Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/10/2003
Publication Date: 3/1/2004
Citation: Oliver, A., Grant, R., Pedersen, J.F., O'Rear, J. 2004. Comparison of brown midrib-6 and 18 forage sorghum with conventional sorghum and corn silage in diets for lactating dairy cows. J.Dairy Sci. 637-644 Interpretive Summary: Sorghum has become an increasingly important forage crop for dairy producers. Forage sorghum can be planted later than corn, use water more efficiently, have high biomass yields, and when exposed to drought, still produce acceptable silage yields. However, the digestibility of many corn hybrids is typically greater than for conventional forage sorghum hybrids. Forage sorghum hybrids with one of several brown midrib (bmr) genes that reduce lignin content and increase digestibility are now commercially available. However, differences among hybrids with different bmr genes have not been previously described. The objective of this research was to compare performance of dairy cattle fed conventional, bmr-6, bmr-18 forage sorghum hybrids, and a corn conventional corn hybrid. Dairy cattle fed the bmr-6 sorghum hybrid outperformed those fed the conventional forage sorghum hybrid. Performance of dairy cattle fed the bmr-18 sorghum hybrid was generally intermediate compared to those fed the bmr-6 and the conventional forage sorghum hybrids. Feeding the bmr-6 forage sorghum hybrid resulted in lactational performance equivalent to feeding the corn hybrid used in this study. Readers should be cautioned that the bmr hybrids used in this study were not identical except for the differing bmr genes. Consequently, the effect of the specific bmr gene is confounded with hybrid. Nevertheless, this is the first report to indicate that not all bmr hybrids will result in similar digestibility and performance responses when fed to dairy cows. We are currently developing near-isogenic conventional and bmr forage sorghum lines to document the independent effect of the bmr genes on feed quality and dairy performance.
Technical Abstract: Total mixed rations containing conventional forage sorghum, brown midrib (bmr)-6 forage sorghum, bmr-18 forage sorghum, or corn silage were fed to Holstein dairy cows to determine the effect on lactation, ruminal fermentation,and total tract nutrient digestion. Sixteen multiparous cows (four ruminally fistulated; 124 'd in milk) were assigned to one of four diets in a replicated Latin square design with 4-wk periods (21 d adaptation and 7 d collection). Diets were comprised of 40% test silage, 10% alfalfa silage, and 50% concentrate mix (dry basis). Acid-detergent lignin concentration was reduced by 21 and 13%, respectively, for the bmr-6 and bmr-18 sorghum silages when compared with the conventional sorghum. Dry matter intake was greater for cows fed the bmr-6 sorghum (25.2 kg/d) compared with the conventional sorghum (23.2 kg/d), but bmr-18 sorghum (23.4 kg/d) and corn silages (24.3 kg/d) were intermediate. Production of 4% fat-corrected milk was greatest for cows fed bmr-6 (33.7 kg/d) and corn silage (33.3 kg/d), least for cows fed the conventional sorghum (29.1 kg/d), and intermediate for the bmr-18 sorghum (31.2 kg/d). Total tract neutral detergent fiber (NDF) digestibility was greatest for the bmr-6 sorghum (54.4%) and corn silage (54.1%) diets, and least for the conventional (40.8%) and bmr-18 sorghum (47.9%) diets. In situ extent of NDF digestion was greatest for the bmr-6 sorghum (76.4%) and corn silage (79.0%), least for the conventional sorghum (70.4%), and intermediate for the bmr-18 sorghum silage (73.1%). Results of this study indicate that the bmr-6 sorghum outperformed the conventional sorghum hybrid, but the bmr-18 sorghum was intermediate in most cases. Additionally, the bmr-6 hybrid resulted in lactational performance equivalent to the corn hybrid used in this study. There are important compositional differences among bmr forage sorghum hybrids that need to be characterized to accurately predict animal response.