Cost-Effective Diets for Pregnant Beef Cows

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K-State researchers examined performance of pregnant beef cows on limit-fed diets containing ammoniated wheat straw treated with two rates of anhydrous ammonia.
By: Katie Allen, K-State Research & Extension News

Dry conditions in Kansas and other areas of the Midwest have caused many cow/calf producers to look at more cost-effective ways to adequately feed their herd. One of the hot topics in the beef sector today, especially in dealing with drought, is that more producers are considering confined feeding for cows using low-quality forages with protein by-products.

The process of using anhydrous ammonia to treat and enhance low-quality forages, such as wheat straw and corn stalks, is not a new concept to help producers save on feed costs, said Justin Waggoner, beef systems specialist for K-State Research and Extension. Ammoniation increases the digestibility and dry matter intake of low-quality forages.

Waggoner, who works at K-State’s Southwest Area Extension Office in Garden City, recently looked at using two different rates of anhydrous ammonia application on wheat straw that is fed with wet distiller’s grain to pregnant beef cows. He said the traditional rate of anhydrous ammonia application recommended for producers has been a 3 percent application (60 lbs/ton) on a dry matter basis. His latest research compares the 3 percent application to a 1.5 percent application (30 lbs/ton).

"Our primary interest in doing so is due to the current cost of anhydrous ammonia," Waggoner said. "When the research was done to establish that rate of 3 percent, anhydrous ammonia cost about $200 a ton. Today, we’re looking at anhydrous ammonia prices at $700-$800 a ton, so there’s an opportunity for some cost savings by reducing the application rate."

A closer look at the research
Although Waggoner and his colleague John Jaeger, a K-State beef cattle scientist at the Western Kansas Agricultural Research Center in Hays, have studied forage quality in the past, they hadn’t had the opportunity to do an actual cow feeding study until now. A total of 132 second-trimester, spring-calving, Angus-cross cows were examined. A majority of the cows were 4-5 years old.

Former research evaluating ammoniated wheat straw as a component of a beef cow diet didn’t include wet distiller’s grain, Waggoner said. This provided an opportunity to study ammoniated forage in a more modern diet with wet distiller’s grain. The cows were limit fed at 1.9 percent of their initial bodyweight.

"On a dry matter basis, the diets were about 65 percent wheat straw, 20 percent wet distiller’s grains and rolled sorghum at 15 percent," he said.

Results of the 84-day study showed that the 1.5 percent anhydrous ammonia application rate increased the ration costs 21 percent, and overall cow performance increased 23 percent in terms of average daily gain (ADG). The 3 percent rate increased the ration costs by 35 percent, and overall cow ADG increased by 25 percent.

"We have this classic argument between maximum response and more of an optimum response when we figure in the cost," Waggoner said. "The important take-home message is the response appears to diminish as we increase the rate of anhydrous application. So the maximum response was at 3 percent, but from an optimum response in terms of cost, it looks like that 1.5 rate might have some benefits."

In addition to examining average daily gain, the researchers also assigned body condition scores, as well as took measurements by ultrasound of backfat thickness at the 13th rib and rump fat thickness at the beginning and end of the study. They concluded that the body condition scores of the cows fed the 3 percent and 1.5 percent ammoniated wheat straw had greater body condition scores overall at the end of the study compared to those cows eating diets containing untreated forage. Backfat and rump fat thickness were not influenced by anhydrous ammonia application.

The full research paper about this study can be found in the 2014 Beef Roundup publication.

To watch a video interview with Waggoner, log on to the K-State Research and Extension YouTube page. A step-by-step video explaining how to ammoniate low-quality forages is also available.

For more information about ammonia treatment of low-quality forages, including techniques and safety considerations, read this FORAGE FACTS publication.


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