Corn silage and alfalfa haylage are great forage sources for dairy cattle. However, there are other forage alternatives available to dairy producers. Increasing the variety of forages grown on a farm can decrease the impact of diseases, pests and climatic changes on a farm’s forage supply.

Two alternative forages are sorghum silage and oat silage.

Sorghum is known for its ability to grow well with limited amounts of water and can be a good option on soils with a low water-holding capacity. Oats can be used as a cover crop in the late summer or fall after wheat grain harvest. A potentially useful trait of oats is that they do not need to be terminated in the spring because they do not survive the winter.

Often, alternative forages such as these are fed only to dry cows and heifers. This, however, limits their usefulness on a dairy farm. Since the lactating cows consume the majority of feed on a dairy farm, we wanted to see if sorghum and oat silages could be fed as part of the lactating cow ration as well.

High-producing lactating cows require highly digestible forages to meet their nutrient demand and, therefore, forage variety selection and harvest timing are quite important. We chose a BMR-6 dwarf forage sorghum because of its reduced lignin content and increased leaf-to-stem ratio compared to standard forage sorghum.

The oats we used in the project were a later-maturing variety bred for forage production and planted in mid-August.

Sorghum harvest was targeted for the soft-dough stage to balance starch accumulation with neutral detergent fiber (NDF) digestibility. Unfortunately, after a delayed planting, we harvested milk-stage sorghum due to a killing frost.

The oats were harvested at the boot stage before the head comes out and digestibility decreases. Both forages were ensiled in Ag Bag products.

The sorghum silage analysis showed 0.8 percent starch, 62.7 percent NDF and 9.5 percent crude protein (CP). The oat silage had 0.3 percent starch, 54.7 percent NDF and 11.7 percent CP. This was contrasted with the corn silage analysis of 34.7 percent starch, 40.2 percent NDF and 6.8 percent CP.

Clearly, the alternative forages contained much less starch, higher NDF and higher CP than the corn silage.

To test how these forages would work in a lactating cow ration, we designed an animal experiment with 12 Holstein cows. A control diet was compared with a diet that included either sorghum or oat silage at 10 percent of the diet dry matter replacing corn silage.

There were three periods in the experiment, so every cow received each diet. With this study design, production effects could be attributed to the alternative silages and, based on these results, further diet changes could be recommended by the farm nutritionist.

The control diet was 44 percent corn silage, 7.5 percent alfalfa haylage, 4 percent hay/straw mixture and 44.5 percent concentrate mix on a percent dry matter basis. We also conducted an in situ (feed incubated in nylon bags in the rumen of the cows) experiment to compare the ruminal degradability of the forages.

How did the cows perform? The diet with sorghum silage decreased feed intake by 3.7 pounds, and the cows yielded 2 pounds less milk and 0.2 pounds less milk protein compared with the control diet. However, milkfat yield was the same among diets due to an increase in the milkfat content by the sorghum silage diet.

The diet with oat silage resulted in the same feed intake (59.7 pounds dry matter per day) and milk (88.6 pounds per day), milkfat (3.13 pounds per day) and milk protein (2.49 pounds per day) yields as the control diet.

Why did the sorghum silage diet decrease production? The in situ test showed that sorghum silage had the lowest dry matter degradability. This may explain the decreased feed intake of the sorghum diet due to rumen fill. The lower feed intake led to lower milk production.

The lower protein yield was a result of the lower milk yield and lower milk protein content. The lower milk protein content was explained with less rumen-available energy in the sorghum diet because of lower starch and less-digestible NDF in the sorghum silage.

Harvesting sorghum at the soft dough stage after starch has accumulated in the grain would mitigate the reduction in rumen-available energy and would likely eliminate the negative effect on milk protein. Ground corn grain could also be added to a diet with sorghum silage to maintain energy content similar to a corn silage diet.

Why did the oat silage diet perform so well? Oats grown in the fall have been shown by other researchers to have 38 percent higher NDF digestibility than spring-grown oats. In our study, the in situ dry matter degradability of oat silage was nearly equal to that of corn silage. NDF digestibility was increased in the oat silage diet, which counterbalanced the decrease in starch content of the diet.

More urea was excreted in the urine of cows on the oat silage diet. This is not surprising since the oat silage contained nearly twice as much CP as the corn silage. This does indicate a waste of protein and an opportunity to reduce purchased protein sources in the diet if oat silage is fed to the lactating cows.

Our research supports the use of limited amounts of BMR sorghum or oat silage in lactating dairy cow rations targeting milk production up to 85 pounds per day.

Both sorghum and oats should be considered on dairy farms from an agronomic perspective. If the farm has some droughty soils, sorghum may be appropriate alternative forage. If wheat is grown for grain in the farm rotation, growing forage oats on those fields during the late summer and fall will be appropriate.

The aim here is not to eliminate the use of corn silage but to improve the resilience of the entire farm by diversifying crops where and when appropriate.

For those interested in trying alternative forages for the first time, it is good to start with only a few acres to feed a relatively small number of animals such as a group of heifers. For those already feeding alternative forages to heifers, some oat or sorghum silage can first be added to the low-production group of lactating cows and expanded from there.

Cows are amazingly adaptable animals and can be quite productive when fed various alternative forage sources such as oat or BMR sorghum silage.  

Michael T. Harper a Ph.D. student in animal science at Penn State University. Email Michael T. Harper.