/d in order to reach an appropriate breeding weight of 910 lb (65% of 1400 lb) by 14 months.
     
  3. Cull rate.
    The cull rate reflects the proportion of cows that are removed from the herd for both voluntary and involuntary reasons, including those that die. The average cull rate for U.S. dairies is 33% (USDA, 2014). To calculate the cull rate, the number of cows that leave the herd within a given time period is divided by the total number of cows (dry and milking).
     
  4. Heifer non-completion rate.
    The heifer non-completion rate (sometimes called the “heifer cull rate”) includes replacements born alive that leave the herd before their first calving. Heifers that are sold for dairy purposes should also be included in this metric. To calculate the heifer non-completion rate, the number of heifers that leave the herd in a period of time should be divided by the total number of heifers in the herd. 

The following equation can be used to calculate the annual number of replacements that need to be retained on the dairy in order to maintain herd size:

herd size × (age @ 1st calving ÷ 24) × cull rate × (1 + heifer non-completion rate)

The table below shows the number of replacements required annually in order to maintain herd size for various herd sizes and ages at first calving. As age at first calving increases, the number of replacements required annually increases.

Table 1. The number of replacements required each year in order to maintain herd size, assuming a cull rate of 30% and a heifer non-completion rate of 10%.

Age at 1st Calving (Months)

Herd Size (Milking + Dry Cows 20 21 22 23 24 25 26 27 28 29
40 11 12 12 13 13 14 14 15 15 6
50 14 14 15 16 17 17 18 19 19 20
60 17 17 18 19 20 21 21 22 23 24
70 19 20 21 22 23 24 25 26 27 28
80 22 23 24 25 26 8 29 30 31 32
90 25 26 27 28 30 31 32 33 35 36
100 28 29 30 32 33 34 36 37 39 40
125 34 36 38 40 41 43 36 46 48 50
150 41 43 45 47 50 52 54 56 58 60
175 48 51 53 55 58 60 63 65 67 70
200 55 58 61 63 66 69 72 74 77 80
250 69 72 76 79 83 86 89 93 96 100
300 83 87 91 95 99 103 107 111 116 120
1000 275 289 303 316 330 344 358 371 385 399

   

When determining the presence of a replacement oversupply, it is important to estimate the number of replacements available each year.  The annual supply of replacements is dependent on several factors.

  1. Herd size.
    This number includes the number of milking cows and the number of dry cows.
     
  2. Calving interval.
    The average calving interval in the U.S. is 13 months (USDA, 2014).  A longer calving interval will reduce the number of replacements born each year.
     
  3. Heifer percentage.
    This is the proportion of calves born that are heifers in a year.  If only conventional semen is used, this number should be around 50%.  If sexed semen is used, the heifer percentage will increase depending on how much is used.
     
  4. Heifer mortality rate.
    This is the proportion of heifer calves that are born alive but die within the first 2 days of life.  This can be calculated by dividing the number of heifer calves that die within 48 of birth by the total number of heifer calves born each year.
     
  5. Age at first calving.
    As age at first calving increases, fewer replacements will be generated each year.

The following equation can be used to estimate the number of replacements generated annually:

herd size × (12 ÷ calving interval) × (heifer percentage × (1 - heifer mortality rate)) × (24 ÷ age @ 1st calving)

The table below shows the estimated number of replacements born each year for different herd sizes and calving interval. As the calving interval increases, fewer replacements are available each year.

Table 2. Estimated number of replacements born each year assuming a heifer mortality rate of 5%, a heifer percentage of 50%, and an age at first calving of 25 months.

Calving Interval (months)

Herd Size (Milking + Dry Cows 12 13 14 15
40 17 16 15 14
50 22 20 19 17
60 26 24 22 21
70 30 28 26 24
80 35 32 30 28
90 39 36 33 31
100 43 40 37 35
125 54 50 46 43
150 65 60 56 52
175 76 70 65 60
200 86 80 74 69
250 108 100 93 86
300 130 120 111 104
1000 432 399 370 346

The Economic Impact

From Tables 1 and 2, it is clear that even with conventional semen use, the number of replacements produced each year will be greater than the number required to maintain herd size.  Because it costs an average of $1,800 to $2,500 to raise a heifer from birth to first calving (Heinrichs et al., 2013; Overton and Dhuyvetter, 2017), selling any extra heifer calves soon after birth represents a substantial cost-savings irrespective of the income they generate at the sale barn.  Because calves begin accumulating rearing costs at birth, the earlier the decision is made to sell a potential replacement, the greater the economic impact.  It is important to account for rearing costs up to the age of sale in order to estimate net return.      

A herd with 200 cows produces approximately 84 replacements per year, assuming a 13-month calving interval age at first calving of 25 months, a heifer percentage of 50%, and heifer mortality of 5% (Table 2).  In order to maintain the same herd at 200 cows, only 69 replacements are required, assuming a heifer non-completion rate of 10% and a cull rate of 30% (Table 1).  If it is assumed that it costs $1,900 to raise each calf from birth to first calving, selling the surplus 15 heifers soon after birth represents an annual projected savings of $12,768 [15 heifer calves × ($1,900 ÷ 25 months [age at first calving]) × 12 months].

If the same farm decided to wait until those surplus heifers were confirmed pregnant to sell them (~17 months) and the estimated rearing cost to that age was approximately $1,200 (Overton and Dhuyvetter, 2017), each heifer must bring at least $1,200 in order to break-even.  In some years, achieving $1,200 for a bred heifer is not an issue; however, in other years, it can be nearly impossible.  For reference, the average price paid for bred heifers in the U.S. for the month of December 2019, was $956/head (USDA AMS National Dairy Comprehensive Report, January 2020).  

Take Action

It is important for producers to take a look at how many replacements they actually need in order to maintain their herd size.  It is also important for producers to take a serious look at how much it costs them to raise their replacements. These two pieces of information can help inform decisions regarding the replacement program.  

If a producer raises their own replacements, it will often be more economical to select which replacements to keep and which ones to sell at the earliest age possible.  Decisions made at an early age will more than likely be based on pedigree or genomic information.  Producers should also consider whether or not implementing a selective breeding strategy would be feasible.  In these types of strategies, a select portion of elite cows and heifers are bred with sexed semen to generate the number of replacements required.  The lower genetic merit cows and heifers are then be bred using quality beef semen in order to add value to the resulting calves for beef production.

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Managing Heifer Inventory on the Dairy (Infographic)

References:

Heinrichs, A. J., C.M. Jones, S.M. Gray, P.A. Heinrichs, S.A. Cornelisse, and R.C. Goodling. 2013. Identifying efficient dairy heifer producers using production costs and data envelopment analysis. J. Dairy Sci. 96:7355–7362. https://doi.org/10.3168/jds.2012-6488

Heinrichs, A. J., G.I. Zanton, G.J. Lascano, and C.M. Jones. 2017. A 100-Year Review: A century of dairy heifer research. J. Dairy Sci. 100:10173–10188. https://doi.org/10.3168/jds.2017-12998

Overton, M.W. and K.C. Dhuyvetter. 2017. Economic considerations regarding the raising of dairy replacement heifers. In D.K. Beede (Eds.), Large Dairy Herd Management, 3rd Ed (699-712). Champaign, IL: American Dairy Science Association.

USDA. 2014. Dairy 2014: Dairy cattle management practices in the United States, 2014. USDA Animal and Plant Health Inspection Service, Veterinary Services, National Animal Health Monitoring System (USDA-APHIS-VS-CEAH-NAHMS), Fort Collins, CO.