Sorghum silage in the spotlight

Sorghum has long resided in the shadow of corn grown for silage. Even though the former species is often touted for its drought tolerance and water-use efficiency, sorghum silage has rarely been a dairy farmer’s first priority. However, as sorghum genetics and processing equipment evolve, there may be potential for it to be more than just dry cow feed.

In a recent episode of “The Hoard’s Dairyman Podcast,” Steve Martin with DNMC Milk discussed how sorghum silage can be effectively substituted for corn silage, especially in regions where water can be scarce. As dairy farm consolidation continues to surge in regions like the Southwest, he suggested larger operations show a rising interest in growing more cost-effective and water-efficient forage.

“[Sorghum] is not new — it’s just gaining traction for some of its traits as making it on less water is becoming more critical,” Martin said.

Before offering any recommendations, the dairy nutritionist gave the disclaimer that he is not an agronomist; however, he advocated for nutritionists, agronomists, and veterinarians working together as a team to find the best feeding solutions for their shared clients. With that said, he has observed sorghum historically taking a backseat to corn in cropping systems despite the former crop’s relatively easy planting requirements and resiliency.

“It just doesn’t get the attention and the high-level management that corn does,” Martin said. “Moving it from that space of just throwing some seeds out there and seeing what happens toward the management structure that we put around corn has been the biggest and most recent change.”

One and done

Farmers can take multiple cuttings of sorghum for silage, but this isn’t typically the route taken by those who use it to replace corn silage. Martin suggested single-harvest systems are more common in these situations; however, plant maturity and harvest timing can significantly impact forage quality.

Harvesting sorghum before it develops a seedhead will secure higher fiber digestibility, but Martin stated that vegetative plant material can hold excess moisture and create challenges when it comes to chopping. On the other hand, one of the biggest problems with harvesting more mature forage is the inability to break sorghum berries with standard kernel processors.

“The number of berries that end up in manure is shocking, and they look just like they did in the bunk,” Martin said. “They have all the risk factors of poor rumen retention: they are slippery, they are dense, and they are round, so they fall through the rumen mat.”

As interest in sorghum has risen, seed genetics have shifted toward taller crops with smaller seedheads. Male-sterile and photoperiod-sensitive varieties have also entered the market, offering more harvest flexibility.

While male-sterile sorghum does not develop a seedhead at all, photoperiod-sensitive varieties wait to develop seedheads until day length is less than 12 hours. Martin said this gives farmers the option to capture higher fiber digestibility by harvesting forage during its extended vegetative stage or delay cutting until after the first frost when plant moisture may be more suitable for chopping and storing.

Store it like corn

For the most part, the best practices for storing corn silage translate to sorghum silage. Martin prefers sorghum silage between 35% to 40% dry matter; however, he contended it can be more forgiving than corn silage if it is put up wetter or drier. He has worked with farmers feeding forage on both ends.

“For sorghum silage, we still prefer it to be 37% dry matter, but 50% dry matter sorghum silage has a better chance of being successful making milk than 50% dry matter corn silage,” he said

Similar spoilage risks still exist, though. Martin warned that very wet sorghum silage may be more prone to butyric fermentation than corn silage, whereas the incidence of white mold development can start to rise when sorghum moisture exceeds 45%.

Improved berry processing

Having more experience with sorghum in the feedbunk than in the field, Martin suggested sorghum silage has the tendency to be considered dry cow feed. That’s a narrative he hopes will change, especially with emerging options to grow, harvest, and process sorghum in ways that enhance silage quality.

In terms of corn silage, there are two major aspects of silage quality: fiber digestibility and starch digestibility. Fiber digestibility is dictated by the stage of maturity at which corn is harvested. On the other hand, starch content and kernel processing at harvest will impact how starch digestibility improves throughout fermentation.

Now, as sorghum berry processing methods evolve, there may be more opportunities to access sorghum starch as an energy source. Martin gave credit to researchers at Texas A&M University and Rock River Laboratory Inc. who have spearheaded berry processing research and development; however, he expects it to receive some of the same skepticism from producers that kernel processing did when it was released. There may be some aspects to iron out before the system is widely adopted.

For example, unlike corn kernels, there can be a wide variation in size among sorghum berries. While this may be less prevalent in well-irrigated stands, having a variable berry size can make it difficult to select the best particle size and adjust the processor accordingly. Overall, Martin suggested there is still some uncertainty surrounding berry processing score and sorghum quality analysis.

“There are a lot of questions there,” he said. “If we can get the gas production realities of these different particle sizes of the broken berries, I think you could take the berry processing score and use it to come up with a seven-hour starch number to put in your ration model. That would be the goal.”

Once these questions are answered and goals are achieved, he believes sorghum silage will be a more attractive ingredient in dairy rations that is able to be utilized more effectively.

“We might not be giving sorghum silage the full opportunity to do what we think it can do, but we can’t have manure full of sorghum berries and be successful,” Martin said.

You can listen to “The Hoard’s Dairyman Podcast” on your favorite podcast app or watch it on YouTube.