Short communication: Meta-analysis of dairy cows fed conventional sorghum or corn silages compared to brown midrib sorghum silage

Authors: SANCHEZ-DUARTE, JUAN - South Dakota State University; Kalscheur, Kenneth; GARCIA, ALVARO - South Dakota State University; CONTRERAS-GOVEA, FRANCISCO - University Of Wisconsin

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/20/2018
Publication Date: 1/2/2019
Citation: Sanchez-Duarte, J.I., Kalscheur, K., Garcia, A.D., Contreras-Govea, F.E. 2019. Short communication: Meta-analysis of dairy cows fed conventional sorghum or corn silages compared to brown midrib sorghum silage. Journal of Dairy Science. 102(1):419-425. https://doi.org/10.3168/jds.2018-14552.
DOI: https://doi.org/10.3168/jds.2018-14552

Interpretive Summary: Forage sorghum is a good alternative for dairy farms in areas with reduced rainfall since this crop is tolerant to low soil moisture conditions while able to produce adequate tonnage per acre. Lignin content present in late vegetative and early flowering stages of conventional sorghum can be quite high, resulting in lower fiber digestibility. Alternatively, brown-mid rib varieties contain less lignin, resulting in improved fiber digestibility of the forage sorghum. This study evaluated the inclusion of conventional sorghum silage and conventional corn silage compared to brown midrib sorghum silage in the diets of lactating dairy cows. This research demonstrated that dry matter intake and milk production responded positively to brown midrib sorghum silage compared to those factors in cows fed conventional sorghum silage, but similarly to cows fed conventional corn silage. Milk fat percentage decreased for cows fed conventional corn silage or sorghum silage compared to brown-midrib sorghum silage. Milk component yields were associated with the increase in milk production when cows were fed brown midrib sorghum silage compared to conventional corn silage. This research will be of interest to dairy producers, nutritionists, and researchers interested in formulating lactating dairy cow diets with alternative forage crops.

Technical Abstract: A meta-analysis was conducted to compare the effects of feeding dairy cows conventional sorghum silage (CSS) or conventional corn silage (CCS) compared to brown midrib sorghum silage (BMRSS) diets on dry matter intake (DMI), milk production, and milk composition. Data from nine published articles (1984 to 2015) were used to contrast diets with CSS (7 means comparisons; 104 cows) or CCS (13 means comparisons; 204 cows) vs. BMRSS diets. Statistical analysis was performed using fixed or random effects models with the Metafor package of R. The degree of heterogeneity was measured with I2 statistic and publication bias was determined with funnel plots and Egger´s regression test. Other sources of heterogeneity of response were analyzed through meta-regression. Estimated effect size (ES) was calculated for DMI, milk production, and milk composition. No evidence of publication bias was observed for all variables tested. The highest degree of heterogeneity (I2=41.5 and 72.6%) was observed for DMI among dependent variables tested in both comparisons, indicating intake responses to silage type are rather inconsistent; while milk production had the lowest degree of heterogeneity (I2=0%) supporting the idea that the responses of this variable to silage type were very consistent across studies. Compared to BMRSS diets, cows fed CSS diets exhibited decreased milk production (1.64 kg/d), milk fat concentration (0.09%), milk fat yield (0.08 kg/d), milk protein yield (0.04 kg/d), and milk lactose yield (0.16 kg/d) and tended to decrease DMI (0.83 kg/d). Compared to CCS diets, cows fed BMRSS diets increased milk fat concentration (0.10%), but decreased milk protein concentration (0.06%) and tended to increase lactose yield (0.08 kg/d). Meta-regression indicated that days in milk affected DMI and milk production when CSS diets were compared to BMRSS diets, and DMI when CCS diets were compared to BMRSS diets. Additionally, the inclusion rate of silage in the diet and the dietary NDF affected yields of milk fat and lactose, respectively, when CCS and BMRSS diets were compared. Overall, lactation performance improved when cows were fed diets formulated with BMRSS compared to cows fed diets formulated with CSS, but performance was not different between cows fed BMRSS and CCS diets. However, the small sample size may have influenced these results by increasing the margin of the error and concurrently, the power of the meta-analysis. Results of this analysis suggest additional research is needed to explore the effects of DIM and the inclusion rates of silages in the diets when comparing BMRSS with CSS or CCS.