Advertisement

Reproductive technologies to consider – genomics, IVF

Kent Weigel for Progressive Dairyman Published on 23 February 2018

Playing the elite genetic merit game is not for the faint of heart. While the rewards are high, like six-figure sale prices, so are the risks. Cattle die, an animal’s estimated genetic worth doesn’t materialize or embryo transfer is performed with limited success.

While most cattle aren’t “elite” top 0.1 percent of the population, genomic testing and advanced reproductive technologies can help all dairy producers greatly improve their herds’ genetic level with minimal risk and investment.

Where should you start (see Figure 1)? First, evaluate your herd’s current genetic status.

The path to genetic progress

Click here or on the image above to view it at full size in a new window.

Calculate the average lifetime net merit (NM$) of your lactating cows, heifers and calves. If your herd has outstanding genetics – average NM$ of at least $500 for your heifer calves – consider building your herd from within by using sexed semen, in vitro fertilization (IVF) or both to propagate your best females and replace the bottom half of your herd.

‘Average’ herd: Purchase outside genetics

With a more average herd – let’s say, NM$ average of approximately $300 – then you may want to consider a different strategy. One option is to use genomics and IVF from outside genetic sources. For example, purchase a group of “sub-elite” heifers that rank in the top 2 percent of the breed.

Rather than spending $100,000 on one exceptional calf with a genomic predicted transmitting ability (PTA) of $1,000, for example, invest approximately the same amount of money on 20 to 30 heifers at the next genetic level, such as a genomic PTA of about $800. Then use these heifers to form the genetic foundation of your herd.

If you are a little more patient when it comes to genetic progress, invest heavily in semen from top genomic young sires for two generations. Then look at propagating your top females with IVF. Dairy producers can make remarkable genetic progress quickly and with a much smaller investment by breeding their cows and heifers to top A.I. bulls with genomic PTA of $850 to $950.

Used properly, genomic testing can yield positive economic returns, as shown in Figure 2. The magnitude of returns depends on the gain in reliability resulting from genomic testing.

Proportion of animals selected

Click here or on the image above to view it at full size in a new window.

Without pedigree information, reliability of heifer calves was 0.00 before testing, compared with 0.48 after testing.

Using genomic testing to identify the top 10, 20 or 30 percent of heifer calves that should be propagated preferentially using sexed semen, embryo transfer or IVF is always economically sensible. Another complementary strategy is to use genomic testing to identify the bottom 30, 20 or 10 percent of heifer calves to cull from the herd.

With pedigree info, just genotype top half

When complete pedigree information is available, gains in reliability resulting from genomic testing are much smaller. Selectively genotyping the top half of heifer calves, as ranked by parent average (PA) for NM$, is a more profitable way to identify potential embryo donors or heifers to mate with sexed semen than genotyping all calves in a herd.

At the other end of the spectrum, this figure shows that the gains from using genomic testing to identify the bottom 30, 20 or 10 percent of heifer calves for culling are small on a per-animal basis, but profits of $10 or $20 per calf can add up over time.

Keep in mind that selective genotyping of specific groups of heifer calves, such as the top, middle or bottom, ranked by PA for NM$, may not be best when one considers all possible uses of genomic information in cattle breeding and herd management decisions.

Identifying the top heifer calves for mating with sexed semen, or identifying the bottom heifer calves for early culling, are just two of the many potential uses of genomic information throughout an animal’s lifetime. Other options include using genomic data to minimize inbreeding, avoid mating carriers of inherited defects and target management of heifers and cows that are at risk for specific health, calving or fertility problems.

Tremendous synergies exist between genomic testing, sexed semen and IVF technologies. One simple strategy involves culling the poorest heifers based on genomic PTA and health history. Selective genotyping tends to be more profitable than full genotyping when complete pedigrees are available.

In contrast, research in 2015 concluded that full genotyping of all heifer calves was optimal with conventional semen, whereas pre-selection of the top two-thirds of calves based on PA was optimal when sexed semen was used. Furthermore, they suggested that a study from 2012 and other previous studies may have overestimated the accuracy of selection decisions based on PA. This overestimation resulted in underestimation of genomic testing’s potential benefits.

Sexed semen on select heifers hastens genetic progress

Some dairies use sexed semen on heifers and/or cows with the highest genomic PTA. The remaining females are inseminated with conventional semen. Economic feasibility studies evaluated this strategy with or without genomic testing. Results showed that using sexed semen in yearling heifers can increase genetic progress per year compared with conventional or sexed semen in lactating cows, particularly when coupled with early culling of inferior calves.

And yet another option is to use beef semen on below-average females. This strategy generates greater market value in the resulting calves. Along with using beef semen on poor females, increase the percentage of above-average females bred with sexed semen.

The main challenge in mating below-average cows and heifers with beef semen is that you will not create a surplus of dairy heifer calves in the next generation (that’s sort of the point), and this means you won’t have an opportunity to sort among those extra heifer calves using genomic testing the next time around.

A study in 2015 simulated varying proportions of using sexed and/or beef semen in yearling heifers and first-parity cows in herds with poor, average or good reproductive performance. For herds with poor reproductive performance, net financial returns per “slot” in the herd were greatest when sexed semen was used in 80 percent of heifers and 0 percent of cows.

For herds with average or good reproductive performance, returns were maximized when sexed semen was used in 60 percent of heifers and 40 percent of cows. Please note that differences exist between this study and one in 2012. In the 2012 study, genomic test results were used for early culling of low-merit heifer calves. In this 2015 study, no heifer calves were culled and genomic test results were used to determine which animals should be bred with sexed semen.

If available genetics warrant, consider using your very best females as IVF donors. Research in 2016 found positive net returns when using IVF on the herd’s best genetics coupled with the next group (genetically) being divided into sexed semen and embryo recipients. (The poorest females were not bred or used as recipients.) Younger donors with higher genomic reliability provide greater returns.

In summary, genomic testing and advanced reproductive technologies work great together. Pairing genomic testing with heavy use of IVF in elite heifers and cows will maximize genetic progress, but at a very high cost. Most of the benefit can be achieved at a tiny fraction of the price by mating the best females – say the top 50 percent of heifers and top 25 percent of first-lactation cows – with sexed semen from the best young genomic bulls available.

If you have a good market for surplus dairy heifer calves, mate the remaining cows and heifers with conventional semen from top young genomic bulls. Otherwise, consider mating your lower-end cows with beef semen to capture a little extra revenue at the auction barn.  end mark

ILLUSTRATION: Illustration by Kristen Phillips.

Kent Weigel
  • Kent Weigel

  • Professor
  • Department of Dairy Science Chair
  • University of Wisconsin
  • Email Kent Weigel

Before commenting on our articles, please note our Terms for Commenting.

LATEST BLOG

LATEST NEWS