Cattle Reproduction: Asking the right questions with Bull Selection

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Saulo Zoca

Dr. Saulo Zoca
Assistant Professor and Beef Cattle Reproduction Specialist
Department of Animal Science
P: 931-486-2129

Bull selection is one of the most economically important jobs in a cattle operation. Whether selecting a bull for natural service or artificial insemination (AI) the impact of that bull’s genetics in the herd is long-lasting. In fact, approximately 87.5% of the current calf crop genetics can be explained by the last 3 bulls used in the operation, further highlighting the long-lasting impact of sire selection. In general, an AI bull will have far more offspring compared to a natural service bull in one breeding season; however, a natural service bull will stay in the herd approximately 4 years. The primary job of a bull is to get cows pregnant. Research has reported that the economic value of reproduction (getting cows pregnant) is at least 5 times more important than growth performance and at least 10 times more important than beef quality traits. That’s not to say that growth performance and meat quality aren’t important but rather that if a cow doesn’t get pregnant, calve, and wean a calf, there is no potential for growth and meat quality, since that calf was never born.

In the last USDA survey report, 92% of beef cows and 76% of beef heifers were exposed only to natural service (no AI performed). These percentages drive home the point that selecting the correct bull for a beef operation is of extreme importance since in most cases only a natural service bull is being used. Currently, there are an overwhelming number of EPDs (Expected Progeny Difference) and Indexes available that a producer can use when picking out a bull. Selecting which one is relevant for your operation can be a difficult job. Combining all the EPDs and Indexes available along with the question of “Which is the best bull?” creates a, in some cases, overwhelming situation; however, the situation can be simplified by answering the questions below and remembering that the best bull depends on the situation!

When selecting a bull, one should first look at their cow herd. The best bull will vary for each operation and their goals. I encourage you to answer the following questions before you try to find the best bull.

  • What is the operation goal? Sell weaned calves, sell yearling/background calves, retain ownership and sell finished cattle, and/or sell replacement females.
  • Where do your replacement females come from? Replacement heifers are selected from the cow herd and developed (at home or at a custom heifer development), or replacements are purchased (open heifers, pregnant heifers, open cows, or pregnant cows).

Further, understanding your marketing goals and plan is important. Selecting when you want to market your animals and understanding what is the best market for your operation is key. Without changing any management, is there a niche market that your product can be sold for a higher price? Are there any management practices that can be changed without great cost that will allow your product to fit in a niche market and capture more money? In other words, we have many different niche markets available that can bring a premium to your product and as an industry we should take advantage of those niche market if that means more profit. Before changing any management practices to fit into a niche market, communicate with your marketing agency (who buys your product) to understand the availability of that market in your region.

  • Next, what is your cow herd type, size, genetic, and color (if hide color matters for your market)? British, continental, exotic, or crossbred; large, moderate, or small framed; maternal or terminal trait females.

This last question will help you understand in an objective way where you are in terms of your cow herd. With this information and your marketing goals, you can figure out what needs to be improved and what needs to be maintained when moving to the next step – the actual bull selection.

Finally, we have established the product that will be sold, the marketing strategy for the product, and the cow herd that we currently have. Now, that you gathered all this information you can make an appropriate decision on selection of the “best bull”. The “best bull” is the bull that will complement your cow herd phenotype and genetics to produce a calf crop that will bring the best product to the market of your chose. That bull selection will start by determining the breed of choice, followed by determining what set of EPDs and/or Indexes will best fit.

Using the tools:

Let’s use the following scenario as an example: the operation retains replacement heifers; sells excess heifers and steers at weaning; breeds in the spring; niche markets aren’t available; black hide pays better; the cow herd is of moderate frame, British, black hided; and the bull breed of choice is Angus.

When this operation is selecting a bull that would improve the current herd, the primary selection could be a maternal index like $M (if the sire breed of choice was a Simmental the all-purpose index API could be used instead, because this operation retains replacement females). Other options for this scenario would be $W and $C instead of $M. After selecting the best $M bulls, this operation could evaluate the HS (hair shedding EPD) as a secondary selection since we are in the fescue belt and their breeding season is during the spring (warmer weather). If the bull will be used in heifers, some emphasis could be placed in calving ease (CED); however, it is important to understand that CED is part of $M calculation. If this operation decides to look at individual EPDs instead of indexes, Angus EPDs that would be economically relevant would be CED, WW, DOC, Claw, Angle, HS, HP, CEM and Milk. Identifying which one of those are more important and selecting a bull that would fit all the minimum criteria established would be extremely hard. Further, evaluating the bull’s phenotype is important, making sure the numbers match the phenotype. Looking at feet and leg structure, making sure that bull’s height (frame score) is appropriate for the operation goals, in this scenario a moderate framed bull would be a great option to maintain a moderate cow size.

We are in the midst of “bull buying season” in the state of Tennessee, I hope this article can assist you in asking the right question to figure out what you need to be looking for when buying your next bull whether for AI or natural service. Last, but not least, remember that all bulls must pass a breeding soundness exam (BSE) before each breeding season, regardless of the age of the bull and if he has been used successfully in previous breeding seasons. Keep in mind that performing a BSE has an economic benefit to cost ratio of 17:1! Getting the cows pregnant is the first job!

If you are in search of a great bull, we will have the University of Tennessee Bull Test Sale on January 11th at the Middle Tennessee AgResearch and Education center in Spring Hill, TN. We will have Angus, Simmental, SimAngus, Hereford, and Black Hereford bulls available on the sale. You can find more information at or contact Saulo Zoca at or (931) 486-2129.