Annual forages can be a great way to provide deferred grazing on permanent perennial pastures that may be in need of recovery time. Depending on commodity and livestock prices, annual forages may result in more economic return than grain crops, particularly on marginal crop ground.Annual forages provide forage for livestock on both dry land and irrigated acres without the long-term commitment of perennial forages.

Whether a producer chooses to plant cool-season or warm-season annuals depends largely on when forages are needed in a livestock production system as well as climatic factors that affect growth.

Summer annual forage options

Forage sorghum, sudangrass, sorghum-sudangrass hybrids and millets are popular forages for summer annual crops. More recently, particularly in no-till farming operations, legumes and brassicas have been added to fix nitrogen and reduce soil compaction.

Some annual legumes have included soybeans, cowpeas and clovers. Brassicas are commonly turnips or radishes, but forage collards have also been included.

Summer annual forages can be difficult to manage for grazing, particularly in dry land cropping systems where dry conditions slow growth and a rain shower increases growth quickly.

If summer annuals are grazed close to maturity, a lot of waste due to trampling can occur. If grazing is desired, it should be initiated once the crop is 18 inches tall and should be managed to keep the crop as vegetative as possible.

This may require dividing the crop into paddocks and rotating cattle, or it may be accomplished by moving an electric fence and allowing cattle to strip graze.

Either one can require labor that may be needed for other farming operations at that time of year. If the crop matures and grazing is going to result in excess waste, producers should consider swathing the crop and windrow grazing the swaths.

Additionally, producers should be aware of high nitrate and prussic acid potentials of summer annuals. This usually only happens when the plant is stressed from drought, hail or frost.

Some varieties have lower nitrate and prussic acid accumulation potential and should be considered for grazing.

Producers should plan to have an alternative forage source available should high nitrates or prussic acid occur.

This could mean moving grazing cattle to a native forage pasture for temporary grazing or feeding hay. More information on managing summer annual forages can be found online (Summer Annual Forages for Beef Cattle in Western Nebraska).

Cool-season annual forages

Cool-season annual forages can be planted in late summer for fall grazing or early spring for spring grazing. Popular cool-season annuals include oats, triticale, rye and wheat.

Annual forage mixtures can be developed by adding legumes, such as forage peas, and brassicas, such as turnips or radishes.

Cool-season forages fit well in irrigated, limited irrigation and dry land systems. More information on forage options in limited water situations can be found online (Utilizing Annual Forages with Limited Irrigation for Beef Cattle During the Following Drought).

Much like warm-season annuals, cool-season annuals are best utilized in a vegetative state. Therefore, developing a system of rotational grazing, staggered planting dates or planting early and later-maturing forages in separate fields can improve forage utilization.

As with summer annuals, if the forage begins to mature too quickly, swathing and windrow grazing may be the best way to graze the forage. 

Managing cattle grazing lush immature forages includes an adequate mineral program. Cattle should be acclimated to high-magnesium, high-calcium mineral before being turned out on lush pasture.

Additionally, cattle should never be hungry when first turned in on lush pasture. Having an alternative pasture for grazing or feeding hay during times of excessive rain or snow will help maintain gains on cattle and prevent damage to the field and crop during adverse weather.

Supplementation on annual forages

Rumen-degradable protein (RDP) is protein easily broken down in the rumen and made available to the rumen bacteria so they can digest feed in the rumen.

On the other hand, rumen-undegradable protein (RUP) is protein that escapes digestion in the rumen and then is available to be absorbed in the small intestine and can be used by the host animal for growth or lactation.

Research conducted at the University of Nebraska has indicated that rotationally grazed summer annuals were adequate in both RDP and RUP. Therefore, supplementing a protein source would not increase pasture gains.

The in vitro organic matter digestibility (similar to total digestible nutrients or TDN) on rotationally grazed summer annuals has been determined to be 63 to 72 percent. This would support acceptable gains for grazing cattle.

As the forage matures, digestibility decreases, so to maintain this level of digestibility it would be important to manage the forage so it stays as vegetative as possible.

Cool-season annuals, however, have been shown to be adequate in RDP but deficient in RUP. In a study conducted at the Texas AgriLife Research and Extension Center near Bushland, Texas, wheat pasture contained 23 percent crude protein and 81 percent TDN.

Most producers would assume growing cattle grazing this type of forage would not respond to supplementation. Yet in this study, growing cattle grazing the wheat pasture had greater gains when supplemented with distillers grains (60 percent RUP) compared to those supplemented with corn or no supplement.

Other studies, at the University of Nebraska, have shown improved gains when cattle grazing perennial smooth bromegrass were supplemented with high-RUP supplements.

The transportation and delivery costs of supplementation should still be carefully evaluated to determine the economical return of providing supplement even though it is likely growing calf gain would be improved.

Impact of gut fill on weight gain

Another factor that can affect the perceived weight gain on high-quality annual forage pastures is gut fill. Cattle are often fed lower-quality hay or mature native range before being turned out on lush cool-season pastures.

These lower-quality forages are very bulky, and the passage rate through the digestive tract is slow. Therefore, these cattle have full digestive tracts, which is often referred to as gut fill.

Conversely, forages that are 80 percent TDN are rapidly digested, have a very fast rate of passage, and therefore result in very little gut fill.

If cattle are weighed while on dormant range or hay and then weighed again after grazing lush cool-season pasture, without accounting for gut fill differences, the result can lead producers to believe the cattle did not gain well on the high-quality forage.

For example, if cattle weighed an extra 50 pounds due to gut fill prior to grazing cool-season pasture, they would appear to gain less than cattle limit-fed or held off feed prior to weighing (Table 1).

If producers cannot limit-feed prior to weighing, providing the same diet before and after cool-season pasture grazing would help equalize gut fill.

When managed properly, both cool-season and warm-season annual forages can provide high-quality grazing for beef cattle, allowing producers to reduce grazing pressure on native range and permanent pasture.  

• Karla H. Jenkins
• University of Nebraska – Lincoln
• Panhandle Research and Extension