Fernando Diaz
Sorghum is a tropical grass grown primarily in semiarid and dry regions. It has become an important cereal crop because it is heat and drought tolerant. As forage, sorghum hybrids with the brown midrib (BMR) gene are becoming popular in the US because their lower water requirement compared with corn. Average starch concentration in BMR sorghum silage is lower than in corn silage; however, fiber and fiber digestibility contents are very similar in these forages.
A recent meta-analyis compared the production response of lactating cows to diets based on corn silage or BMR sorghum silage. The researchers (Sanchez-Duarte y col., 2019) used data from 9 published articles (1984–2015) to contrast conventional corn silage (13 comparisons; 204 cows) vs. BMR sorghum silage. The table below shows nutrient composition of both forages used in this study. Average protein content was similar in the two silages (around 8.0% in a dry matter basis; DM). Compared with corn silage, NDF, ADF and lignin concentration were greater in BMR sorghum.
| Nutrient | BMR Sorghum Silage | Corn Silage |
| Dry Matter (DM) % | 30.2 | 36.5 |
| Crude Protein (%DM) | 8.2 | 7.8 |
| NDF (%DM) | 53.6 | 49.6 |
| ADF (%DM) | 36.1 | 28.2 |
| Lignin (%NDF) | 3.9 | 5.8 |
| NDF Digestibility (%NDF) | 55.1 | 53.2 |
On average, diets included 42% silages (either BMR sorghum or corn) with a minimum and maximum inclusion rate of 23 and 65% DM. Average protein content was similar for both forage diets (17.0% DM); however, average NDF and ADF were higher in the BMR sorghum silage (36.7 and 24.0% DM) than in the corn silage diets (34.9 and 20.6% DM).
The results, published in the Journal of Dairy Science, showed no difference in cow performance between forages. Dry matter intake, milk production, protein yield, and fat yield were not affected by forage type. However, compared with corn silage, cows fed BMR sorghum silage increased milk fat content (0.10%) but decreased milk protein (0.06%) percentage.
This evaluation suggests that BMR sorghum silage can support similar milk performance than conventional corn silage. However, these results should be taken carefully. BMR sorghum silage has a lower energy content than corn silage, thus, feeding this forage at high-inclusion rate to high-production cows in early lactation may affect their production performance negatively.
Reference
I. Sánchez-Duarte, K. F. Kalscheur, A. D. García, and F. E. Contreras-Govea. 2019. Short communication: Meta-analysis of dairy cows fed conventional sorghum or corn silages compared with brown midrib sorghum silage. J. Dairy Sci. 102:419–425.
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