Selecting a bull to breed replacements

Selecting a bull to breed replacements

There is plenty to consider when searching for a new stock bull; health status, if the animal is fit for purpose, fertility checks, historical management and feeding practices, and whether the animal fits the objectives you have for your herd. The most accurate and proven way of doing this for the last point is paying close attention to Estimated Breeding Values (EBVs).

What is an EBV?

An EBV is the best estimate of an animal’s ability to pass characteristics onto its offspring.

Many traits that we value in cattle breeding can’t be fully assessed by eye. This is because the animal you see, and the raw data on its performance, is influenced by multiple factors – yes, genetics plays a part, but you also see the results of; feeding and management, health status, and any careful preparation that may have gone into the sale of that animal – none of which will be passed onto its offspring.

EBVs are one of the most accurate measures we have to strip out all that noise, and give you an objective measure of that animals breeding value, and they exist for both maternal (e.g. milking ability and calving ease) and terminal (e.g. growth rate and carcase) traits. Using them can help us to choose bulls that are genetically compatible with our herd’s breeding objectives.

Why are bull EBVs important if breeding females?

A calf inherits half its genetics from the sire and half from the dam. Often in suckler herds, we don’t have EBVs to assess the dams genetics, so sire choice becomes even more important.

Regardless of your end goal for the offspring, it’s important to consider EBVs, especially calving traits, but if breeding replacement females, EBVs are essential. You won’t learn anything about the maternal characteristics of a bull’s daughters simply by looking at him.

A recent Nuffield Scholarship by Sarah Pick found that fertility traits are five times more important than improvements in terminal traits, and yet, in the UK, our maternal genetic influence in the suckler herd is falling. BCMS data highlights this issue, with only 82% of suckler cows registering a calf each year, and the average age at first calving being 32.8 months (calving at 24 months is the norm in much of the rest of the world).

To remain profitable in a post-BPS world, British suckler herds must increase the number of cows calving successfully every 365 days, and decrease the average age at first calving. Improved genetics aren’t a silver bullet, but choosing bulls with good maternal EBVs to breed female replacements will lay a solid foundation for progress.

Interpreting sale catalogues

Below is an example of a bull advertised in a sale catalogue. Depending on breed, catalogue formats and trait names can vary slightly, so check with the breed society if you need support, but below is a general guide to what you should expect to see.

 

	Calving Ease Direct (%)	Calving Ease Daughters (%)	Gestation Length (days)	Birth Weight (kg)	200 Day Weight (kg)	400 Day Weight (kg)	600 Day Weight (kg)	200 Day Milk (kg)
EBVs	+2.9	+6.8	-0.6	+3.5	+50	+97	+100	+16
Accuracy	86%	82%	84%	96%	93%	93%	91%	89%
Average 19 Calves	-1.3	+0.1	+0.6	+3.1	+39	+70	+87	+12

 

	Scrotal Size (cm)	Carcase Weight (kg)	Eye Muscle Area (sq cm)	Fat (mm)	Retail Beef Yield (%)	IMF (%)	Terminal  Index	Self Replacing Index
EBVs	+1.9	+77	+8.1	-1.3	+3.0	-0.6	+54	+68
Accuracy	90%	86%	76%	85%	78%	74%
Average 19 Calves	+1.0	+56	+3.8	-1.4	+1.0	+0.1	+33	+43

 

• Self Replacing/Maternal Index – An index is an ‘all-round’ figure that makes interpreting EBVs easier. It combines several economically important traits into one number. This index highlights animals that will produce superior female replacements by focussing on maternal traits like calving ease and milking ability, but still includes growth and carcase to ensure these traits are not lost in the slaughter generation
  • The example – Positive values = greater profitability. This bull should produce more profitable female replacements than breed average

 

• Calving ease – Difficult calvings create cost in a system and negatively affect fertility and welfare. Direct calving ease assesses how easily a bulls calves will be born, maternal/daughters calving ease indicates how easily his daughters will calve.
  • The example – Positive values = more unassisted calvings. This bull should produce calves that are born easier, and daughters that calve more easily than breed average

 

• 200 day milk – An indication of milking ability. For sires, this relates to the milking ability of his daughters.
  • The example – Positive values = more productive daughters. This bulls daughters should be more productive and milk better than breed average

 

• Scrotal size – Calving at two is essential to a profitable suckler herd, and larger scrotal size in bulls is related to earlier puberty in heifers.
  • The example – Positive values = higher scrotal size. This bulls daughters should reach puberty sooner than breed average

 

Accuracy – Each trait is accompanied by an accuracy value, which shows you how close the EBV is to the animal’s true genetic value. Accuracy is influenced by the heritability of a trait and what data is available on each animal and its relatives. Accuracy is expressed between 0% and 100%.

EBVs change over time as more information comes in, the higher the accuracy value, the lower the likelihood of variation.

Accuracy values will be highest for bulls with many recorded progeny, e.g. AI sires, which is great if buying semen, but if you’re in the market for a natural service bull, a lower level of accuracy should be expected.

There isn’t a minimum or maximum accuracy you should be looking for, this is a personal decision for each herd and will depend on the type of animal you’re after, but it does help bring some context to the EBVs you have in front of you.

Average 19 Calves – This is the benchmark and allows you to compare the EBV of the animal you’re interested in with the breed average. ‘19’ refers to the calving year set as the benchmark, so this will change over time.

Where to go for help?

• AHDB Choosing Bulls for Better Returns - available in hard copy and online and explains all the information in this article in more detail and tips for choosing a bull
• The breeder – Speak to the vendor. A good breeder should be able to explain the EBVs and history of their stock. For further information on getting the most out of your vendor, go to episode 316 of the AHDB Food and Farming podcast
• The breed society – the breed society should be able to explain to you the format of their sale catalogues, where to find the information you require and how to interpret it