Supplementing Forages With Grain

Livestock Update, February 1999

Mark Wahlberg, Extension Animal Scientist, 4-H Livestock, Animal and Poultry Sciences, Virginia Tech

Forages are not all the same. One review paper from Kansas looked at 42 different studies of forages where intake was measured. These forages ranged from 1.9% to 27.8% crude protein, from 42% to 82% neutral detergent fiber, and 37% to 78% digestible organic matter (roughly equal to % TDN). When forages have this much variability, to make blanket statements about supplementation is not just foolish, it will be incorrect in many cases.

There have been recent articles indicating that supplementation with grains to forages is harmful and counterproductive. Well, that depends, and it depends on the quality of the forage. The microbes that inhabit the rumen have first access to the feed consumed by the animal. Those microbes require certain nutrients to perform their life processes, just as all animals do. Basically, they require an energy source, a nitrogen source, and certain minerals and vitamins. If one of these is lacking, microbial activity in the rumen is suppressed.

Lots of research studies have shown a benefit from supplementing with high protein feeds - under certain conditions. For example, Mathis et al (1998a) found an increase in forage intake and total diet digestibility from supplementing steers with a high protein supplement. However, in a companion study using the same procedures and the same supplement, (Mathis et al, 1998b) forage intake was reduced and diet digestibility was unchanged.

What was the difference? The forage. The study that produced the response used mature bromegrass hay that was 65.4% NDF and 5.9% crude protein. The study with no response used bermudagrass hay that was 70.8% NDF and 8.2% crude protein. In the first study the rumen microbes didn't have enough nitrogen to function to their potential and to utilize the feed energy that the hay provided. In the second trial, there was enough nitrogen, so no response to the protein supplement was seen.

There has been enough work done around the country that we can confidently make a recommendation. If forage crude protein is less than 7%, a high protein supplement should be provided. No response will be seen from a high-energy feed, such as corn, under these circumstances because the rumen microbes first-limiting nutrient was nitrogen. However, if forage crude protein exceeds 7%, then rumen microbes might benefit from an energy source. They may also benefit from protein. So what do we in Virginia do? Forage analyses for our forages rarely show a crude protein level below 7%. Yes, that will happen with corn stalks, but rarely with our hay or with stockpiled fescue. Our cool-season grasses just don't normally get protein levels that low. However, in the western range country they often find protein below 7%. Their warm-season grass hay is often low in protein, and the winter pasture they use is almost always well below 7%.

Virginia forages often are below requirements for energy. The requirements for a pregnant beef cow are 45 to 50% TDN and 7 to 9% crude protein. Since few of our forages fall below 7% crude protein, we rarely have to supplement the pregnant cow with that nutrient. But we often have hay that is less than 50% TDN, so energy will often need to be supplemented.

We can get pretty good utilization of grain supplements (as long as protein in the forage exceeds 7%), when we feed it at no more than 1/2% of the bodyweight of the animal. This equals 3 pounds to a 600-pound steer, or 6 pounds to a 1200-pound cow. At higher levels than this the grain replaces or substitutes for a good portion of the forage and reduces the efficiency of digestion of the forage part of the animal's ration.

The Bottom Line: Our forages are different from those in the western range areas. Research based on their forages is not necessarily applicable to us. They find a benefit to protein supplementation because their forage is too low in protein to support optimum rumen microbial activity. Ours usually have adequate levels. Draw the line at 7% crude protein. Energy (TDN) is usually our first limiting nutrient, so pay close attention to that first.

The best way to avoid this problem entirely is to manage forages so that quality is good enough. Cut hay at the earlier stages of maturity when both TDN and protein are high enough to meet the needs of cattle. Then no supplement is needed at all, and there is no need to purchase any.

References
Bandyk, C A and R C Cochran. 1998. Predicting Voluntary Forage Intake of Cattle. 1998 Cattlemen's Day, Report of Progress 804, Kansas State University, pp22-24.

Mathis, C P et al. 1998a. Effects of Supplemental Degradable Intake Protein on Intake and Digestibility of Low-Quality Brome Hay. 1998 Cattlemen's Day, Report of Progress 804, Kansas State University, pp1-2.

Mathis, C P et al. 1998b. Effects of Supplemental Degradable Intake Protein on Intake and Digestibility of Bermuda Hay. 1998 Cattlemen's Day, Report of Progress 804, Kansas State University, pp3-4.

National Research Council. 1996. Nutrient Requirements of Beef Cattle, Seventh Revised Edition. Washington, DC: National Academy Press.

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