The Basics of Cow Herd Nutrition

February 9, 2016 03:29 PM

By: John Maday, Bovine Veterinarian 

During the recent Cattlemen’s College at the Cattle Industry Convention in San Diego, Clay Mathis, PhD, director and endowed chair at Texas A&M’s, King Ranch Institute for Ranch Management, discussed the importance of protein in maintaining cow condition and some basics for determining supplementation levels.

Nutritional programs in cow-calf production should involve two primary goals, Mathis says; getting heifers to calve by two years of age and keeping on a 365-day calving interval. Maintaining adequate body condition, particularly through the calving season, is critical in meeting those goals.

Mathis notes that the first priority in protein feeding is to meet the requirements of rumen microbes, which need adequate nitrogen to digest forage roughage efficiently.

Research has shown that forage intake for cows on pasture increase as dietary protein increases up to about 7% of body weight on a dry-matter basis. Below that 7% sweet spot, rumen microbes cannot break down fiber efficiently and intake drops off. If ranchers supplement above that level, intake levels off and supplementation becomes less cost-effective.

In Texas trials with cows on dormant native tall-grass rangeland from December 2 through February 10, cows supplemented with 1 pound of soybean meal (SBM) as a protein source lost about 1.2 body condition scores. That loss of BCS moderated with higher levels of SBM up to about 4 pounds per day, then leveled off.

Mathis also encourages producers to look closely at protein costs on a per-cow, per-day basis. In a Texas trial, researchers compared the effects of feeding cows range cubes containing 20% crude protein (CP) at 4 pounds per day versus 40% at 2 pounds per day. The researchers fed those supplements over a 49-day trial on winter range. Performance was essentially the same for the two groups, but the cost was considerably different. The 20% CP cubes cost $233 per ton, while the 40% cubes cost somewhat more, at $273 per ton. However, on a per-cow-per-day basis, the 20% cubes cost about $1.02, while the 40% cubes cut the cost almost in half, to $0.57.

Mathis also reminds producers to watch the energy content and source in their supplements, as excess starch intake will interfere with rumen microbes’ ability to break down fiber and reduce forage intake. Supplementing energy-deficient cows with corn at about 2.2 pounds per day improves energy intake without reducing forage intake, he says. But at higher levels of corn supplementation, forage intake declines. For every pound of corn supplement above 3 pounds per day, forage intake declines by 1.5 to 2 pounds per day, Mathis says.  

Mathis says that in trials using soy hulls, which provide energy from highly digestible fiber, at 2.2 pounds, 4.4 pounds and 6.6 pounds per day, researchers saw a 20% increase in energy at 6.6 pounds compared with no supplement, without a decline in forage intake.

In devising a cost-effective protein and energy supplementation plan based on forage condition and cow condition, Mathis recommends using the Beef Cow Supplement Decision Guide he developed while at New Mexico State University. The decision tree begins by asking simply whether cows have enough to eat in the pasture. If the answer is no, the rancher clearly needs to provide supplements or reduce stocking rates. The next question addresses the color of the forage. If cows do not have adequate forage supplies, but the forage is green, protein likely is sufficient but energy is deficient, and an appropriate energy supplement, fed at 0.4% to 0.8% of body weight per day can contain less than 20 percent CP.  

Cows have adequate forage and the forage is green, it probably supplies adequate energy and protein. If the forage is brown, protein content likely is below 7% and limits forage intake.

The next question asks about cow body condition scores (BCS). If cows on brown forage have BCS of 4.5 or better, they can be fed a supplement with less than 32% CP at a rate of 0.1% to 0.3% of body weight per day to improve rumen efficiency. If the cows average below BCS 4.5, they need more energy, and the supplement, fed at 0.24% to 0.4% of body weight per day, should contain between 28 and 32 percent CP.

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