Sorghum research highlights high sugar, low cost and drought tolerant silage for dairy cows

Step into any grocery store nowadays and food prices have sky-rocketed. Some statistics show essential food items rising as much as 65% in 2023. This sticker shock on the items needed for a balanced diet, such as eggs, milk, meat and bread, has left consumers looking for comparable alternatives to avoid a pricey bill at the checkout line.

Comparatively, dairy farmers are facing the same challenges as they shop for feed for their cows. An extended drought in 2022 and 2023 has driven up feed and hay prices, making corn silage for dairy cattle an expensive commodity, particularly in the Texas High Plains where more and more dairy cattle operations are expanding. Texas A&M AgriLife Extension service dairy specialist Dr. Juan Piñeiro, Ph.D., DVM, said prices for corn silage have reached $120 a ton and some dairy farms are buying and transporting corn silage from 200 to 300 miles away, adding to their input expenses.

Piñeiro and Texas A&M graduate research and Extension assistant Douglas Duhatschek, both of Amarillo, Texas, have been researching drought tolerant sorghum silage alternatives to corn silage. Piñeiro said the research project began two years ago and based on the needs of dairy operations in the High Plains, the duo began looking into sorghum that would produce high yield and high quality forage. Additionally, they considered the factors limiting the use of forage sorghum versus corn silage in dairies. For dairy cows, corn silage is king because it provides the highest metabolizable energy—the biggest concern for lactating cows.

However, by planting sorghum instead of corn, Piñeiro said the seed cost alone is roughly 10 times less expensive and irrigation water use requirements for sorghum is about 30% lower than corn. He said yield is a little lower for sorghum, but that is highly variable and it can depend on the hybrid used.

“The main advantage is drought tolerance and that’s one of the reasons dairy farmers are strongly considering this,” Piñeiro said. “Sorghum can survive those drought events and when we do get the rain, the quality won’t be impacted as much compared to corn.”

As far as nutrition, sorghum silage has less starch than corn silage.

“That starch is less digestible, mostly explained by the difficulty of breaking down the sorghum berries compared to how much easier it is to break the corn kernels down,” Piñeiro said. “It also has decreased fiber digestibility, but that can be addressed by using BMR (Brown Midrib) hybrids that will have lower lignin and higher fiber digestibility.”

Research findings

In the 2021 trial, Piñeiro and Duhatschek tried to increase the starch digestibility in the sorghum to make it more comparable to corn. “We tried to do that through increasing the grain size, and harvesting at soft dough stage when it’s easier to break that grain and we did not see any improvements in rumen starch digestibility,” Piñeiro said.

In 2022, they compared non-sterile and male-sterile sorghum hybrids. Regarding non-sterile hybrids, they experimented with shorter plants that had more grain than leaves and stems to see if that scenario would increase the overall starch digestibility. Piñeiro and Duhatschek seeded three non-sterile sorghum hybrids—non-BMR F10; BMR12, F382, and F431; Richardson Seeds—and two male-sterile sorghum hybrids—Non-BMR, F465; and BMR12, F430. Male-sterile sorghum is unique because it will not develop grain unless there is cross pollination. The male-sterile hybrids were seeded on the west side of the plots and the non-sterile on the east side to minimize cross pollination from winds from the southwest.

Piñeiro cited research studies in New York, which showed male-sterile plants trade off sugars for starch because the plant does not need to move the water-soluble carbohydrates—or sugars—from the leaves to the grain to produce starch in the grain, thus it has a much higher sugar concentration.

“It has roughly about three times more sugar and with that we are trying to address the issue of not being able to use the starch and the protein from the grain if we cannot process it by replacing some of that starch with higher sugars in that male-sterile BMR sorghum,” Piñeiro said.

The average sugar percentage for the male-sterile sorghum varieties in this trial was 18%, comparatively, Piñeiro said most forage sorghum will be 4% sugar. “The starch was half of it because it won’t develop grain. But since we harvest the non-sterile hybrids that develop grain at hard dough stage and at that time it’s very difficult to process the grain even though on paper it might look as though starch content is greater, a lot of that is not going to be digested by the cow and it’s going to end up in the manure.”

On the flip side, Piñeiro said the digestibility of the sugars in male-sterile sorghum is high. Another advantage of BMR sorghum hybrids is the lower lignin content and higher fiber digestibility.

“That’s why BMR male-sterile sorghum is such an attractive option,” he said. “BMR on average will have half a percentage point less of lignin and roughly 5%-points more fiber digestibility (NDFD30%) and that will lead to more milk production.”

Another contrast to non-sterile and male-sterile hybrids is harvest flexibility.

“If you use a forage sorghum that develops grain, to be able to process that grain you cannot harvest after the soft dough stage,” Piñeiro explained. “That harvest window is sometimes just a matter of days. It doesn’t give much flexibility for some dairy farmers that may have to wait on the custom harvester that is working with another client or maybe they can’t get in the field because of rain. It can get complicated, whereas when you work with male-sterile hybrids, we see these increases in sugars six to nine weeks after the boot stage, where you have a lot longer time span where you can harvest.”

However, there are disadvantages for male-sterile hybrids due to the absence of grain development in the plant leading to higher humidity. Piñeiro said male-sterile hybrids in the study were around 72% humidity with dry matter between 26 to 31%.

“The concern for dairy farmers is because of the high humidity, it can increase the risk for leachates and abnormal fermentation,” he said.

Part of the next phase of this research project will be to look into management practices to reduce leachates and undesired fermentation. Piñeiro said one element they will examine is increasing the chop length to reduce leachate risk. He will also experiment with using an inoculant to drop the pH as fast as possible and reduce the risk of abnormal fermentation.

For the next chapter of the project, the researchers will repeat the same trial they conducted last year on plant proportions and researching the berry processing score. Additionally, they will evaluate milk yield and composition when cows are fed male-sterile sorghum silage. Even after only one year of research into the use of male-sterile sorghum hybrids, this alternative holds a great deal of promise and potential to conserve water and benefit sorghum growers and dairy farmers. Both dairymen and grocery shoppers appreciate alternative on the shelf so they can make decisions for their budget, rather than being forced to choose the only option available.

“With BMR male-sterile hybrids, we hope to have good fiber digestibility and higher sugars that will partially replace the energy that we will lose when we replace corn silage with sorghum silage,” Piñeiro said. “We may have to adjust concentrates in the rations of lactating cows fed this sorghum silage, most likely by increasing the corn grain and perhaps if we have higher protein concentration, we can decrease a little bit of the protein concentration. This could help the producers save some money on that end.”

Lacey Vilhauer can be reached at 620-227-1871 or [email protected].