PREGNANCY testing is a valuable management tool in any breeding program. The information allows producers to identify and remove non-pregnant females, freeing up feed for those in calf.

It also provides a starting point for planning calving, estimating weaning numbers and anticipating turn-off.

However, pregnancy testing only tells producers which females are in calf at the time of testing. It doesn’t mean they will all produce a live calf or rear that calf through to weaning.

The CashCow project in northern Australia reported an overall median foetal and calf loss of 9.5pc between confirmed pregnancy and weaning. The CashCow project focussed on northern breeding herds.

In southern Australia, a survey of southern beef producers conducted by the University of Melbourne’s Peter Mansell, Carolina Munoz, David Beggs, John Webb-Ware and Kelly Stanger, and published by MLA in 2021, reported that the number of live calves born averaged 93.3pc of the number of cows and heifers reported as pregnant.

This leaves an apparent difference of 6.7 calves for every 100 females reported as pregnant. However, the report did not identify this as a measured pregnancy-loss rate. The survey relied on producer-supplied records and, in many cases, producers’ best estimates.

Losses later in the reproductive cycle

The two figures shouldn’t be compared as though they measure the same thing. CashCow followed losses from confirmed pregnancy through to weaning, while the 93.3pc figure from the southern survey stopped at live birth.

The important message that can be taken from both studies is that a positive pregnancy test doesn’t account for losses that may occur later in the reproductive cycle.

There are many reasons why a confirmed pregnancy may not result in a live calf. These include disease, nutritional challenges, environmental stress, genetic abnormalities and problems affecting the cow or developing calf. In many cases, the exact cause is never identified.

Does genetics play a part?

Most attention has traditionally focused on these health, nutritional and environmental causes. However, genetics may also influence whether a pregnancy is maintained. In May 2026, a mainly Brazilian research team, with Flávia Bis from the University of São Paulo as lead author, published its findings in the Journal of Animal Science.

The study examined how much of pregnancy loss was genetic and whether selection for other economically important traits could change the risk of pregnancy loss.

This project used pregnancy diagnosis records from 23,507 Nellore (Brazilian Bos Indicus) heifers across 44 commercial farms in four regions of Brazil. Genomic information was available for just over 17,000 of those heifers. Unlike earlier genetic research in Nellore cattle that was based on closed experimental herds, this project used pasture-run commercial cattle exposed to a broader range of environments and management.

The heifers were pregnancy tested around 60 days after the end of joining. Any heifer confirmed pregnant that did not have a subsequent calving record was classified as having lost the pregnancy. This meant early embryonic losses before pregnancy testing and calf losses after birth were not included.

Under this definition, the study recorded a pregnancy loss of 15.46pc. However, some missing calving records may have resulted from heifers being culled or moved between farms, or from gaps in recording.

The figure therefore reflects the study’s definition of pregnancy loss rather than a confirmed biological loss in every case.

The research team found that the genetic influence on pregnancy loss was extremely small, with a heritability of just 0.03. This is consistent with earlier research in dairy cattle, Brahmans and Nellore.

With heritability this low, pregnancy loss is unlikely to be useful as a direct selection trait because genetic improvement would be very slow.

Genetic relationships between pregnancy loss and several traits

However, direct selection for pregnancy loss was only one part of the study. Producers select cattle for a range of traits, and there is often concern that selecting for greater growth, carcase performance or feed efficiency may compromise reproduction. The study examined the genetic relationships between pregnancy loss and several of these traits.

For producers who have selected for growth and carcase traits, the results suggest there is very little relationship between these traits and pregnancy loss. The genetic correlations for 240-day weight, 455-day weight, eye muscle area, rump fat and marbling were all low, ranging from −0.16 to 0.01.

Based on these results, selection for the traits examined would not be expected to increase pregnancy loss between pregnancy testing and calving.

The study did not examine whether these traits were related to conception rates, calving ease or calf survival after birth. The results therefore apply only to the period between a confirmed pregnancy and a recorded calving.

The clearest genetic relationship was with earlier female reproduction. Heifers genetically more likely to calve by 30 months, or at a younger age, were less likely to lose a pregnancy.

Scrotal circumference also had a smaller favourable relationship with pregnancy loss, although the result was less certain. The direction of the relationship suggests that selecting bulls with greater scrotal circumference may help reduce pregnancy loss in their daughters, but the result was not conclusive.

Interpretation

It is important that producers have some care when interpreting the early-calving results. Both the probability of calving by 30 months and age at first calving were based on calving records. These records were also used to determine whether a pregnancy had been lost. This overlap may have made the genetic relationships appear stronger than they actually are.

The study also considered feed efficiency and recorded a genetic correlation of −0.44 between residual feed intake and pregnancy loss. Because a lower residual feed intake indicates a more feed-efficient animal, the direction of this result suggests that more efficient cattle could have a higher risk of pregnancy loss.

However, the range around the estimate extended from −0.89 to 0.01 and included zero, meaning the result wasn’t conclusive.

Dry matter intake showed no meaningful relationship with pregnancy loss. Previous research into feed efficiency and fertility has also produced mixed results.

The study raises a possible relationship between residual feed intake and pregnancy loss, but it doesn’t show that selecting for improved feed efficiency will increase losses. Residual feed intake is a useful selection trait, but it should be considered as part of a balanced breeding objective, with reproductive performance continuing to be monitored.

From a practical standpoint, a positive pregnancy test is only one point in the reproductive cycle.

Genetics can influence the risk of loss, but nutrition, health, environment and management remain the main areas producers can influence to improve the likelihood that a confirmed pregnancy results in a calf at calving and, ultimately, a calf at weaning.

Alastair Rayner is the Strategic Account Manager for Southern Australia with Vytelle and Principal of RaynerAg. He has over 30 years’ experience advising beef producers and graziers across Australia. Alastair can be contacted here or through his website: www.raynerag.com.au