Replacement supply starts with today’s breeding decisions

Beef-on-dairy has given dairy farmers a valuable extra income stream from calf sales, but it has also reduced the number of dairy heifers entering the replacement pipeline. A beef-cross calf earns its return within weeks of birth, whereas a dairy replacement is an investment whose outcome will not be known for more than two years.

The effect is now visible in national inventories. In June 2026, CoBank reported that US dairy heifers expected to calve were equivalent to 26.1% of the dairy cow herd, based on USDA’s January 2026 Cattle report, compared with more than 30% in every year from 2012 to 2022. It put replacement values above $3,000 per head and projected only a slow rebuild of around 360,200 additional replacements across 2027 and 2028. [1]

The picture in Great Britain is similar. AHDB reported that 60% of calves registered to dairy dams in 2025 had a beef sire, while only 32% were dairy heifer calves. Registrations of dairy-sired females fell to 463,373 head, the lowest on record, and AHDB expects the national milking herd to tighten as older cohorts leave. [2]

For individual farms, the real question is whether the breeding programme will deliver enough suitable replacements when they are needed.

PLAN FROM THE FUTURE MILKING HERD

Replacement requirements should start with the number of cows expe[CB1] [PJ2] cted to leave the herd, adjusted for any planned change in herd size. Historical exit rates are a useful starting point, but deaths, involuntary culls and elective replacements should be looked at separately. A farm improving cow health and longevity may need fewer heifers in future, while a herd planning to expand will need more.

The worked example below takes a stable 1,000-cow herd, with no bought-in replacements, back from cows leaving the herd to the dairy-sired calvings needed to replace them. The final step shows why semen choice matters, because the number of calvings required can almost double depending on the semen mix.

Calving figures are before stillbirths and pregnancy losses, so real requirements are higher. Sex ratios are the planning assumptions used by Ferrari and colleagues [9].

These are illustrative assumptions, not industry targets. The 10% loss from birth to first calving is optimistic for many herds, and the calculation becomes far more useful when it is based on the farm’s own heifer completion rate and expected cow exits rather than a standard replacement percentage. [3]

FORECAST FIRST CALVINGS, NOT JUST HEIFER NUMBERS[CB3] 

A herd can carry enough heifers overall and still have too few due to calve in particular months. Projected first calvings should therefore be compared with expected and targeted cow exits month by month.

Confirmed pregnancies give the most reliable near-term forecast, although an allowance is still needed for losses between pregnancy diagnosis and calving. For younger heifers, expected breeding age, conception rate and age at first calving indicate when they are likely to join the milking herd. Beyond that, forecasting combines what is known about the herd today, including pregnancy losses, calves born dead and losses during rearing, with a degree of crystal ball gazing. A breeding made today will not deliver a first-calving heifer for around 33 months, allowing nine months of gestation and a 24-month age at first calving.

Total monthly calvings and first calvings should be tracked separately. Every calving, whether a cow or a heifer, places demands on transition facilities and milk production forecasts, but only first-calving heifers add new animals to replace the cows that leave. If the example herd projects 20 first calvings in a month against its average requirement of 25, that signals a possible imbalance.

Annual averages also hide month-to-month variation, and exits can run higher than planned. The forecast should therefore be tested with a ‘what if’ scenario in which more cows leave than expected. A shortfall over several consecutive months may justify changing future dairy semen allocation, whereas a single low month may not. In block-calving herds the same logic applies to the calving block rather than the month, and a heifer that misses her target block can fall a long way behind.

Seasonal fertility needs particular attention. Summer heat stress commonly depresses conception rates in lactating cows, and the effect shows up as fewer calvings the following spring. Fewer spring calvings mean fewer heifer calves born in those months and, assuming a 24-month age at first calving, that gap reappears as a shortfall of replacements two springs later. Increasing the use of dairy semen, and sexed semen in particular, during the summer breeding months can help offset it. Heifers, which are generally less affected by heat stress than lactating cows, are often the most reliable place to make that adjustment.

Monthly fresh cows over two years in one herd. Calvings dip in March to May in both 2025 and 2026, around nine months after summer breeding. The first and last bars are part months. View the report in BoviSync: Monthly Fresh for Last 2 Years

PROTECT THE OPTION TO REPLACE UNDERPERFORMING COWS

A tight heifer supply does more than leave a herd short of replacements. It takes away the flexibility to make economically sound replacement decisions.

Overton and Eicker argue that failing to produce enough replacements lowers rearing costs but reduces profitability, because it delays the replacement of poorer-performing cows. Herds short of heifers can end up keeping low-producing cows, or cows with recurring reproductive and health problems, beyond the point at which replacement would pay. The saving on rearing is easy to see, but the lost milk income and the opportunity cost of an underperforming cow often go unrecognised. They also point out that a steady flow of replacements allows problem cows to leave earlier, which benefits both welfare and cull-cow value. [4, 5]

None of this is an argument for culling productive cows simply because heifers are available. The right comparison is between an existing cow’s expected future economic contribution and that of her replacement, taking account of milk income, reproductive prospects, health, replacement cost and cull value.

Kulkarni and colleagues’ 2024 simulation of a 100-cow Dutch herd supports this. Severely constrained, excess and variable heifer supply all reduced the herd’s average gross margin compared with the model’s optimal replacement policy. A simulated herd does not set a universal economic threshold, but the results show why neither the lowest nor the highest replacement rate is necessarily the most profitable. [6]

USE BEEF AND DAIRY SEMEN TO MEET THE FORECAST

Genomic evaluations and reliable performance records identify the females with the greatest potential to produce future replacements. Sexed dairy semen can then be directed to those animals, while beef semen adds value from the remaining pregnancies.

Basiel and colleagues’ 2025 analysis of US national herd records documented the growing use of genomic testing, sexed dairy semen and beef semen. Calves born in herds that combined all three had the highest genetic merit for Net Merit (NM$), followed by herds that used all three semen types without genotyping heifers. These findings support more deliberate selection, although it is important to recognise they do not identify a single semen allocation that suits every farm. [7]

The right balance depends on reproductive performance, the proportion of heifer calves born alive, heifer survival and expected future demand. A 2026 economic simulation by Lauber and colleagues showed that the 21-day pregnancy rate, semen type and heifer survival all influence the economic outcome of strategies combining dairy and beef semen, including how long cows should remain eligible for insemination. [8]

Buying in replacements is the fallback when home-reared supply falls short, but it brings its own cost, availability and biosecurity risks. In GB, the AHDB has warned that herds dependent on purchased replacements are most exposed to shortages, and that disease risk could further limit supply. [2]

KEEP THE FORECAST REALISTIC

A projected dairy heifer birth is not a guaranteed replacement. Losses during rearing and poor reproductive performance affect both numbers and timing, and reviewing heifer completion rates by birth cohort shows whether the breeding programme is producing the animals that actually enter the herd. Heifers also need adequate growth and development to perform after calving. An underdeveloped heifer that calves on target does not solve an inventory shortfall. It moves the problem into first lactation, where lower yield, a higher risk of calving difficulty and poorer fertility can see her leave the herd early and create the need for another replacement.

Age at first calving has a large effect on inventory. Every month of delay adds rearing cost, increases the number of heifers that must be carried to supply the same number of replacements, and pushes first calvings later than forecast.

An allowance for unexpected losses and changes in cow health protects flexibility, but the buffer has a cost. Ferrari and colleagues’ replacement tool, tested on a 350-cow Italian Holstein herd, found that combining sexed dairy and beef semen to match heifer production more closely to replacement demand reduced replacement-related costs under the study’s assumptions. [9]

Breeding plans should be reassessed regularly as cows leave, pregnancy outcomes change and market demands fluctuate, rather than applying a fixed percentage of beef inseminations year after year.

MANAGE THE FUTURE, NOT JUST THE INVENTORY

The aim is to produce enough healthy, well-grown replacements to keep the option of replacing an economically underperforming cow when the numbers justify it.

Beef-on-dairy income is valuable, but a replacement shortage carries a less visible cost. Linking projected monthly first calvings to expected cow exits, and to the economic value of each place in the herd, allows today’s breeding decisions to support the milking herd several years ahead.

REFERENCES

1.  Geiger, C., & Prins, A. (2026, June 18). Dairy replacements should begin a slow rebuild in 2027 and 2028. CoBank Knowledge Exchange. https://www.cobank.com/knowledge-exchange/dairy-replacements-should-begin-a-slow-rebuild-in-2027-and-2028

2.  Agriculture and Horticulture Development Board. (2026, July 9). Will there be enough milking cows to meet future demand? Weighing up beef vs milk. https://ahdb.org.uk/news/will-there-be-enough-milking-cows-to-meet-future-demand-weighing-up-beef-vs-milk

3.  Potts, S. (2022). Managing heifer inventory on the dairy. University of Maryland Extension. https://extension.umd.edu/resource/managing-heifer-inventory-dairy

4.  Overton, M. W., & Eicker, S. (2022). Too many? Not enough? Costs and opportunities associated with dairy replacement heifer inventory. American Association of Bovine Practitioners Conference Proceedings, 55(2). https://doi.org/10.21423/aabppro20228595

5.  Overton, M. W., & Eicker, S. (2025). Costs and opportunities regarding the replacement of dairy cows. American Association of Bovine Practitioners Conference Proceedings, 58(2). Published online April 2026. https://doi.org/10.21423/aabppro20259334

6.  Kulkarni, P. S., Haijema, R., Hogeveen, H., Steeneveld, W., & Mourits, M. C. M. (2024). Economic impacts of constrained replacement heifer supply in dairy herds. Agricultural Systems, 217, 103943. https://doi.org/10.1016/j.agsy.2024.103943

7.  Basiel, B. L., Graham, J. R., & VanRaden, P. M. (2025). Quantifying the use of and the genetic progress from advanced mating strategies in US dairy herds. Journal of Dairy Science, 108(9), 9901–9914. https://doi.org/10.3168/jds.2025-26600

8.  Lauber, M. R., Cabrera, V. E., & Fricke, P. M. (2026). An economic simulation model to assess the effect of the 21-day pregnancy rate, semen type, and heifer survival rate on the optimal insemination eligibility period for lactating dairy cows. Journal of Dairy Science, 109(1), 452–468. https://doi.org/10.3168/jds.2025-27021

9.  Ferrari, V., Marusi, M., Penasa, M., van Kaam, J. B. C. H. M., Finocchiaro, R., & Cassandro, M. (2024). A tool to optimise dairy herd replacements combining conventional, sexed, and beef semen. Italian Journal of Animal Science, 23(1), 409–415. https://doi.org/10.1080/1828051X.2024.2324130