The Perfect Mating

by Lindsay Upperman, Beef Geneticist

Every year when the month of February comes around, relationships seem to come into focus. For cattle producers, the next calf crop is already processing, but mating decisions for the following calf crop may not be set in stone yet. As producers look to the next set of matings, the perfect match is the ultimate prize. Or better yet, the perfect sire to match the herd of females is the paramount prize. Yet, is the perfect sire or perfect match out there, or is it just a tall tale?

Let’s start at the beginning. A calf inherits 50% of its genes from its sire and 50% from its dam. Each sperm or egg produced by a sire or dam is a random sample of that parent’s chromosomes and genes. Now, if we consider that cattle have 30 chromosomes, that means that each sperm or egg produced is 30 flips of a coin. This equates to more than 1 billion possible combinations of the sire and dam’s chromosomes! In other words, with billions of possible combinations, the chances are rare that a given parent would have two sperm or two eggs that are exactly the same.

Looking at families throughout your community, this is easily shown. For instance, two siblings could effortlessly be identified to be from the same family, while another set of siblings could not be more different from one another. Maybe it’s hair color, height or even nose shape, but there are both similarities and differences due to those genes which are shared or not shared between siblings.

Usually, siblings share 50% of their DNA on average, but this can vary between 40% to 60%. As cattle have genomes similar in size to humans, the distribution of shared genes in cattle is expected to be comparable.

Shown mathematically, the EPDs reported can be calculated as half of the sire’s breeding value (sire EPD) plus half of the dam’s breeding value (dam EPD) plus the Mendelian sampling term.

The Mendelian sampling term represents a calf’s difference from the average of the parent’s breeding value. This is due to the random sample of chromosomes and genes that the given progeny inherited from its parents.

Initially, when a calf is born, no data is collected yet, which is why the Mendelian sampling term is assumed to be zero and the reported EPD is the parent average. Like most parental-average EPDs, they are not precise (this is reported as EPD accuracy), due to the EPD calculations not having enough data to predict the genes inherited from the sire and dam. Yet, as data is collected on the calf and it eventually has progeny, the Mendelian sampling term is better estimated. Ultimately, this will increase EPD accuracy and either increase or decrease the reported EPD estimates of the calf.

A Quick Recap

A calf gets 50% of its DNA from the sire and 50% from the dam. As well, two siblings share 50% of their DNA. However, which chromosomes or genes are shared between parents and progeny or two full sibling progeny is unknown. Only when data is collected and turned in, can the EPD calculations become more precise due to having more knowledge of which genes were inherited from the parents.

Thus, the perfect match is out there! However, in order to know if the chosen mating or chosen sire for your herd is “perfect,” data has to be collected and turned in on the resulting progeny. Ideally, collecting and reporting every available data point on an animal would be great, although it’s understandable with associated costs or production restraints this may not be possible. Therefore, collecting as many data points as possible can still give an animal more precise EPD estimates than no data at all.

So, do you already have the perfect match? Ultimately, the answer to this question relies on you, as a producer. If you are collecting and submitting data, you should already have a good idea of how your calf crops are doing at market. If