Surrogate sire research: Precision genetics to improve the sustainability of steak

Maci Mueller

2018-2021 FFAR Fellow

University of California, Davis

Beef cattle are raised all around the world. They are able to convert one of nature’s most abundant and raw resources – grass – into one of the most nutrient dense food sources available. However, some breeds of cattle can convert feed into beef more efficiently than others.

Efficiency is defined as achieving maximum productivity with minimum waste. In other words, producing more product with less resources, which is critical for agricultural sustainability.

Beef production efficiency around the world varies. For example, we can see from the graph below that in 2019 both Brazil and the U.S. each produced over 10 million metric tons of beef, but accomplishing this required more than twice as many cattle in Brazil. While some of this difference in efficiency is due to production practices, a large part is due to genetics.

Examples of cattle breeds around the world

If we look around the world, we can see that cattle have been selected for different characteristics depending on the environment. The Scottish Highlander breed (red coat), known for its shaggy coat and distinct horns has been selected to survive harsh winters of Northern Europe. Another breed that originated in Scotland is Angus (black coat). Angus cattle do well in temperate climates, like the U.S. and are known for their superior beef production characteristics. On the other hand, the Nellore breed (grey/white coat) in Brazil have primarily been selected for their ability to survive in tropical climates due to their heat tolerance and parasite resistance. Unfortunately, these tropical cattle are less efficient beef producers than their temperate breed counterparts.

As an aspiring geneticist, I see these breed differences as both a challenge and an opportunity. I believe genetic improvement is a powerful tool for sustainability. Unlike other farm inputs (e.g., feed, vaccinations, or labor), genetic improvements are cumulative and permanent. Improved genetics can result in producing more beef from fewer natural resources, permanently improving sustainability.

How can we have efficient beef producing genetics in tropical regions?

Farmers could use Angus bulls (adult males) to breed tropical cows (adult females). The calves (offspring) produced from this mating would be a hybrid, or cross of both breeds, so they would have the superior beef producing genetics from their father but also the tropical adaptability genetics from their mother.

Currently, tropical region farmers only have two options to accomplish this.

One option is to physically transport Angus males to the tropical region farms and the males will instinctively breed the tropically-adapted cows. Typically, one bull can breed approximately 30 cows each year. But the problem is, Angus bulls that have been selected for temperate climates will not survive well in tropical climates.

Another option is to use reproductive technologies that can allow for the reproductive cells, or sperm, of superior bulls to be transported and used to breed cows on different farms around the world using artificial insemination. But using this technology requires special equipment, access to cattle handling facilities and skilled labor, all of which increase farmer costs.

2018 FFAR Fellowship recipient, Maci Mueller, microinjecting gene editing components into a cattle embryo as part of her research.

The goal of my research at the University of California, Davis, is to give farmers a third and better option.

First, I plan to use gene editing technology to introduce genetic changes into single cell cattle embryos, just after fertilization as pictured below. Gene editing is an advanced biological tool to precisely add, delete or replace letters of the genetic code. An animal’s genetic code contains the instructions for making and maintaining the different traits of the animal, similar to a recipe book. If we change the genetic code, or recipe, then we can change the characteristics of the animal. We can think of gene editing as using molecular scissors to cut and change the genetic code.

My target for gene editing is the deletion of the part of the genetic code that instructs the production of reproductive cells in bulls. This gene edited bull would not have any reproductive cells of his own. However, I plan to substitute in reproductive cells from a different highly efficient beef producing breed. My ultimate research goal is to develop a system that can produce a tropically-adapted bull that carries reproductive cells derived from a bull of a different, highly efficient beef producing breed.

The resulting bull would be called a “surrogate” sire, or father. The surrogate sire would be carrying reproductive cells that are not his own genetics, similar to the concept of a surrogate mother. We can imagine a surrogate sire carrying around highly efficient beef producing genetics in his genetic backpack, so that he can pass on improved beef genetics to his offspring through his reproductive cells.

Diagram of how surrogate sires could produce tropically adapted and highly efficient beef producing offspring.

Surrogate sires will be able survive the heat and parasites common in tropical environments, enabling them to mate with tropical cows; they will pass on the substituted highly efficient beef producing genetics to their calves. These calves will be the best of both worlds, with good adaptation to tropical climates and the ability to convert feed into beef more efficiently. As an added bonus, unlike other current reproductive technologies, there will be no extra work or equipment required by farmers, because the surrogate sires will do all the work.

Overall, the application of this research could improve global beef production efficiency. In other words, producing more beef with fewer natural resources, thereby improving the sustainability of producing steak!

The FFAR Fellows Professional Development Program has helped better prepare me for the diverse career field of public and private agricultural research. As a FFAR Fellow, the science communication training, industry networking opportunities and peer cohort building have truly been invaluable experiences.

I would like to thank the Foundation for Food & Agriculture Research, my industry sponsor, Recombinetics and my advisor, Dr. Alison Van Eenennaam, for their support of my growth as a future agricultural research leader.


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