Cow-Calf Commentary for Iowa Cattleman Magazine

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By Erika Lundy, Extension Beef Specialist, and Denise Schwab, Extension Beef Specialist

November 2020

Developing bulls for longevity
One of the biggest frustrations in the cattle business is watching a yearling bull fall apart on pasture. In Iowa, it can seem like there’s a bull for sale for about every 6 cows in the state, so here’s some tips to keep you competitive when developing and selling bulls. Likewise, if you will be purchasing a bull in the next year, here are some things you may ask of the seller.

The most important things to consider when visually evaluating a bull for longevity should be the same things that prevent a bull from taking a final ride to town. Bad feet or lameness issues are a big culprit. Everything starts at the ground. If a bull has bad feet now, cut him, send him to the feedyard, and save your resources. Bulls that are fed hard in development will likely grow longer toes, which can certainly lead to lameness issues in the breeding season. Likewise, if a bull’s feet have been trimmed prior to the sale, that’s a red flag that the bull either had poor foot shape or needed assistance in correcting toe growth after an aggressive development ration. Without going into a full lecture of livestock judging 101, a bull’s mobility should appear effortless if the animal is structured correctly.

Another part of phenotype that can cull a herd bull is their sheath. Avoid bulls with a prolapsed prepuce. Basically, if you can see anything pink at the bottom of their sheath when the bull is standing in the sale pen, scratch him off the short list. These bulls are more prone to physical injury or infections from thorn bushes, underbrush, etc.

Nutritional management plan
Research has shown conflicting results of correlation between feed efficiency on a forage-based diet compared to feed efficiency on a high concentrate diet. For best results, bulls should be developed and if feed efficiency tested, tested on diets similar to the environment that they will be asked to perform in while covering cows. Otherwise, any feed efficiency numbers may be of little value.   

Often, bulls are fed to achieve high average daily gains, which require high levels of grain. Too much high-starch grain, like corn, can increase the risk for digestive upset, foundering, and compromised rumen integrity. A general rule of thumb is to keep high-starch content grains limited to approximately 0.5% BW (ie - for a 1,000 lb bull, that’s 5 lb of corn). To achieve higher gains, utilize other high energy supplements that are lower in starch such as corn coproducts, soyhull pellets, or even corn silage.

A critical component to avoid bulls falling apart or ‘melting’ on pasture is to return to a predominately forage-based diet once yearling data has been collected.

Impact of excess body fat on fertility
Much of the older research dating from the 1980’s indicated that when fed higher energy diets, bulls were heavier, reached puberty quicker, had larger scrotal circumference, and therefore, improved semen quality and quantity. However, given the selection emphasis the beef industry has placed on growth over the last several decades, fertility has likely been negatively impacted. Additionally, the seedstock industry has migrated bulls to a much higher plane of nutrition during development. The excess body fat can certainly lead to thermoregulation issues with sperm motility and morphology.

More recent bull development studies (2016, 2017) with the ISU McNay Angus herd found that while faster growing bulls were leaner, heavier muscled, and had larger scrotal circumferences, those bulls also had poorer breeding soundness exam (BSE) scores as indicated by sperm motility and morphology. This data suggests that with today’s genetic base, selection for larger scrotal circumference might not result in better BSE scores and overall bull fertility.

Importance of full BSE
Industry benchmarks indicate 35 – 45% of bulls will pass a BSE near 12 months of age with an additional 20 – 30% of bulls passing at 14 months of age. Approximately 1 out of every 5 yearling bulls may never pass a BSE, even when developed in optimum conditions.

A full breeding soundness exam (BSE) should be completed annually prior to the breeding season and should contain 3 parts: a physical exam, a reproductive exam, and a semen check. Utilizing a sub-fertile bull comes with consequences of downward slide in cow herd reproduction including later bred females resulting in pounds given up at weaning, or worse, open cows.

In summary, a strategic, comprehensive management plan is needed to optimize bull performance while allowing individuals to express genetic potential for growth without compromising developmental fundamentals and longevity.  For individualize assistance developing yearling bulls, contact your local extension beef specialist. This year, what works for your neighbor, may not work for you. For individual assistance specific to your farm, call your extension beef specialist.