It is that time of year, bull selection season.  Many producers find this very overwhelming especially when bombarded with numbers, actual weights, adjusted weights, EPDs, ABCs, ultrasound measurements, selection indexes.  How do you make sense of it?

If you are the average Ontario beef producer running 25 cows you most likely buy a bull every 2-4 years.  Keeping track of the numbers and what they all mean can be difficult.  Following is a brief primer on the numbers and how they can be used when making that all important selection decision.  Table 1 provides an example to assist with the explanations.

Actual weights of the animal at birth, weaning, yearling and start of test are easy to visualize but are influenced by many factors, like age, birth weight, feeding and cow milking ability.

Adjusted weights are more appropriate as they adjust for age and sex of calf and age of dam.  However, they are influenced by feed, birth weight and cow milking ability.

Expected progeny differences (EPDs) are an estimate of how progeny of an animal are expected to perform in each of the traits measured.  An animal with a +5 for birth weight EPD, would produce progeny that are 4 lbs heavier on average than an animal with a BWT EPD of +1 when bred to the same cows.   EPDs are calculated using pedigree information, performance records of the individual and relatives (when available) and take into account genetic correlations and heritabilities of the trait(s) in question.  EPDs are provided by breed associations and are only comparable within the same breed.

Across breed comparisons (ABCs) are derived in a similar fashion as EPDs but allow comparisons both within and across breeds.  Beef Improvement Ontario (BIO) provides ABCs for bulls completing their bull evaluation program and are designed for use by both seedstock and commercial producers.

Accuracy values are provided for every genetic evaluation.  They range from 1 to 100 and relate to the reliability of the estimate.  Genetic evaluations with high accuracies are based on more performance information and are more reliable.  Young bulls with limited information will have lower accuracies then older proven bulls with progeny records. 

Percentile ranks were developed to provide a measure of how good an individual animal’s genetic evaluation (i.e. EPD or ABC) is, compared to the current population of animals.  Breed associations provide percentile tables that allows you to look up EPDs to determine where an animal would rank within the breed (i.e. Top 1% or 10% etc).  BIO provides two percentile ranks for ABCs - one indicating the rank of the animal compared to all breeds (%ab), and a second indicating its rank compared to animals of the same breed (%wb).  BIO’s percentile ranks range from 1 to 99 – higher numbers are better – a bull with a 99%ab ranks in the top 1% of all breeds for the trait. 

 Selection indexes combine performance records from several traits or measurements into a single value for each animal taking into account their economic importance.  BIO provides two indexes on bulls completing test, the Prime Plus and the Beef Builder. 

Prime Plus rewards bulls that are predicted to sire calves with moderate carcass weight and good marbling.  Emphasis is also placed on maternal traits as heifers are targeted for replacements.

Beef Builder is focused on producing market animals that have high lean meat yield and larger carcass weights, with few or no heifers kept for replacements.

Depending on your market you would select the index based on your end goals and select from bull’s that rank high for that index.  This helps avoid sorting through a number of individual traits to find the combination that suits you.  If you narrow the field of bulls down based on the index you can then evaluate the remaining group of bulls for physical and structural soundness, as well as their individual traits to ensure the bull you do select will complement your herd’s weaknesses.  Table 2 provides an example of two bulls with similar indexes.  To decide which bull to purchase you would evaluate the individual traits important to your herd.  If you are concerned with high birth weights you would select Bull B, if you are looking for more pounds at weaning and aren’t too concerned about birth weights you’d likely select Bull A. More information on genetic evaluations and indexes is provided on BIO’s website, www.biobeef.com.
 

What numbers do you use in your selection process?  If you are comfortable with the selection indexes that were developed with Ontario markets in mind, select the one that matches your market and goals and go through the process above.  If you prefer to select a bull with the goal to make progress in specific traits, select sires that express ABCs or EPDs that meet your criteria, whether it is low birth weight with moderate weaning weights or moderate post weaning gain with high marbling (for example).  Selection based on a single trait is discouraged due to the negative impacts that can have on other economically important traits, balance is key.  Percentiles provide a quick way of determining where a bull ranks for a specific trait.  You may wish to select a sire in the top 10% for birth weight (low birth weight), but the top 50% for weaning weight and marbling. Percentiles allow you to determine the rank of a bull in regards to his EPDs/ABCs quickly and easily. 

Remember a sire will influence every calf he sires as well as every calf his daughter’s produce for years to come.  Ensure you take the time and use the available information, to make a well informed decision.

This infosheet was authored by Joanne Handley, Beef Cattle Geneticist, OMAFRA.